JuiceBox 40 cable heat

[davewill]

10 gauge?!?! Seriously? I'm kind of angry at them just thinking about this, that they intentionally decided to build a device to use 40A continuous current draw and only used extremely undersized 10 gauge conductors. Regardless of how short, that's dangerously thin and resistive for that level of current. I'm not surprised at all that it feels hot. I would definitely keep the current turned down into the 20's, probably 24A, since 10 gauge is normally used for 30A circuits.

I agree with you that they should have used a 50a rated pigtail, but the one they used probably meets specs. A little searching finds that the 40a rated range cords generally have 10awg wire and the 50a rated ones have 8awg. Once you're past the wallbox, it's a different set of rules, and cables in air have different ratings than cables in wall or in conduit.

I'm also pretty sure the whole 80% rule no longer applies once you're out of the wall. However, if the cord is regularly getting that hot, they should have bumped it up...and the OP may want to do so for his own comfort and peace of mind. He could also simply set the JuiceBox for 30a and I'm sure it would be much cooler.

I just had to make a similar decision. I have an OpenEVSE and the J1772 cord and plug was rated for 40a, so I had my unit set to deliver 40a. The Rav4EV has the same charger as the original Model S, so it happily charged at 40a. Everything seemed OK, but I recently found that the plug was getting hot, and opened the housing to find that the wires inside had the insulation burnt off.

I bought a replacement cord and plug that was was more sturdily built and I now run the unit at 30a.

Here's the new one:

Funnily enough, it's Leviton branded, but the wire gauge is much thicker than the one I was using. It also has a much higher quality Yazaki branded plug which I've been using on my other EVSE for years. It's only rated for 30a, but unlike the one I was using, it really IS rated for that and specifically for EV use.

 

[DMC-Orangeville]

Well - the Canadian electrical code publishes tables showing maximum amperage allowed by a cable. Here is table 2, copper wire Not free air rated (your cable) You'll see that a 10 AWG cable should be rated for 30 amps (60C). If a cable has a 90C insulation, it could be used *in certain circumstances* for a 40 amp load.

Now....the cable used to supply the power to the Juicebox is NMD. NMD has its' own rating in Canada see below: NMD 8 AWG has a rating of 45 amps - too small for a 50 amp rated circuit. NMD 6 AWG is rated for 65 amps - so the electrician used the correct cable.. NOTE to the Americans on this post: This is a Canadian application, only. Why can an 8AWG cable be used on the Juicebox vs 6 wiring it in?(your question): - from CEC table, above- a 60C cable, 8 AWG, is rated at 40 amps. A 90C cable, 8 AWG, is rated for 55 amps. It will still get warm, but shouldn't get hot. I'd probably still recommend a 6 AWG cable.

 

[DMC-Orangeville]

Oh, well that answer is easy about 6 or 8. I'm more concerned about what is 10 gauge though.

Look at this ampacity table that shows the allowed current ratings for different wire gauge.
Ampacity Charts - Cerrowire

Look at the row for 8 gauge wire. See how under those first two columns, the 8 gauge is rated for up to either 40 or 50 amps? So this question of whether you can use it for a 50A circuit isn't just a "yes" or "no". It depends on the conditions of the installation--if someone is using Romex cable inside a wall (first column) or separate wires in conduit (second column).

Look at the row for 6 gauge. Those columns are rated for 55 or 65A. So can you use 6 gauge wire for a 50A circuit? Yes--always. So this is kind of the one simple answer factor. You can always recommend 6 gauge for a 50A circuit, no matter what type of install someone is doing.

Your explanation is correct, However, "Romex" (NMD or NMWU) in Canada has different current ratings than NM-B in the USA. See my post, above

 

[Rocky_H]

If a cable has a 90C insulation, it could be used *in certain circumstances* for a 40 amp load.

Very unusual circumstances that probably aren't applicable here, because you have to stay within the rated temperature limits of everything along the chain, including all of the connection lugs that clamp the wires. And most residential or normal commercial breakers and junction boxes don't have connection points rated to use above the 75 degree C rating, so you almost never get to use the 90 C column unless it's on very particular industrial kinds of things.

 

[TheRFMan]

Well - the Canadian electrical code publishes tables showing maximum amperage allowed by a cable. Here is table 2, copper wire Not free air rated (your cable) You'll see that a 10 AWG cable should be rated for 30 amps (60C). If a cable has a 90C insulation, it could be used *in certain circumstances* for a 40 amp load.
View attachment 641066
Now....the cable used to supply the power to the Juicebox is NMD. NMD has its' own rating in Canada see below: NMD 8 AWG has a rating of 45 amps - too small for a 50 amp rated circuit. NMD 6 AWG is rated for 65 amps - so the electrician used the correct cable.. NOTE to the Americans on this post: This is a Canadian application, only. Why can an 8AWG cable be used on the Juicebox vs 6 wiring it in?(your question): - from CEC table, above- a 60C cable, 8 AWG, is rated at 40 amps. A 90C cable, 8 AWG, is rated for 55 amps. It will still get warm, but shouldn't get hot. I'd probably still recommend a 6 AWG cable.

I though we were talking about the cord from the 14-50 plug to the JuiceBox. That is stranded flexible cord, not NMD, isn't it? I can't find the standard off hand, but I thought those were rated to higher currents because they are assumed to be in air, not in walls surrounded by insulation (which is why the electrical code prohibits their use walls or ceilings). Surely, if the device received UL certification, the cord must be adequate as per regulation.

That being said, I'm not too fond of regulations or standards that allow cables to get hot under load.

 

[Gasaraki]

Took apart the box and plug, everything looks brand new and it's over 3 years old used almost daily. I don't get the feeling the issue is the plug as it never gets hot. The line going from the breaker to the plug box is cool to the touch.

The only thing I can think of is the line going from the breaker to the plug box is 6AWG and the plug from the evse to the plug box is 10AWG. I'm going to try setting my M3 to charge at less than 32 amp. Can anyone else confirm if there JuiceBox 40 uses a 10AWG plug it better?

Umm, there's your problem... I would switch to 6 gauge between the plug and the wall connector box.

 

[MY-Y]

The Tesla HPWC Gen 3 provides 48 amps to my car through a cord much thinner than the pigtail between my 14-50 and JuiceBox. Yes, the HPWC cord gets warm. If I have two loops across the holder (top of the HPWC), it gets pretty hot.

I was concerned about the warmth of the 14-50 on my JuiceBox as well. Even charging at 32 amps (max for my other EV), it got quite toasty. At Rocky's recommendation, I swapped out the Leviton outlet for a higher quality one. I got a Hubbell 14-50 on Amazon for $70 and a new faceplate because the outlet is bigher. This dropped the temperature quite a bit. I posted about replacing the outlet in post #8 and the warmth of the HPWC cord in post #11 here: JuiceBox 40

 

[nateads]

With my JuiceBox being indoor wall mounted I'm tempted just to open the box again and run a 6AWG hardline right from the breaker strait to the JuiceBox with no plug. I cannot see that idea being any worse than the plug that is there now as it's I think a 8AWG and I don't find the breaker or white 6AWG wire to get warm at all.

 

[davewill]

Getting a beefier plug pigtail would accomplish the same thing and leave the possibility of using your UMC if the JuiceBox went down for any reason.

 

[MN-MS100D]

Do you know what size and what type of terminations were made by the manufacturer inside the unit? Do you still have a warranty? Do you care if you negate the listing of the EVSE?

I'd leave it as the manufacturer designed and constructed it. Contact them and tell them that the cable is too warm. Maybe they will do something about it.