Electrical experts: problem with breakers

[Victoria3]

Hi,

I recently picked up a model 3 a few weeks back. I installed a NEMA 14-50 outlet in my garage and I have been using the UMC to charge with no trouble.

Recently as the weather gets colder my heat pump has been tripping it's breaker. This never happened before and my first thought was that it might have something to do with the Tesla on the NEMA 14-50. Tried removing the UMC for a few days and it stopped happening. I didn't quite understand, so did some Google-ing and turns out that with a voltage slump (brownout) an a/c or heat pump condenser motor can over current causing its breaker to trip. I noticed with the UMC connected voltage is showing around 238v, but when the heat pump is on it drops to around 230v which I guess is enough to cause the heat pump to eventually trip the breaker after a while.

My house has 200amp service and overall load should not be a problem. Heat pump is only a 6kw unit and I have a 4.5kw electric hot water tank and these are the only 2 significant loads.

What is the solution to this problem? I always like to know what I'm up against before calling out the pros to fix a problem $$$.

 

[jjrandorin]

Not any expert by any means, but when you say "I installed a nema 14-50 outlet" do you actually mean "you" or do you mean "I had it professionally installed"?

If by "you" you actually mean "you, yourself", what gauge of wire did you use, and what breaker did you use?

 

[Victoria3]

50 amp breaker and 6 gauge wire as per Tesla's installation guide. Zero issues with the NEMA 14-50 circuit, it's the heat pump that's giving me grief cause of the voltage slump caused by the UMC.

 

[mswlogo]

It doesn’t matter how the 14-50 was installed (unless on the same circuit ).

You may have a problem upstream that should be checked.

You could have a Hard Start or Soft Start added or upgraded on the Heat Pump. The drops your getting might be out of your control or not that bad and the heat pump should handle it. It’s possible all the issues are the heat pump itself, how it was installed or an upstream fault in your home or outside your home.

I’d get a few opinions.

The last thing of concern is your 14-50. Because you can’t install that “wrong” and make it pull to hard or to much causing heat pump to fail. If anything it shows it was installed correctly.

 

[Sophias_dad]

230v is well within tolerances for the 240V supply, it shouldn't cause tripping, and I suspect the power company won't do much about it.

Your problem is in the heat pump itself, or maybe it just has an undersized wiring or breaker installed. Get the model number of the heat pump(compressor), the circuit breaker rating, and the wire gauge(if you can) leading to the compressor. Its also entirely possible that the breaker has just gotten old and weak.

I live in a condo. The main breaker is only 70A. Now what? has mention of a startup capacitor that helped their situation...

 

[SSedan]

If voltage slumps to 230volts when everything is running then the transformer at the road might be a little undersized bit not enough they will replace. Can you still charge enough if you lower amperage to the car? This should keep voltage up.

 

[mswlogo]

230v is well within tolerances for the 240V supply, it shouldn't cause tripping, and I suspect the power company won't do much about it.

Your problem is in the heat pump itself, or maybe it just has an undersized wiring or breaker installed. Get the model number of the heat pump(compressor), the circuit breaker rating, and the wire gauge(if you can) leading to the compressor. Its also entirely possible that the breaker has just gotten old and weak.

I live in a condo. The main breaker is only 70A. Now what? has mention of a startup capacitor that helped their situation...

Keep in mind 230v is what the Tesla says it’s seeing. We have no idea what the heat pump is seeing when the Tesla is charging.

But the same recommendations apply.

 

[Victoria3]

Pulled the power supply panel off the heat pump and its minimum amp draw is 29.8...on a 30amp breaker so that right there explains the issue I think. Says max breaker for circuit should be 50amp not 30.

 

[mswlogo]

Pulled the power supply panel off the heat pump and its minimum amp draw is 29.8...on a 30amp breaker so that right there explains the issue I think. Says max breaker for circuit should be 50amp not 30.

What is the wiring size though? Don't just slap a 50 Amp on there unless the wiring meets that spec.

