Floating/Open Neutral

[andyw]

Have a question regarding damage to wiring as a result of a floating/open neutral. I am familiar with appliances/equipment frying, as well as grounding conductors/connections overheating from this condition. Has anyone seen damage to branch circuit wiring or service entrance conductors/equipment? Any suggestions on how to evaluate such damage after condition?

Thanks for your help!

 

[charlie tuna]

Re: Floating/Open Neutral

andy,
the major problem which happens when a neutral opens is to loads associated with this neutral and it is a "common" neutral. because all of a sudden you have 240/208 volts applied to 120 rated equipment. this is usually only used on branch circuits. the last few years we have seen about four times, that when plug strips with surge protection looses it's neutral they burn up!
one place burnt a hole in the carpet!!! must have something to do with the electronics??? the last time we saw it we asked if someone was working on the electric system??? we found out another contractor was working in another tenant space and mistakenly disconnected the wrong neutral in the panel. that was expensive!!!

 

[kiloamp7]

Re: Floating/Open Neutral

I have not witnessed it first hand, but have heard several horror stories over the years about an open or severely loose neutral.

Yes, I believe we think of it usually on a multiwire branch ckt., but remember the typical 1-phase 3-wire 120/240V. service to a dwelling is also a multiwire ckt.

One of the horror stories involved the whole house.

 

[charlie tuna]

Re: Floating/Open Neutral

when you loose the neutral on the service the load determines the voltages applied to each phase leg -- as i remember?

 

[brian john]

Re: Floating/Open Neutral

When you lose a neutral on a multi wire circuit or to the service panel, the loads see what ever voltage is across the loads. The loads are in series and the resistance of the load will determine the voltage across that load. if the loads are equally balanced you don't need the neutral, till such time as you shut off one component in the distribution system (The neutral carries the unbalance).

Over voltage should not be an issue with the branch circuit wiring, the maximum voltage should not exceed the phase to phase voltage. Though there could be momentary impulses/surges do to a piece of equipment blowing up.