Well, I have a question that I have been scratching my head over. Since moving to the midwest, I have been saving to get my electrical wired for the shop. I finally started yesterday. I have to wire 220 for:
- Dust Collector 2HP 12A
- Band Saw (Grizzly G0513) 2HP 10A
- Table Saw (Grizzly 1023SLX) 3HP 20A
Here’s the delima. I was reading the documentation yesterday about the bandsaw and it said that it had to be protected by a 10 amp breaker to avoid damage to the motor, should an overload condition arise. I can get a 2 pole 10A and 20A breaker for my Cutler-Hammer box, but I don’t know of anyone who makes a 12A breaker. The closest thing I can get is a 15A breaker. It’s a 20 percent variance. Is there any issues here? Should I look at some type of in-line (plug to motor) protection at 12Amps. Before I moved here, I had it on a 15A and now I’m wondering if that was a mistake? I guess what I’m saying is an additional 3 amps worth worrying over?
Edited 1/22/2006 11:48 am ET by bones
Replies
That doesn't make any sense. The starter should have melting or probably electronic overload relay. If so the motor is protected for overload by the starter. The breaker in your panel protects the receptacle and wiring to it from overload and short circuit. You can go with 20A receptacles and breakers and #12 wiring which should be enough or go 30A with #10 wiring. Put the DC on one circuit and the BS & TS on another since you won't be using them simultaneously.
John O'Connell - JKO Handcrafted Woodworking
The more things change ...
We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized. I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.
Petronious Arbiter, 210 BC
Thanks for the reply. As to which amp to which breaker I understand those are standard breakers that are easy to come by. If the mfg wants a certain breaker I will comply with the request. The issue was the 12A motor on the DC. I was curious if the 3A over motor rating made a big difference i.e. 15A is the closest I can come to the rating. Each machine will have a home run with it's own breaker. I would not think the difference matters, but just curious.
I agree. The panel breaker is to prevent current overdraw on the line. The device (BS, DC, whatever) should be wired for its own protection. A 100 watt bulb draws less than an amp- but it can be wired on a 20 amp circuit- with ~ 19 other lights. It doesn't need a 2 amp breaker to prevent it from failing.
I'd wire the DC separately homerunned to the panel, and the other two tools on a 20 amp circuit, provided they will not be used together (e.g. a one man shop). Glaucon
If you don't think too good, then don't think too much...
If I could add my .02¢, if the equipment does in fact provide overcurrent ...(.overload protection)....,. then the breaker can be sized for the wiring and not the equipment......if you consider that thermal overloads and circuit breakers or fuses provide different types of protection when used together. select breakers or fuses for short circuit protection and ..thermal overloads for ....mechanical overload... now if the mfr. wants a certain size breaker or circuit. ....it is for warranty protection as much as equipment...I have acutually installed fuses that were 300% larger than the wire size because of motors with high inertia loads and therefore high starting currents such as....large fans ,flywheels,compressors,etc. the wiring is then protected by the thermals.!However if there is NO such overload protection then the OCPD or the fuses must be sized properly...but
using a breaker that exactly matches the nameplate current will most likely cause nuisance tripping .
...even though breakers have both a thermal and magnetic component ...the next closest size should be used. additionally, fuses should never be used as the only source of protection for a motor...,in this case, both hots would have to open simultaneously during either type of fault, and fuses ,although they are very reliable, simply can't do that.....
I agree... but I can't see any logical reason to require a 10 amp breaker for individual instrument protection. When building electronic equipment, I have isolated the expensive components with their own fusible links (i.e. low current, low potential)- but I have never heard of any power equipment requiring external breakers to protect itself- I'm not even sure how widely available they would be. Seems to me that the manufacturer should be designing their equipment with this in mind...Glaucon
If you don't think too good, then don't think too much...
I don't know..
.maybe mfrs' feel it's necessary to CYA while they builld less ....and less.... quality into their products. I don't want to insult any one here, but that seems to be the way things are going ...put the onus of responsibility on the shoulders of the consumer.
..it is possible that a breaker that size is not widely available ....and if a problem crops up they can say ..."sorry this item was abused " I agree that, especially with motor contollers getting smaller by the day, some simple OL could be built in,
but they would have to pass the cost onto the consumer, so they promote themselves to being committed to holding costs down....while NOT building a quality item........
We've covered this ground before, so I'll just kick in my traditional caveat that if you intend your electrical work to conform to your local code, you may have to homerun each 220 receptacle.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
And to your post, since it is a requirement, there is a reason for that requirement, so would be a good idea anyway. The reason being that if it is possible to turn on two things at once, it will happen.
Edited 1/23/2006 8:10 pm ET by tinkerer2
Not being expert on these matters, I'm not saying the other method is dangerous. This is, in part, because other credible posters have said it's a reasonable, safe practice, and in part because it makes sense to me, too. 220 isn't magic, and you don't homerun every 110 receptacle. Why 220?
