I need to wire a 240v single phase circuit for my new planer.I have available already in the wall some 12/2 with ground and a 20amp double pole breaker ready to go in my shop panel.So can anyone tell me how to wire it? Thanks
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Replies
Drater:
I'm not an electrician and by the sounds of it you aren't either! Here's my best shot: I don't think 12/2 is heavy enough for this purpose mine is wired with 10/2 and this size wire was determined by the electrician who did the work for us. I would suggest you call your electrician and pay him or her to do the job. You'll live to tell about it and you will never wake up at night wondering if your house/shop is going to burn down!
Be careful!
Madison
Good advice is using an electrician for help. Check the manual that came with your planer, it should list the required service. If it is a used tool, check your motor for the amp draw.
A 3 hp motor will draw about 17 to 18 amps, so a20 amp circuit is undersized. At start up a motor draws more amps and it will likely trip on you. If your planer has a 2 hp motor then it will work.
I wired my shop myself, and used 10 guage 30 amp service for my 220 runs and 3 hp motors with the ability to use 5 hp motors in the future. My advice is do it right, an electrical fire or wire meltdown in a wood shop is not a good idea.
AZMO
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Azmo, my 1998 Unisaw has a 3HP motor and runs just fine on a 20-amp 220V circuit. Can't remember off the top of my head how many amps are stated on the motor plate, but 17-18 sounds kinda high. Will check tomorrow.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
3-HP is roughly 2250-Watts. (2237.099615-Watts, to six decimals, but I use 750-Watt/HP, instead of 745.6998, because it is easier to remember and use in my head.)
Volts X Amps is Watts, so: Amps = Watts/Volts
2250/200=11.25 (I know it is 220 Volts, and not 200, but 200 is easier to do in my head, and gives a 10% safety factor.)
The normal draw is roughly 11.25-Amps.
Add a 50% over rate for the start up, and you are at around 16 or 17-Amps.
Go up to the next available breaker size, and you need a 20-amp circuit.
When you start sizing the wire, you need to consider length of run. Short runs can get away with smaller wire, long runs need heavier wire.
There are some good online calculators that do wire calcs. http://www.paigewire.com/calculatorinstructions.htm
Using this calculator: A 20-amp, 240-Volt circuit, 40 foot long, with 3% maximum voltage drop would require 16AWG copper feed, at 100-feet it would require a 12AWG copper feed.
The math is close, but you allowed quite a bit of error."The normal draw is roughly 11.25-Amps"Well, at 230 volts (why not use a real voltage number?) a 3 hp motor should draw 9.7 amps (746 x 3 / 230). But that's only if it is 100% efficient. Induction motors in the 3 hp range typically have efficiencies of about 75%, give or take, when running at loads of about 50-75% of their rated capacity. At lower or higher loads, the efficiency can drop to much lower levels.At loads, approaching 3 hp the motor could well be operating at 50% efficiency and that must be accommodated. That's a current approaching 9.7 x 2 = 19.4 Amps. The start-up current could also approach this value, but it is transient and will not cause much heating of the wiring. But the full-load current will.I agree that a breaker of 20 amps will do, but the wiring needs to be heavier than 12 gauge for safety.Rich
Edited 11/24/2008 12:59 pm ET by Rich14
I'm familiar with the equation, and aware of start-up draw -- doesn't mean I understand it all -- but I do understand what the motor plate says, that's always my reference. My Unisaw (3hp) states 12 (or is it 12.5?) amps. A 20-amp circuit is more than enough for that saw. Whether it would be enough for our OP and his planer may still be up for discussion, but I'd guess it would suffice.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
In addition to to the motor efficiency POWER FACTOR is usually ignored in these discussions.For those that don't know power factor is the measurement of how the current move in phase relationship to the voltage.If current is exactly in phase with the voltage (100% power factor) then all of the current produces work and P = VA.If the current is 90 degrees out of phase (0 power factor) then work being done is zero. But still the wiring need to be sized for the amount of current.For industrial user the power company will surcharge for low power factors as they have size their equipment to supply the current, but they are only being paid for the power that is used.For AC circuit P = pf*V*AHi eff 3 hp motors will draw about 12-13 amps. Those are usually capacitor start capacitor run. And the run capacitor both increase the motor effiency and also improves the power factor.For the common imported motor they typically have 16-17 amp operating currents.Even include the required 125 over rating for the wire that give a max of 21 amps and since #12 copper is rated for 25 amps it is fine.YES #12 IS RATED FOR 25 AMPS. CHECK NEC TABLE 310.16.Starting currents are 6-8 time starting current.But that is not a problem. They are for a short period of time and the wire won't get hot.And for the breaker they don't trip at 20.00001 amps. Common breakers are Time Inverse HACR.They have a combination bimetal trip with a "heater" and a magnetic trip. The magnetic trips near instaneous for short circuits.The thermal trip is is time inverse and will allow large overloads for a few second and smaller overloads for minutes.But, typically woodworking equipment is easy starting as they don't start with a large load.If it was a something like a air compressor then you might have trouble with the breaker tripping. And if this is used as a dedicated motor circuit then you could go to a 30 or 40 amp breaker on the #12..
