Portable AC Tripping 15-amp Breaker

[shortcircuit2]

My buddy's portable room AC unit is tripping the 15-amp breaker so he asked me to take a look. He has 2 of the exact same standup room 120-volt plug in AC units that nameplate draw 10.2 amps. 1 unit on a 1st floor 20-amp circuit and 1 unit in a 2nd floor bedroom on a 15-amp circuit. The 2nd floor unit trips the 15-amp breaker in about first 2-minutes of operation.

20-amp branch circuit AC drawing 12.4 amps and 15-amp AC drawing 14.8 amps...
Swapped 15-amp breaker with new 15-amp and same thing happens...
Then we tried switching AC units...but same thing happened...
Now I am thinking voltage drop on 15-amp branch circuit due to loose connections or back stabbed receptacles. Nope, all connections are tight with wrap around screw connections...
There is 103-volts to ground at the branch breaker, main breaker and at the weather head...
The nameplate on the AC unit(s) says minimum 103-volts...
So i throw my amprobe on the wire at the 15-amp breaker and watch the amps rise from 12-amps all the way to 30-amps which trips the breaker...
During another test, I watch the voltage drop to 98-volts just before the breaker trips.

So my conclusion is that the 103-volts coming in from the Utility transformer is the root of the problem. It is only causing the problem on the 15-amp branch circuit. The 20-amp circuit holds at just under 13-amps. There are 6-houses all running their AC on a wicked humid day on 1 pole mounted 25kva transformer.

I may go back today to see if the voltage is any higher. It is much cooler today.

 

[ptonsparky]

You have an overloaded CB. It needs a 20 amp circuit.

 

[mopowr steve]

Get ahold of the power company and tell them your readings. That transformer was way overloaded if it dropped to 103 volts , unless you have a loose neutral to home.

 

[hillbilly1]

Did you check the voltage on the other leg at the panel? Did you try temporarily moving the 15 amp circuit to the other leg? Most likely an overloaded poco transformer, the time delay is the compressor trying to start with too low of voltage. I would assume this issue just started, and was working fine before.

 

[ptonsparky]

You do have a voltage problem. Simultaneous voltage checks of L1-L2, L1-N, & L2-N would help considerably.

 

[OldBroadcastTech]

Possible Power Co regulator stuck ?? Plus an undersized transformer ?

 

[hillbilly1]

Possible Power Co regulator stuck ?? Plus an undersized transformer ?

Most likely undersized transformer/line. Op did not mention distance to transformer. If it was a regulator there would be a lot more customers affected, as those are usually at the main line or substation.

 

[ptonsparky]

Most likely undersized transformer/line. Op did not mention distance to transformer. If it was a regulator there would be a lot more customers affected, as those are usually at the main line or substation.

Likewise, the neighbors should be seeing an issue if it is just the transformer undersized.

 

[LarryFine]

Is the low voltage consistent, or does it fluctuate? Does it ever approach 120v?

 

[hillbilly1]

Likewise, the neighbors should be seeing an issue if it is just the transformer undersized.

The op said 6 houses on that one transformer, so probably #2 AL. The house in question may be the farthest from the transformer, or maybe all of the houses are having voltage issues, but they may be 240 volt center air. Not enough info to make a definitive answer.

 

[shortcircuit2]

I did try moving the circuit to the other phase...same problem tripping.

L1-L2 was 206-volts
L1-N was 104-volts
L2-N was 103-volts
Voltage did not fluctuate during tests with AC units off.

My buddys house is one of the closer homes (of 6) to the pole mounted transformer. Yes 2/AL utility drop to the 100-amp service. No loose neutral anywhere.

My buddy stopped using the portable stand-up heat pump AC unit with the 10.2 nameplate amps that was tripping the breaker. He replaced with a typical window room AC unit with a 6-amp nameplate and 15-amp breaker has not tripped.

It is much cooler here in Massachusetts today, so I hope to have time to swing by his house and test the voltage. I do think it is the Utility Transformer browning out on a heavy load of AC units from 6-homes during the hot day. We will try and get the POCO (Eversource) to check their side of things this week.

There is a big political push in our area to go "all electric" with heat-pump systems and all electric appliances. Eliminate use of fossil fuels. Well, the grid will need many upgrades to reach this goal.

 

[LarryFine]

I did try moving the circuit to the other phase...same problem tripping.

No doubt a result of the low voltage causing higher current.

L1-L2 was 206-volts
L1-N was 104-volts
L2-N was 103-volts
Voltage did not fluctuate during tests with AC units off.

Clearly a power problem only the power co. can correct.

 

[ptonsparky]

No doubt a result of the low voltage causing higher current.


Clearly a power problem only the power co. can correct.

Details

 

[shortcircuit2]

The voltage at the home was back to normal today with no AC units running in the area. My buddy has placed a call to the power company.

L1-L2 234-volts
L1-N 117-volts
L2-N 117-volts

Thanks for all the input. Hope this thread might help others with mystery breaker tripping problems.

 

[ptonsparky]

The voltage at the home was back to normal today with no AC units running in the area. My buddy has placed a call to the power company.

L1-L2 234-volts
L1-N 117-volts
L2-N 117-volts

Thanks for all the input. Hope this thread might help others with mystery breaker tripping problems.

Good follow up. Thanks.

 

[BarryO]

unless you have a loose neutral to home.

Something that's way more common that it should be. Linemen seem too often to check L-to-L voltage and assume if that's good, all is fine.