My sole and only point is that meeting code requirements may dictate one practice or another -- where I live, residential installs require every 220 receptacle to have its own homerun.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
The breaker in your panel protects the receptacle and wiring to it from overload and short circuit
It must be the biggest "internet myth" about electrical wiring that circuit breakers only protect the branch circuit wiring and the receptacle. This is not true; the NEC considers flexible cords, and appliance and fixture wiring as "taps" to the branch circuit, and there's a separate section of the Code covering them. The ratings are not the same as those for in-wall branch circuit wiring for various reasons; e.g., the wiring is not buried in a wall, the equipment is tested by UL, etc. But this is the reason you can't put a 15A receptacle on a 50A circuit - the breaker would not provide sufficent protection for the cord plugged into it.
In any case, the equipment should have motor overload protection built into it. The warnings in the Grizzly manual are technical-writer-boilerplate left over from the "old Grizzly" when they used to "cheat" on things like not providing motor overload protection as required by the Code. A 20A breaker should be fine. Remember that 15A plugs can be inserted into 20A outlets, so a 20A breaker will provide proper protection for any Code-compliant equipment that can be plugged into it.
"But this is the reason you can't put a 15A receptacle on a 50A circuit - the breaker would not provide sufficent protection for the cord plugged into it."
Not sure what you mean by "can't" - but NEC certainly allows 15A receptacles on a 50A branch circuit.
As noted, the breaker is sized to protect the branch circuit wiring, per NEC.
but NEC certainly allows 15A receptacles on a 50A branch circuit.
No it doesn't. Per Article 210-21, the only receptacles that can be put on a 50A branch are 50A receptacles. See Table 210-21(b)(3) in the NEC.
As noted, the breaker is sized to protect the branch circuit wiring, per NEC.
Not exclusively. See Article 240-4, which specifies overvcurrent protection for flexible cords and fixture wiring. When 240-4(b) applies, overcurrent protection for this wiring is provided by the branch circuit overcurrent protection device.
but NEC certainly allows 15A receptacles on a 50A branch circuit.
No it doesn't. Per Article 210-21, the only receptacles that can be put on a 50A branch are 50A receptacles. See Table 210-21(b)(3) in the NEC.
With respect, your view is not consistent with the commonly accepted interpretation of NEC, at least in the US. With the NEC, it has to be interpreted in context to get the "whole picture". The table you cite are MAXIMUMS - so NEC does not allow a receptacle larger than 50A on a 50A branch - but multiple smaller receptacles (15A or 20A, for example) is fine.
As noted, the breaker is sized to protect the branch circuit wiring, per NEC.
With respect, your view is not consistent with the commonly accepted interpretation of NEC, at least in the US. With the NEC, it has to be interpreted in context to get the "whole picture". The table you cite are MAXIMUMS - so NEC does not allow a receptacle larger than 50A on a 50A branch - but multiple smaller receptacles (15A or 20A, for example) is fine.
??? There's only one way to interpret the following:
210-21. Outlet Devices.(b) Receptacles.(3) Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210-21(b)(3), or, where larger than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.
Table 210-21(b)(3). Receptacle Ratings for Various Size Circuits
Circuit Rating (Amperes)
Receptacle Rating(Amperes)
15
Not over 15
20
15 or 20
30
30
40
40 or 50
50
50
The rating for 15A circuits is indeed a maximum, indicated by the "not over 15" entry (although I don't think NEMA defined a smaller size). But clearly, the rating for the 50A circuit is not a maximum as is does not include the "not over" phrase; also, the entries for 15A and 40A circuits show that the intent of this table is to enumerate all the allowable receptacle ratings.
BTW, your assertion that NEC does not allow a receptacle larger than 50A on a 50A branch is not true in all cases. For the case of a single receptacle on an individual branch circuit, the receptacke rating may be larger, but not smaller, than the branch circuit rating.
Individual jurisdictions can make whatever exceptions they want, but the NEC says what it says. But from an engineering and safety point of view, it is a bad idea to permit receptacles with rating substantially smaller than the branch circuit ratings.
As noted, the breaker is sized to protect the branch circuit wiring, per NEC.
No, not exclusively. Examples:
240-4. Protection of Flexible Cords and Fixture Wires. Flexible cord, including tinsel cord and extension cords, and fixture wires shall be protected against overcurrent by either (a) or (b).(b) Branch Circuit Overcurrent Device. Flexible cord shall be protected where supplied by a branch circuit in accordance with one of the methods described below...
Another one:
Article 422 — Appliances422-11. Overcurrent Protection. Appliances shall be protected against overcurrent in accordance with (a) through (g) and Section 422-10.(a) Branch-Circuit Overcurrent Protection. Branch circuits shall be protected in accordance with Section 240-3. If a protective device rating is marked on an appliance, the branch-circuit overcurrent device rating shall not exceed the protective device rating marked on the appliance.
There are others, but these give the idea. The requirement to, in some circumstances, extent the protection from the branch circuit breaker to the utilitization equipment supplied by the circuit is the motivation for the receptacle requirements in 210-21.
Unless you can provide evidence supporting your assertions, I respectfully disagree with them.
Barry, that's the way I read the Code book as well. I was thinking about responding to him earlier myself, but I didn't want to do all that typing... :-)
Individual jurisdictions can make whatever exceptions they want, but the NEC says what it says. But from an engineering and safety point of view, it is a bad idea to permit receptacles with rating substantially smaller than the branch circuit ratings.
