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I have installed an EV level 2 charger in my garage. It is a 30 amp charger. It is around 8 feet away from the breaker box. I used 8/2 wire to be on the safe side for future possible upgrades and used a 2 pole 40 amp breaker, as required by the EVSE instructions.

The EV charger is working fine. The question I have is that the two hot wires are 8 gauge but the ground wire is a bare 10 gauge wire. Is this OK or should I replace the ground with an 8 gauge wire?

Jacob Krall
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Ali
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    If the data plate on the charger calls for a 30A circuit, you should use a 30A breaker to protect it. Using bigger wire is fine, but the breaker needs to be sized for the "appliance" requirements. – JPhi1618 Feb 10 '20 at 19:26
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    Does this answer your question? Why are ground wires required to be so large if a short results in an immediate breaker trip?, and this answer specifically has the NEC chart that lists the conductor sizes. You should be fine. – JPhi1618 Feb 10 '20 at 19:33
  • JPhil1618 Thank you for your reply. The appliance requires a 40 amp breaker. My concern is with the ground wire being thinner than the 2 hot wires. – Ali Feb 10 '20 at 19:36
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    For "the next time" consider that it's usually easy to run conduit 8 feet, and if the device's terminals go to 75C (and your breakers do - mine do, certainly) you can carry more current on THHN in conduit than you can on "the same size wire" as a cable (limited to 60C rating.) In the case of 8 Ga copper, 50 rather than 40 A. – Ecnerwal Feb 11 '20 at 01:21

2 Answers2

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Yes, a 10 AWG ground wire is fine for up to a 60A circuit.

The 8/2 Romex (NM) cable is good for amperage up to 40 amps. However, the breaker must match the socket / EV charger spec. If the socket is a NEMA 6-30 or 14-30, the breaker must be 30A. If the EV charger docs specify 30A breaker, then that must be so.

Again, the 8/2 cable is perfectly fine for 30A or really any size up to 40A. So if your spec calls for a 30A breaker, you only need to change the breaker. 30A sockets will accept #8 wire.

It is possible that a 30A-nameplate charger might want a 40A breaker. The documentation will tell the tale.

Harper - Reinstate Monica
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  • Thank you so much for your help. So to make sure I have a good enough understanding of this thing, the ground wire is actually not in constant use and it is only there in case of a short or malfunction, that's why it does not need to be as thick as the 2 hot wires, right? – Ali Feb 10 '20 at 19:48
  • @Ali Correct. Flow on equipment safety ground only occurs during fault conditions. – Harper - Reinstate Monica Feb 10 '20 at 20:15
  • Thank you so much for your kind help. You guys are AWESOME. – Ali Feb 10 '20 at 20:20
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#10 then is only good for 30 amps , correct this before too many people see this

As requested, correcting this: using the chart from https://diy.stackexchange.com/a/151175/18078

enter image description here

Ecnerwal
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Jason Brookins
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