pulling wire; what gauge?

Just came home with a cayenne red Leaf and have been loving it so far.

We need to pull wires to make a dedicated circuit for charging. The 110V trickle charger is adequate for our driving needs now, but we want to future-proof the electrical installation in the event that we upgrade to a 220/240V EVSE later.

The panel is at least 50 feet from where the outlet will be.

AFAICT, for 110V charging we need:
- 20A breaker
- 12 gauge wire preferred (rather than 14), to reduce voltage loss
- standard polarized, grounded outlet (NEMA 5-15)

If we mod or buy a 220/240V EVSE, we would need:
- 40A breaker
- 8 gauge wire?
- whatever outlet the EVSE needs

First question: is any of the above incorrect?

Second: is there any harm in pulling 8-gauge wire now, to run at 110V?

Third: Can we get away with 10-gauge? I'm sure it's fine for 110V, but would it be safe for 220V?

20a breaker requires #12 minimum and #8 is fine.
Ampacity and length determine the wire size not voltage.

The marginal cost of larger wire is negligable.

Lots of info in this earlier thread.

TT

redzev said:

Second: is there any harm in pulling 8-gauge wire now, to run at 110V?

Click to expand...

Here's what I would do in your shoes.
Pull the 8 gauge, but pull 4 wires (hot, hot, neutral, and ground). Use a double 20a breaker and wire both a 240v and a 120v (5-20R) receptacle. Use the 5-20R for 120v 12a charging now, later upgrade your EVSE (use an L6-20R) or buy the SPX PowerXpress (can be set for 12/16/24/32a, use a 6-30R), and use the 240v receptacle for 240v 16a charging. In the future, you can remove the 5-20R and convert the circuit to to 40a 240v if and when you get a car that can utilize the higher capacity.

OR (what I'd really do)

Forget about 120v charging and run the 40a 240v circuit now. Buy the SPX, set it for 32a, and wire it up. All done and future proofed for a reasonable cost.

davewill said:

redzev said:

Second: is there any harm in pulling 8-gauge wire now, to run at 110V?

Click to expand...

Here's what I would do in your shoes.
Pull the 8 gauge, but pull 4 wires (hot, hot, neutral, and ground). Use a double 20a breaker and wire both a 240v and a 120v (5-20R) receptacle. Use the 5-20R for 120v 12a charging now, later upgrade your EVSE (use an L6-20R) or buy the SPX PowerXpress (can be set for 12/16/24/32a, use a 6-30R), and use the 240v receptacle for 240v 16a charging. In the future, you can remove the 5-20R and convert the circuit to to 40a 240v if and when you get a car that can utilize the higher capacity.

OR (what I'd really do)

Forget about 120v charging and run the 40a 240v circuit now. Buy the SPX, set it for 32a, and wire it up. All done and future proofed for a reasonable cost.

Click to expand...

Agree, but even in option 1, it is not recommended to install a receptacle for a higher current (6-30R) in a circuit rated for less (20A) even if you set the EVSE to 16A; it may lead to confusions and if an inspector is called in (which you should in any case, just to get the peace of mind and to have proof for your home insurance that the circuit is up to code) he/she will reject it.

Use #8 wire (#10 is still ok, but you get less voltage drop with #8) and a 30A two-pole breaker (or 40A if you want.

I just installer my SPX, consider buying it, it is a very nice unit.

davewill said:

Pull the 8 gauge, but pull 4 wires (hot, hot, neutral, and ground). Use a double 20a breaker and wire both a 240v and a 120v (5-20R) receptacle.

Click to expand...

Does code allow the 240V and the 120V outlet on the same circuit??? I'm guessing you have to pull 5 wires: hot & neutral for the 120V outlet, 2 hots for the 240V outlet, and they can share the ground, so long as it can handle the full fault current from either circuit.

tps said:

davewill said:

Pull the 8 gauge, but pull 4 wires (hot, hot, neutral, and ground). Use a double 20a breaker and wire both a 240v and a 120v (5-20R) receptacle.

