"An open neutral outlet voltage reading of 87 volts could indicate a phantom voltage to a completely open neutral. This could be due to a bad connection, such as a loose neutral termination or a faulty neutral splice. Other causes of low voltage at an outlet include: loose wiring, an overloaded circuit, a tripped breaker, and issues within the wall wiring.
Here are some steps you can try to find the problem:
- Turn off the breaker
- Find all devices and lights that are off or reading 0 volts
- Turn the breaker back on
- Trace the circuit
- Look for a place where the devices and fixtures are reading 120V nominal and the next device or fixture is reading 80V
- Check all splices and connections for a loose wire
You can also use a low impedance voltmeter or a separate load to confirm that you are reading a phantom voltage to a completely open neutral.
The industry generally considers 2 volts or less of neutral to ground voltage at the receptacle to be okay, while a few volts or more indicates overloading. 5 volts is seen as the upper limit."
I looked it up on the interwebs.