William the Geezer, the sequel to Billy the Kid - Shoe
"YES #12 IS RATED FOR 25 AMPS. CHECK NEC TABLE 310.16."Not inside walls or other applications where heat can't dissipate quickly. That's a situation that calls for the next larger gauge for safety. Why push the envelope?50 ft of 3 conductor 10 ga Romex costs $35. 50 ft of 12 ga costs $28. How much is it going save to cut corners?Rich
Rich,
I want to put in a 100 Amp sub-panel in the woodshop. I have a Square-D main panel and Square-D 100 Amp 120/240 beaker. The sub-panel is a Siemens and have the Siemens 100 Amp breaker for that end.
The run from the main to the sub is ~ 30' and am not sure what wire to use but am thinking of using 6-3 to connect the main to the sub. Does that sound to you like a safe thing to do?
From the sub to the machines I would use 10-3 for the 240 machines with 20 Amp breakers from the sub. These runs will be less than 20'.
What are your thoughts on this setup?
Regards,Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
6-3 is WAY to small for 100 amps.You did not indicate what type of wiring or cable that is. But it if is NM-B then you are limited to 55 amps.You either need to increase the size of the feeder or reduce the size of the breaker that feeds it. It does not matter what size a the sub-panel is if it is equal to or greater than that of the feeding breaker in the main panel.BTW, most home woodworking shop (single user) are fine with 50-60 amps. That is enough for one major machine, dust collector, lights, and heat/cooling in most cases..
William the Geezer, the sequel to Billy the Kid - Shoe
Bob,I'm going to back out of this. I am not an electrician. I think the information I have given is accurate and safe regarding the OP's situation, despite the vitriol that has resulted.I'm not qualified to give you advice about your sub-panel. I have had a sub-panel, exactly as you are contemplating installed by an electrician. My house service is 200 amp and the sub panel is 100 amp.I'm traveling right now, I'll be in Iowa until Saturday for Thanksgiving with my son and his family. When I get home, I'll check out my installation and tell you what the electrician installed for the sub-panel.Rich
Clearly you did not look at table 310-15 and the corresponding sections.That is not limited to free air. It is normal installation of cables and wire in conduit in normal spaces of normal temperature.Yes wire and cables can be derated, but not this case.They are derated if you have a conduit or cables bundled together for more than 24" AND you have more than 3 equivalent current carrying conductors in that conduit or bundle.And you derate if it is been run through areas of high temperate.And depending on the details and the specific wire you can sometimes start the derating from 30 amps. That is what is specified for either NM-B or THHN in conduit. And those are probably the 2 most only wiring methods.He is not pushing anything..