 

[eprosenx]

Hi,

I recently picked up a model 3 a few weeks back. I installed a NEMA 14-50 outlet in my garage and I have been using the UMC to charge with no trouble.

Recently as the weather gets colder my heat pump has been tripping it's breaker. This never happened before and my first thought was that it might have something to do with the Tesla on the NEMA 14-50. Tried removing the UMC for a few days and it stopped happening. I didn't quite understand, so did some Google-ing and turns out that with a voltage slump (brownout) an a/c or heat pump condenser motor can over current causing its breaker to trip. I noticed with the UMC connected voltage is showing around 238v, but when the heat pump is on it drops to around 230v which I guess is enough to cause the heat pump to eventually trip the breaker after a while.

My house has 200amp service and overall load should not be a problem. Heat pump is only a 6kw unit and I have a 4.5kw electric hot water tank and these are the only 2 significant loads.

What is the solution to this problem? I always like to know what I'm up against before calling out the pros to fix a problem $$$.

I am on my phone so hard to write a long note, but a few thoughts:

I see two potential reasons for this tripping. One would be voltage drop causing more current flow as you suggest. That raises my eyebrows as it would mean you are very close on margins for that heat pump. I would not expect a properly sized circuit and breaker to have this issue.

The other is heat generated in the panel by the UMC breaker. Are they by chance next to each other in the panel? (Or if say your main breaker or wires from the utility are not connected well they could be generating heat into the bus under load).

Can you post pictures of your main panel including photos that show the amperage of all the breakers and the “schedule” of what each breaker is for? The stickers on the door that have specs on the panel are also useful.

Then I would like to see the “nameplate” label on the AC unit so we can see what kind of draw it is *supposed* to have.

Then I would propose two tests:

Connect the car to charge without the heat pump running. Note the voltage *immediately* when you connect it (before it starts drawing current). Then note it after a couple of minutes once the car ramps up and it stabilizes.

Then do the same test with the heat pump running.

This is a rather interesting scenario. Something is clearly not right. It could even be out at the utility transformer or something.

Let us know what you find!!!

P.S. More advanced troubleshooting includes taking the panel cover off and using a voltmeter and/or current probe to measure things at various points. I even have my Flir camera that will tell me where any hot spots are.

 

[eprosenx]

Pulled the power supply panel off the heat pump and its minimum amp draw is 29.8...on a 30amp breaker so that right there explains the issue I think. Says max breaker for circuit should be 50amp not 30.

Ah yes! That is right on the margins. Breakers are not particularly precise. As others have mentioned, a new breaker might just solve it.

It would be helpful to know what gauge and wire type (copper or aluminum) feeds your unit. Also, do you have fuses at the disconnect? If so what size?

The code does allow for larger breakers than the wire can support for motors (for this exact reason due to the startup current). The motors themselves need to be “thermally protected”. So overload protection is provided by the motor itself. The breaker is just for short circuit prevention then not overload prevention. I am not an expert in all those details.

 

[Rocky_H]

Pulled the power supply panel off the heat pump and its minimum amp draw is 29.8...on a 30amp breaker so that right there explains the issue I think. Says max breaker for circuit should be 50amp not 30.

Oh yeah, that makes perfect sense. This is a very common issue about how air conditioners and heat pumps are set up. Kind of a general motor thing overall. They have a very large spike at activation and then low steady load. So, they have specific instructions printed in them about what their steady load is and then what the recommended (higher) level of circuit they should be installed on so that they do not trip breakers all the time like this. This kind of seems like a bit of carelessness by the original installer. If 29.8 is its steady load, then it obviously will need a bigger circuit than 30A for startup current.

What is the wiring size though? Don't just slap a 50 Amp on there unless the wiring meets that spec.

The code does allow for larger breakers than the wire can support for motors (for this exact reason due to the startup current). The motors themselves need to be “thermally protected”. So overload protection is provided by the motor itself. The breaker is just for short circuit prevention then not overload prevention. I am not an expert in all those details.

