What would trip the main house breaker?

DJM

DJM

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Power went out during a storm yesterday. Lightning was right on top of us. I pulled out the generator and went to work keeping the fridges and sump pump running. Local news said power was out in my area so I patiently waited. 3 hours later it's getting dark and I notice the houses around me have lights on. Decided to check panel and the main breaker (2x100a) was tripped. Reset it and back in business. Just wondering if I should call someone or chalk it up as a fluke.
 
It definitely wasn't you, while you were fiddling with the generator? :P

Otherwise it could have tripped when power came back on, if you had a bunch of stuff with high start-up loads. I don't know what that would be in a house though... did you leave your air compressor, cement mixer, and electric dryer on?
 
could have been high level surge from a nearby lightening strike? It did its job and poped instead of cooking your house circuits
 
Did you power the fridge and sump pump directly with extension cords, use a transfer switch, or backfeed the panel? Obligatory warning: you should never feed a panel without an approved method. If you backfed it with the main still on, the utility coming back could explain why it tripped.
 
Yikes , back feeding a panel could light up repairmen down the street. I’ve heard this can make them cranky .


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crankcall said:
Yikes , back feeding a panel could light up repairmen down the street. I’ve heard this can make them cranky .


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While theoretically possible, it's mostly a myth. If you backfed into a dark grid, your generator would instantly trip as you are trying to power up every house on your transformer and potentially more upstream. When cres are working on the lines, they ground the lines to protect themselves against stupidity. Again, your generator would blow into the dead short.
 
In over 40 years as an electrician I’ve only had to reset a main 100 Amp breaker once in a home, the cause was loose terminations on the main lugs causing the main breaker to heat up and trip prematurely. I tightened them, problem solved. Your problem may have been from the inrush current when the power came back on, can’t say for sure. It’s always a good idea to get an electrician every few years to go through your main panel and snug up terminations on your main breaker as well as your branch circuit breakers, money well spent. 90 % of my after hours emergency calls on commercial/industrial buildings were from terminations that had worked themselves loose from thermal expansion/contraction from varying loads over the years.
 
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Gaoler said:
You mean wizard...
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Yes, to some what I do seems like voodoo black magic. It’s been an interesting career. At the risk of sounding like a name dropper, I’ve decorated Conrad Blacks Christmas tree many times, reset the power bar Keith Richard had his tea kettle plugged into, set up Mick Jaggers dressing room, did a reno for Mila Mulroney (Ben’s mom), she was smokin’ hot for a woman her age.
 
So mostly a myth and they mandate bypass switches to make sure it can’t happen . You know more about this stuff than me but it makes me wonder


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crankcall said:
So mostly a myth and they mandate bypass switches to make sure it can’t happen . You know more about this stuff than me but it makes me wonder


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Not a myth.You can absolutely backfeed the grid from your home under the right/wrong circumstances. Tying in a 240v generator to your main panel can backfeed a transformer on the street and step it up to thousands of volts on lines that someone is working on. Consider getting a “Generlink” if this sounds like you.
 
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crankcall said:
So mostly a myth and they mandate bypass switches to make sure it can’t happen . You know more about this stuff than me but it makes me wonder


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Swiss cheese model. When life safety is involved, put many obstacles in the path to ensure people don't get hurt. Aside from hurting people upstream, if you try to feed your house from two different out of phase sources (grid and generator), there is a giant impulse of power that needs to go somewhere when the phases align.
 
GreyGhost said:
Swiss cheese model. When life safety is involved, put many obstacles in the path to ensure people don't get hurt. Aside from hurting people upstream, if you try to feed your house from two different out of phase sources (grid and generator), there is a giant impulse of power that needs to go somewhere when the phases align.
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You did make a very good point about the generator breaker tripping while trying to feed the grid. Zapping lineworkers was what I was taught in trade school, and it stuck with me. Now that you made me think about it, generally the generator should overload and trip. However, generators and solar panels do not have the massive fault-current capacity of batteries or the grid. You can connect an ammeter across a small solar panel to measure its short-circuit current. I think an inverter generator without adequate protection could potentially remain on at virtually 0V. When utility power returned, the unsynchronized sources would trip or damage something.
 
Bobo said:
In over 40 years as an electrician I’ve only had to reset a main 100 Amp breaker once in a home, the cause was loose terminations on the main lugs causing the main breaker to heat up and trip prematurely. I tightened them, problem solved. Your problem may have been from the inrush current when the power came back on, can’t say for sure. It’s always a good idea to get an electrician every few years to go through your main panel and snug up terminations on your main breaker as well as your branch circuit breakers, money well spent. 90 % of my after hours emergency calls on commercial/industrial buildings were from terminations that had worked themselves loose from thermal expansion/contraction from varying loads over the years.
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If you are too cheap to go that route till things go black and you have a infrared thermometer kicking around doing a slow sweep across the panel looking for hot spots can spot problems that you should call in a licensed sparky to look at.
Keep in mind that circuits with load will be warmer and the thermometer reads in a cone that grows with distance so you want to have it fairly close to the surface that you want to read.
A hot breaker with no load is a big red flag FWIW.
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