I guess we will have to "agree to disagree". But I think you are "reading into" the code things that weren't intended and simply aren't there. As we have revised the code, we have tried to make it as clear and unambiguous as possible, but it's still not perfect.
FWIW, in 25 years as a professional engineer, practicing electrician, and code inspector in 5 states in the US, I have not previously encountered this interpretation or had any issues with multiple 20A (minimum of 3) receptacles on 50A branch circuits.
Well, as an electrical engineer for over 25 years, if I thought the NEC allowed 20A receptacles on a 50A branch, I'd be the first one proposing a change to for the 2008 cycle.
Your assertion allows for a potentially dangerous situation. 20A receptacles will accept 15A plugs, which include light duty devices. Permitting a light duty portable lamp with a 18 AWG cord (or sometimes smaller) to be fused by a 50 amp OCPD is asking for trouble.
I haven't found an electrical professional that supports your view. I even posted a query over at Mike Holt's site for electrical professionals, and the responders, including the chief moderator, agree with me. You may only use the the size receptacles listed in the table.
>>I guess we will have to "agree to disagree".Coming from over at Breaktime:In addition to all of the other disagreements with your (to me, unique) views assuming your 50A circuit is 220v (I've never seen one wired as 110) you seem to be advocating (i) multiple devices on a major appliance circuit and (ii) 110 devices on a 220 circuit; both of which are code violations in my area.And, if you read the receptacle size chart posted in this thread: on the 20 A breaker row, they show that they know how to indicate when multiple sizes are allowed: so when they have a row that only shows 1 size, they must mean that size only.In my opinion, you are giving dangerous advice,
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Sojourners: Christians for Justice and Peace
In addition to all of the other disagreements with your (to me, unique) views assuming your 50A circuit is 220v (I've never seen one wired as 110) you seem to be advocating (i) multiple devices on a major appliance circuit and (ii) 110 devices on a 220 circuit; both of which are code violations in my area.
I'm sorry that wasn't clear - I was referring to a 110 VAC circuit, not a 220 VAC circuit.
Generally 110 VAC devices are not permitted on 220 VAC circuits, the primary exception being 220 VAC electric dryers, which often use 110 VAC for the lower heat setting on the heater. That's one reason a 4 wire circuit is required for a dryer (3 wire plus external ground in some jurisdictions - still effectively 4 wire).
That's also why it violates NEC to use a dryer receptacle for 220 VAC power tools.
"Generally 110 VAC devices are not permitted on 220 VAC circuits, the primary exception being 220 VAC electric dryers, which often use 110 VAC for the lower heat setting on the heater."Acutally the main purpose of havee 120 and on dryers and STOVES is for lights and motors (including timers). Years ago stoves used to have 2 element burners and by using a combination of elements and connecting them in series or parallel and between 120 and 240 they got the different fixed heat ranges. But that was long ago. But your basic premise is wrong. 240 and 120 volt loads are allowed on the same circuit if it uses a 2 pole breaker. Read the section on multiwire circuits."That's also why it violates NEC to use a dryer receptacle for 220 VAC power tools." But it does not.And BTW, the power in the US is 120/240 volts not 110/220.
240 and 120 volt loads are allowed on the same circuit if it uses a 2 pole breaker. Read the section on multiwire circuits.
Under particular, specific circumstances ONLY, not as a general condition.
"That's also why it violates NEC to use a dryer receptacle for 220 VAC power tools." But it does not.
Actually, it does. In particular, it is not "legal" to wire a 220VAC power tool with a 3 wire dryer plug, in part because that 3 wire circuit does not include a ground. The "legal" plug is a 3 wire plug, but consists of two "hots" and a ground, while the dryer plug has a two hots and a NEUTRAL.
And BTW, the power in the US is 120/240 volts not 110/220.
If you want to be technical, neither is universally accurate. While both 120/240 and 110/220 references are commonly used colloquially, the 110/220 reference seems to be more common, but it is largely a matter of local convention. Which you actually get in a particular circuit derives from the form of the power distribution system. In practice, you will typically find 100 - 125 VAC at a "110 VAC" receptacle - assuming you are measuring with a meter that accurately and correctly measures AC (many, particularly less expensive DVMs, do not) and that you understand how it is measuring the AC and how to convert the numbers to "real" numbers. I'll spare you the RMS vs peak debate ;-)
I think part of the confusion in this discussion is differing backgrounds and levels of understanding. I suspect most of the posters have experience in their local municipality and are assuming that experience applies across the country. In many cases, it does not - in spite of all the regulation, there are significant differences in the local power system throughout the country. Your 120/240 comment is an example - I assume that is the colloquial reference in your area, but it is not the common reference in other parts of the country. I'm trying to post information that is correct throughout the US, but even that seems to be confusing some folks whose local practices are different.