There are those very specific sections of NEC about motor installs like this, so I don't quite know how the wire size needs to be set for these kinds of circuits that only need to handle brief spikes of higher current.

 

[Victoria3]

I did some reading on the minimum circuit ampacity (MCA, which is 29.8). This is what the electrician uses for wire sizing. The maximum over current protection (MOCP, otherwise known as the breaker) is 50 amps. So any breaker under 50 amps and any wire rated for 29.8 amps is okay. Obviously the breaker was undersized. We definitely had some nuisance trips last winter, but only a couple. Since the NEMA 14-50 was added to the panel there have been many. I upgraded the breaker to a 40 amp and I'll see if that helps. Still a bit confused by all this, but when you see shoddy work by so called professionals like this it really fuels my desire to tackle these issues myself.

 

[eprosenx]

I did some reading on the minimum circuit ampacity (MCA, which is 29.8). This is what the electrician uses for wire sizing. The maximum over current protection (MOCP, otherwise known as the breaker) is 50 amps. So any breaker under 50 amps and any wire rated for 29.8 amps is okay. Obviously the breaker was undersized. We definitely had some nuisance trips last winter, but only a couple. Since the NEMA 14-50 was added to the panel there have been many. I upgraded the breaker to a 40 amp and I'll see if that helps. Still a bit confused by all this, but when you see shoddy work by so called professionals like this it really fuels my desire to tackle these issues myself.

Did you check what wire size and type was run to the unit? (normally one size to the disconnect box and it is not uncommon for the wire in the whip to the unit to be different entirely)

I think you probably have done something totally within code but I am just curious what wire gauge you have. If the wire is rated to 40 amps then there is zero chance of a code issue. Even if it is only rated to 30 amps it probably is allowed by code but those rules are more complex.

I think that while the unit is happy with up to a 50a breaker, code might not let you go that large in some cases as you are only allowed to over size the breaker by a certain amount.

 

[Victoria3]

The wire is at minimum 10 gauge, if not 8 copper. Couldn't tell for sure cause there are no visible markings on the exposed part of the wire. So it's either 30 or 40 amp rated...

 

[brkaus]

You might also check the run capacitor in the heat pump. Mine failed and one of the symptoms was under voltage at the unit (infinity controls measure everything) and higher current.

I didn’t match the symptoms to a cap issue and had a service guy out. He immediately pulled the cap, tested it, and found it to be at a 30% it’s label value. Replaced and no issues.

I pulled the cap in the second unit right after he left and found it to be 40% value. Replaced it for 1/6 the cost I paid the service guy.

how old is your ac unit?

 

[Victoria3]

7 years old.

 

[brkaus]

7 years old.

That’s same as mine. If you have a reasonable quality multi-meter and know electrical safety the capacitor is easy to test. If not, call an expert on the AC unit.

 

[eprosenx]

The wire is at minimum 10 gauge, if not 8 copper. Couldn't tell for sure cause there are no visible markings on the exposed part of the wire. So it's either 30 or 40 amp rated...

If the wire was one solid conductor, it is probably 10 AWG. If it is stranded wire then it could be 10 awg still, but would more likely be 8awg or larger.

I also should mention that the AC unit wants a minimum circuit ampacity of basically 30 amps, though it likely has the 80% derate factored in and so it should not be drawing more than 24 amps. So still odd that it trips your breaker... I am guessing the trip is on startup or is it after it runs for a bit?

Basically there could still be something else going on here.

 

[derotam]

Maybe I missed something in this thread, but IF the wire going to the Heat Pump is 10 gauge, then there is an issue right? Either the wire is undersized, or the Heat Pump is drawing too much for some reason. Obviously the breaker is not correct for a 30A constant draw, but I am concerned about the wire gauge.

If it is 8 Gauge, then a 29-30amp draw is perfectly fine and you can carry on without me.