What causes voltage to be too low?

You've probably got an open circuit. Try removing the fixture and testing each wire to ground

Its bad wiring at some point. Dirty or lose connections at the junction box or at the breaker/fuse box. Or perhaps a bad breaker. You can check the voltage back at the breaker box if you know how to keep from electrocuting yourself. If its good there you can trace it through the junction boxes or the throw switch. Somewhere you have a bad connection. You have to trace it down. Also do you have a dimmer somewhere? That would do it also.

Let me guess..... You got one of those old round florescent fixtures that were so popular in the 1940's and early 50's. The heat above this fixture, from the old iron core ballast caused the wiring to burn up and you no longer have any neutral connection. What you are seeing is bleed through from the ballast.

First off, replace the fixture with something new. Then rewire all burnt cables. Replace the switch at the same time. Then, go into the basement and replace the old plug-fuse box with some modern breakers. I'd recommend a licensed electrician for this part of the job, if not the whole job. You should be back to normal lighting.

PS. The size of the house has no effect on the voltage. Big houses and small houses all have 120volts (or close to that).

PS2. Even if you wanted to save that old round florescent fixture, (and I know you love it), you can not find bulbs for them anymore.

IT

snipped-for-privacy@Notwoman.com

you may just have a bad outlet, cost a buck or two, not passing the voltage thru it, on the way to your problem location. numbering all outlet plates and switch plates in the home to match the electric panel circuit numbers stamped into the cover plate inside the panel will help narrow down your circuit chasing. if your electrician has funny voltages measured in the panel with all breakers and main off, he will check the panel connections. call the power company. they do like to promptly repair that supply stuff. and the long version of the project we all really would like to do someday (to reduce the imaginary expensive feared voltage leak we all dream of) besides noting the individual wattages of each device in standby mode with a kill-a-watt meter: after the panel and all device outlets are working with perfect voltages without any devices plugged in, the power meter should not be turning if all lights and switches are off. start lighting one at a time, then start gfi testing of each device as you add it, watching for voltage variations. the phantom voltage may be ac induced on one conductor to the tester or you, i find odd stuff in the older wiring lacking grounds, sometimes wet insulation of a wire passing thru a damp area can electrify a reverse path measured as an electrified wet floor measured to ground at outlet, if there is a motorized or compressor driven device sometimes a portable GFI can show an appliance defect. also see:

I'll bet you are using a digital meter to measure the voltage. The voltage you are testing is being picked up by a circuit that is turned off or disconnected somewhere. If you had an old analog meter it would read zero. Digital meters generally have very very high internal resistance.

You need to look at the rest of the circuit until you find a disconnected wire, or switch turned off.

Thanks for the many responses, this has given me food for thought - and work for the weekend...

No. A reading of 120V = okay. A reading of 0 to 90 or so means zero volts.

The 33v or 18v is simply your meter lying to you.

Don't believe me? Stick your tongue on the wire. You'll be okay.

Get an analog volt meter. I think you'll find drastically different reading than what you're seeing on the digital. Then ask again.

Or, just wire a 6 watt night light in parallel with a digital meter's test leads and see if you still measure those "lower" voltages.

Jeff