Click to expand...

Does code allow the 240V and the 120V outlet on the same circuit??? I'm guessing you have to pull 5 wires: hot & neutral for the 120V outlet, 2 hots for the 240V outlet, and they can share the ground, so long as it can handle the full fault current from either circuit.

Click to expand...

I think you would need to go to a subpanel and branch as needed.

redzev said:

If we mod or buy a 220/240V EVSE, we would need:
- 40A breaker
- 8 gauge wire?
- whatever outlet the EVSE needs

First question: is any of the above incorrect?

Click to expand...

Some of the responses addressed this implicitly, but it might be well to state explicitly that this isn't exactly correct. Only certain 240v EVSEs need a 40A breaker, and the current LEAF never uses more than 16A, so anything larger than 20A is only useful if you are planning for the future. (That includes the case of getting a 30A or 32A EVSE now.) And of course you don't need #8, or even #10, wire for a 20A breaker, though it never hurts to have heavier wire.

What you do need, though, is two breakers, at least 20A each, ganged together.

Ray

amtoro said:

Agree, but even in option 1, it is not recommended to install a receptacle for a higher current (6-30R) in a circuit rated for less (20A) even if you set the EVSE to 16A; it may lead to confusions and if an inspector is called in (which you should in any case, just to get the peace of mind and to have proof for your home insurance that the circuit is up to code) he/she will reject it.

Click to expand...

If you have a single receptacle on a circuit, then the rating can be anything equal to or greater than the breaker. If you have multiple receptacles on a circuit, then all their ratings should match the breaker rating. [Exceptions: 50A receptacles on a 40A breaker, and 15A receptacles on a 20A breaker.]

amtoro said:

Use #8 wire (#10 is still ok, but you get less voltage drop with #8) and a 30A two-pole breaker (or 40A if you want).

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If you use #10 wire, your breaker must be at most 30A [for almost all circuits, including EVSEs].

Cheers, Wayne

tps said:

Does code allow the 240V and the 120V outlet on the same circuit???

Click to expand...

Yes, I believe that you can do this, although since it is a multi-receptacle circuit, their ratings will have to match the breaker, e.g. 20A 240V and 20A 120V receptacles on a 20A breaker. Since the current on one of the hot legs will be additive, you couldn't use a full 20A on each receptacle simultaneouly, but this is no different than any other multi-receptacle circuit.

Cheers, Wayne

planet4ever said:

What you do need, though, is two breakers, at least 20A each, ganged together.

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Actually you need to use a double pole breaker, which is typically manufactured as two single pole breaker ganged together with a common internal trip mechanism. If you take two separate single pole breakers and put a handle tie on them, then you will not get the common internal trip, which is a requirement for 240V loads.

Cheers, Wayne

tps said:

davewill said:

Pull the 8 gauge, but pull 4 wires (hot, hot, neutral, and ground). Use a double 20a breaker and wire both a 240v and a 120v (5-20R) receptacle.

Click to expand...

Does code allow the 240V and the 120V outlet on the same circuit??? I'm guessing you have to pull 5 wires: hot & neutral for the 120V outlet, 2 hots for the 240V outlet, and they can share the ground, so long as it can handle the full fault current from either circuit.

Click to expand...

I don't believe that is "legal". You will have to run separate neutral and hot for the 120V AND use a separate breaker.

Why add a 120v receptacle at all? Just run the 240v circuit for L2 and use an existing 120v outlet for trickle charging. If there's really no 120v outlet around, you could still charge at 120v off the 240v outlet. Just install a 4 prong type of outlet (hot, hot, neutral, ground) like a 14-30 (although you probably want either a 20 amp or 40 amp circuit, not 30) and make a simple adapter. Cut off the female end of a 12 or 14 gauge extension cord and wire the other end to a plug to match your 240v outlet. Black to either of the hots, white to neutral and green to ground.

Appliances like dryers that use these types of outlets use both 240v and 120v by making circuits with hot-hot or hot-neutral, so there's no reason you'd have any code problems or anything running 120v off a 240v outlet. But I think the external adapter solution is cleaner than adding an extra 120v receptacle on the circuit.