""That's also why it violates NEC to use a dryer receptacle for 220 VAC power tools." But it does not.Actually, it does. In particular, it is not "legal" to wire a 220VAC power tool with a 3 wire dryer plug, in part because that 3 wire circuit does not include a ground. The "legal" plug is a 3 wire plug, but consists of two "hots" and a ground, while the dryer plug has a two hots and a NEUTRAL."WHAT 3 WIRE CIRCUIT?????This is what you posted."That's one reason a 4 wire circuit is required for a dryer (3 wire plus external ground in some jurisdictions - still effectively 4 wire).That's also why it violates NEC to use a dryer receptacle for 220 VAC power tools."We are talking about a FOUR WIRE CIRUCIT."Which you actually get in a particular circuit derives from the form of the power distribution system. In practice, you will typically find 100 - 125 VAC at a "110 VAC" receptacle - assuming you are measuring with a meter that accurately and correctly measures AC (many, particularly less expensive DVMs, do not) and that you understand how it is measuring the AC and how to convert the numbers to "real" numbers. I'll spare you the RMS vs peak debate ;-)""ANSI standard C84.1 and Canadian standard CAN3-C235 specify that the nominal voltage at the output should be 120 V and allow a range of 114 to 126 V."A supply of 100 volts is serious low and should be corrected.And look at the label on electronic equipment (motors are different) and you will find that they are labeled as 120v (unless they have switching power supplies and some will might be something like 100-250, common on computer equipment).
decolores9, do you have any more of that stuff your smoking?
My suggestion- Give that stuff up!!!!
LOL
While decolores9 may be technically wrong, his thoughts are correct.You can plug a 15amp DEVICE into a 50amp circuit if the plug matches the recept.Also you can put a 15amp recept on a 50amp circuit IF there is an upstream breaker that limits the current to 15amps (perhaps 20amps).
You can plug a 15amp DEVICE into a 50amp circuit if the plug matches the recept
I don't know what the definition of "15amp DEVICE" is, but if a listed piece of utilization equipment includes a 50A plug, then it is approved to attach to a 50A circuit.
Also you can put a 15amp recept on a 50amp circuit IF there is an upstream breaker that limits the current to 15amps (perhaps 20amps).
If by "upstream" you mean between the receptacle and the 50A circuit, then yes of course this is permissible. In this case the 50A circuit is a feeder, and the branch circuit OCPD for the receptacle is the 20A breaker.
Nevermind, others made my point.
Edited 1/29/2006 11:07 am by Elcoholic
Edited 1/29/2006 11:08 am by Elcoholic
Sorry, let me clarify. Documentation on the BS and TS are easy. They call for 10A and 20A breaker. The question is the DC. I don't have the documentation on it. It is made by SEKO. The motor has a rating of 12A. There is no 12A breaker. Hence the dilemma! I am just wondering if going with a 15A on the DC is ok, or should I look at a fuse type inline protection for the motor. My first thought is that a 20% over, would not kill the motor i.e. with a 15A trip, would the three additional amps cause damage to the motor. The TS and BS are no problem, because I can compy with the requested breaker in the documentation.
A 15 amp breaker would be good in my opinion.
Mike
I assume the dust collector was built somewhere overseas. I'd have to look around the Web to confirm this, but I believe that in some countries a 12 amp branch circuit is standard size, like how we have 15 amp circuits here in the US. That may be why they called for a 12 amp circuit, but I doubt you'll be able to find a circuit breaker in that size. I think you'll be just fine with a 15 amp circuit.
If it was built overseas for overseas useage it would most likely be fifty cycle so wouldn't work to well anyway. I agree,it was probably built overseas but for the US market.
On my shop, all outlets are 20amp duplex with 12ga and 20 amp breakers. All lighting circuits are 15 amp. The saw is 220 with a breaker inside a switch panel, which I assume is 30amp.This is really simple, and you're making it too complicated.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Edited 1/23/2006 8:18 pm ET by tinkerer2
Using the breaker for overload protection of the machine seems bass-akwards. Sure it'll work, but does it make sense long term? What if you buy a different machine, do you change the breaker?
I'd run all the workshop circuits at 20A, and get some used machine starters for overload protection at the machine. It's unfortunate that Griz expects their customers to use a circuit breaker to provide a function that should have been on the machine in the first place, but it's easily remedied.
Pete
Bones...
However you decide to wire it, when you first start using your machine keep an eye on the motor for a while. Whatever you do DO NOT let the smoke out. They put the smoke in at the factory and once you let the smoke out of any electrical device it is ruined. (LOL)
Ed
I'll keep that in mind. I know what you mean. That smoke leaves then the smell then then you have to buy new equipment. Thanks for the laugh.
Well, this post has transformed into an interesting discussion. I did find out some more information. I spoke with Grizzly today, and they do not provide any circuit protection on the motor. They did say however that a 15A 220v breaker should be sufficient to avoid issues. If I truly wanted to protect the saw at 10A, and not use a 10A breaker, I could utilize a magnetic switch sold by Grizzly. It's 49$ and can be set to trip between 8 and 12 amps.
My cutler hammer box is currently at capacity. I could free up some slots by replacing some breakers with slim line breakers that allow you to get two 20A breakers in on slot, or add a sub panel. I was considering of exteding my table saw circuit (20A) and allow them to share. I know each machine should have it's own home run, but since I will never be running my table saw and band saw at the same time, I don't see the harm.
