I have a circuit that supplies lights and receptacles on two small bedrooms in my 1957-construction house. The circuit appears to be original, and the home, for the past few months, has been vacant (but heated to about 50 degrees over the winter).
The circuit was operating normally until recently, but suddenly has stopped. Strangely, instead of just being dead, it indicates about 28.3 volts on a digital multimeter. The meter indicates about 123 on the other circuits. The low voltage appears both across open switches and at receptacles... BUT, the circuit measures 123 at the breaker. Plus, the circuit isn't loaded (except for the negligible multimeter), so it seems that it shouldn't be line loss. Besides, that would be huge and possibly fire-inducing line loss.
I earned a degree in electrical engineering 20 years ago, but have never worked as an engineer... so, I have what I think is a good theoretical understanding of what should be happening, but little practical knowledge. Have you seen such a (presumably static) drop before?
Having low voltage on a outlet or a light fixture indicates a open neutral some where along the line. In the panel see if you can find the neutral wire that feeds the circuit,make sure it is tight.Then you will have to check the rest of outlets and lighting on this circuit. The problem you will have is not being able to test the hot wire to ground as in the 1957 homes they ran no ground wire in most installations. If you do have a ground in the box test the hot wire to ground you should then get a 120 Volts + or -. You will then have to find where the neutral is broken.Start with the first outlet close to the panel then work your way around the circuit that's having the problem. Good Luck at trouble shooting it is time consuming.
(Thats why electricians charge so much )