Installing Level 2 at Home (SOOW vs. NM-B) Which one?

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pr0lab

Active member
Joined
Nov 17, 2021
Messages
25
I am looking to install the level 2 charger myself and I was wondering which cable to do I need for an outdoor application for a 40 AMP breaker. I know that Romex 8/3 Stranded CU SIMpull NM-B Wire works for the inside but I actually need a cable for outside and I think the only one I can find is the SOOW, 600V cable but I am not sure if it's right for the 40 AMP breaker.
 
I've always used Romex UF cable for outside/underground use. Are you talking about above ground use like I believe SOOW is or underground wiring and yes 8G is good for 40a and the minimum for continuous Leaf charging with the OEM or a 30a EVSE.
 
thank you! it's actually mostly going to come from the basement and just about 5 ft. will go outside to where I need to install the outlet. and it will run under the deck. in this scenario, do I need just the SOOW (since UF is underground)? also, do I need 3 or 4 wires in that cable? I see that there are different variations for 3 and 4 wires that connect to the 14-50 receptacle and the 40 amp braker?
 
https://nassaunationalcable.com/blogs/blog/nm-b-electrical-wire-vs-uf-b-electrical-cable-are-they-really-interchangeable

I presume (needs to be verified) that any cable rated for direct burial is good for your outside run. 8G is enough copper.
If you want to, you can use a j-box to have NM-B inside and UF-B outside.
As a rule of thumb, you want the outside wire in conduit
 
Do I need a 50 amp breaker for a leaf? I read that 40 Amp is more than enough. please see below.

https://www.youtube.com/watch?v=UwdjWEV8tWA&t=621s&ab_channel=DIYable
 
pr0lab said:
Do I need a 50 amp breaker for a leaf? I read that 40 Amp is more than enough. please see below.
The electrical code says you want a 50A breaker for a NEMA 14-50 receptacle; then it be used for a continuous load at 80% (40A). If you put the 14-50 on a 40A circuit, you risk someone plugging something in that attempts to pull 40A. That could be ... bad.

Either way, your LEAF will max out at 27.5A when charging.
 
jlv said:
pr0lab said:
Do I need a 50 amp breaker for a leaf? I read that 40 Amp is more than enough. please see below.
The electrical code says you want a 50A breaker for a NEMA 15-50 receptacle;

You meant 14-50 receptacle

Like you, I match the breaker, receptacle, and wire. The possible safety repercussions are not worth the savings to me.

The way to save money is to wire for 6-30. Then 3 wires are used instead of 4, and it is a 24 continuous Amp circuit instead of 40 Amps. OP can also split the difference by installing 6-50: 3 wires, but more copper per wire to support 40 Amp continuous. It really depends whether OP wants to future proof his install for faster charging, or use it for things other than EV charging.

The difference between 30 Amp and 50 Amp copper for LEAF is ~ 10% charging time
 
I agree on the 50A breaker, but if you do use a 40, then clearly and permanently label the outlet "40 Amp Maximum." If you use a 30A EVSE then that does better match the breaker to the actual load.
 
Here is a table with the meanings of the insulation prefixes

https://www.multicable.com/resources/reference-data/wire-abbreviations-and-descriptions/
 
You can use a 40A breaker and 40A wiring with a 14-50 receptacle since there are no 40A NEMA receptacles. It is not uncommon.

I don't think SOO cable is what you want though. I would look for either SER, UF or something similar. You need wiring that is rated for outdoor (wet) applications. Al cable will be much cheaper but if it only has to go 5' that probably isn't an issue.

If you are under the 2020 NEC, the breaker should be GFCI protected meaning it would be best to use a 4-wire application.

Another option would be PVC conduit and THWN-2 wiring. Conduit is nice for protection and THWN-2 wire is cheap and can often carry more current for the same diameter but the conduit has to be installed correctly. Unless the wire is buried or protected somehow conduit may be the best choice.

I'd recommend getting the installation permitted and inspected. It doesn't cost that much and then you will know it was done correctly.
 
goldbrick said:
If you are under the 2020 NEC, the breaker should be GFCI protected meaning it would be best to use a 4-wire application.

I don't think this is correct. See
https://www.go-usg.com/t-publication-022019.aspx

So not only is it not required, I've read multiple threads of people that have the GFCI installed at the breaker and it causes EVSE faults. A decent EVSE has its own GFCI, and I think having two of them causes issues.

