The NEMA 10-30R has 2 Hots and a ground (not neutral) #8 wires running to it. There is also pair of wires (12 gauge black and white) running to the shed for a separate 120v circuit. It appears that the #8 ground is also being used for the 120v circuit as well. I would like to convert the 10-30 to a more common 14-30 recept for use with Level 2 car charger. Do I have the appropriate wiring running to the shed to achieve this conversion? (On a side note....since I have a ground on the 10-30 instead of a neutral and there are Level 2 chargers out there that are already set up to plug into a 10-30 recept, am I ok just leaving as is?) I still want to consider the conversion, since 14-30s are more common, having a charger with this plug configuration could then be utilized at other places besides mine. My existing circuit is 240v and has a 30 amp double breaker and the Level 2 charger I want to get only requires 240v / 16 amp. Thanks!
2 Answers
NEMA 10-30 does not have ground. That is incorrect. It does have neutral. You should not be using 10-30 for anything at all - it was outlawed at the same time 2-prong sockets were outlawed, when grounding went in in the 60s. Except due to lobbying by the appliance industry, NEMA 10 got a reprieve for ranges and dryers ONLY, until it was banned for that also in 1996.
They continue to be sold at retail, but only for repair of broken receptacles. But this is America, so there are no government jackboots restricting sales. As such, the banning of this socket type is widely flouted by suicide jockeys. Don't be one of them. There's a right thing. Use it.
How to convert your legacy NEMA 10 outlet to modern.
Generally we see 4 styles of wiring to those dangerous NEMA 10s.
4-wire (insulated neutral + ground)
Easy peasy - slap a NEMA 6 or NEMA 14 receptacle here as you please.
Hot, Hot, Insulated neutral (/3 without ground)
Your options are limited here. This is only legal if installed before 1996 (certainly true since this wire vanished in the 70s). If legal, you can convert this to NEMA 14, one of two ways - and again you cannot relocate this outlet.
You can retrofit a 10 AWG ground to this existing receptacle location, using the Retrofit Ground rules, chasing the ground wire back to either the panel, the Grounding Electrode, or any junction box with a valid #10 or larger ground back to the panel. Same panel, that is!
You can fit a 2-pole GFCI breaker, convert to NEMA 14 but ignore ground altogether, and label the receptacle "GFCI Protected / No Equipment Ground". It's a bit of a waste since an EVSE already has GFCI protection if it's not mail-order cheap Chinese.
Note that for the GFCI protection to work properly, the socket must be changed to a NEMA 14, and ground must be isolated from neutral!
NM or UF /2: Black-White w/ Bare ground wire
This was never legal for dryers or ranges. Lots of cheaters did it anyway.
But this works out great for you. You do want ground, so you can make it ground again, and use it with a NEMA 6-30 or 6-50 receptacle. (no NEMA 14).
You are using the white wire as a hot, so it must be marked with tape or paint (that is not white, green nor gray).
NM and UF cables are limited to 60C thermal ampacity rating (in table 310.15(B)(16).
- NM/UF #8 Cu must be breaker'd at 40A with a 6-50 receptacle, allowing 32A true charge rate.
- NM/UF #8 AL must breaker at 30A with a 6-30 receptacle, allowing 24A true charge rate.
SE cable: 2 black or red hots + BARE neutral web
Weird, huh? SE cable is Service Entrance cable which is mainly used on the utility side of the main breaker, where ground isn't established yet. It was legal for dryer/range circuits prior to 1996.
Yes, you CAN permanently re-task that bare web from neutral to ground, including moving it from the neutral to the ground bar in the panel.
This will allow you to fit a NEMA 6-50 receptacle. (no NEMA 14-50).
SE cable is allowed the higher 75C thermal ampacity, so
- #8 Cu is allowed 50A breaker, allowing 40A true charge rate
- #8 AL is allowed 35A breaker, allowing 28A true charge rate
EVSE's don't use neutral. NEMA 14 is wasted.
I don't understand why NEMA 14 is a fixation of people in the EV community. EVSE's don't use neutral (unless they are cheapo and use a 120V module inside their internal GFCI, which is stupid because it makes the EVSE unsellable outside North America).
You know the charger is on the EV... the EVSE is just a GFCI and disconnect. Really. Check out this video for a full rundown on that. Don't take my word on it, look right down the barrel of your J1772 connector (or Tesla equivalent). 3 terminals - ground and 2 conductors. NO NEUTRAL.
Installing a NEMA 14 receptacle requires you bring a fourth wire all the way from the panel. This is pointless and wasteful. Come on EVSE industry, stop with the NEMA 14 already!
The only viable reason to run a 4-wire to a NEMA 14 is if that outlet will be swapped out to power other things, such as an RV, which does take neutral for its numerous 120V loads. I suspect that versatility, or fear of old circuits, is why EVSE manufacturers is trying to "tear that decision out of your hands". Tell them to shag off.
If the EVSE needs a NEMA 14, it's stupid. Send it back.
If the EVSE has no requirement at all for neutral, but gives a 14-30/50 plug for no reason whatsoever, change the plug to NEMA 6-30/50.
NEC 2020 requires GFCI protection for receptacles
If your location is under NEC 2020, you need to have GFCI protection on all your 240V sockets. (which, again, is redundant for EVSEs). So if you are under NEC 2020, eliminate the socket and plug, and hard-wire the EVSE. If the EVSE does not support hardwiring, then send it back.
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It depends on what your charger requires! If it is a 240v charger hot-hot-ground yes you can use 10-30 or 10-50 they are not obsolete I just installed one recently for a 240v air compressor. (They don’t make a 40). The 50 with #8 wire is limited to a 40 amp breaker, most of us just bite the bullet and wire in #6 but since you have the 8 in place install a 10-50 and a 40 amp breaker and this is code compliant see NEC table 210.21.b.3 .
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