timk225
Active Member
Or people could quit trying to cheap out on proper electrical work and built their systems correctly in the first place, just sayin'........
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40 Amp Circuit for UMC Gen 2
- Thread starter Dynastar
- Start date
Or people could quit trying to cheap out on proper electrical work and built their systems correctly in the first place, just sayin'........
eprosenx
Active Member
I think the one with the fixed plug on the end is a Gen 1 unit but just with a fixed plug.
Not sure how you would tell... Do they look different? Or actually, I know. Does it have a UL listing? I don't think the Gen 1 device was UL listed but the Gen 2 device is UL listed. I am pretty sure the UL listing I looked up in their database did not list a version with a fixed NEMA 14-50 plug on it.
eladts
Member
What's the reason for not installing a 50A circuit? Unless 50A is too much load for your panel, the cost difference between 40A and 50A circuit is negligible. If that's the case, you can also install a 30A circuit with a 14-30 socket which will give you 24A charging and won't max out your panel.
eprosenx
Active Member
My reading of the code is that this would be totally fine. A 14-50 outlet is allowed on a 40a circuit from my reading of the code and the UMC Gen 2 with a 14-50 adapter nameplate value is 32 amps and so that meets the 80% rule.
With that being said, unless the wire was already existing and it was going to be prohibitively expensive to change, I would personally absolutely spend the few extra bucks to do proper wire for a 50a circuit and do a 50a breaker. The only delta cost would be the wire and any added install costs for larger gauge wire.
FWIW, my reading of the code from a load calculation standpoint would be that you would do the load calcs based on the actual load you will be plugging into that outlet, which is a UMC Gen 2 and it can only draw 32 amps. So I do not believe it would matter whether the breaker installed was a 40a or a 50a breaker. The actual power draw would be the same and I *think (check me on this), that the load calcs would be done the same way for either. The actual installed breaker capacity is not what matters.
Also, even if this did have an impact on your load calcs, I would totally install wire capable for 50a even on a 40a breaker. If you later upgraded your panel or service (or reduced load elsewhere like by installing a gas oven) you could up it to a 50a breaker later.
dhrivnak
Active Member
While the UMC will work perfectly I too would not advise as I can’t imagine it being more than $30 to put in a proper NEMA 14-50. Who knows what the next owner would do or if you may have a friend in an RV stop by expecting a full NEMA 14-50. Most people seeing a NEMA 14-50 would be expecting a 50 amp service.
Yay.
For more detail see eprosenx's response.
Ok, good, since that's what my electrician ended up doing for my Gen 2 MC.
- 50 amp stainless receptacle cover
- 50 amp receptical
- 50 amp double pole breaker
- 30' 8-3 romex
My understanding is 8-3 romex is fine for a 40 amp circuit (and 32 amp devices after 20% reduction), while 6-3 would be needed to run a 40 amp device on a 14-50 outlet (like a HPWC).
If the wire is sized for 40a (32a continuous), it should be in a 40a breaker.
eprosenx
Active Member
Yeah, all of this is fine except for the 50a breaker on 8/3 romex. That is DANGEROUS. That needs fixed. It would be fine on a 40a breaker.
I would label the receptacle “Fed from a 40a branch circuit” (i.e. it is not good for a full 50 amps as some might expect)
Yeah, that part doesn't meet code. You can do 8 gauge on a 50A circuit if it's separate wires in conduit, (more heat dissipation) but for Romex bundled wires, 8 gauge doesn't meet the rating up to a 50A circuit.
Ugh, I'll have to double check, but pretty sure when I took a look it was a 50A breaker.
So the wiring as it currently stands is fine for my current setup (using 32A Gen 2 MC), but needs to be corrected (replace 50A with 40A breaker or rewire with 6/3 gauge wire) to bring it up to code since someone could potentially plug in a 40A device in the future?
I'll also have to check the actual wire that was used to confirm it is 8/3. If it is actually 6/3, I am good to go, right?
This is not what I "yay'ed" to! Everything but the 50A breaker is fine. With the Gen2 UMC, you only need the 40A breaker. And for that wire you *should* only be using a 40A breaker because of its temp limitation. All else is fine. Swapping the breakers is super easy... and should be done.
If it is 6-3 you are golden. If it is a 40A breaker with 8-3 you are golden. And if you can't fit more than 8 gauge, then don't use ROMEX, and you can still create a safe, to-code 50A circuit with 8-gage wire rated for 75 degrees C (which is most spooled wire made for use in AC circuits and should be stamped right on there).
Just curious, is there any instance where the 50A breaker and 8 gauge ROMEX for a 14-50 is OK? Is it because the Tesla UMC is considered "continuous load" that the 8 gauge/50A breaker issue comes into play?
davewill
Active Member
No, a 50a breaker and 8 ga Romex are never OK. It has nothing to do with the continuous load part. The continuous load part is why you need a 50a circuit for a 40a EVSE or a 40a circuit for a 32a EVSE. I'd have done the 6-3 romex and 50a breaker, but the 40a circuit you have will work just fine. Just get the breaker changed. This was inspected? Inspectors DO miss things, but I wouldn't have expected them to miss this.
No, didn't get it inspected. However, this could all be a moot point if the electrician used 6 gauge wire. I see in a more recent quote he sent me it lists "6/3 wire" in the materials section. When I get home I'll confirm if the wire is 8 or 6 gauge. If not, I'll have him come back and swap out the 50A breaker for a 40A one.
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