To install a 240V/40A circuit to my garage, my electrician recommends running two #8 hot wires and one #10 ground wire through a to be installed underground conduit at a depth of 6 inches below ground. He didn't say anything about the type or size of the conduit or the type of wire. I assume it will be THWN rated wire through a 3/4" rigid metal conduit. Is there any advantage using rigid vs intermediate metal conduit or going to a smaller or bigger size? Thanks.

lukati said:

To install a 240V/40A circuit to my garage, my electrician recommends running two #8 hot wires and one #10 ground wire through a to be installed underground conduit at a depth of 6 inches below ground. He didn't say anything about the type or size of the conduit or the type of wire. I assume it will be THWN rated wire through a 3/4" rigid metal conduit.

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I take it this is a detached garage, since you are talking about burial? 6" burial depth is quite shallow, but it is allowed as long as you use rigid or intermediate metal conduit, and you don't go under your driveway. The 6" is a minimum cover requirement, so your trench will need to be 7" or 8" deep.

Note that you are only allowed one circuit or feeder per structure (under most conditions). So a single circuit for your EVSE will be fine if your garage doesn't already have an electrical circuit or feeder. If it does, you need to run a single feeder for all the electrical loads, which would require including a neutral conductor and installing a grounding system at the detached garage, if there isn't one already.

lukati said:

Is there any advantage using rigid vs intermediate metal conduit or going to a smaller or bigger size? Thanks.

Click to expand...

For this application, I don't seen any advantages for rigid versus intermediate, so just use whatever is cheaper, probably rigid. As for the conductors, #8 Cu is the minimum for 40A circuit (in almost all applications), so downsizing would mean switching to a 20A circuit for a 16A EVSE. Upsizing should be considered depending on the distance involved to avoid excessive voltage drop, although if you are only going to be drawing 16A on the circuit for the LEAF, it is already upsized. As for upsizing the conduit, the only advantage would be the possibility of upgrading the conductors in the future through the same conduit. Plus, depending on the distance, it might be noticeably easier to pull your conductors through a 1" conduit than through a 3/4" conduit.

Cheers, Wayne

lukati said:

To install a 240V/40A circuit to my garage, my electrician recommends running two #8 hot wires and one #10 ground wire through a to be installed underground conduit at a depth of 6 inches below ground. He didn't say anything about the type or size of the conduit or the type of wire. I assume it will be THWN rated wire through a 3/4" rigid metal conduit. Is there any advantage using rigid vs intermediate metal conduit or going to a smaller or bigger size? Thanks.

Click to expand...

I have a similar situation. I'm getting ready to have a garage built and the electrician I talked to recommended a 60 amp sub-panel be installed in the garage and that I install a 1" gray PVC? conduit at 12" below grade from the basement main-panel to the garage (about 40 ft).

I was putting in an underground sprinkler system at the time (last year), so I trenched a little deeper, and put it down about 15"-18" below grade (about 3" below the white PVC for the sprinklers). Now, last week, when I talked to my contractor, he thought the 1" conduit might be too small to pull the wires. What size wire and cable will be needed for the 60 A sub-panel? I'm assuming it's probably four wires, two hot, one ground, and one neutral and probably #6. Is that do-able? It's a straight run (except two 90 degree elbows, one about 4 ft from the main panel and one at the garage coming out of the ground. I've even put a pull rope inside the conduit, so it's ready for pulling.

Reddy
Driving the only Red Leaf in town since 8/18

Reddy said:

I have a similar situation. I'm getting ready to have a garage built and the electrician I talked to recommended a 60 amp sub-panel be installed in the garage and that I install a 1" gray PVC? conduit at 12" below grade from the basement main-panel to the garage (about 40 ft).

