Suddenly my charge AMP limit isn’t being respected

[Zorak03]

Are usually charge my car at my work shop. I only have a 30 amp breaker so I set the charge limit to 29 A. It always worked fine before, but now after about an hour the charge limit drops to 16 A, and then about 30 minutes later iit jumps up to the 32 A max. I find I must constantly walk out to the car and reset the charge limit. This just started happening. Any idea why or how to fix it? So far, the breaker has not flipped but I don’t want to accidentally start a fire or something.

 

[w0ss]

Is there anything else on the circuit? You are supposed to set the limit to 80% of the breaker, so 24amps.

 

[brkaus]

Tell us more about this circuit with a 30a breaker? What type of outlet is on it? (or how are you connecting it to the car). What type of wiring. If possible, what is the starting voltage on the screen when it starts charging and does it change as the current ramps up?

As mentioned above, a 30a circuit should charge at a maximum of 24a.

If the car detects a problem in the circuit (voltage drops for example indicate high resistance, which may result in heat and then fire) it will automatically lower the current for safety.

If you have a proper 30a outlet and the matching Tesla 30a plug adapter the car will automatically limit the current to prescribed safe 24a.

 

[Zorak03]

Tell us more about this circuit with a 30a breaker? What type of outlet is on it? (or how are you connecting it to the car). What type of wiring. If possible, what is the starting voltage on the screen when it starts charging and does it change as the current ramps up?

As mentioned above, a 30a circuit should charge at a maximum of 24a.

If the car detects a problem in the circuit (voltage drops for example indicate high resistance, which may result in heat and then fire) it will automatically lower the current for safety.

If you have a proper 30a outlet and the matching Tesla 30a plug adapter the car will automatically limit the current to prescribed safe 24a.

I’m an idiot. I found the problem, I set the limit but didn’t confirm it. The outlet is 240 dryer plug, it was originally used to occasionally hook up a camper the previous owner owned. I’ve been using it for the last 9 months to charge my car while working. I usually just leave the mobile charger plugged in 24/7 but flip the breaker off when not using it (not sure if it’s necessary or not). I’m not sure what type of wiring but I believe the main circuit is 40 a (at least there are two 40 a breakers at the main circuit). I really know almost nothing about electrical stuff.

I was totally unaware of the 80% rule so just went and set the limit to 24 a.

It’s a small converted storage shed, about 350sq/ft we made into an art studio, the only other major electrical appliance is a window A/C unit that is connected to a 20 a plug. When it is running I lower the charging limit to 10 a.

 

[Zorak03]

Is there anything else on the circuit? You are supposed to set the limit to 80% of the breaker, so 24amps.

Sorry for the disagree. It was accidental. I’m on a cellphone and must have hit it by mistake. I corrected it, apologies

 

[davewill]

I’m an idiot. I found the problem, I set the limit but didn’t confirm it. The outlet is 240 dryer plug, it was originally used to occasionally hook up a camper the previous owner owned. I’ve been using it for the last 9 months to charge my car while working. I usually just leave the mobile charger plugged in 24/7 but flip the breaker off when not using it (not sure if it’s necessary or not). I’m not sure what type of wiring but I believe the main circuit is 40 a (at least there are two 40 a breakers at the main circuit). I really know almost nothing about electrical stuff.

I was totally unaware of the 80% rule so just went and set the limit to 24 a.

It’s a small converted storage shed, about 350sq/ft we made into an art studio, the only other major electrical appliance is a window A/C unit that is connected to a 20 a plug. When it is running I lower the charging limit to 10 a.

If he was plugging his RV into it, and it has a 40a breaker, then it is probably a 14-50 rather than a 14-30 "dryer plug". Check the chart below. Assuming it is, you can just let the car charge at the default 32a.

 

[Cosmacelf]

why do you have to set the amps at all? If you were using a dryer plug adapter, it would set the amps correctly.

 

[AlanSubie4Life]

found the problem, I set the limit but didn’t confirm it

So do you still have a problem with the amp limit or not?

A picture of the panel and the outlet would be worth thousands of words here - if you are still having some issue...

 

[Zorak03]

Here is the plug.

Here is the panel (inside the studio)

The breaker is on the far right. Everything was installed by a licensed electrician. I’m not having anymore problems with the amp limit, I set it down to 20 A just to be on the safe side. If I don’t set the limit it will charge happily at 32 A.

 

[Lindamon]

I’m confused, you say it was installed by an electrician? I’m not an electrician but I am an RV owner. That looks to me like a 14-50 50 amp service plug that I would plug my RV into. If it’s got a 30 amp breaker, I’m pretty sure that’s the incorrect plug type for the breaker amperage.

Can’t say whether it’s unsafe that way, I’m not an electrician and also have no idea how it’s wired, but I’d have an another electrician look at it, just to be sure.

 

[w0ss]

That is definitely a 50A RV plug 14-50. But based on the orange wire(10 guage) a 30 amp breaker would be correct. As long as you didn't pay for a 50 amp circuit and it works for you I would just leave it as is

 

[davewill]

Here is the plug.
View attachment 449175
Here is the panel (inside the studio)
View attachment 449177
The breaker is on the far right. Everything was installed by a licensed electrician. I’m not having anymore problems with the amp limit, I set it down to 20 A just to be on the safe side. If I don’t set the limit it will charge happily at 32 A.

Yeah, it's a legal installation, but the mismatch of the 30a breaker and the 14-50 does mean you have to manually dial the car down. It's not unusual to be able to pull a little more than the breaker's rating for a short time. I expect that the breaker would trip after some period of time at 32a. Keep it at 24a or less and you'll be fine without doing anything else, just keep an eye on the setting to make sure it doesn't reset on you.

If you were interested, you could investigate and see whether the wiring and panel would support a 40a or 50a circuit with just a change in the breaker, but as @w0ss pointed out, it doesn't look like it. If upgrading the breaker isn't in the cards, there is something to be said about the notion of switching it for a 14-30 outlet and buying the 14-30 adapter so that you don't have to rely on the setting in the car to keep from overloading the circuit. The main downside would be that using it for an RV again would require changing it back. You could also install a wall connector. You would simply wire it to the existing circuit in place of the outlet and set it for a 30a circuit.

 

[AlanSubie4Life]

but now after about an hour the charge limit drops to 16 A, and then about 30 minutes later iit jumps up to the 32 A max.

This is the only thing left that is a mystery to me now. I have never seen how the car throttles current in reaction to excessive voltage drop, so I don’t know, but it seems odd that it dialed down all the way to 16A. Unless that is just what it does. In this case I am not even sure whether it would have throttled, since originally the limit was set to 29A (incorrectly as mentioned)...and it could be a short run of 10AWG...but then it jumped up to 32A? So confusing.

But then there was mention of not confirming the limit? Not even sure what that means.

 

[NR427]

I don't think an inspector would like the exposed romex hanging down.

 

[Rocky_H]

I’m confused, you say it was installed by an electrician? I’m not an electrician but I am an RV owner. That looks to me like a 14-50 50 amp service plug that I would plug my RV into. If it’s got a 30 amp breaker, I’m pretty sure that’s the incorrect plug type for the breaker amperage.

It does technically pass code, as @davewill mentioned, but I would also use the term "wrong" to describe this because it is just dumb. There are 30A outlet types, so that is really what should be used for that.

there is something to be said about the notion of switching it for a 14-30 outlet and buying the 14-30 adapter so that you don't have to rely on the setting in the car to keep from overloading the circuit.

I would certainly just do that.

I don't think an inspector would like the exposed romex hanging down.

Yep--that's definitely not allowed.