Maybe it would help if I explained the situation in which multiple receptacles are typically installed on a 50A circuit, and why.
I'll use my own shop as an example. I have typical midrange/light industrial tools. For example, I have a Makita 2030 jointer/planer. It has a 2 HP motor and draws 18A when running. Typical startup current is double that, 36 A (double is a rule of thumb for motor startup).
Suppose I use a 20A circuit, with 10 guage wire, which appears to meet NEC for a motor circuit. I also use arc fault circuit interruptors and a GFCI. What happens when I turn on the motor? The breaker trips - the AFCI breakers respond quickly to overcurrent, unlike traditional breakers that respond slowly (if at all) to faults. If I use a traditional breaker, the motor will start, but the lights will dim and the motor voltage will drop, stressing the motor. That, and traditional breakers will only trip due to a sustained, significant overcurrent condition - so they often don't trip if a motor winding shorts, for example. (which is why AFCI's should be used for all circuits, even though that is not yet a code requirement - currently AFCIs are only required for bedrooms)
There are a couple of solutions to this problem. I could wire a dedicated 40A circuit with 6 guage wire to each machine. That would work, but is overly expensive. In addition, even with derating there are practical limits to how many such circuits I can legally put in my breaker panel. It's likely 200A service would not be sufficient if I am running my house off the same panel.
The better (IMHO) solution is to use a single 40A or 50A circuit with multiple 20A receptacles. I typically would wire this with 6 guage wire ( 4 is even better), which resolves the light dimming/motor drop issue. As noted previously, this meets NEC requirements. One significant benefit is that only one 40A or 50A circuit is added to the breaker panel, so I can still power my house with 200A sercvice. The only real disadvantage is that you can't start multiple machines simultaneously, but for most of us with small shops that's not a big deal.
That is wrong and dangerous. When your drill press, circular saw, halogen light, shop vac or oscilating fan shorts the result will be far more dangerous. 50 Amps will likely turn an oscillating fan motor into a molten fire ball of insulation, plastic and adhesives. Very few tools, even larger machines, that run under 15 amps have any protection. They don't need it because if they are pluged into a 15 amp breaker they are sufficiently protected by the perscribed 15 amp breaker.
Mike
They don't need it because if they are pluged into a 15 amp breaker they are sufficiently protected by the perscribed 15 amp breaker.
If circuit breakers worked the way people expect them to, that would be true. The problem is, they don't.
A regular circuit breaker trips due to one of two conditions:
1. A SUSTAINED SIGNIFICANT overcurrent condition. On a 20A breaker, that typically means 40A or more for several seconds - long enough to start a fire in some cases (specifications vary between breakers, but that is a typical number)
2. Thermal heating - drawing enough AVERAGE current for long enough to cause a thermal trip. That is typically tens of seconds to minutes, but will trip at lower current (e.g. 30A for 5 minutes). Still long enough to cause a fire.
Eaton (big maker of circuit breakers) published a research report in which they applied a dead short across a 110 VAC line. In most cases, the breaker did not trip.
That's the benefit of Arc Fault Circuit Interruptors (AFCI) - they WILL trip. Problem is, they will also trip when you start a motor, due to the substantial overcurrent.
There is another solution - a fuse. But most folks don't want to revert to fuses, and they are against local codes in some placed, because people tend to bypass them.
The circuit I described is a safe, NEC compliant solution. It may not be the only solution. I would not recommend it with a conventional breaker, because of potential risks of the delayed trip. It works fine and is safe with an AFCI. An AFCI will trip before your shorted halogen light, etc. will heat up - unlike a conventional breaker, which is likely to take several minutes to trip (if it ever does) in the situation you described.
Here is a link that discusses the issue:http://www.askthebuilder.com/320_New_Arc_Fault_Breakers_-_Small_Price_To_Pay_For_Peace_Of_Mind.shtml
Here is a report from Eaton about AFCIs:http://www.eatonelectrical.com/unsecure/cms1/RE00402001E.pdf
Here is a report from Eaton about AFCIs:http://www.eatonelectrical.com/unsecure/cms1/RE00402001E.pdf
Sorry, there is a typo in the link. It should be:
http://www.eatonelectrical.com/unsecure/cms1/RE00402001E.PDF
The Eaton article is quite good. It describes the purpose of an AFCI quite well. It also clearly differentiates between overcurrent and arc faults, which is a critical distinction.I think everyone realizes that a lot of the information posted on any internet forum is misleading or even incorrect. When it comes to electricity, there's no substitute for a licensed electrician.Pete
Yes, the Eaton site does explain arc-fault breakers, so why do you not know what they are to protect? They do not respond to short circuit current or overload current, that is the duty of a regular circuit breaker (and the regular section of the arc-fault). The arc-fault section is to look for varying currents that would be in both series and parallel (shorting type) arcs. Yes, this is more protection than regular breakers, but will not protect your 50 amp circuit from shorts or overloads any better than regular breakers. They will protect you from arcing faults. BTW, where did you find a 50 amp arc-fault breaker?Also, as stated earlier, the NEC does not allow 15, 20 or 30amp receptacles on a circuit protected by a 50 amp breaker, not even under the tap rules. And, how do you connect that 6 or 4 ga wire you speak of to the 20 amp receptacles? And if you run out of spaces in a panel, that is what sub panels are made for. Run a 50 amp or larger feeder to your shop and then a properly wired subpanel with 20 amp breakers for 20 amp receptacles. You are allowed to have more than 3 20 amp breakers on a 50 amp feeder. Others,
You can always check with the local AHJ ( Authority Having Jurisdiction)i.e. electrical inspector, with any questions regarding local code rules.Frank DuVal, P.E.You can never make something foolproof because fools are so ingenious.
