Wiring 240 volt machine circuits

I'm running some new 120 and 240 volt branch circuits in my attached garage. I have a few machines that run on 240 (single phase) volts, including a table saw, an air compressor, a couple of other woodworking machines, and two welders. Thus far, I've been running all of the 240 volt machines on an extension cord (one at a time) connected to the clothes dryer receptacle, which uses the " old fashioned" three wire circuit; two 120 volt hot leads and a neutral to supply both 240 volts and 120 volts to the dryer. The neutral wire must also function as the equipment ground in this case. All of my 240 volt machines have run fine using that extension cord. If a 240 volt machine only needs 240 volts ( and not also 120) then running two 120 volt hot leads plus a green safety equipment ground wire, and no neutral, would be adequate. However, I'm concerned that some of my machines may need a dual voltage circuit, and I'll have to use the old three wire approach like my clothes dryer. My air compressor and my table saw both use Dayton Motor Control magnetic starters , and I'm not sure if they need 120 volts for the coils or not. My welders have fans in them, and they may need 120 volts also. All of my 240 volt machines have 3 wire plugs. Older machines that I may acquire in the future may also need both 120 and 240 volts . My question is, how should I wire my garage without putting new 4 wire cords on all my machines and going to 4 wire 240 volt circuits ? It might be difficult to convert three wire 120/240 volt machines to use a four wire circuit (two 120 hots, a neutral, and a ground) since the neutral wire may be grounded to the equipment case or motor in more than one place. Connecting a green safety ground to the equipment case might only result in accidently connecting the neutral wire to the ground wire inside the machine, which I assume is not desirable. I suppose I could run my new 240 volt circuits with 3 wires like my clothes dryer, but I've never been comfortable with the idea of using the neutral as an equipment ground, and I believe the recent NEC rules say not to use that type of circuit for new wiring. My wiring needs are only homeowner level, and not industrial.

"I believe the recent NEC rules say not to use that type of circuit for new wiring."

They were never allowed for anything other then ranges and dryers, & now even those are for existing circuits not any new installations. Once you leave your main panel (service equipment) the neutral (grounded conductor) and the grounding conductor must be seperate.

I'm not sure what the hassle is.

4 wire 240 is standard now for dryers etc. No biggie, and the plugs are cheap.

At the machine end, if it wants neutral, it will NOT be connected to the frame of teh machine, and if it IS, it should be a "protective earth" wire, i,.e. green wire.

If your machines are wired to use the "protective earth" or "equipment grounding conductor" as a power conductor, you need to FIX that.

You also have the option of using a transformer at the machine to supply 120V from the 240V. If that is an isolated 120V output, you DO ground one end of the secondary to the machine, so that can fix a wiring hassle right there.

To put this another way:

Some of your machines may only need 240 volts, and some of them may need
120 and 240 volts. You need to find this out.

The ones that only require 240 volts, will be wired with a connector that has three
conductors - the two hot legs, and a green wire protective ground, or groundING wire.

The machines that need both 120 and 240 will be wired with a connector that has
four conductors - the two hot legs, the white neutral, or groundED wire, and the
green protective ground wire, or groundING wire.

So you will provide receptacles appropriate for each machine, some with four
contacts, and some with only three. This means your shop will have various
branch circuits, some with the neutral, and some without.

In any case each one will be fed from a two pole breaker, just like your dryer.

The difference, because you are doing this correctly, you will never allow the
green wire, protective ground to ever carry any load current, the way your dryer
is set up now. So if there are any 120 volt loads, that load current will be returned
through the white wire (groundED wire) which is what it is there for.

You maybe need to brush up on the basics for this stuff by reading a book about
wiring, or even consulting with an electrician to help you put in the branch circuits.
If it is all exposed, in conduit, the cost would not be that much, and you could
be secure in the knowledge it was done correctly for sure.

Jim

Thanks for your replies. To clarify, none of my machines or appliances uses the green equipment grounding wire as a current carrying conductor. The clothes dryer, and the stove, however, do use the neutral ( white) conductor as a current carrying conductor as well as the equipment grounding conductor. I'll simply have to make sure that none of my shop machines also need a dual voltage circuit. If not, I can retain the three prong plugs on all of the shop machines, and make sure the third prong is used solely for the equipment safety ground. As you point out, if one of them does need a dual voltage, I can use the the white neutral wire and one hot lead to provide the 120 volts, which will require a 4 prong plug and receptacle.

You are still laboring under a minor misconception sir.

