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Wire size for wall charger
- Thread starter bbwex
- Start date
OK, a little physics. Let's see what drives the code
Copper #6 has a resistance of .8 mohm / ft at 20C (that's round trip, both the black and red).
Loss is i^2 r, for 48A, 1.8 W / ft
For #4, it's 1.12 W / ft
The code writers said that it's safe to have 1.8 W when the wire is high-temp in a pipe
It's not going to have a lot of temp rise unless well insulated
now for 40A, the #6 loss 1.28 w/ft.
In most real world application, either would "work". But it's not to code, and that itself could be an issue.
I have never worked on a house, and not found things not to code. The inspectors don't check (can't spend the time) to that level, and the code has a lot of margin.
If you can get the electrician to change the wire. If your run is long, you'll loose less energy in the wire. If your run is 100', you'll save 70ish watts.
Copper #6 has a resistance of .8 mohm / ft at 20C (that's round trip, both the black and red).
Loss is i^2 r, for 48A, 1.8 W / ft
For #4, it's 1.12 W / ft
The code writers said that it's safe to have 1.8 W when the wire is high-temp in a pipe
It's not going to have a lot of temp rise unless well insulated
now for 40A, the #6 loss 1.28 w/ft.
In most real world application, either would "work". But it's not to code, and that itself could be an issue.
I have never worked on a house, and not found things not to code. The inspectors don't check (can't spend the time) to that level, and the code has a lot of margin.
If you can get the electrician to change the wire. If your run is long, you'll loose less energy in the wire. If your run is 100', you'll save 70ish watts.
mcorf
Member
In this situation I would not consider the charging setup to be safe until the Wall Connector is reconfigured for a 50A circuit. This can be done immediately. Once this has been accomplished you have time to deal with the electrician, the inspector and decide on a permanent solution that is satisfactory for all parties.
If an electrician installed your wiring, and if an inspector actually inspected it, then they both need to be fired. The LFMC installation in a garage is dubious and could be a Code violation because it is subject to physical damage, but more troubling is what we can't see. If your electrician fished the 6/3 NM-B in the 3/4" conduit, then it violates the 40% fill rule and could overheat. If he stripped the outer jacket off the NM-B and routed the unmarked conductors through the length of the LMFC, that is also a Code violation. Maybe he transitioned to THHN on the other side of the wall in a j-box. Also, where is the firestopping/vapor barrier? More pix please if possible.
There are some really good points on this thread. What many don't realize before owning an EV is how much heat a charging circuit makes. Not many devices come close to an 11 kW many-hour constant draw. It makes the circuit breaker very warm, the cord from the HPWC warm, my other EV makes the 14-50 plug quite warm (and that's just 6.6 kW). Bottom line, it's not a circuit to play code games with.
It looks like your wall is painted flat white. That's the easiest color to repaint. Why not just cut some holes, route 4-2 NM, 6 gauge THHN in conduit, or 6 gauge MC? Drywall repairs aren't that hard. (BTW the insulator on THHN and MC are rated for higher temperatures, which is why they can be 6 gauge). Cuttung the drywall makes it easier to route the correct wire and makes the final install look nicer.
It looks like your wall is painted flat white. That's the easiest color to repaint. Why not just cut some holes, route 4-2 NM, 6 gauge THHN in conduit, or 6 gauge MC? Drywall repairs aren't that hard. (BTW the insulator on THHN and MC are rated for higher temperatures, which is why they can be 6 gauge). Cuttung the drywall makes it easier to route the correct wire and makes the final install look nicer.
Uh, this is just now clicking with me from seeing the pictures again. I was thinking this was one wall connector. Are both of those wall connectors on this one circuit? The version 3 wall connector doesn't have circuit sharing enabled yet.
Huh, I hadn't noticed that was the same person. Yeah, that certainly could have. The Gen3 wall connectors do seem to be pretty twitchy about seeing heat problems and cutting their current down, and running as if it's a 60A circuit with this undersized wire might do that.
mcorf
Member
mcorf
Member
The wires run 30 feet from the breaker box above the drop ceiling, then a 90 degree turn and 17feet behind the dry wall in the garage to the chargers. The only place where there is the 3/4 inch conduit is when it comes out of the drywall in the garage.
I think we're kind of beating this beyond what it needs. That's a pretty involved install that they are not going to want to redo for free. They installed a 50A capable circuit. Demand the partial refund from what you paid for the 60A circuit that you did not get, and have them swap the breakers down to 50A to make it code compliant. Two complete separate 50A circuits is generally sufficient for the vast majority of uses.
Magnetic Flux
Member
As a licensed professional electrical engineer, I agree with what Rocky_H has said and what others have mentioned regarding the code requirements. What is installed there is not meeting code the way it is and should be remedied by one of the options listed previously. If you need specific code excerpts for reference or anything, I can supply you with them, just send me a private message.
Due to my background and being a bit crazy, I installed #4AWG THHN in conduit from my panelboard to a NEMA 14-50R receptacle (that was a pain!). Total overkill, but I wanted to future proof myself a bit since I expect EV chargers to keep going up in amperage for faster charge speeds and/or wireless charging to be common over the next 10 years. I wanted to be able to simply swap out my circuit breaker and go to a different charger later if needed.
No, a GFCI is not required in this case because these are hard-wired circuits. If the circuit included a NEMA 14-50R then it would require a GFCI.
So, your electrician apparently fished the NM-B in the undersized conduit. If so, it is not compliant even if you change the breakers out with 50A/2P breakers (which you need to do regardless).
Did your electrician do a house loading measurement to see if you have capacity to charge 2 Teslas?
The junction box would need to be accessible, so transitioning properly is unlikely.
Putting NM cable into short sections of conduit is sometimes code conformant if you call it a 'sleeve' instead of a conduit. But there are lots of limits on that, and you need to understand both the code and the local restrictions and conventions.
Stripping the sheath off of NM cable to fish through a conduit is a code violation for several reasons.
Conduit coming out of the wall like that isn't often seen in professional installations. Not just because it looks sloppy. There needs to be fire and vapor barriers. You can use mechanical support and firestop putty, but that is usually more expensive than doing it the standard way with an electrical box and plate. Every inspector that look at that will be thinking "I'll bet it's done wrong."
I do note that GE breakers are mixed with QP (probably Siemens) breakers. It's unlikely that the panel is listed for use with both. That's a good example of a common code violation is
Speaking of house loading measurements...while looking at the load calculation worksheet that was part of my permit package handled by the electrician for the install of a gen 3 HPWC with a 60a breaker I noticed that he used 60a x 240 = 14,440 watts. Since the charger is hardwired and rated to 48a, shouldn't it only be 48a x 240 = 11,520 watts?
No. The wall connector is rated for a 60A circuit. The maximum continuous load that can be drawn on a circuit is 80% of the nominal circuit amperage...but it's entirely feasible to draw the full 60A for short periods. Your car won't draw more that 48A but the calculation is for a generic device pulling the full current the circuit can provide.
Are you sure? I read the load calculation rules as using nameplate rating for hardwired devices, which would be 48A. The 125% derating on top of that is to account for said 48A being a continuous load.
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