My garage has a 50A 250V three-prong outlet on a 60A breaker that was used for a welder. I want to convert my PM 64A to the 230V setup and take advantage of this dedicated outlet which is not being used.
My question is, can I use this for my saw? I assume I would need to get the correct plug and receptacle (small 3-prong w/ the horizontal “blades”) and swap out the breaker to one w/ less amperage. Is it as simple as that? Obviously the three wires in place are heavy guage, so I don’t know if that will pose any problems. But I’m hoping it is as simple as that. If so, what amp breaker do I need? The saw is 15A on 115 (and 7.5 on 230).
thanks, Jake
Replies
I would call an electrician. A 60 amp circuit is probably wired with 6 or 8 AWG wire. Even though your saw will only draw 7.5 amp and a 20 amp breaker would be fine, you will have a problem wiring a 20 amp receptacle onto wire with that large a diameter. You will not be able to connect the wire to the device directly.
Leave the breaker alone and get the correct plug for the outlet. However you may/propbaly will have to rewire your motor. Instructions should be in your manual or you should be able to contact PM (maybe their website has the instructions or an online manual) to get the info.
Do NOT leave the breaker alone. The wire is fine being too large but a 60 amp breaker would not protect the machine or the proper outlet. A single outlet on a circuit must match the breaker ie: one 30 amp reciptical must have a 30 amp breaker. Safety wise (I don't know if an inspector would approve) you can properly splice #12 to the line end of the supply wire as long as the breaker is no more then 20 amps. If the original wire fits on the smaller breaker all the good. The wire is copper, I hope?
KDM, retired electrician
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
Thanks, I figured that would be the most important thing since 60A breaker is way too much to trip and prevent the saw from overloading. So, since the saw (wired for 230) draws only 7.5A, would a 20A breaker be too much? Do double pole breakers even come smaller than that?
I was wondering if the heavy guage wiring would be too thick for the smaller receptacle. I'll give it a try, but if not I'll run some lighter guage wire.
I have already taken a look at what is needed to rewire the motor. Very simple switch of two wires, so that is the least of my worries.
thanks everyone, I'm going to bed.
Edited 7/28/2005 11:54 pm ET by flamedmaple
Fifteen would be fine in this case and is the smallest you will find locally though other smaller ones are sometimes available from serious electric suppliers or the manufacturer. KDMKenneth Duke Masters
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
So what is the problem with switching to a smaller (20 or 15A) breaker but using the existing receptacle and simply wiring in the matching plug, which I found rated for 30A?
I keep getting conflicting info on that with some saying the plug/receptacle amperage needs to match the breaker and others saying that it is much like the wiring; i.e. as long as it is not rated for less amps, more is OK. Kind of overbuilding it in a sense. What is the risk in using the existing receptacle?
By code the plug needs to match the breaker.please excuse my spelling.
I keep getting conflicting info ...
because some of that info is coming from electricians or electrical engineers, and some isn't. ;)
Like BarryO said you'll get some good advice and some bad advice. The problem with using the existing receptacle is that
1) You or someone might plug it into a 30 amp circuit at some point and that would leave the motor unprotected.
2) Mixing sizes and types of plugs and receptacles is just bad in a general sense (and non-code). They make many kinds of noninterchangeable setups to avoid wrong voltage/current/phase/frequency connections. Overamperage is not the worst: If a 120 volt machine was hooked up to a 480 volt plug and somehow got plugged into a 480 source: BIG smoke!!
So larger wire in the wall is not a problem (other then the connectors on receptacles and breakers) but use the proper breaker, plug, receptacle it will avoid problems and worry, even if it costs a few bucks for parts or an electricians visit.
KDMKenneth Duke Masters
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
OK guys, thanks for all the input and the lesson in electrical connections.
I think I'll go the route of looking into a subpanel in the garage and have it done right (i.e. not by me). Even switching out receptacles would be a pain since the existing wiring is 6 ga and would likely be a bear to get it wired to the appropriate (smaller) outlet and done right.