Your stove, and dryer, both have a groundING wire - the personal protection ground.

They do NOT have a groundED wire, or neutral wire.

There was a code rule exception that used to exist, which allowed ranges
and dryers, to return small amounts of load current (timers, lights) via the
personal protection ground wire.

So the bare wires that connect to the third prong in your dryer and range outlets
are really green, not white. Sounds funny I know but the exception (which no
longer exists for new construction BTW) says they are ground wires and not neturals
by definition. Even if the conductor happens to be white, it really should have
been tagged green, with tape, when installed, to signify this.

Jim

jim rozen said:

You are still laboring under a minor misconception sir.

Your stove, and dryer, both have a groundING wire - the personal protection ground.

They do NOT have a groundED wire, or neutral wire.

There was a code rule exception that used to exist, which allowed ranges
and dryers, to return small amounts of load current (timers, lights) via the
personal protection ground wire.

So the bare wires that connect to the third prong in your dryer and range outlets
are really green, not white. Sounds funny I know but the exception (which no
longer exists for new construction BTW) says they are ground wires and not neturals
by definition. Even if the conductor happens to be white, it really should have
been tagged green, with tape, when installed, to signify this.


Jim

Click to expand...

Wrong wrong , ranges and dryers are dual voltage appliances and they are grounded to the neutral when a 3 wire receptacle is used if one were to read the rating on the face of the receptacle it says 30A or 50A 125/250 volts which means it is not a grounding device.

I would defer to peter H. here on the matter, but if
you read the code rule exception, it allows return of
load currents through the groundING wire. NOT the
grounding via the groundED wire.

It's a ground, not a neutral. At least according to the
code book, unless I read (past tense, the exception
no longer exists) it wrong.

Jim

It is never allowed to use the grounding conductor as a current carrying conductor it was legal for frames of ranges and dryers to be grounded to the neutral prior to the adoption of the 1996 NEC (Section 250-60 1996 ed. , see 250.140 in newer editions) now it is only allowed for existing installations. Since ranges use 120 volt controls & lighting and a dryer uses a 115V rated motor & and 120V volt timer a neutral is required .

jim rozen said:

I would defer to peter H. here on the matter, but if
you read the code rule exception, it allows return of
load currents through the groundING wire. NOT the
grounding via the groundED wire.

It's a ground, not a neutral. At least according to the
code book, unless I read (past tense, the exception
no longer exists) it wrong.

Jim

Click to expand...

My copy of 1993 specifically reads "grounded circuit conductor", i.e. "neutral".

RMyers is correct.

Since it no longer is acceptable other than existing installations, and since it NEVER applied to ANY machine tools, the point IS a bit moot!

Well if that's what the book says, that's what it says.

So *I've* been laboring under the misconception all these years!

Folks thanks for educating me. Never too old to learn new stuff,
that's one of the benefits of this site.

Jim

"So the bare wires that connect to the third prong in your dryer and range outlets are really green, not white. Sounds funny I know but the exception (which no longer exists for new construction BTW) says they are ground wires and not neturals by definition. Even if the conductor happens to be white, it really should have been tagged green, with tape, when installed, to signify this."

There WAS an exception which allowed Class SE (service entrance) cable to be used for range, oven, cooktop and dryer branch circuits, and Class SE cable does have a bare groundED conductor, when used for its originally intended application: services.

This exception no longer exists.

Therefore, three insulated wires are required, one, the white one, being the combined return (groundED) and protection (groundING) conductor, for "old work".

For "new work", and for "old work manufactured residences", four wires are required, one being white, the groundED conductor, and one being green, the groundING conductor.

Whenever the exception was allowed, it applied only to ranges, ovens, cooktops and dryers, and never to any other "utilization equipment", and most particularly never to machinery nor to manufactured residences.

"Since ranges use 120 volt controls & lighting and a dryer uses a 115V rated motor & and 120V volt timer a neutral is required."

My clothes washer and clothes dryer use VFDs for their motors.

I suppose the lighting (dryer) is 120, but the heating (dryer) is 120/240, and the motors (washer and dryer) certainly appear to be 240 single-phase in and 240 three-phase out, with tachometer feedback.

peterh5322 said:

My clothes washer and clothes dryer use VFDs for their motors.

Click to expand...

At the moment, that is the exception rather then the rule there are millions of applicances ultilizing 120 volt componants...

Hmm. Sounds like Bosch......

Jim

"Sounds like Bosch..."

Sears, manufactured by someone else.

It IS Bosch-like, in some respects.