240 volt wiring - how many wires required?

[OptionalStop]

Does NEC require all 240v circuits to have a neutral wire in new construction? I know that the neutral is required for some appliances such as washers and dryers that would utilize 120v thus requiring the neutral but what about our garage tools like tablesaws and welders? Is it OK to use 3 wires (hot, hot, ground)?

 

[wyliesdiesels]

Does NEC require all 240v circuits to have a neutral wire in new construction? I know that the neutral is required for some appliances such as washers and dryers that would utilize 120v thus requiring the neutral but what about our garage tools like tablesaws and welders? Is it OK to use 3 wires (hot, hot, ground)?

There is no requirement for a neutral in a circuit for 240v utilization equipment.

Also, washers are 120v not 240v.

 

[Falcon67]

I used 10-3 for the lift because 10 was the manual spec (overkill IMHO for the motor draw but whatever) so I could peal off a 120V plug at the lift. The compressor uses a 240V run if 12-2 w/ground romex because it's only 3.2HP. The white is re-tagged as the other hot for the motor - no neutral required. The heater uses 10-2, no neutral required. Unless the end piece needs a neutral for something specific, you could pull whatever was cheaper.

 

[OptionalStop]

I used 10-3 for the lift because 10 was the manual spec (overkill IMHO for the motor draw but whatever) so I could peal off a 120V plug at the lift. The compressor uses a 240V run if 12-2 w/ground romex because it's only 3.2HP. The white is re-tagged as the other hot for the motor - no neutral required. The heater uses 10-2, no neutral required. Unless the end piece needs a neutral for something specific, you could pull whatever was cheaper.

Thanks. And, re-labeling white neutral wires as hot in romex is code compliant?

 

[wyliesdiesels]

I used 10-3 for the lift because 10 was the manual spec (overkill IMHO for the motor draw but whatever) so I could peal off a 120V plug at the lift.

What did you breaker the circuit at?

The compressor uses a 240V run if 12-2 w/ground romex because it's only 3.2HP. The white is re-tagged as the other hot for the motor - no neutral required. The heater uses 10-2, no neutral required. Unless the end piece needs a neutral for something specific, you could pull whatever was cheaper.

Technically, NM-b 12/2 is too small for that motor because a 3HP(17a FLC) motor needs ~21a rated wired. #12 NM-b is limited to 20a and your motor is a bit over 3HP.

 

[exranger06]

Thanks. And, re-labeling white neutral wires as hot in romex is code compliant?

Yes, it's code compliant.

 

[Norcal]

Thanks. And, re-labeling white neutral wires as hot in romex is code compliant?

As long as it is part of a cable assembly it is permitted to re-mark the white conductor but it is not allowed to do it with a white conductor in a conduit.

 

[Terry D]

Does NEC require all 240v circuits to have a neutral wire in new construction? I know that the neutral is required for some appliances such as washers and dryers that would utilize 120v thus requiring the neutral but what about our garage tools like tablesaws and welders? Is it OK to use 3 wires (hot, hot, ground)?

You are correct, if its a straight 240 v load, water heater, AC condenser, electric furnace then yes, all you need is 2 hots and a ground. In the old days, electric dryers and ranges only had a 3-prong plug. They bonded the neutral and equipment ground together, but later figured out that this was not such a good idea. So now, all new circuits installed for these appliances has to be 4 wire, which separates the neutral and ground. You can still buy 3-prong cords and receptacles for replacement. But if you are running a new circuit for these appliances, it should and needs to be a 4 wire circuit. You would use a 10/3 or 8/3 and so on depending on the load. And yes the neutral in these appliances is required because they also need 120 volts, like a electric dryer, the heating element is 240v but the motor is 120v

 

[sberry]

I change dryers to 4 wire when I get the chance.

 

[snickers muncher]

On mine and my family's hot water heaters I've always installed a neutral. Later someone might want to put a timer on it.

 

[Norcal]

On mine and my family's hot water heaters I've always installed a neutral. Later someone might want to put a timer on it.

Why do you need to heat hot water? Water heater timers have 240 volt timer motors.

 

[checkthisout]

What did you breaker the circuit at?



Technically, NM-b 12/2 is too small for that motor because a 3HP(17a FLC) motor needs ~21a rated wired. #12 NM-b is limited to 20a and your motor is a bit over 3HP.

All the automotive lifts I have installed in the last 10 years or so have always spec'd a 25 AMP breaker and 10 gauge wiring.

Of course there are different lifts but most automotive lifts seem to use the same SPX pump/motor assembly.

 

[snickers muncher]

Why do you need to heat hot water? Water heater timers have 240 volt timer motors.

You got me there.

I've only seen 120 timers. I didn't know 240 ones existed, but then again I haven't seen one newer than the 90's. That's certainly simpler and easier.