As for whether it is worth it; it is. I have one outlet (std 110/15a) in the garage and due to layout I have to run the saw off an extension cord. It works fine for everyday stuff, but 8/4 type stock bogs the saw down, and the mess of having to plug and unplug the saw and then router table, shop vac, etc is a PITA. Having a subpanel out there w/ one or two dedicated 230 outlets for the saw and whatever my next bigger tool is will be a nice luxury.
thanks again, Jake
Jake,
Circuit breakers are not sized for the motor, they are sized to protect the wiring in the wall. Providing that the circuit breaker is sized properly for the wiring in the wall, you can leave it alone.
Ordinary home circuit breakers will also fail to open under certain conditions that could cause damage to the motor. To fully protect the motor you need a properly sized magnetic switch which will also contain a circuit breaker designed specifically for motor protection.
You can also leave the wall socket in the garage in place and just install a matching plug on the cord from the saw. The motor in the saw will need a minor wiring change to convert it to higher voltage, the instructions should be on the motor's name plate or on the cover of the motor's junction box. It is possible that the motor won't be dual voltage, but most are.
If the switch on the saw is rated for dual voltages, it will contain a wiring diagram for any changes needed. If it isn't rated for the higher voltage, which is quite possible, it will have to be replaced. A good source for magnetic switches is Grizzly.
If the existing switch is a magnetic that can handle the higher voltage, you may have to change a component called a heater in the switch that matches the overload protection of the switch to the motor size. Not all magnetic switches have replaceable heaters, some have a control that can be adjusted to the motor's rating.
John W.
Circuit breakers do NOT only protect the wiring in the wall!
This is turning into one of those Internet Urban Myths; one sees it stated alot.
Article 240-4(b) of the NEC describes how flexible cords and fixture wires are protected by the branch circuit overcurrent device, in those cases where a separate overcurrent device is not used (for example, with a plug-mounted fuse, as is common in the UK). Ampacity rating for these wires are different than those in-wall, and are described in Article 400.
As described in Article 430, the branch circuit breaker is sometimes used for motor protection, for small motors.
Bottom line here is, do not put a 60A plug on the saw; it is unlikely the ampacities of the saw wiring are this high. Do what Duke says, and replace the receptacle and breaker.
Both the breaker and receptacle will have the maximum wire size they can handle marked on them. If the existing wire is too small, you can "pigtail" on smaller guage wires. This assumes there is enough room in the receptacle junction box and the electrical panel, and that the existing wire is copper. Some inspectors don't like splices in electrical panels, but it is explicitly allowed in the Code provided there is enough room.
Edited 7/29/2005 1:19 pm ET by BarryO
Hi,
First of all, if it's running OK on at 110v I'd leave it alone. The only real advantage to running it on at 220v is a reduction in conductor size (the lower current draw allows for a smaller and cheaper wire) and the motor will run a little cooler. and some say it will be a little more efficient. But in your case it will probably not be worth the trouble. As far as power savings it will draw the same about the same wattage at either voltage. Since the power company is charging in KWH, you'll pay the same either way. But if you change the wiring to 220v, you will need to change the breaker to a double pole 15 amp which is the smallest size I believe you will be able to find for your panel. This will protect the receptacle which is rated for 15 or 20 amps and offer a lower trip level in case your motor fails or jams up. Since your existing wiring will handle the load OK, I would pigtail a #12 (rated for 20 amps) wire to it providing you have the space in the box and panel. Be sure to ground everything. The use of a magnetic starter on your saw is also a good idea since it affords motor protection through the overload relay. The heaters can be sized to trip at a current level close to the rating of the motor. Also if you have any doubts whatsoever about doing the work yourself, call a qualified electrician!
Pah
Edited 7/29/2005 1:58 pm ET by pah51
Circuit breakers are not sized for the motor, they are sized to protect the wiring in the wall. Providing that the circuit breaker is sized properly for the wiring in the wall, you can leave it alone....
I FULLY agree.. But you could always put in a small circuit breaker box. Four or so and tap off of that heavy gauge stuff...
John W. is correct, however there is no reason to leave the 50 amp breaker in there. A 20 amp will be more than enough and provide a little more piece of mind and it costs $10 or less. I've seen many posts on this site of people whos motors burned without ever tripping the motor over current protector. Really though if I were you I set up a little subpanel there and make use of the 50 amps.
Mike
This forum post is now archived. Commenting has been disabled