220 V wiring question

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I recently inherited my dad's Delta/Rockwell Unisaw with a 220V motor. The saw is a dream to use compared to my old Craftsman.
Luckily my shop is wired for 220 but I have a wiring question...
The wall plug is a 4 blade and the saw has a 3 blade plug so I need a new plug for the saw. I was going to just buy a new 4 blade male plug and replace the existing 3 blade on the saw.
So do I wire the ground/common from the saw to the ground or to the common on the plug? I can't seem to figure out which is appropriate.
Or should I just buy a length of 12/3 and use all 4 lugs? Does it matter? I assume if I did that all I would need to do is screw the ground to the saw frame somewhere... right?
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No.
The saw needs two hots (of opposite phase) and a ground to function. It does not want or need neutral. The 4-prong plug will work fine. From the saw, connect hot, hot and ground to the appropriate prongs. Do not connect anything to the neutral prong. Its that simple.
Regards,
Steve
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Thanks Steve. That IS simple!
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"LA" wrote in message

If it's wired correctly, in your four plug wall receptacle there should be two hot leads, a ground, and a common (white) for a total of four. The latter (white) is used with one of the hot leads to supply 120v to appliance lights, timers, etc.
All you need to wire the saw correctly is the two hot leads and a ground.
If it were mine, I would change the wall plug to an appropriate female receptacle, wired as last above, for your saw's male plug, and cap off the common (white) with a wire nut and some electrician's tape, just in case you/next owner ever wants to plug a dryer/appliance back in.
--
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Last update: 6/21/06
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Thanks Swingman!
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First, before you make any changes, check the rating of the wiring to your 240V receptacle and check the rating of the fuse or circuit breaker protecting the wiring. The rating of the circuit breaker and wiring determines the receptacle used. If the circuit is not rated for 20 Amperes or is rated for more than 20 Amperes, then you'll be best served by having an electrician do what is necessary to get you a 240V 20A circuit.
Note that running your saw on a 50A dryer or range circuit is very dangerous, as the saw internal wiring, cord wiring and motor are not able to handle the large overcurrents that the 50A circuit is capable of providing.
If the circuit is a 20A 240V circuit and the wiring is at least 12AWG, replace the wall receptacle with the correct NEMA fitting to match the plug on the saw.
What you have on the saw is either a NEMA 6-15P or 6-20P. What you have on the wall is probably a NEMA 14-30R (or 14-50R).
Replace the NEMA 14-[53]0R on the wall with a NEMA 6-20R (which will accomodate either a NEMA 6-15P or 6-20P plug). When you replace the receptacle, clip the stripped end of the grounded (neutral/white) conductor, tape it off and stuff it back in the box; the NEMA 6-20R receptacle needs only the two current carrying conductors(typ. black & red) and the grounding (bare/green) conductor.
There is no point in running the grounded (aka neutral) conductor from the receptacle to the saw.
For NEMA patterns: <http://www.leviton.com/sections/techsupp/nema.htm>
scott
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writes:

This statement makes no sense to me. I can run my 3.5A drill just fine on a 15A 120V circuit. I can run a 100W light (0.8A?) just fine on the same 120V circuit. Heck, I can run a 6W (0.05A) light off a 120V 20A circuit, if I like. None of these are considered dangerous.
I'm not an electrician and I don't play one on TV, but my understanding is that the circuit breakers are designed to protect the circuit and plug, not the devices plugged into them. The motors typically have a thermal overload protector that switches them off if they over-heat or draw too much power. If the manufacturer is really concerned about that, they can provide a fuse on the device to protect it.
Clint
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Circuit breakers are designed to protect, first and foremost, the wiring from the circuit breaker to the protected device. The code makes exceptions for 20A circuits, as UL-listed small-appliance wiring is rated sufficiently to handle the transient overcurrent conditions on 20A circuits.
However, once the circuit breaker is rated higher than 20A, the code requires that everything downstream of the breaker (wiring, switches and motors) to be rated for minimum current matching the breaker.
Feeding 50A through #12AWG wiring is a recipe for disaster. Just because your saw doesn't pull 50A normally, doesn't mean that it won't pull that during a blade stall, for example. Melted wiring smells bad and causes other inconvenient events, like fires.

While the motor _may_ have thermal overload protection, and if you have an industrial motor controller, it also has thermal protection, the O.P. was planning on plugging his saw into the recept. That means #12 awg in the path between the overcurrent protection device (the circuit breaker) and the motor/motor-controller. That's your weak spot, and one of the areas the code is intending to protect.

Please read and understand the code. The manufacturer has no control over the wiring between the circuit breaker and his device.
scott
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NEC stops at the socket for devices that plug in. Put a plug to match the exisiting socket on your saw and you'll be fine.
--

Larry Wasserman Baltimore, Maryland
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Scott Lurndal wrote:

The code does not address anything that happens from the plug plugged into the outlet on out. You're confusing requirements for permanently installed equipment with requirements for stuff that is plugged into the wall.

If your saw doesn't have overcurrent protection then your saw is a piece of shit.

Please identify a UL listed saw that does not.

The code doesn't protect anything with a plug on it.

