voltage drop

Paul S_3

its 120v...but if there was a short by the furnace wouldnt it just trip the breaker for the furnace not the whole house breaker 100 amp

Paul S_3

voltage drop

what can cause voltage to drop @ a furnace (from 120v to 90v) making the lights in the house flicker and eventually tripping the MAIN breaker.....

World Plumber

Something is shorting out

Try disconecting the blowermotor. Is this a 220 unit? It's not so commont to have a single circuit kick the main. In other countries where the mains are ground fault we see it all the time. Something is causing esentually a direct short if i's doing that. make sure the wires are not pinched somewhere and check all the electrical componets.

[Deleted User]

wouldnt it just trip the breaker for the furnace?

not always. and i've seen similar with no explanation from MEs.

put an ammeter on the blower motor and watch to see if it over-amps/trips it

Todd_46

The problem may not be at the furnace. Check the incoming service to the home. Check both hot legs to ground, they should read the same voltage. I had a customer this year that was having voltage issues. When I checked there service, there was a big difference in the incoming voltages. At that point I called the power company. They found that a tree branch had grone through the power line. Just a thought.

Mark dewolfe

power issue

in this case I would bet you have one leg of the main breaker gone intermitted. the contacts are heating up and the breaker is tripping on a thermal fault. There are very few reasons for a main breaker to trip in a residential panel so I would get a replacemnt out there pronto. sounds like a fire waiting to happen. Peace Mark

hot_rod

the transformer on the utility pole

the utility can test, even data log a step down transformer to see if it is the cause.

A neighbor, on the same transformer with a large load, a sawmill for instance

hr

Larry C_13

120V to 90V is a RED FLAG that indicates a serious problem. The causes can be many. This is best left to a professional! Get a compentant electrician in there ASAP.

Problems could be bad circuit breaker, loose connection in branch circuit wiring, open neutral in branch circuit, bad connection(s) in main panel, bad main breaker, bad connection in service drop, bad connection in utility equipment, over heating in main panel, open neutral connection, poor neutral ground bond, etc.

I STRONGLY RECOMMEND GETTING A COMPENTENT ELECTRICIAN IN THERE ASAP.

Larry C

Jamie Hall

Pull the Plug!

I second the comments -- get an electrician out there pronto! And until he comes, turn the main power to the building OFF and leave it off.

Your two least desirable options on this one are someone gets killed or the place burns down; either one is moderately likely.

A general rule I like for electrics: if a breaker -- any breaker -- or fuse blows, find the problem and fix it before you reset if at all possible. If the breaker is mission critical (here's the former pilot speaking) you can reset it once, and once only; otherwise leave it popped until you find and fix the problem.

I don't care to speculate on the problem -- but an open neutral will do this. Among other things...

Mike C._4

voltage problem

This problem needs serious attention as stated above. It sounds like one side (90v) is getting partially grounded some how. Finding the cause will take checking each circuit on that leg when loaded to isolate the cause. Don't fool with this. There is some wire/motor overheated somewhere. Let us know what you find.

Mike