Reading Between Earth and Neutral 120V

Where about in the world are you, it may give us a clue to what should be your normal supply voltage.

To be honest I would be getting the supply company involved.

And, are you saying you have a generator connected in addition to the incoming utiliity?

Mtonyole,

Sounds like an open neutral somewhere.

Hire a qualified and experienced electrician to find and correct it.

dmtonyole

You have a floating neutral. That is an earthing problem which manifests as a neatral voltage above earth potential. An assymetrical neatral point in the three phase system. Thats why when the generator is running unloaded all is well until you connect your assymetrical load. Get a qualified electrician to sort it out...chop chop.

Hi dmtonyole,

I agree to the two previous comments, you have a floating or loss connection neutral cable, causing high and abnormal voltage. I experience this several times in our huge site & I told to my electrician to check & re-tight all neutral terminal from the whole circuit, & they were found loss connection after tightening the power supply back to normal.

regards

Yep. The neutral is broken somewhere upstream of the user connection.

The 400V thing merely indicates the generator and the utility supply are out-of-phase.

It's a utility company distribution network problem, which needs sorting without any delay. Do not use the installation until the problem has been sorted out.

My thoughts for you: 1. Incoming supply could be from star connected system and may be neutral earthing defective. 2. Severely unbalanced load could cause floating neutral 3. Your generator neutral not effectively earthed. 4. Check all earthing system to ensure no loose connections.

If this is an old building, the wiring may not comply with the modern requirement of a continuously grounded neutral. In another life my workplace was a converted house built in 1880, with the original wiring. There was a 120-240 volt single phase electric service, and all three lines were fused.

One day, the fuse on the conductor connected to the "neutral" blew. Some of the lights in the building got very dim, and the rest were burning much too brightly. Some light bulbs and small appliances just gave up the ghost.

Don't let this happen to you. Call a qualified electrician.