Main Breaker Tripping

Insert · Dec 11, 2018

Got a new 5hp compressor, and it was running fine for a while.
All of a sudden it started tripping the main breaker, and not the breaker that its connected to.
Main Breaker is 100amp, Breaker of the compressor circuit is 40 amp. The circuit is not new, already had it and it worked fine with my welder.

So I checked the other day, when compressor started up and running, with a few small appliances on in the house, the entire panel was seeing a total of 43 amps, well below the 100. Obviously that day when testing, it didn't trip.

But a few days later the problem was back.

So today, I turned off all the breakers, except the one the compressor is connected to. I left the drain open and it ran for a while, never tripped the breaker. Total panel was seeing about 35 amps.

Then I started turning on the other breakers, and the main breaker tripped almost immediately. Turned the compressor off, and checked the entire panel was only pulling 4 amps. So definitely wasn't a combined load issue, as compressor draws about 35 plus the 4 from various other items that were on.

Any idea what could cause this ?
Could it be some kind of faulty wiring on another circuit,that is causing this, and it only trips when a large amount of amps are being drawn, even though its on a different circuit. Seems kind of weird though.

I'm thinking of disconnecting all the wires from the other breakers, and letting the compressor run. If it still trips its an issue with the Panel/Breakers, if it doesn't it must be a wiring issue.

Any help would be appreciated.

Bill D · Dec 11, 2018

I would replace the main breaker.

EmGo · Dec 12, 2018

In my experience, once a breaker has tripped several times it will no longer carry its rated load.

Sounds like you need a new 100 amper to me ...

Dan from Oakland · Dec 12, 2018

Check the tightness of the connections in the panel- ALL the connections- lugs on breakers etc.

https://www.practicalmachinist.com/...reaker-not-tripping-311095/?highlight=breaker

RJT · Dec 12, 2018

I second all the above. Check all connections to see if something is loose, then replace breaker if it all checks out.

Bobw · Dec 12, 2018

Besides checking to make sure everything is tight, I'd also pull all the breakers and
check for corrosion or arcing.

And already been said.. If that all checks out. Replace the main breaker.

It will most likely be the main breaker, but it never hurts to go through
every so often and make sure everything is all tightened up.

EmGo · Dec 12, 2018

Bobw said:
Besides checking to make sure everything is tight, I'd also pull all the breakers and check for corrosion or arcing.

Oh yeah, there's this black di-electric grease that electricians put on aluminum wire. That stuff works good. Had an aluminum wire feed to the shop that was always a problem until I scooged some of that on the ends.

After that I used it on everything.

adama · Dec 12, 2018

With a large inductive load like a 5hp motor, you need what ever is equivalent to a class D breaker over here, aka slow blow in old fuses, the starting current on that motor will be at least 5x running load, possibly more.

other thing to look at is the start capacitor on the motor too.

Insert · Dec 12, 2018

adama said:
With a large inductive load like a 5hp motor, you need what ever is equivalent to a class D breaker over here, aka slow blow in old fuses, the starting current on that motor will be at least 5x running load, possibly more.

other thing to look at is the start capacitor on the motor too.

It never happens when it starts up, happens toward the end of filling. Initially thought maybe as the PSI was increasing the motor/pump had to work harder and was drawing more AMPS but meter shows that it wasn't. So I am assuming its heat related and gets worse with time.

Will check all the breakers/wires and report back.
Even if that solves the problem, I think I might just change the box, its old and can't find new breakers.

Terry Lingle · Dec 12, 2018

A heat gun will quickly locate poor connections and localized heat sources. If you find any of them fix them first if the problem persists it is new breaker time.

Insert · Dec 12, 2018

Terry Lingle said:
A heat gun will quickly locate poor connections and localized heat sources. If you find any of them fix them first if the problem persists it is new breaker time.

I ordered one, should arrive tomorrow.

Coadster32 · Dec 13, 2018

Insert said:
I ordered one, should arrive tomorrow.

Be cautious....a heat gun can mess up a-lot of things pretty quickly. I side with replacement of the 100amp breaker myself, but keep us posted. I'm interested in your findings.

Tony Quiring · Dec 13, 2018

If zinco breaker it is toast.

Also buss bar gets dirty so remove all breakers and clean

Sent from my SAMSUNG-SM-G930A using Tapatalk

CatMan · Dec 13, 2018

Coadster32 said:
Be cautious....a heat gun can mess up a-lot of things pretty quickly. I side with replacement of the 100amp breaker myself, but keep us posted. I'm interested in your findings.

I sure hope "heat gun" in this case is a thermal imaging camera of some sort and not that thing used to melt heat shrink tubing.

Newman109 · Dec 13, 2018

Tony Quiring said:
If zinco breaker it is toast.

Also buss bar gets dirty so remove all breakers and clean

Sent from my SAMSUNG-SM-G930A using Tapatalk

I agree, Zinsco breakers are not the best. They are incredibly expensive, too. That said, I installed a panel in my barn years ago that was for Zinsco breakers because I didn't know any better at the time. When I heard how bad they are, I was thinking of replacing the panel for one with better breakers. In more than 40 years, however none of the breakers has ever failed so I forgot about it.

EPAIII · Dec 14, 2018

Yes, replace the main breaker.

If Zinsco, replace the whole box before your house/shop burns down.

TDegenhart · Dec 14, 2018

More per Wikipedia,
"Currently, Zinsco electrical equipment is considered obsolete due to a design flaw in which the circuit breaker's connection to the bus bar becomes loose, causing arcing and subsequent overheating. Long-term exposure to this heat can cause the breaker to fuse to the bus bar, making it impossible to remove. Even worse, it can cause the breaker's contacts to fuse together, thus preventing the breaker from tripping even in an overcurrent situation, thereby causing a potential fire hazard.[2]"
Zinsco - Wikipedia

Tom

Edit: Read the reference provided on Zinsco as the basic design has moved from mfr to mfr and exists under various names. You may have a Zinsco breaker and not even know it.

T

Newman109 · Dec 14, 2018

EPAIII said:
Yes, replace the main breaker.

If Zinsco, replace the whole box before your house/shop burns down.

I mentioned in an earlier post that I have a panel in my shop that contains Zinsco breakers. I bought it before I knew about them and from what I've heard no one likes them.

They were installed in 1979 when we built the barn. None of them has ever caused a problem in 39 years so I guess I'll just wait.

adama · Dec 14, 2018

Insert said:
It never happens when it starts up, happens toward the end of filling. Initially thought maybe as the PSI was increasing the motor/pump had to work harder and was drawing more AMPS but meter shows that it wasn't.

Yeah, but theres the old magic of phase angle, a large single phase motor will pull more power when working harder, your amp meter may well not show it as the phase angle will shift a bunch, but the way breakers work, they very often do feel it!

TDegenhart · Dec 14, 2018

Newman109 said:
I mentioned in an earlier post that I have a panel in my shop that contains Zinsco breakers. I bought it before I knew about them and from what I've heard no one likes them.

They were installed in 1979 when we built the barn. None of them has ever caused a problem in 39 years so I guess I'll just wait.

Unfortunately, those are the ones that can cause problems. If you read some of the articles on these breakers, there is a slow deterioration of the electrical connections. They oxidize and slowly rise in resistance that causes more heating and then spirals into failure. It would pay you to carefully check all of the connections for looseness and corrosion. Check all the buss work. Do you have aluminum wire?

Tom

Main Breaker Tripping

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