And the electrician has no control over what gets plugged into the wall.
--
--John
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Oh My My, I hear some truth here, and I hear some weird ideas here.
I am not an expert by any means, but having worked with electrical power and electrical circuits all my life, Up through 00000 gage wiring and copper bus bars, 100,000 amp motor generators, and 10,000 amp switches, and having rewound some motors, and rewiring several houses, I think that with close to 70 years of experience, that I am entitled to voice what I know to be true.
1. You will NOT melt the insulation from off of the wires by drawing more current through a wire than it can handle if it is fused (read that circuit breaker) correctly, for the fuse will open the circuit before any damage is done. The wire will not even heat up. And that is what the standards are for.
2. If a motor locks up for any reason, it will draw full current through it, even more current than when it starts, thus burning up the windings in seconds if the fuse does not open right away, or your thermal switch on the motor does not open. the reason - - When you first turn on the switch to the motor (the equipment type does not matter)there is applied across the windings the full electrical voltage and the resulting draw of current.(virtually a short circuit) But on this application, the motor starts to turn, and this results in a back voltage (reverse voltage) being created by the windings and turning armature, which then limits and reduces the apparent voltage across the windings to only one to two volts, which is what limits the current through the motor. This is what the windings of every motor is designed for. Under normal use, the actual voltage across the windings will remain in that one to two volt range throughout its normal usage, with its resulting current draw. It does not matter that you have 120 V. coming from the wall socket. (or 220, or 440 if designed for it)
3. It does not matter how much current or wattage a circuit is capable of providing, You will draw from that circuit only what the unit you are operating is designed to use, It is like you holding a water glass under the surface of a lake, it does not matter how much water the lake is capable of providing, you still will only get one glass full. . You cannot hurt it by running off of a Dryer, or electric range line assuming you are needing 220 volts.
Zap
J. Clarke wrote:

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your post, but the last sentence of the first paragraph, and the whole second paragraph quoted above are just SO WRONG!
--

Larry Wasserman Baltimore, Maryland
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Not to put too fine a point on it, but your saw only *needs* the two hots to run. True, there *ought* to be a ground, too, but that's a safety issue (and a pretty significant one), not a requirement for the motor to run.
If it were me, I'd get a length of 12 ga SJ cord (it has black, white, and green wires--all you need) at the big box and make myself an extension cord. Get an inline receptacle to match the plug on your saw and put it on one end of the cord, wired hot-hot-ground, and get an inline plug to match the receptacle on your wall and wire it hot-hot-ground. Ignore the neutral connection on the plug.
The nice thing about the SJ is it's usually bright yellow, so as to not readily disappear when/if underfoot.
Finally, what kind of plug is on the saw? If it's a molded (to the cord) plug, with a (--.--) configuration (which is a 240V 15 A Nema style), I'd leave it on. I consider the molded 240V cordsets to be like gold, but that's only in terms of trying to replace one.
Lots of people like the twist locks (I have one on my feed from the ceiling, but it's the first one I've had in 30 years), but they are bulkier and more expensive than the equivalent to your plug.
If there's a different plug on the cord, either put whatever you want on it or just select a matching receptacle when making up the extension cord.
--
LRod

Master Woodbutcher and seasoned termite
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I've found it's usually cheaper (and easier) to just get an extension cord with the right ends to match one side, and cut off the other end. That leaves just one plug end to buy and wire up. Less work and less money than building your own from scratch.
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Thanks all... I think you straightened me out and I know what to do next.
I appreciate the help!
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On Mon, 10 Jul 2006 21:39:06 +0000 (UTC), snipped-for-privacy@panix.com (Roy Smith) wrote:

Great idea for 120V. Where do you find 240V extension cords?
--
LRod

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LRod wrote:

There are several Ace Hardwares in my city that would have these. I usually buy extension cords for wire stock and buy any plugs needed for special applications.
Bob AZ
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LRod wrote:
>Great idea for 120V. Where do you find 240V extension cords?
You don't care, all you want is the wire.
Buy the lowest cost, #10, 2Wire with ground, molded cord set you can find.
Whack of the female and wire that end to the saw.
If the male plug is not what you want, whack it off and wire the correct one on to that end.
For a table saw, I like a 30A, locking plug, but that is my preference.
Problem solved, you'll be money ahead.
Lew
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On Tue, 11 Jul 2006 02:38:04 GMT, Lew Hodgett

Huh? Keep reading.

Okay, I get that part, although finding the #10 might be a chore...

This is my point. NEITHER of the ends will be what you want if the cord isn't a 240V extension cord. And to those who pointed out the 6' A/C extension cords, your saw must sit a lot closer to the wall with the socket than mine does. I figured 10-15' every time I've done it.

Well, the "money ahead" may amount to as much as $5-10, and none at all if you use the locking sets, which makes my SJ roll-your-own look just as attractive.
But, producing feline leather can be done a number of different ways.
--
LRod

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LRod wrote:
> Okay, I get that part, although finding the #10 might be a chore...
That's called shopping<G>.
Home Desparate should have them.
> This is my point. NEITHER of the ends will be what you want if the > cord isn't a 240V extension cord.
Sure they will. One end is hard wired to the saw, the other to a plug req'd.
BTW, the minimum insulation for cordage like SJ is 300V.
> And to those who pointed out the 6' > A/C extension cords, your saw must sit a lot closer to the wall with > the socket than mine does.
I'm with you which is why I suggested a 25 ft extension cord in the first place.
A molded cordset is the lowest cost way to get a piece of cable.
> Well, the "money ahead" may amount to as much as $5-10, and none at > all if you use the locking sets, which makes my SJ roll-your-own look > just as attractive.
You don't have to buy Hubbel. Lots of people make locking devices<G>.
> But, producing feline leather can be done a number of different ways.
I like my Model 12 Winchester for felines.
Lew
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