William the Geezer, the sequel to Billy the Kid - Shoe
Bill:You wrote:"They are only allowed to be connected at one and only one point. That is that the service disconnect."That is assuming they are in the same structure, right? This guy seems to be, but others have detached workshops.Joe
"That is assuming they are in the same structure, right? This guy seems to be, but others have detached workshops."While that gets into lot of more discussion that I was trying to avoid by saying to find match the the other ground.It is an "it depends" answer.Within a structure you can only have one place, the service entrance, where the neutral is bonded to the grounding electrodes and the equipment grounding conductors (the ground). Any other panels in the structure are treated as sub-panels with the neutral bus isolated from the grounds.Usually it is clear that you have a main panel and then anothers are sub-panels. But not always. Sometimes because of local requirements for an external disconnect or because it was not practical for the panel to be near where the power enters the building. That often happens with remodeling that might leave a panel that was on the outside of the building now in the middle.Under the NEC until the 2008 code separate structures there was the option to treat that as being a new service entrance with 3 wire feed (2 hots and neutral) and the ground is bonded to the neutral ground electrodes. This option is only valid if there is NO OTHER METALLIC paths between the 2 structures. Those would include water pipes, but also telephone or TV cables.Otherwise a 4 wire feeder is needed. Two hots, neutral, and equipment grounding conductor. The panel in the separate structure is treated as sub-panel with the neutral bus isolated. The 2008 NEC removed the option of the 3 wire feeder. And I understand that at least one state code removed that option earlier..
William the Geezer, the sequel to Billy the Kid - Shoe
Hi All,
I am an electrical inspector for a large city in Washington. Bill is absolutely correct with his explanation on 3 and 4 wire feeders. As of 2008 NEC 3-wire feeders are only allowed for existing installations where a 4 wire feeder can not be installed. The state of Washington has had this requirement for better than 2 code cycles (6 years). Duane Reynolds
Sr. Electrical Inspector
Would you care to explain the reason for running four instead of three wires, the danger of the three wire setup, the differences of voltages encountered between the ground and the neutral and the terminology of both? I have a pretty good idea of the reasons but I feel there are some posters on this forum who don't.
drater,
12 ga wire can safely carry 20 amps IF the wire is in free air. It is common practice to "derate" the current-carrying ability by one wire size for more than 100' OR if the wire is in conduit OR if it is in close proximity to other wires OR if it is in a place where it can't dissipate heat readily (in a wall).
Use 10 gauge wire, not 12 gauge for your 3 hp motor, which will probably draw no more than about 17 amps at full load. 20 amp breakers are the right size. Remember, fuses and breakers are NOT there to protect the equipment. They protect the WIRING, so your house doesn't burn down!
Rich
Edited 11/24/2008 7:06 am ET by Rich14
drater,
I did a hodge podge of the above. Talked with an electrician who told me what to buy, I ran the wires and he came in and did the final hook-up and initial start-up. Cost me $50 and I was comfortable everything was safe.
Hey Jeff,According to the manual that came with my machine a double pole 20 amp breaker is called for.The motor draws 15amps.The plug and receptacle specified is an L6-20.As far as wire gauge goes 10 would be better but 12 should be ok.Since the wire was already in the wall and available I'll use it.The run is about 15 feet.I am going to add at least one more 220 circuit and will use 10 gauge for that one.How to wire it is my question.Thanks
"as wire gauge goes 10 would be better but 12 should be ok.Since the wire was already in the wall and available I'll use it"It's funny how often insurance adjusters report that was the last thing the homeowner said before the fire burned the place down. That and, "Reimbursement denied for violation of electrical codes."You have already admitted it, "10 would be better." Do not ignore that admission. You are literally playing with fire.It is absolutely amazing that someone who has to ask the most basic advice about electrical issues would be so willing to take chances. Electricians divide homeowners into 2 groups. Those who are smart enough to get an electrician to handle the work and those whose homes burn down. This is no joke.At least get an electrician for an opinion. If you had some experience or working knowledge, that would be another matter, but you sound like a rank amateur regarding electrical power and safety. And that is scary. If the electrician says to go ahead with 12 gauge, than do it. But don't be so cheap with this part of the project that you put yourself (and others) in peril.Rich
"It's funny how often insurance adjusters report that was the last thing the homeowner said before the fire burned the place down. That and, "Reimbursement denied for violation of electrical codes.""It is funny how often I have seen statements like that in many different forums.It is also funny how often I have asked people to quote where it says that in their insurance policies.And it is funny that I have gotten EXACTLT zero listings of such wording.In fact I have not responses from insurance underwriters and adjuster indicating that they do cover such problems. As one said "they insure stupidity".
.
William the Geezer, the sequel to Billy the Kid - Shoe
A not so funny story about this very thing.
A nice 3.5 million dollar house was just finished in a posh golf burg in Scottsdale, AZ. The owers borrowed the builders truck so they could get their mattress and haul it up to the new house for the first night! They were turning on lights and trying things out. They left some lights on after the first trip, went back to town and returned the truck, got some dinner and went back home.
