AC tripping

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MiamiValleyelec

Senior Member
Location
Columbus
Occupation
Master electrician, licensed contractor
I have a customer who thinks they have an electrical issue. The AC is tripping, they also have a single pole 15 amp AFCI the nuisance trips. I went over there put a hair dryer and at a different time a vacuum load on the 15 amp breaker and took voltage measurements everything was reading 123.5-124 volts A to neutral and B to Neutral. Line to line was 246-247. I couldn’t get it to trip. I made sure connections were tight. So far it hasn’t tripped again. House built in 2014 I told them the older afci breakers nuisance trip and if it does it again I’ll swap it out for a newer one. Hasn’t tripped in 2 weeks.

The house is 4300 square feet and has 1-5tonn unit that keeps tripping the breaker. It’s on a 2-pole 50, which name plate says is max. Minimum circuit amps is 32.5 amps. Wire is 6awg AL. I checked connections and everything was tight. I told them the unit is too small for the house. It tripped again today 90+ degrees outside.

Is there anything else I can/should check out before I send them to the HVAC guy?
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
IMHO take an amp reading for both legs supplying the AC, and measure the voltage drop across the breaker as @ptonsparky suggests.

Also: where is the breaker panel located, and how hot is the panel?

Even if the AC is undersized for the house, it shouldn't be tripping the breaker unless something is wrong.

Breakers trip on heat. If the AC is drawing too much current (because it is broken), then it will heat up the sense element in the breaker and cause a trip.

But anything else that causes that element to heat up will make the breaker trip. Thus could be a poor contact in the breaker, a bad connection from breaker to bus stab, a bad connection from breaker to wire, or external heat applied to the panel.

Jonathan
 
M

MiamiValleyelec

Senior Member
Location
Columbus
Occupation
Master electrician, licensed contractor
winnie said:
IMHO take an amp reading for both legs supplying the AC, and measure the voltage drop across the breaker as @ptonsparky suggests.

Also: where is the breaker panel located, and how hot is the panel?

Even if the AC is undersized for the house, it shouldn't be tripping the breaker unless something is wrong.

Breakers trip on heat. If the AC is drawing too much current (because it is broken), then it will heat up the sense element in the breaker and cause a trip.

But anything else that causes that element to heat up will make the breaker trip. Thus could be a poor contact in the breaker, a bad connection from breaker to bus stab, a bad connection from breaker to wire, or external heat applied to the panel.

Jonathan
Click to expand...
Breaker tripped again last night multiple times.

I went out there this morning.

Amperage when the compressor is running is 17.5-18 amps on both phases.

Voltage at the breaker with the ac running 244-245. Voltage is 122 to neutral on both phases on load side of breaker and line side of main. Voltage to grounding conductor at HVAC disconnect ( about 60 feet away) 119.5-120. Voltage line to line at disconnect 239.5.

I changed out the breaker. No signs of heating or arcing. Connections are tight.

Breaker did not heat up in the hour I was there testing. I do not believe it is an electrical issue. I just want to make sure I covered all my bases
 
M

MiamiValleyelec

Senior Member
Location
Columbus
Occupation
Master electrician, licensed contractor
winnie said:
IMHO take an amp reading for both legs supplying the AC, and measure the voltage drop across the breaker as @ptonsparky suggests.

Also: where is the breaker panel located, and how hot is the panel?

Even if the AC is undersized for the house, it shouldn't be tripping the breaker unless something is wrong.

Breakers trip on heat. If the AC is drawing too much current (because it is broken), then it will heat up the sense element in the breaker and cause a trip.

But anything else that causes that element to heat up will make the breaker trip. Thus could be a poor contact in the breaker, a bad connection from breaker to bus stab, a bad connection from breaker to wire, or external heat applied to the panel.

Jonathan
Click to expand...
Panel is in the basement. It is not as hot this morning as last night but it was still 84 degrees at 10am
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
VD across the breaker meaning a Fall of Potential. It takes a meter capable of millivolt measurements. Line side to load side of each hot while it's under load. Should be not much more than 100mvolt. Try to load up each line equally. Each should have similar VD. This measure's the connection of the internal contacts. Depending on where you take the readings it will flag bad buss connection as well.
 
N

nizak

Senior Member
Did you check the connection at the disconnect?

I’ve open many A/C disconnects only to find the wires burnt back .
 
M

MiamiValleyelec

Senior Member
Location
Columbus
Occupation
Master electrician, licensed contractor
ptonsparky said:
VD across the breaker meaning a Fall of Potential. It takes a meter capable of millivolt measurements. Line side to load side of each hot while it's under load. Should be not much more than 100mvolt. Try to load up each line equally. Each should have similar VD. This measure's the connection of the internal contacts. Depending on where you take the readings it will flag bad buss connection as well.
Click to expand...
Ok I will test from line side of the main to load side of breaker under load with my fluke 87
 
mtnelect

mtnelect

HVAC & Electrical Contractor
Location
Southern California
Occupation
Contractor, C10 & C20 - Semi Retired
4,300 sq ft and a 5 Ton ... They must have used the "Rule of Thumb".

Before they install a replacement ... Have a "Heat Load" engineering study done.
 
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