50 amp circuit with 8 AWG, ENT

[marrt]

I'd like to verify my NEC understanding on 50 amp circuits...specifically, it's ok to run 2 hots and a ground, 8 awg in 1/2" ENT (gray flexible brand of choice) for a 50 amp (6-50r) receptacle, using a 4x2 (30.3 cu, in.) metal box. Further, box fill requirements would also be met using 6 AWG if a raised cover is used (adds 5 cu. in.). I realize, in theory, I could/should calculate these answers but I currently don't have access to the NEC code book and, to be honest, this question can be confusing. I'm looking for understanding/experience based answers. Thanks in advance.

 

[Dennis Alwon]

Number 8 wire is good for 50 amps at 75C assuming there is no nm cable involved you would be okay with that.
#8 has a value of 3 cu.in plus 2 for the recep, 1 for the equipment grounding conductor

2-#8 = 16 cu.in
1-#10 equipment grounding conductor = 2.5 cu. in
2- #8 for receptacle assuming it takes up only one gang= 16 cu .in

That is 34.5 cu. in-- no good for your box

 

[Dennis Alwon]

Btw, are you an electrician or a homeowner?

 

[wwhitney]

The NEC is available to read online at nfpa.org/70. Requires a free account, clunky interface.

For the 2017 NEC in use by VA, you can also read it at https://up.codes/viewer/virginia/nfpa-70-2017

Cheers, Wayne

 

[wwhitney]

BTW, I thought perhaps ENT was limited to a 60C rating, but the UL standard (1653) section 1.2a specifies a maximum continuous operating temperature of 75C. So #8 Cu in ENT does have an ampacity of 50A before any adjustment or correction. If do have to do adjustment or correction, you can't use the 90C rating of 55A as your starting point.

Cheers, Wayne

 

[marrt]

Thank you Wayne! I didn't know that was available.

Dennis,

I'm a shop owner. The last time I paid an electrician to run a 50 amp circuit, he used Al SE cable to a blue box (standard 18 cu. in. Home Depot special). Oddly, I've never seen anything to suggest the SE cable is not to code (assuming it's sized properly), but it's scary. The blue box is definitely too small.

As to your comment...

• I'm using 90C THHN+...no "romex" or SE
• Regarding 2-#8 = 16 cu. in., I'm confused (due to my lack of knowledge). What is the math to get a 16 cu. in. requirement from 2 #8 conductors with a volume allowance of 3 cu. in. per conductor?
• I'm using a green #8 for ground because it's what I have handy.
• It's a one gang receptacle. No loops or pass throughs. But the math for the volume allowance of the receptacle I don't understand. I "assumed" it was 2x the volume allowance for the conductors, or 2x3=6 cu. in.

I'm not challenging your answer, just trying to learn. Thanks for your help.

Tom

 

[Little Bill]

Thank you Wayne! I didn't know that was available.

Dennis,

I'm a shop owner. The last time I paid an electrician to run a 50 amp circuit, he used Al SE cable to a blue box (standard 18 cu. in. Home Depot special). Oddly, I've never seen anything to suggest the SE cable is not to code (assuming it's sized properly), but it's scary. The blue box is definitely too small.

As to your comment...

• I'm using 90C THHN+...no "romex" or SE
• Regarding 2-#8 = 16 cu. in., I'm confused (due to my lack of knowledge). What is the math to get a 16 cu. in. requirement from 2 #8 conductors with a volume allowance of 3 cu. in. per conductor?
• I'm using a green #8 for ground because it's what I have handy.
• It's a one gang receptacle. No loops or pass throughs. But the math for the volume allowance of the receptacle I don't understand. I "assumed" it was 2x the volume allowance for the conductors, or 2x3=6 cu. in.

I'm not challenging your answer, just trying to learn. Thanks for your help.

Tom

Sorry, but we are not allowed, per the forum rules, to assist those not in the electrical industry. There may be important things you fail to ask or you may not understand.