I was putting in an underground sprinkler system at the time (last year), so I trenched a little deeper, and put it down about 15"-18" below grade (about 3" below the white PVC for the sprinklers). Now, last week, when I talked to my contractor, he thought the 1" conduit might be too small to pull the wires. What size wire and cable will be needed for the 60 A sub-panel? I'm assuming it's probably four wires, two hot, one ground, and one neutral and probably #6. Is that do-able? It's a straight run (except two 90 degree elbows, one about 4 ft from the main panel and one at the garage coming out of the ground. I've even put a pull rope inside the conduit, so it's ready for pulling.

Reddy
Driving the only Red Leaf in town since 8/18

Click to expand...

I have a 60A Service to my existing garage, its run in a 1" PVC conduit, about 25' total, 2 underground 90 degree sweeps, and a few 30 degree ones as well to change directions. It was NOT easy to pull the 4 wires in it, I would recomend going with at least a 1 1/4" or a 1 1/2" conduit and upsizing your service to 100A minimum. Of course if you already have the 1" conduit, you are limited to the 60A service, and make sure you use a lot of lube pulling the cables, its not easy. FYI, my service is using (4) #6 THHN wires (hot/hot/neutral/ground)

Thanks!

Reddy said:

I have a similar situation. I'm getting ready to have a garage built and the electrician I talked to recommended a 60 amp sub-panel be installed in the garage and that I install a 1" gray PVC? conduit at 12" below grade from the basement main-panel to the garage (about 40 ft).

Click to expand...

The minimum cover for non-metallic conduit is 18" in general.

Reddy said:

What size wire and cable will be needed for the 60 A sub-panel? I'm assuming it's probably four wires, two hot, one ground, and one neutral and probably #6. Is that do-able?

Click to expand...

According to the NEC Chapter 9 Tables, 1" schedule 40 PVC conduit can hold a maximum of 6 #6 wires. So 4 #6 wires will fit fine, although depending on the length it could still be a difficult pull. Note that if you emerge from the ground outside, you need to use schedule 80 PVC for the sweep and the exposed portion of conduit, and 1" schedule 80 PVC conduit can only handle 5 #6 wires.

As for sizing the wires, it is a little complicated. For the ground (EGC), you only need a #10 copper conductor for 60 amps or less. #6 Cu @ 75C (e.g. THWN conductors) is rated at 65 amps, so it will work for the hots. If you use #8 Cu @ 75C, your rating is 50 amps, so you'd need to use a 50 amp breaker. [There is a complicated way to use #8 Cu @ 90C (THWN-2) with a 60 amp breaker, but I will omit it.]

As for the neutral, you only need to size it for the maximum unbalanced load (120V loads not balanced by another load on the opposite phase). Since the EVSE is a 240V load (balanced), then if you are using a 16A EVSE, and your load for everything else is 40A or under, then you could size the neutral for 40A and use #8 Cu.

So I suggest (2) #6 Cu hots, (1) #8 Cu neutral, and (1) #10 Cu EGC. Don't forget the grounding electrode system for the detached garage--if you are pouring a new foundation for the garage, you need to install a concrete encased electrode (Ufer ground), which can be your only grounding electrode.

Cheers, Wayne

Wayne:

Thanks for all the great info. I'll have to dig down and check to see whether I actually got 18" deep. I'm starting to think that my previous electrician didn't really provide me with the best info. Well, at least it didn't cost me much, a couple of pieces of PVC conduit, since I was already digging the trench.

So now two things confuse me about what you said. I assumed that all four wires would be in a single cable (you know, standard for that application, pick your service needs, size it up and purchase all in one like the 7 wire cable I used for my sprinkler valve controls). However, it sounds like you are choosing individual wires and running all four down the conduit. Is either method acceptable?

Second question on the ground. I'm not planning on doing any of this work, just interested. Yes, I am having a new foundation poured and assumed that a ground would be required. So I would assume that the ground spike is connected to the sub-panel ground bus. Then the ground wire in the conduit must connect the main panel ground bus and sub-panel ground bus. Is that correct? Boy that seems like a simple question now that I re-read it, so I guess it shows how simple my mind really works.

Reddy