When they got there the house burned right down the middle and was near a total loss. Hoses, firetrucks, water on wood floors etc. The cause of the fire? A low voltage lighting ciruit in the Theater room. Seems an installer could not find the wire he installed before drywall. No problem just jump off of another light circuit. It is only 3 lights so no big deal. Well they were using 16 guage wire and 50 watt bulbs. The transformers were big ring transformers with no thermal protection etc. The wire got hot, reallllly hot and melted all the insulation off. Since they were run in a common gang they heated the other wires as well which then had enough plastic to catch fire and then the whole thing has heat source and the fire was on.
The owner had closed on the house, so it was their HO insurance that was the lead insurance investigation. The builder, and the installer of the lights (theater company), and the electricans insurance were called in as well. I was also brought in, we did the landscape lighting, but were released.
Bottom line, 2.5 million to rebuild the house, 9 months to do so. The builders insurance company did not renew him, when he found a company do so it was 4 times the rate. 36000 a year. His reputation was ruined, and he has moved. The Theater company lost their ability to install and has suffered as well.
Yes they insured stupidity, but why BE STUPID in the first place.
If you don't know what you are doing with electrical work, hire someone to do it for you, and check their work! They may be licensed, but they can make mistakes.
AZMO <!----><!----><!---->
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-------(*)/ (*) http://www.EarthArtLandscape.com
How right you are. For instance up here in Canada we get the spiel from retailers that if we buy something like appliances in the US for our home, our house insurance will be invalid if they don't have the CSA (Canadian Standards Association) sticker on them and the joint burns down. That is so much bull s*it. No such clauses in homeowner policies. And I read these things from beginning to end (comes from being an underwriter about 45 years ago).Commercial operations are a completely different story however.Cheers,Peter
Better life through Zoodles and poutine...
"Two hot wires go to the hot leads on the wall receptacle, and neutral/ground goes to the third. "
There is no such thing as a neutral/ground.
The grounded conductor (the neutral) and the equipment grounding conductor (the ground) are two completely different conductors and serve different purposes.
The grounded conductor is identified by being white or gray.
The equipment grounding conductor is bare or green or it might be metal raceway (conduit)
They are only allowed to be connected at one and only one point. That is that the service disconnect.
We don't know if the panel where is he connecting the ground wire is the service disconnect or not.
The correct instructions would be to connect it to the bus bar that has other ground conductors connected to it.
The other thing is that the white wire in the 12/2 is not being used and the grounded conductor, but rather as a one of the hot legs for the 240.
Thus the white wire is suppose to be remarked a different color. Typically it is black or red tape or markers. Do this at each end.
William the Geezer, the sequel to Billy the Kid - Shoe
I suggest that you get one of the basic wiring books such as Rex Cauldwells "How to Wire a House" or Black and Deckers Advance Wiring.
There are lot so little details such how long to leave the wires and the use of romex connects that it hard to spell out everthing in the forum.
You can get those at most home horror store, bookstore, or library.
William the Geezer, the sequel to Billy the Kid - Shoe
"You sent this to me. You should have sent it to the OP. "
I sent it to you because you are the one that is give out wrong information. Like you just did with the message above where you said that it was OK to use 6-3 on a 100 amp circuit.
And by sending to you we can discuss which details are correct.
Otherwise the OP just see someone says to do it one way and another says to do it a different way and the only thing that they have learned is confusion.
"green goes to the neutral/ground bus bar (whatever the f@##$ you wann call it)."
What you don't realize that not all panels have a neutral/ground bus. Was trying to point that out without getting into all of the hairy details.
In some cases the panels have a ground bus and a separate bus that is ISOLATED from the grounds.
"Whatever color (in this case, white) becomes a hot lead gets marked with either red or blue tape in the service panel, to signify that it is carrying load."
Yes, but you did not say that.
And that is an import step.
A step that is probably more often not done than done. It prevents problems later such a the next HO wondering why there is a funny receptacle and replacing it with a 120 volt one.
In another forum I often see message where some one has changed a light fixture in a circuit with a switch leg. They say that they connect all white wires together and all the black wires together and can't figure out why the circuit breaker pops when they turn on the switch.