Calling @wwhitney for the real answer.
 
jlv said:
pr0lab said:
Do I need a 50 amp breaker for a leaf? I read that 40 Amp is more than enough. please see below.
The electrical code says you want a 50A breaker for a NEMA 15-50 receptacle; then it be used for a continuous load at 80% (40A). If you put the 14-50 on a 40A circuit, you risk someone plugging something in that attempts to pull 40A. That could be ... bad.

Either way, your LEAF will max out at 27.5A when charging.


Thank you, this is very helpful. My circuit board is 100 amp. is there a problem putting a 50 amp on that board? will be charging mostly at night so it won't be working with the washer or dryer but just thinking that it take a lot of the available amps. not sure if in reality that really matters.
 
The real answer will come from the AHJ, but I agree that Wayne is the guy on this forum. I was referring to 210.8(F) but as anyone who has tried to make sense of the NEC knows, there is usually a lot of room for interpretations in the specs.
 
pr0lab said:
Thank you, this is very helpful. My circuit board is 100 amp. is there a problem putting a 50 amp on that board? will be charging mostly at night so it won't be working with the washer or dryer but just thinking that it take a lot of the available amps. not sure if in reality that really matters.

Technically you should do a load analysis to see whether or not your panel can support the EVSE. Once again, I'd recommend getting a permit and inspection.
 
make sense on the permit and inspection.

It looks like the 14-50 can work with the 40 amp cable. I thinking of getting the following. Please let me know what you think folks!

1. Power Outlet Receptacle
https://www.amazon.com/gp/product/B082TV9B99/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&th=1

2. Conduit for the cable that is going to be outside
https://www.amazon.com/dp/B0756MLLD...uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

3. 8/3 NM-B wire
https://www.amazon.com/Romex-639492...s=50-Feet+8/3+NM-B&qid=1637262155&s=hi&sr=1-2

4. 40 Amp Double-Pole Type QP Circuit Breaker
https://www.homedepot.com/p/Siemens-40-Amp-Double-Pole-Type-QP-Circuit-Breaker-Q240U/100059673

a few questions:
1. how do I know if I need CFGI breaker?
2. what is the difference between 3 wire and 4 wire cables? and what breaker do I need for each?
3. can I purchase the 8/4 SOOW cable which is rated for outdoors and install it all the way from the basement to the receptacle outside? also for some reason this cable is rated for 35 amps even thought it's 8/4
https://www.ebay.com/itm/302179576000?hash=item465b4e68c0:g:vE8AAOSwawpXtfKo
 
pr0lab said:
a few questions:
1. how do I know if I need CFGI breaker?
2. what is the difference between 3 wire and 4 wire cables? and what breaker do I need for each?
3. can I purchase the 8/4 SOOW cable which is rated for outdoors and install it all the way from the basement to the receptacle outside? also for some reason this cable is rated for 35 amps even thought it's 8/4

1. Ask your inspector. It depends on what version of the NEC you are under and whether there are local ammendments to it.

2. For this application, 3 wire will have 2 hots and a bare ground. 4 wire will have 2 hots, 1 neutral and 1 bare (or green) ground. The hots connect to L1 and L2 in the breaker box. The ground wire connects to the ground bus in the breaker box. The neutral connects to the neutral bus in the breaker box. The 40A breaker you listed will work with a 3 wire circuit. If you need a GFCI breaker you will need to add an additional wire to the flexible conduit wiring.

3. You can't use SOOW for home wiring. The 8/3 cabling you referenced above should work fine with or without a GFCI breaker. If you need to use a GFCI breaker, you will need an additional wire in the 8/2 whip for the neutral. You could probably just buy 6' of white THWN-2 at your local store and run it through the conduit or maybe you can find an 8/3 whip pre-assembled. This assume the NM-B (Romex) is used inside with the transition to the 8/3 whip in a junction box for the outside run.

4. You probably already know this but be sure to buy a breaker that is compatible with your existing breaker box.
 
Thank you. I was able to locate the Massachusetts guide for EVSE and there is nothing there for CFGI

What is the reason for which I cannot use SOOW inside? Ideally I want to have 1 cable that goes uninterruptedly from the circuit board to the outlet. Is it possible to use the NM-B wire and put it in a conduit for the 6 ft that it needs to go outside?
 
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