How do electricians track down a breaker that trips without obvious load?

[HenryMacDowell]

I’m trying to understand breaker tripping basics and this one has me nervous because I cannot see a clear pattern. It is not like we turned on a heater or microwave and it immediately popped. It just trips sometimes and I’m worried it could be something like a loose connection or a circuit that is feeding more than I realize. I want to approach it logically and safely instead of doing random trial and error.

This weekend I went around the house and started noting what was on and off when it happened, and it was honestly satisfying to feel like I was at least collecting useful information. But I still do not know what the right next step is. For the pros here, what do you check first when a breaker trips with light loads, and what information should a homeowner gather that actually helps you diagnose it faster?

 

[Alan]

Good instincts collecting notes. A breaker that trips with “nothing heavy” can still be a real overload, or it can be a loose connection heating up, or even a tired breaker. Since it’s late January and loads shift in winter, I’d treat this as a real issue to solve, not something to ignore.

 

[install4you]

Not an official electrician-just experienced homeowner.
Harbor Freight, Circuit Breaker Detective, SKU: 96934, about $30.
It worked great for me.
Cautions:
1. You MUST read & follow instructions carefully. It's not hard, just specific. Lot's of online comments say it doesn't work, which I interpret as user error.
2. The on switch for the sensor part turns it on if you look at it too hard; that is to say, with the slightest touch. That can drain the battery fast. The packaging makes a good storage case if you open it right, but the transmitter part bumps the sensor switch. If you use it at least once a month, put something between the parts to keep the switch from getting bumped. If you use it once a year, just take the battery out (which you should do anyway in any removable-battery device).
3. I don't remember if the circuit has to be on for it to work, so it might not help you. You can access instructions on the Harbor Freight site.
Best wishes, Eddie

 

[PGB1]

This can be hard to diagnose, Henry.

First Test:
If you're comfortable working in the load center, swap the circuit breaker for a known good one of the same amperage to find if that breaker also trips. They do get weak, as Alan mentioned.

Should that not solve the problem, it is wise to leave the circuit off until you find the source.


Another test would indicate if you have a poor or loose connection. To do this, put some load on the circuit breaker and read voltage at every device on that circuit. Start at the device that you think is the first device and move down the line. If you find low voltage at a device, back up one and look in there (power off) for a poor connection.

Why do this?
Often a poor connection or a bad device which feeds another may be fine until a load is imposed. Then the connection separates more and the amperage of the circuit goes up and the voltage drops. Unfortunately, sometimes this is a cut in the wire- often from a mouse chew.



Maybe try this Henry (Only if you are comfortable working in the load center):
Disconnect the line wire from the circuit breaker.
Disconnect the neutral from the neutral bar & make sure it is out in free air.
With your Ohm meter, read the line wire to ground.
If you find anything but infinite resistance, something is leaking to ground.

We do this with a meg-Ohm meter, but that is a high expense for a one time use at home.

Now comes the tedious detective work. Open every box and look for anything suspicious.

I wish you the best of luck finding the problem. You'll get it!
Paul