50amp circuits, wire size & type

[cliffcharb]

I'm getting ready to wire up my 240v circuits in the garage and trying to determine benefit of using conduit/8ga THHN, or 6ga NM. Material costs are similar and will be run within the studs, nothing exposed
50amp circuit for the compressor, 6-50r Short run of a couple feet
50amp circuit for welder/plasma cutter. 6-50r. Max amperage 45amps (Plasma) with a run of approx 40 feet
50amp for the RV. 14-50r. A Longer run of approximately 80 feet as its going up and over to the opposite corner.
Is 80' considered too long of a run for 50amp service using 8ga thhn, or should i just move up to the 6ga nm cable?

 

[sparky 1971]

I'm getting ready to wire up my 240v circuits in the garage and trying to determine benefit of using conduit/8ga THHN, or 6ga NM. Material costs are similar and will be run within the studs, nothing exposed

3/4" conduit in metal studs isn't easy, even worse in wooden studs. I see no reason not to use NM.

50amp circuit for the compressor, 6-50r Short run of a couple feet

If the compressor needs a 50 amp breaker it must be a 5HP and thus, cannot be plugged into a 6-50. It is supposed to be hardwired or plugged into a 5HP rated pin and sleeve connector.

50amp circuit for welder/plasma cutter. 6-50r. Max amperage 45amps (Plasma) with a run of approx 40 feet

Fine

50amp for the RV. 14-50r. A Longer run of approximately 80 feet as its going up and over to the opposite corner.
Is 80' considered too long of a run for 50amp service using 8ga thhn,

No

or should i just move up to the 6ga nm cable?

Yes, but only for ease of installation

 

[dcg9381]

50amp for the RV. 14-50r. A Longer run of approximately 80 feet as its going up and over to the opposite corner.

I've always done 14-50Rs (for RVs) in 6ga copper.
I looked at 8 awg thhn, was surprised to find it's rated for 50A at 70F.

But you might be missing this.. If it's in conduit, it gets de-rated:


Note, RVs won't pull anywhere near 50A (unless you've got one of Willie Nelson's busses with 3-4 ACs). I've "cheated" before and put them on 240V 30A circuits with a 14-50R labelled "30A" (and the appropriate breaker). You still have over 6kW available, which has run all the RVs that I've thrown at it, including 5th wheels.

 

[u2slow]

240V does not require heavy wire/cable unless the equipment needs the higher amperage.

My 5hp compressor is fine on #10 wire. (22Amp FLA).

My welders are on the modest side and run fine on a 20A circuit. There is a duty cycle calculation in Code to determine the minimum wire size.

 

[Wiz02]

@cliffcharb , are you running 50 A circuit, just because, which I totally get, since as @u2slow noted above, "5hp" compressor may really need only 22 fla, same type of situation may apply for your other loads. Unless you are running multiple devices simultaneously. Just a thought.

 

[theoldwizard1]

I'm getting ready to wire up my 240v circuits in the garage and trying to determine benefit of using conduit/8ga THHN, or 6ga NM.

6ga NM is a BEAR TO HANDLE !

 

[wyliesdiesels]

50amp circuit for the compressor, 6-50r Short run of a couple feet

what is the HP rating on the compressor? if more than ~3hp it will need to be hardwired as nema plugs and receptacles are not rated for higher HP....

 

[wyliesdiesels]

My 5hp compressor is fine on #10 wire. (22Amp FLA).

since as @u2slow noted above, "5hp" compressor may really need only 22 fla

NEC requires motor circuits to be sized based on table FLC not nameplate FLA. for 5hp, you need #10 in conduit or #8 NM-b...

 

[whateg01]

My 5hp compressor is fine on #10 wire. (22Amp FLA).

Because it's not 5hp. It's "5hp".

 

[Wiz02]

NEC requires motor circuits to be sized based on table FLC not nameplate FLA. for 5hp, you need #10 in conduit or #8 NM-b...

Thanks for the correction

 

[cliffcharb]

The shop has its own 200 amp service, and 40 space panel. Since I have lots of room each device will have its own circuit.
Some of this is planning for the future and just do it once now while everything is exposed.
Current compressor is a 3hp single stage, with a plan of upgrading to a 5hp two-stage.

My welder and plasma list 42-48 amp with 50 amp breaker. I think it’s a 40% duty cycle.

I have ran all of this equipment on a 50amp breaker in my attached garage on #10, but the plug is directly off the panel, so wasn’t sure if the length of the new runs were going to be an issue.

The #8 for the rv plug popped in my head as that’s what the electrician installed on my home during a remodel a couple years back. Again only a 25 foot run vs 80 in the shop.

As far as installation it will leave the top of the panel, up into the trusses then back down a stud to the receptacle.

 

[wyliesdiesels]

Because it's not 5hp. It's "5hp".

22FLA is about right for a true 5HP motor

 

[whateg01]

22FLA is about right for a true 5HP motor

Dang it! I've been thinking vfds lately which are often rated in kilowatts. 2.2 KW is 3 horsepower and that's where my mind went. My bad

 

[alfredeneuman]

You could run "Flexible Metal Conduit" as easily as NM (Romex) and have the option of adding circuits in the future by pulling additional wires.