What size AL SER for 50a RV feeder?

[LarryFine]

I need to run a 50a circuit about 70 ft for an RV receptacle. Is #6 aluminum SER large enough, or should I use #4? I think SER is supposed to be used according to the 60-deg column in Table 316 like NM cable is.

The run will be about 45' in the crawl space, and about 25' under the deck to a W/P receptacle on a deck post. There will also be a 50' copper RV extension cord and the RV's own 25' power cord in the circuit pathway, too.

With all of the above taken into consideration, I'm leaning heavily toward going with the #4 cable. Opinions?

 

[Dsg319]

Me personally I would just go #4, without VD calculations and being unsure of wether to use 60/75 degree column.

 

[wwhitney]

I think SER is supposed to be used according to the 60-deg column in Table 316 like NM cable is.

The relevant NEC section (338.10(B)(4) for 2017) has changed a lot over the past decade, so you need to check your version of the NEC. For example the 2017 says:

For Type SE cable with ungrounded conductor sizes 10 AWG and smaller, where installed in thermal insulation, the ampacity shall be in accordance with 60°C (140°F) conductor temperature rating.

Meaning you'd be able to use the 75C column in your application.

Cheers, Wayne

 

[LarryFine]

I agree with both assessments above. I can use #6, but will opt for #4 to compensate for voltage drop.

The #6 would be right at its limit, and the price difference is small enough to choose performance over cost.