[chhfsc]

The outlets and light switches in several room of my vacant rental went dead last week, with practically nothing plugged in and using power. Checked the breaker on the weekend, one of the 15A breaker was tripped. No luck with resetting the breaker.
The tripped breaker seems to work properly. When the breaker is opened, no voltage. When it is closed, breaker only has 115V instead of 120V.
Is something shorted some where and loaded down the voltage?
Also notice one of the adjacent is loaded down by the tripped breaker. When the tripped breaker is opened, 120V on the adjacent breaker. When the tripped breaker is closed, the adjacent breaker only has 115V.
Please advise possible cause and trouble shoot tips.

 

[TimPa]

did you remove the load wire from the circuit breaker to take the "closed CB" voltage readings?

what I would do:
you can try a replacement circuit breaker to verify it is working
with the load wire removed, check it for voltage
if no voltage measure the resistance to ground
a short will show a very low reading 10 ohms or less
follow the wire visibly, and check all outlets/lights to see what does not have power
start going though those boxes (closest to the panel first) checking resistance there, disconnect wires and recheck resistance at load wire
the problem may exist in the box prior to the ones without power
keep rechecking resistance at load wire until you find the problem

 

[AllanJ]

If the voltage drops from 120 to 115 and various receptacles (outlets) and lights are dead then you have a loose connection, not a short circuit.

A reminder, turn off power before measuring resistance (ohms). Also, in order to get meaningful resistance measurements, at least one of the two places or things you touch the meter probes to must have everything else attached to it unhooked. Label every wire end when unhooking it.

 

[jimn]

115 V is within the acceptable range of North American electrical supply. Measure the voltage on another circuit . If it's 120v then you may have a lose connection on the circuit you are
Having trouble with

 

[chhfsc]

did you remove the load wire from the circuit breaker to take the "closed CB" voltage readings?

what I would do:
you can try a replacement circuit breaker to verify it is working
with the load wire removed, check it for voltage
if no voltage measure the resistance to ground
a short will show a very low reading 10 ohms or less
follow the wire visibly, and check all outlets/lights to see what does not have power
start going though those boxes (closest to the panel first) checking resistance there, disconnect wires and recheck resistance at load wire
the problem may exist in the box prior to the ones without power
keep rechecking resistance at load wire until you find the problem[The "closed CB" reading is with the load wire still attached. The voltage on the main side is 123V with the CB opened.]

 

[chhfsc]

did you remove the load wire from the circuit breaker to take the "closed CB" voltage readings?

what I would do:
you can try a replacement circuit breaker to verify it is working
with the load wire removed, check it for voltage
if no voltage measure the resistance to ground
a short will show a very low reading 10 ohms or less
follow the wire visibly, and check all outlets/lights to see what does not have power
start going though those boxes (closest to the panel first) checking resistance there, disconnect wires and recheck resistance at load wire
the problem may exist in the box prior to the ones without power
keep rechecking resistance at load wire until you find the problem
[The "closed CB" reading is with the load wire still attached. The voltage on the main side is 123V with the CB opened.]

 

[Oso954]

While circuit breakers do fail occasionally, I would first suspect a loose or open connection somewhere.
Have you you tried taking voltage readings on the circuit ? Hot to neutral, hot to grnd, neutral to grnd?

 

[TimPa]

[did you remove the load wire from the circuit breaker to take the "closed CB" voltage readings?]

The "closed CB" reading is with the load wire still attached. The voltage on the main side is 123V with the CB opened.

does the cb still want to trip?

a few volt drop on a loaded ckt is not surprising.

 

[emtnut]

Not sure where you are, but CEC does not allow a landlord to do his own electrical work.
When you think of it ... is it worth the risk ?