They do not respond to short circuit current or overload current, that is the duty of a regular circuit breaker (and the regular section of the arc-fault).
Exactly - and if you read the article, it explains that virtually ALL faults are effectively arc faults - which is why conventional breakers are undependable.
Typical example - motor shorts on a table saw. Say the windings short, and it's a dead short, drawing 50A. Very quickly, the motor wire burns through, and the circuit opens - so the breaker doesn't trip. Then, the molten metal from the burned wire shorts other windings, so the circuit is completed and high current flows again. When that winding burns through, the process repeats. The point is that the current flow is not continuous, so a conventional breaker won't trip under those conditions - but an AFCI will.
Frank DuVal, P.E.
If you are intending your post to be an engineering report, you should state your license number and discipline. I suppose if you are PE you would know that requirement.
For the record, I am a P.E. Electrical, but am not submitting my posts as an engineering report, but simply posting my opinions. There is insufficient information in this thread for any PE to make an engineering report.
For those not familiar with P.E.s, P.E. is a "professional engineer" - it's a license to practice engineering. In the U.S., engineers must be licensed to practice engineering in all 50 states (There is an "industrial exemption" that allows a manufacturing company to title their employees as "engineers", as long as they do not engage in the legally specified "practice of engineering") When a identifies himself or herself as a P.E., they are required to state their area of expertise and license number, and specifically state that the information is not an engineering report, or it will be considered an engineering report, making the PE legally liable for it's contents.
I am in agreement with Bill Hartmann, Roger67 and Charlie K, that decolores9 is flat wrong in some of his statements, but not all (just to throw us off!). Decolors9 please feel free to answer these questions:Are you running a 50 amp single pole breaker feeding a circuit of 20 amp receptacles at 120 nominal volts?You stated you use arc-fault breakers on this circuit. Where did you find a single pole 50 amp arc-fault breaker?What protects the 20 amp outlet from melting if a 40 amp load is plugged into it?What protects the 20 amp outlet from getting warm and starting a fire if a 25 amp load is plugged into it? I have seen three irons plugged into one receptacle, so do not tell me it cannot happen! And yes, the breaker did its job.You say: "Maybe - but maybe not. That's the risk - that the breaker won't trip. A new breaker that meets manufactured specs often will - but a 5 year old breaker that hasn't been activated since it was installed may not."
If breakers were so prone to failure they would have been outlawed years ago. Even Federal Pacific breakers have not been recalled. Do you only install fuses in your work?You said: "FWIW, in 25 years as a professional engineer, practicing electrician, and code inspector in 5 states in the US, I have not previously encountered this interpretation or had any issues with multiple 20A (minimum of 3) receptacles on 50A branch circuits." So you stated you were a PE, but did not, as you say :"When a identifies himself or herself as a P.E., they are required to state their area of expertise and license number, and specifically state that the information is not an engineering report, or it will be considered an engineering report, making the PE legally liable for it's contents." SO if I say I am a PE then I have to follow your state's rules, but you do not? BTW, we here in the Commonwealth of Virgina do not have such a rule, just like medical doctors put MD after their name and people with doctorate degrees put PHD after their name whether it is required in the situation or not.You said: "... multiple 20A (minimum of 3) receptacles on 50A branch circuits." So how does the number of receptacles being 3 magically make this a legal circuit? Only one receptacle could be used at a time, so 50 amps could be drawn through one receptacle. Doesn't sound legal to me.You said:" That's also why it violates NEC to use a dryer receptacle for 220 VAC power tools." What???? A receptacle rated for the voltage and current requirements of the device certainly can be used. i.e. a 4 wire ( hot, hot, neutral, and ground) 30 amp dryer receptacle can be used for 240 volt equipment that draws up to 30 amps. Even if there was no need for a neutral in the equipment. And if you wanted to roll this equipment around the shop, one could put several of these receptacles on one circuit fed by one two pole breaker of 30 amps. A three pin dryer receptacle has not been legal for new work in 20 years (around here) even for dryers! No ground.Somewhere the original question in the original post got lost. I apologize for further leading it astray, but I feel compelled to correct misleading electrical advise that can cause harm. Here the standards of practice for PE's begin with "The primary obligation of the professional is to the public. If the professional judgment of the regulant is overruled under circumstances when the saftey, health, property and welfare of the public are endangered, the professional shall inform the employer or client of the possible consequences and notify appropriate authorities." So when I am made aware of situations I jump in with both feet and inform anyone who listens!Frank DuVal
PE #012542
Master 2710 016265
Contractor 2705 001083
since you asked me to list
You can never make something foolproof because fools are so ingenious.