 

[Falcon67]

>What did you breaker the circuit at?

20A. The wires in the motor control box are 14 gauge so 20A is plenty even though I pulled 10 gauge. No trips.

Technically, NM-b 12/2 is too small for that motor because a 3HP(17a FLC) motor needs ~21a rated wired. #12 NM-b is limited to 20a and your motor is a bit over 3HP.

Interesting. No trips in 8 years. (3.2 HP x 745w/HP) ./ 240v = 9.93A. Assume the 21A requirement is for that momentary start surge?

 

[Falcon67]

Found a table that listed 3 HP motor as 17A FLA, 30A "Optimal branch circuit protection" and "Min copper wire Table 310.16" as 12. This should right? 3.2 is a bit over, agree. I should put a clamp on it running and see if that import motor is really pulling the expected current.

 

[MattT]

Interesting. No trips in 8 years. (3.2 HP x 745w/HP) ./ 240v = 9.93A. Assume the 21A requirement is for that momentary start surge?

Your calc is for output mechanical power not input electrical power. Motor isn't 100% efficient.

21A is a 1.25 times FLA sizing requirement in the NEC. It's basically so the motor can be ran continuously at FLA without the wire overheating.

Found a table that listed 3 HP motor as 17A FLA, 30A "Optimal branch circuit protection" and "Min copper wire Table 310.16" as 12. This should right? 3.2 is a bit over, agree. I should put a clamp on it running and see if that import motor is really pulling the expected current.

That table is for THHN wire which is good for 25A. #12 romex is only good for 20A which is why Wylie said you should have used #10.

And don't read too much into whatever amp readings you get. A lot of modern motors actual FLA is lower than the NEC FLA. And the compressor might not be designed to load the motor to 100% either.

 

[u2slow]

Found a table that listed 3 HP motor as 17A FLA, 30A "Optimal branch circuit protection" and "Min copper wire Table 310.16" as 12. This should right? 3.2 is a bit over, agree. I should put a clamp on it running and see if that import motor is really pulling the expected current.

Are we not using nameplate data before we revert to generic table values?

I have a 3hp 240V compressor also. (Speedaire portable.) Nameplate says 15.7amps FLA. Ships with a 6-20P plug. You guessed it... I wired it with #12 and 6-20R on a 20A breaker. Has worked that way in two different shops for 20 years.

 

[exranger06]

Are we not using nameplate data before we revert to generic table values?

I have a 3hp 240V compressor also. (Speedaire portable.) Nameplate says 15.7amps FLA. Ships with a 6-20P plug. You guessed it... I wired it with #12 and 6-20R on a 20A breaker. Has worked that way in two different shops for 20 years.

These NEC tables don't apply to cord-and-plug connected portable equipment. If you're hard-wiring a compressor, you're supposed to go by HP rating and follow the tables in the NEC. The nameplate data is basically irrelevant.

 

[u2slow]

These NEC tables don't apply to cord-and-plug connected portable equipment. If you're hard-wiring a compressor, you're supposed to go by HP rating and follow the tables in the NEC. The nameplate data is basically irrelevant.

That's funny. CEC says go by the nameplate. And somehow a cord-and-plug and makes undersized wire ok (according to NEC).

Its hard to take either Code seriously at times

 

[MattT]

That's funny. CEC says go by the nameplate.

NEC method makes more sense IMO. Their FLA covers any ** HP motor so you know the wire is good for a replacement motor so long as it's the same HP. Using the CEC method you might need to pull new wire if your replacement motor is less efficient.

NEC also makes quoting & running motor circuits really easy. All you need to know is HP. No trying to hunt down nameplate data, which can be a real problem if the motor isn't even on site yet.

 

[u2slow]

NEC method makes more sense IMO. Their FLA covers any ** HP motor so you know the wire is good for a replacement motor so long as it's the same HP. Using the CEC method you might need to pull new wire if your replacement motor is less efficient.

NEC also makes quoting & running motor circuits really easy. All you need to know is HP. No trying to hunt down nameplate data, which can be a real problem if the motor isn't even on site yet.

Not really... you simply size and quote on the info you have available. Machine first, table second. Its not like we get a choice which Code to use.

 

[Falcon67]

These NEC tables don't apply to cord-and-plug connected portable equipment. If you're hard-wiring a compressor, you're supposed to go by HP rating and follow the tables in the NEC. The nameplate data is basically irrelevant.

LOL, I'm off the hook - my 60 gallon compressor is cord-and-plug. Portable....well, sure - it sits on a skid in a closet and can be slid out and pushed around for service.

 

[exranger06]

LOL, I'm off the hook - my 60 gallon compressor is cord-and-plug. Portable....well, sure - it sits on a skid in a closet and can be slid out and pushed around for service.