If the circuit would have been properly installed then the white on the switch leg would have been remarked. And not seeing black and white they might have ask questions first. Even if they had not the worst thing would have been that the light was on all the time.
William the Geezer, the sequel to Billy the Kid - Shoe
You must be the sparky cop.
There is a right way and a wrong way to send a message, or have a discussion with someone to let them know you disagree with them.
The tone of your posts to me is, by a large margin, the wrong way to try and communicate with me. 'Nuff said.
drater--
12 gauge with a 20 amp breaker will be plenty, but you cannot use the bare copper wire in the 12/2/G as a neutral. You need two hot wires and an insulated neutral for a 220V circuit that services a 220V tool.
Better to run 12/3/G Romex (black and red (hots), white (neutral) and a bare copper ground).
Or run 12 gauge THHN (stranded) black, red and white in conduit. The metal conduit will be the ground. If you use plastic conduit, run a green wire, also.
kreuzie
Why do you need a neutral for a 220V tool?
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Men will never be free until the last king is strangled with the entrails of the last priest.~ Denis Diderot
That's what the NEC says. You need the neutral as the third current-carrying conductor. This is for 220V applications. A bare copper wire is to be used as a safety ground only.
kreuzberg
For 220v applications the neutral carries no current. The machine will function perfectly if it is absent. Even if the code requires it ( I have my doubts but don't have time to look it up) the tool certainly does not.
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Men will never be free until the last king is strangled with the entrails of the last priest.~ Denis Diderot
Kreuzie,
My 220v shop machines are 3 hp or less and use a NEMA-style 6-15 plug and receptacle. Two hots and a ground. No neutral. A neutral would be needed only if the machine also employed a 110v circuit.
Why do you need a neutral for a 220V tool?
You don't! There is no neutral in a 240 circuit. However, I am sure you already know this.
After the last "electrical" discussion I decided to stay away from them. I answered a question and got all manner of questions/responses with little ASCII drawings and what not. I was a journeyman electrician (about 15 years ago) till I pursued a different career path (I got tired of crawling through attics full of fiberglass because some little old lady wanted another outlet to plug her favorite knick-knack in.) I guess that doesn't matter much -- most are convinced they know how electrical circuits function. There's more to it than simply knowing the pertinent equations, or even the relevant section of the NEC. Knowing how to pull wire is also an important aspect that is overlooked. You wouldn't believe the wiring jobs I've seen: wire pulled tight in the corners, (it should have a nice gentle loop passing through a corner so it can give as the buidling settles) wire all twisted and snotted up, romex wire with the outer skin torn or abraded through. Believe it or not, I've seen wire that was pulled so hard that the actual conductors thinned as though they had been extruded. Scary!
Bottom line: wiring your shop is not difficult. Get a good book, follow the relevant codes and get it inspected. You'll save money and learn something in the process.
It was as you surmised a rhetorical question. Sometimes asking a question goes over better than telling someone they are full of cr*p.
I've done my own wiring for nearly 40 years (son of an electrician) and two degrees in electronics theory and design. Always have things requiring inspection inspected and always pass.
Agree completely about the importance of lead dress and the shocking lack thereof demonstrated by some supposed professionals.
Like you said, it aint rocket science.
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Men will never be free until the last king is strangled with the entrails of the last priest.~ Denis Diderot
"12 gauge with a 20 amp breaker will be plenty, but you cannot use the bare copper wire in the 12/2/G as a neutral."That is true."You need two hot wires and an insulated neutral for a 220V circuit that services a 220V tool."But you don't need a neutral for 240 circuit.I suspect that you are confusing it with a 120/240 volt circuit such as used on dryers and stoves.He is using the nema 6-20 (240) receptacle.http://www.stayonline.com/reference-nema-straight-blade.aspxIf you look you will see that there is only a ground and 2 hot connections.The modern connection for a stove or dryer is a 14 series. 2 hots, neutral and ground for 120/240 loads.To be complete older stoves and dryers used the 10 series. They have 2 hots and the neutral. AND NO GROUND..
William the Geezer, the sequel to Billy the Kid - Shoe
So far this post, your replies have been the most factual regarding both the NEC and sound installation practices. Kudos!
Thank you.
.
William the Geezer, the sequel to Billy the Kid - Shoe
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