Bad 30 amp breaker for air compressor

[3rdgendslmech]

It's been a year and a month just about since I installed my compressor. Ran a 10 gauge 6' whip line to a 30 amp QO breaker. I think the total start times is probably between 15-20 between then and now. Went to use it today doing a couple of oil changes and notice that the air gauge was at 80 lbs and hadn't kicked on yet and usually kicks in at 100 PSI.
Finished what I had to do, had some lunch and went back to investigate since I'd recently been in the panel when I ran the circuit for my lift. One wire at the pressure switch was reading 123 volts and the other was only reading 45. Breaker wasn't tripped, everything looked clean. Both legs in the panel had 123 volts. What I found was that one side of the breaker was open.
So now I'm starting to question if the breaker is too small for the motor???
When I purchased the compressor I talked to a guy that is usually in the electric department of the store I purchased the compressor from, and said that a 30 amp breaker should be more than enough.
Here's some pictures along with the tag on the motor. It's a 60 gallon 2 stage compressor you can get from Lowes.

 

[BillK]

The paperwork that came with the compressor should tell you what size breaker is required.

 

[wyliesdiesels]

gallon size means NOTHING. 3.7HP?

How is this compressor connected to the panel? outlet or hardwired? technically it should be hardwired since nema outlets are only rated up to about ~3-3.5HP.

But a breaker is not gonna wear out with that load because in-rush current is only for split seconds and the FLA is 17a.

Since the breaker wasnt tripped only thing i can think of is are you using the breaker to disconnect power to the compressor?

 

[BillK]

gallon size means NOTHING. 3.7HP?

How is this compressor connected to the panel? outlet or hardwired? technically it should be hardwired since nema outlets are only rated up to about ~3-3.5HP.

But a breaker is not gonna wear out with that load because in-rush current is only for split seconds and the FLA is 17a.

Since the breaker wasnt tripped only thing i can think of is are you using the breaker to disconnect power to the compressor?

He said it was hard wired.

I turn the one at my shop on and off every day and have done so for 20 years. Breaker is still fine.

But I have had a couple of other bad breakers over the years.

 

[3rdgendslmech]

The manual for the compressor is damn near useless. It only said to use a minimum of 12 gauge wiring and no mention of what size breaker. Looking at the specs on Lowes' website it states 16.5 amps. Mine is 17.5 amps. Best I can remember when I checked amp draw at start up it was around 12, only on one of the hots so roughly 24 amps at start up I'm guessing.

 

[BillK]

Probably just a bad breaker. Just curious do you leave it on all the time ? I have never liked the thought of doing that.

 

[3rdgendslmech]

gallon size means NOTHING. 3.7HP?

How is this compressor connected to the panel? outlet or hardwired? technically it should be hardwired since nema outlets are only rated up to about ~3-3.5HP.

But a breaker is not gonna wear out with that load because in-rush current is only for split seconds and the FLA is 17a.

Since the breaker wasnt tripped only thing i can think of is are you using the breaker to disconnect power to the compressor?

It's hardwired with a 6' whip with 10 gauge THHN wire in liquidtite conduit. I just use the OFF/ON knob on the pressure switch.

Only thing I can think of is if the breaker failed pre-maturely. It doesnt look burnt or anything....beats me

 

[3rdgendslmech]

Yeah The breaker stays on all the time

 

[Bert_]

30 is the right size. Replace it and move on.

 

[paul.nmedia.net]

The manual for the compressor is damn near useless. It only said to use a minimum of 12 gauge wiring and no mention of what size breaker. Looking at the specs on Lowes' website it states 16.5 amps. Mine is 17.5 amps. Best I can remember when I checked amp draw at start up it was around 12, only on one of the hots so roughly 24 amps at start up I'm guessing.

17.5 A is the correct maximum size. Branch circuit breaker should be 30 A for a general purpose breaker. Little ones occasionally fail. Replace. Don’t get hung up on this.

There is a little variation in motor current depending on how efficient the motor is. You use a breaker based on worst case in case you ever replace the motor. Don’t get too deep into HP on compressors. 3.7 is a made up number or a nonstandard motor.’This is common practice on compressors unlike everything else. Nonstandard service factor is very typical in compressors too.

 

[wyliesdiesels]

The manual for the compressor is damn near useless. It only said to use a minimum of 12 gauge wiring and no mention of what size breaker. Looking at the specs on Lowes' website it states 16.5 amps. Mine is 17.5 amps. Best I can remember when I checked amp draw at start up it was around 12, only on one of the hots so roughly 24 amps at start up I'm guessing.

This will depend on whether its hardwired or cord and plug connected.

If hardwired, then the breaker can be upto 250% of the NEC FLC listed in 430.248.

If cord and plug connected, then the breaker should match the outlet rating.

As to the amp draw on startup, 12a would be incorrect seeing as how the FLA is 17.2a. In-rush for motors is 4x-8x FLA. And you wouldn't add up each leg because its a 240v load.

The issue here is with your meter. unless your meter is rated for in-rush current metering, it will not properly meter the in-rush draw. I use a Fluke 381 which is specifically rated for in-rush current metering.

 

[BillK]

Yeah The breaker stays on all the time

One of my good friends fried his compressor pump when it sprung a leak while he was away for a weekend. It ran and ran till it could not take it any more and spun a bearing. He will never leave it on again. I refuse to leave the one on at the shop. Just too many things can go wrong.

Just my opinion,

 

[3rdgendslmech]

One of my good friends fried his compressor pump when it sprung a leak while he was away for a weekend. It ran and ran till it could not take it any more and spun a bearing. He will never leave it on again. I refuse to leave the one on at the shop. Just too many things can go wrong.

Just my opinion,

The breaker stays on......but the off on switch gets turned off every time I lock up for the evening

 

[BillK]

The breaker stays on......but the off on switch gets turned off every time I lock up for the evening

Ok No on/off on mine or his.

 

[Bretny]

My 60gal Kobalt is on a 20a and has been for years.

Wires can get loose on the breakers. I had this happen on my 30a 240v circuit for my plasma cutter.

 

[teamextreme]

Looks like you have a bad breaker. They occasionally go bad. Nothing in this installation that is incorrect or would cause this. Replace and move on, as others have said.

 

[3rdgendslmech]

That's also what I'm going with. I'll snap a new one in tomorrow afternoon and double check things and see what happens

 

[wyliesdiesels]

My 60gal Kobalt is on a 20a and has been for years.

Wires can get loose on the breakers. I had this happen on my 30a 240v circuit for my plasma cutter.

the wires connecting to the breaker lugs werent loose.

The connection inside the breaker went bad.

Also if wires are coming loose its because they were properly torqued to spec. There should be little to no vibration on an electrical panel and expansion and contraction would be minimal on a small circuit like that.

Buy a torque driver and torque to spec listed on breaker

 

[3rdgendslmech]

Installed new breaker, torqued the screws to 35 in/lb per what's on the breaker. At start up amps hit 50, running between 15-17. Important thing is I have air.