But, is it ALLOWED to be cord-and-plug connected? Motors over 3 HP must be hard-wired, unless you're using a pin and sleeve type plug/receptacle that's rated for the HP.

 

[u2slow]

But, is it ALLOWED to be cord-and-plug connected? Motors over 3 HP must be hard-wired, unless you're using a pin and sleeve type plug/receptacle that's rated for the HP.

So why are 3-5HP compressors in the tool stores and Costco with 6-20P and 6-30P cords?

 

[alfredeneuman]

So why are 3-5HP compressors in the tool stores and Costco with 6-20P and 6-30P cords?

Those are "SP" HP ratings and greatly inflated^^^^^ due to the different way of computing versus the "true hp".

 

[u2slow]

Those are "SP" HP ratings and greatly inflated^^^^^ due to the different way of computing versus the "true hp".

Agreed... in which case my compressor is '6HP' per the propaganda. My shop vac is at least 4HP.

 

[wyliesdiesels]

So why are 3-5HP compressors in the tool stores and Costco with 6-20P and 6-30P cords?

where are you reading the HP rating? On the tank label or the motor nameplate?

 

[sberry]

My pressure washer is 5, heavy duty Baldor motor came cord and plug 30A

 

[u2slow]

where are you reading the HP rating? On the tank label or the motor nameplate?

Motor nameplate. (The one that matters.)

 

[wyliesdiesels]

Motor nameplate. (The one that matters.)

And the plate says 5HP or SPL?

Ive never seen a motor rated 5HP with a cord and plug.

 

[u2slow]

And the plate says 5HP or SPL?

Ive never seen a motor rated 5HP with a cord and plug.

Plate says SPL. FLA 15A. Then further down it says electrical output: 2.98kW (which is almost 4hp). Motor is a Dayton. KMS Tools called it 6hp. Acklands/Grainger calls it 3hp. Factory 6-20P cord.

The 5HP/6-30p corded machine was something I saw at Costco a couple years ago. Coleman or DeWalt 60gal upright model, I forget. Odd electrical things stick in my head.

 

[Norcal]

Plate says SPL. FLA 15A. Then further down it says electrical output: 2.98kW (which is almost 4hp). Motor is a Dayton. KMS Tools called it 6hp. Acklands/Grainger calls it 3hp. Factory 6-20P cord.

The 5HP/6-30p corded machine was something I saw at Costco a couple years ago. Coleman or DeWalt 60gal upright model, I forget. Odd electrical things stick in my head.

CEC may have different rules then the NEC.

 

[checkthisout]

750 watts per horsepower.

5 Hp harbor freight plug in compressor working off a 15 amp outlet. The math doesn't really workout.

 

[u2slow]

CEC may have different rules then the NEC.

Sure. Don't have my book, but IIRC, cord-connected things get to skip motor circuit sizing.

The speedaire 1NNF7 3hp portable compressor lists on US websites just the same. The online manual says it uses a plug connection. Would be an odd 'portable' if it needed hardwiring.

 

[wyliesdiesels]

Plate says SPL. FLA 15A. Then further down it says electrical output: 2.98kW (which is almost 4hp). Motor is a Dayton. KMS Tools called it 6hp. Acklands/Grainger calls it 3hp. Factory 6-20P cord.

The 5HP/6-30p corded machine was something I saw at Costco a couple years ago. Coleman or DeWalt 60gal upright model, I forget. Odd electrical things stick in my head.

SPL is meaning less. 15a FLA is close to 3HP and can be plug connected.

Was the 5HP with the 6-30p labeled 5HP on the motor nameplate?

750 watts per horsepower.

5 Hp harbor freight plug in compressor working off a 15 amp outlet. The math doesn't really workout.

That figure is for 100% efficiency but no motor is 100% efficient

Sure. Don't have my book, but IIRC, cord-connected things get to skip motor circuit sizing.

The speedaire 1NNF7 3hp portable compressor lists on US websites just the same. The online manual says it uses a plug connection. Would be an odd 'portable' if it needed hardwiring.

The issue with plug connected motors above 3HP is that there are no NEMA plugs rated for more than about 3HP and NEC code requires that the plug HP rating matches the motor HP rating

 

[sberry]

My pressure washer is on the motor name plate. It's heavy duty but has a 22 run plus a couple for the burner.

 

[u2slow]

Was the 5HP with the 6-30p labeled 5HP on the motor nameplate?

I can't remember. What I do remember is it needed more power and had a higher cfm than my Speedaire. Vertical 40-60gal tank. Probably a 3.7 or 5hp motor. I'm beginning to wonder if it was pre-wired with an minimal contactor/disconnect; I do know Costco often has products tailored for them specifically.