"You stated you use arc-fault breakers on this circuit. Where did you find a single pole 50 amp arc-fault breaker?"Yes, I was coming back to this thread to comment on this.At one place he indicates that it is too "damgerous" to use motor on an ordinary 20 amp breaker and that an AFCI is needed for protection as it will "hopefully" detect the signature of a failing motor.However, as an alternative he want to connect the same motor to a 50 amp breaker that also, according to his claim will also be unreliable. And if there is an a 50 amp AFCI (which I don't think that there is one) the arc signature will have to be that much bigger so motor that is designed to work on 20 amp circuit could still have large arcing fault that would not trip it.And ordinary breakers are so prone to failure what will be the reliability of AFCI's? There is big question about the performance of the "self test" in the breakers. While the GFCI self-test does exactly simulate an ground fault by connecting a resistor from the hot after the GFCI sensor to the neutral before, but how can an AFCI ACCURATE simulate 60 amp arc?And if there was such a problem with motors and "non-working breakers" how come it it not a well known problem. With all of the large motor drive appliance in a house (refigerators, freezers,n clothes wahsers, sump pumps, well pumps, garage door openers, dryers, AC, etc, etc) there much be a billion active motors in US homes.And hundres thousands more of larger motors in woodworking and air compressors in home workshops.When you look at what all he has said it just is not consistant with himself or know facts.
You and I both know that is not true from experience. If you are running a table saw (120 volt contractors style) and turn on a shop vac, a 15 amp breaker trips instantly (less than 2 seconds). While the saw is running under a mild load the current drawn is around 10 amps the shop vac will draw 20 or so amps for a half a second. That is one example off the top of my head; before I rewired my garage I learned many different combinations of tools that would trip breakers very quickly, and these were not extreme situations. I am certain that you have had at least as much experience as I have with tripping breakers and know all this from experience. I know of no responsible electrician who would recomend running a chain of 15/20 amp outlets off a 50 amp breaker. The idea is absurd, regardless of code. Why take the risk? to save pulling some wire? save a few bucks?
Mike
Edited 2/2/2006 8:07 pm ET by mudman
If you are running a table saw (120 volt contractors style) and turn on a shop vac, a 15 amp breaker trips instantly (less than 2 seconds).
Maybe - but maybe not. That's the risk - that the breaker won't trip. A new breaker that meets manufactured specs often will - but a 5 year old breaker that hasn't been activated since it was installed may not.
BTW, a 15A circuit is undersized for most contractors saws.
I know politicians believe that they can make something true by repeating it over and over, but saying that multiple 20A receptacles on a 50A branch "meets NEC requirements" is flat out wrong, and dangerous. There is nothing in the NEC that says there is an exception that would allow this for AFCI's.
The unfortunate thing here is that many DIY'ers, with no professional experience, read this forum and come here sekking advice on doing some of their own electrical wiring. It would be very unfortunate if some of them follow your incorrect guidance and hurt themselves and/or their property in the process.
You provide no evidence, other than your personal opinion, to support your view. The NEC itself is very clear that you are wrong. Everyone of the dozen electrical engineers, electricians, and inspectors I've contacted on this says you are wrong.
No one agrees with you. Unless you can come up with something better than "I say I'm an expert, therefore I must be right", the rest of us have no reason to change our minds.
I don't see how he could be right but I'm no expert. So my very strong recommendation to anyone considering that course is merely that they check with their code inspector prior to committing to this course. The inspector in my city was very helpful as I designed and installed my electrical upgrades.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
saying that multiple 20A receptacles on a 50A branch "meets NEC requirements" is flat out wrong, and dangerous.
Again, you appear to be "reading into" the NEC limitations that were unintended. It's on the list to clarify for the next revison of NEC
while everyone else is trying to straighten this mess out........I just want to say
.
...
YOU"RE NUTS !!!
It's on the list to clarify for the next revison of NEC
Prove it.
To all that are reading this thread, decolores9 is flat out wrong.
Decolores9, at the risk of insulting you, I must question your claim as to your status and involvement in the electrical industry, although you have some correct, you have made statements and claims are completely wrong.
Others have posted the appropriate NEC articles and sections and have provided good explanations of their requirements, there is no agreeing to disagree, you are simply wrong.
Roger67
In the Trade since 1975, Master electrician, Electrical Contractor, and amateur woodworker.
Edited 2/3/2006 8:02 pm ET by Roger67
Thank You Roger for wording this so well. I agree with you 100%.
Charlie K. In the trade since 1975, Journeyman electrician and amateur woodworker.
Hello Charlie, thank you, and it's nice to see a familiar name here. ;)
Roger67
This discussion seems to be deteriorating into personal attacks and arguing, so I'm not sure it's worth continuing the debate. I don't see any benefit in personal attacks, and don't want to stoop to that level.
However, I think there are some good points that have come out, or at least been hinted at, in this discussion:
1. If you aren't absolutely confident you fully understand NEC and your local amendments, seriously consider consulting an electrician.
