One circuit in house losing voltage

Question

One circuit in our house is behaving very strangely, and isolating the issue has proven difficult. It's a house built in the late 60s and the electrician who wired this did add what I think is quite a bit to the circuit, two bathrooms and two bedrooms (5 outlets, 6 light fixtures). One of the bedrooms is converted to a home office where I use my laptop on two monitors. There are no GFCI outlets in any of these rooms.

The issue is that all of a sudden we are seeing low voltage (by multimeter test) at the outlets when one or more of the lights is switched on. I can also see this at the fixtures because some of the bulbs are incadescent and they now only operate as if dimmed, and the led lights will cut off completely when I add any load to the circuit.

We haven't really added anything new, although the issue did seem to get a lot worse immediately after I plugged in a 240W power adapter for a new laptop. My daughter confirmed she had seen the lights flicker/ dim the day before, so I think this was starting before I used the laptop, but maybe the laptop made it worse? (not enough electrical knowledge to know why that would be).

I have replaced the 20A breaker, and I've disassembled a few of the outlets and one fixture looking for an obvious culprit. I am going to do this for the rest of the outlets on the circuit, but any pointers re: possible other culprits would be greatly appreciated.

Answer 1

Sounds like a bad connection.

99.9% of the time, that will be at a device or in a junction box - wire breaks in the wall (away from a device or junction box) are exceedingly rare.

If any of the devices use "backstab" connections, those are highly suspect and a common cause of issues (including fires. The voltage that drops is making heat wherever this problem is.) In the usual case that they also have side-screw connections, you can move wires to those, but if any device is severely heat damaged, it should be replaced. Not unconmon to find the culprit partly melted or charred.

It would not be a terrible idea to purchase 5 new receptacles of decent quality and replace them all. Also be on the lookout for blank electrical box covers that would be on a junction box without a receptacle or switch associated, to open and inspect for potential loose connections (ensuring power to them is off.)

Loose wirenut connections (from poorly made wirenut connections) are also a common cause.

At that particular era, you might also want to check that you don't have aluminum branch wring, and if you do, you need to take special care. If the stripped wire ends are silvery rather than pink-to-brown copper colors, you have some extra steps to take.