When this happens the breaker does not appear to be tripped (stays in ‘on’ position rather than floating the the middle) but is not locked in place. Switching it to off then on restores power. Our house was built in the 70s and I believe the breaker box is the original.
How serious is this problem? Is it just an annoyance or could it be dangerous?
Which problem are you referring to? The breaker tripping that often or it not appearing to trip ‘all the way’?
I wouldn’t be concerned with it not fully tripping. As long as it cut the power, it did it’s job. The only reason for it to trip all the way is to let you know which breaker tripped.
I’d be more concerned with how often it’s tripping. It’s probably worth checking to see if you can move at least one load to a different breaker or turn something off when you turn on whatever normally trips it or remove any extension that aren’t rated for the loads you’re using them for (and plug things directly into the wall or get heavier cords).
I was mostly worried about it not appearing to trip ‘all the way’ and wondering if the breaker was going bad. It only seems to happen on the tandem breakers which also makes me wonder.
Square D is an excellent brand and hold up well but tandems have a greater chance of breaking down. I’ve never liked those. 50 year old tandems could well be at end of life.
BTW: Changing a breaker is actually not that hard. You do have to turn off the main breaker to do it though, killing the power for the entire house.
How many circuits are blowing and how regularly. Do you have anything with a potential high draw on those circuits. An older toaster oven, a fridge, a window AC unit, something like that?
If they’re lighting circuits and you still have incandescent bulbs, just switching to LED bulbs can wipe out a large portion of the load.
But from what I see in your OP, I suspect you have breakers breaking down.
It’s usually two different tandem breakers and one of them does power a window AC unit. I’ll try buying a couple replacements and see if it makes a difference.
Window AC, huh? Those things can stress any circuit.
It’s a bit unusual to have Square D QO breakers in a house - they’re a more industrial grade, and if you have space, you may decide to go with two full-size breakers when you see the price of tandem QO. There may be generic “kinda-fits” breakers, but this really isn’t where you want “kinda.”
Do you know what position it is supposed to go to when tripped? I know that they don’t go to “off”, but I don’t know that the ‘middle’ is where they go to when tripped???
The breaker for our water heater was tripping a few times a day at the cottage. Since the normal breaker load should not cause a trip, I knew it’s either the breaker or an element was failing. Replacing the breaker was a 10 minute trip to the store and 5 minutes to swap vs. having to get a service call for the rented water tank.
3 days later, it appears that the breaker was prematurely tripping and we have hot water still.
I’ve always assumed it’s not so much that they fail safe, but there’s a lot of engineering worked into them to make sure they work very reliably. I assume the spring holds the breaker closed, not pushes it open. If the spring breaks or weakens, the circuit opens. I know they have to have a way to deal with arcing so the contacts don’t weld closed. They have two ways of tripping, over heating and over amperage, not so much for redundancy, but to protect against different failure modes the circuit may experience, but it’s still good that if you go beyond the rated amperage for some reason, the heat will eventually trip the breaker (hopefully) or vice versa.
Might be stupid, but it’s not an unheard of diagnosing method for finding a short. I’ve heard multiple people (often factory workers) comment that the fastest way to find a short it to replace the fuse with a copper lug and look for the smoke.
For troubleshooting, sure. Still not best, but sure. We occasionally blew circuits on purpose to identify the correct breaker. But these were fuses bypassed for convenience and the long haul not to troubleshoot.
Both cases were two-pole 240 volt breakers and only one side of the breaker went bad. Took me a while to troubleshoot the first one because i didn’t realize that only one side of the breaker could fail.
Old Zinsco and (American) Federal Pacific Electric (FPE) panels are notorious for this and lost their UL rating. The breaker I replaced this week was in a Canadian FPE panel which didn’t have the same issues.
When I removed the old breaker there was obvious arcing and the screw for one of the poles was half melted
I always believed it was thermal and magnetic modes to trip. Thermal covers overcurrent and magnetic covers short circuit and ground fault modes. With high ambient temps at the breaker lowering the actual current that the breaker trips at.
While it may be a breaker failure I’d recommend checking the load on the circuits and inspect the buss and wire connections for proper connections.
I’m sure there’s a number of different set ups. The ones I’ve seen IIRC, have two distinct ways of opening the switch. A thermal method (ie bi-metallic switch) that responds to heat due to current passing through it. And, a solenoid that will snap open when a certain amount of amps passes through it. The solenoid, I believe, will open at a higher amperage than the number on the breaker. It’s meant to deal with short circuits but not open the breaker due to a momentary over current situation, such as a motor turning on.
ETA, I don’t recall the details, but I remember the NEC listing specific circumstances where you’d want one that only tripped one way or the other.
I’m confident we’re both describing a thermal-magnetic circuit breaker. Many are different or have added functions but the most common are inverse time. The solenoid action you mentioned is what I’m referring to as the magnetic trip. There are curves and charts for how these two functions relate for any specific breaker so that coordinations can be made across a system.
I added the bit about ambient temperatures and bad connections becuase that added heat would cause the breaker to trip on thermal even though the actual current was under the rated current.
The nec addresses when, where and how they are used and when allowed or disallowed. The whys and why nots for one over another are shoehorned into the scene by anyone who cares to argue about it. Ussually engineers, inspectors and electricians, the last two tend to carry their own personal NFPA branded Dead Horse Whippin’-Sticks, but the electricians are better with them😁.
