I have an existing solar PV system; conduit to the house carries DC pairs for two "strings" of solar panels plus EGC ground. It'd be very convenient for wiring of an EV charger (EVSE), if I could run its AC wiring in the same conduit. The EVSE would mount near the solar panels.

Conduit fill is no issue. We're talking five 10awg wires (for the solar PV) and three 8awg wires (for the EVSE). The conduit is 1-1/4". All the conductors are THWN.

I suppose Table 310.15.B.3.A requires me to de-rate the wires by 80%. Not an issue for the solar wiring, as the panels' short-circuit current is about 9 amps. But the EVSE can draw 40 amps (continuous, meant to be protected by a 50-amp breaker).

(1) Does Table 310.15(B)(16) and the 80% de-rating prevent my running the 8awg for the EVSE in the same conduit as the solar PV ? (I'm unclear which column to use).

(2) Do I need to run an EGC for the EVSE, or does the existing 10awg wire for the solar suffice ? The existing wire grounds the panels and racking and there is a ground rod installed at the panels.

(3) Is it ok to mix AC and DC wiring like this, if so is there some other restriction that would disallow it ?

NOTE: To those who have answered my question about adding an EVSE to an existing subpanel, this question refers to a different site.

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    Why do you need such a big EV -- oh, it's you :) Yeah, we've had these conversations I don't need to raise it again. Commented May 11, 2023 at 3:37
  • Seems kinda spastic to have an EVSE that's permanently set to a specific amperage. Wishing that adjustable Emporia (I'm gonna add at the other house) had existed when I bought this Clipper Creek one. Of course, the car will let me turn down the current, but pretty sure that's not an acceptable solution when sizing and de-rating conductors. Commented May 11, 2023 at 3:43
  • Yeah, I'm not happy about ClipperCreek on account of that. But I do recognize they were a pioneer who was out there doing it before all the best practices were figured out yet. I just wish they'd give their product lines another design cycle and get them updated. Probably UL Listing cost has something to do with that. Commented May 11, 2023 at 4:09

1 Answer 1


That 4-6 wire derate in 310.15(B)(3)(a)

Afraid so. The 4-6 wire derate will affect your circuit, smashing the 8 AWG copper down to 44 amps. 8 AWG Cu (and 6 AWG Al) are odd ones...the way the rounding happened, the 90C rating is unusually close to the 75C rating.

And since they don't let me help design EVSEs, major EVSEs do not have a 44A setting :)

Moot point anyway.

Solar + AC in the same conduit

Doesn't look that way.

690.31(B) Identfificaton and Grouping. PV source circuits and PV output circuits shall not be contained in the same raceway, cable tray, cable, outlet box, junction box, or similar fitting as conductors, feeders, branch circuits of other non-PV systems, or inverter output circuits, unless the conductors of the different systems are separated by a partition.

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    Actually, even though the install instructions for the Emporia don't list 44 amps as a possibility (instead they have the maximum for every multiple-of-5-or-10 breaker size, so skip from 40 to 48 amps) a response to my inquiry at their wesbite suggests that 44 amps is indeed possible: "The EV Charger can charge in single amp increments between 6A and up to the max charge rate set within the app. By default, that max charge rate will be 40A, but if you go with a hardwire installation then you can ramp that up to 48A as well. So max range would be 6A-48A, with any whole amp value in between. " Commented May 11, 2023 at 4:50
  • Sorry @Rusty I meant 44A breaker. Charge amps need to be 80% of that or <=35.2A. However, a "soft setting" you can do from the car or your easy chair does not count. The setting that prevents it from exceeeding (here) 35A must be welded down and not practicably accessible to the end user. Either by a) ClipperCreek's method, b) having to take it apart to access DIP switches (Wallbox), or c) a sufficiently byzantine Rube Goldberg commissioning procedure involving secret WiFi networks and singing "Pirates of Penzance" very loudly :) (Tesla Wall Connector 3.0). Commented May 11, 2023 at 23:07
  • Hmm, ok, so (at my other site) I'm installing this Emporia on a 25-amp breaker and planning to set it to draw 20 amps (as we hashed out in that other question). Seems like that 20 amps isn't "welded down" very hard, if it can be changed in the associated app. Still reasonably safe, I suppose, since the breaker limits the current to what the 10awg conducotrs can safely carry. Commented May 12, 2023 at 0:40

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