2. In most municipalities, all electrical work must be inspected. Often, homeowners are permitted to work on their own homes without an electrician's license, but the work must still be inspected. The inspector is often a great source of information.
3. Get the work inspected. If you don't, you may be subject to fines. In addition, if you have a house fire, the insurance company can deny your claim because you have unpermitted electrical work. (it really does happen - a friend had his house burn to the ground, his insurance company denied coverage because a prior owner had done unpermitted work, unbeknownst to him. The courts upheld the denial). In addition, when you sell the house, many buyers will require copies of your permits and inspections. If you have to have the inspection done after the fact to sell the house, it will cost more and there will likely be fines.
4. Be wary of those who state they are P.E.s, but do not provide a license number, discipline, or comment on whether their post is an engineering report. It's a legal requirement in all 50 states, if one is issuing an engineering report. At least they are not following the legal requirements, and may well not be a P.E.
5. There is often more than one "legal" solution to a given wiring issue. I explained how I wire shops, and while others' attacked my solution, no one has proposed an alternative. I'm sure there are alternative solutions, but have yet to hear any alternatives to the options I proposed, that address the issues present in a shop. What I proposed is NEC compliant and safe, but there are likely other solutions. More importantly, your local inspector may like it, or not. It's best not to "fight" with the inspector - it's better in the long run to make the minor modifications they want to avoid antagonizing them, even if want they want is not required by NEC or local code. It's better to make friends than enemies of inspectors.
6. Use AFCI breakers - conventional breakers do not reliably trip in many cases. The exception, IMHO, would be a shop with a dedicated branch panel in which you turn off the main breaker when you are not in the shop. In that case, conventional breakers are OK - if there is a problem, you will be in the area to manually trip the main before a significant fire can develop. Keep the door to the panel closed, and try to locate the panel away from heavy dust areas, as dust - wood or otherwise - can contribute to the breakers "sticking".
7. Understand the practical wire size and current requirements for motor startup. NEC only requires one wire size larger for motors, but that is insufficient in most cases to prevent the voltage drop on motor startup (that's the primary benefit of using a 40A or 50A branch circuit - it solves the voltage drop and startup surge problems). Remember, too, that the LENGTH of the wire is critical in determining correct wire size. NEC has tables to use as a starting point.
8. Be cautious with any advice you receive on the internet. Many of the self proclaimed experts on this thread have a very flawed understanding of NEC, IMHO. The "majority" comment is often wrong - most people don't understand the subtleties of the NEC, or any other topic for that matter, but that doesn't stop them from attacking those who have a better understanding. Before you act on advice, confirm it with someone locally, whose credentials you can verify and whose authority YOU trust.
9. Use a GFCI in shop circuits - it may save your life one day. A GFCI receptacle will protect downstream receptacles, so it should be the first receptacle (i.e. closest to the circiut breaker). GFCI receptacles can be combined with AFCI breakers.
Thanks. I hope this helps.
Civil Engineer?
A good post decolores9.I never meant my posts to be a personal attack, these are never good for discussion boards. A good argument - yes!I agree with all the points in your post except for one sentence:
"What I proposed is NEC compliant and safe".
I still have not found in the NEC where 20 amp receptacles are allowed on 50 amp circuits. And this is where the argument started. Maybe it is semantics.To others with NEC questions, I suggest visiting a website referenced by ECM magazine: mikeholt.com.Be careful out there!
Frank DuVal You can never make something foolproof because fools are so ingenious.
I never meant my posts to be a personal attack
My comment was not directed at your posts - I'm sorry if it seemed that way. And my comments about PEs were not directed at you, either, but were intended as general guidelines and things to think about.
I'm still curious, though, how others would address the issues I raised. I haven't been able to think of a good alternative that addresses the issues.
Thanks.
dec
I think you are confusing a few things...such as nameplate rating, manufacturers' instructions, and circuit design.
Machinery is marked with a "Full Load Amp" rating. This number represents the largest operating current draw, under the heaviest load, that the machine is desinged for. This bit of information is but one piece in the puzzle of designing the correct circuit for that machine. The machine does not often draw anywhere near this much current.
Some equipemnt- air conditioners are an example- have other information for the electrician as well. The nameplate may specify "minimum circuit ampacity"...which determines the smallest wire to use. It may also state maximum and minimum circuit breaker sizes.
If the breaker sizes are not specified on the nameplate, the electrician will select a size. His selection will be based upon the full load amp figure, the type of equipment, how much it is used, and so on.
As you found out, circuit breakers have a fairly large gap between the different sizes. One of the functions of a "motor starter" is to allow you to protect the motor at a value much closer to what the machine actually draws. The "heaters" in a starter can be changed, or adjusted, over a range of values.
A magnetic starter also has the side benefit of not allowing the machint to automatically re-start, if the power is interrupted. A worthy safety feature, if you ask me!
Unless a maching comes from the factory with a "normal" household plug, you should probably have a separate, dedicated circuit for it.
whatthe..,I......reno? you've been a knothead since '02well.....blow me....down
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