Reasons for main breaker tripping?

We have only lived in our house since November so I'm still learning things about it. We have a somewhat unusual setup with our main breaker on a pole outside the house, just below the meter. Inside the house we have the standard panel with another main and then the other assorted typical breakers. We have electric water, and electric dryer, and two heating/cooling units (1 upstairs and 1 in the basement)

From November until just now in July everything has worked fine, but just this week twice now our main outside breaker has tripped. Both times it was very hot (mid to high 90's and high humidity) and both times at least 1 of the ac's and the dryer were running.

From what I've been reading it seems like either we need an electrician to check our breakers and/or an ac tech to check the central air units. Where would you start? Thoughts and ideas are welcome, this is the first time I've ever had central air and also the first time I've lived in a place were the main was outside.

 

AC uses a lot of juice. You are probably exceeding the amperage draw of the breaker outside. Possibly the breaker itself need replacing, or if the rest of your system can handle it, like the drop wires and breaker panel in the house, you can put a bigger breaker in outside.

 

I'd go with the electrician first.

I've seen breakers wear out so they tripped when they shouldn't.

 

What is the main rated for? Can't say that I've ever seen a main trip before. To me that sounds like a bad main or wiring near the main. If it was an a/c system fault then their individual breakers would most likely be tripping.

 

It's a 100 amp system. The first time it happened an electrician came out and took a quick look at things but didn't charge me anything and didn't look at things in detail.

My inside panels isn't great, it's a mix of parts and it looks like whoever put it in used whatever was in their bag instead of using all matching pieces. Not sure if that has anything to do with the issue or not.

 

It sounds like it's tripping because it's old and because of the conditions - hot outside temp and multiple larger appliances running. Breakers have a thermal overload which can cause them to trip at a load of over 80% of their rating for a prolonged period. So 80 amps of load over a long period (60 minutes or more) could trip a 100A breaker.

If the circuit breaker is old (>25 years), the thermal link might be worn down and become more sensitive especially in very hot ambient conditions. If the main was in direct sunlight at the time that could have made it worse. So even if the dryer and AC and a few smaller lighting or outlet loads combined were pulling only 60 amps, it's possible the breaker is overheating and false-tripping.

Don't try to change out the main breaker yourself, though. The incoming power from the utility pole can't be turned off. Electricians have professional training and insurance, let them handle the risk.

 

Thanks for the info. I'm not sure how old the outside breaker is, the original house was from 1927 so things have been here a while. There's no way to tell by looking how old it is, is there?

 

Maybe, if it's a Pushmatic brand it's old, I had a house with a pushmatic breaker panel, they kept dying, it was hard to find new ones. Sold the house. The buyer's inspector said the panel was a POS, I agreed.

The only way to shut off power to the main panel is to remove the meter, you shouldn't do that yourself. The power company puts a seal on it so they can tell if it's been tampered with.

 

I totally agree with this gentleman. As a retired EE and a former Professional Home Inspector in Texas I have to say that a 100A panel is somewhat puny these days. Definitely call an electrician and have him evaluate what upgrades might be needed to handle your electrical/power needs. Don't know how old the house is, but you might need a 200A main breaker, an upgraded subpanel with new breakers, some obvious wiring upgrades, etc.. As the man said ....don't try to do this yourself!!

 

^^This

^^ This too


I'd have the electrician check to see if the lugs of the SER cable are of the right torque. A fairly loose connection will heat up and trip a breaker. Every year I remove the panel covers and tighten down every breaker in my panels, I'm always surprised as to how loose some get over time with expansion/contraction from the heat it generates.

 

Could very well be a bunch of things

100 amp breaker to many Motors all starting at the same time inrush current draw is to high

Then breakers tend to trip always far from the load The main breaker every time.

Could be effected by a local Brown out effect due to the high AC use.

As the grid voltage drops the amps needed to start motors rise

I grew up with a 60 Amp service tube and knob wiring.

Living in Mass it could get expensive if you need to upgrade the box