Neutral Removed at Pole by Utility Co!!! oops!

[e57]

I've left de-energized all of the multiwire branch circuits.

The service itself is a Multi-wire circuit - the same hazards exist on ALL circuits if the poco has a high/low voltage event (lost neutral). They should ALL be off.

Any load imbalance will change voltages and amperages available to each leg or phase. Depending on where the neutral is cut - all down stream circuits are effected. A heavier load on A will drop it's voltage (increase its amperage) and that voltage decrease will be an increase of voltage on the otherside of the transformer leg windings for say... B - All of leg B's voltages will be increased (lowering its amperages) - Someone is bound or about to explain it better....

Anyway - stuff don't like it and it lets smoke and sometimes flames out.....

 

[Den]

I don't think there is a linman out there that in a storm repair hasnt cut the wrong wire our cut a wire with a chain saw trying to get trees of the line. That is the hazards of long hours trying to get people back on and stay on. I'm guessing that the trans was still grounded and then the voltage wouldn't have gone too wild. Probably hurt the stuff that was on at the time and electronics but maybe the wire is still ok but it all needs checked out. Unfornunate but this does happen.

 

[readydave8]

Am I correct in thinking that the most voltage caused by the missing neutral would be 240v? And that would not hurt romex rated for 600 volt?

 

[mkgrady]

Am I correct in thinking that the most voltage caused by the missing neutral would be 240v? And that would not hurt romex rated for 600 volt?

That sounds right to me. And as already said, the breakers would still operate at the appropriate level, so overheating conductors should not be an issue. The damage from this kind of problem is equipment that is rated at 120 volts seeing a higher voltage thereby damaging components.

 

[kbsparky]

If any breakers are tripping after power is restored, it is because the connected loads have internally fried. The wiring itself should not be affected.

 

[e57]

In the past - the kind of damage I see:

• GFCI's and AFCI's fried
• Power supply circuits in any over-voltage affected circuit burn, some to the point of ingition.
• Some other devices (if in operation at the time) and the conductors feeding them - once voltages are low enough do suffer from heat and current damage. e.g. some conductors will have the insulation melt off... (V down - A up) Since the voltage and current changes, and even changes direction dependant on the load - and takes all available odd paths - what may seem fine could change. (Shutting off one set of lights could change voltages and currents all over the building.)

Some of the fun stuff I've seen....

• 200' of #8 single in free air run on insulators had all of the insulation drip off like a Dali painting. (Requiring 100's of amps - while the loads of this 3 phase wye circuit did not change, one phase became the CCC for the other two on top its own load.)
• Computer ingite while screaming woman backed away from keyboard. (Co-worker and bosses brother pulled wrong neutral while describing the dangers I already knew - Doh!...)
• 120v Braun Coffee maker nearly ignite a maple cutting table 2" thick - the elements in the machine (which was off at the time - electronic controls) dropped out of the machine through the plast and left a 3/4" deep 'brand' in the wood.

Bottom line is it is dangerous - and would suggest megging the conductors afterwards. As well as a full inventory of not just the stuff that doesn't work - but the stuff that still seems to work as well - as it's life has been shortened subject to the event. It may not work much further in time...

 

[e57]

Am I correct in thinking that the most voltage caused by the missing neutral would be 240v? And that would not hurt romex rated for 600 volt?

Draw a diagram of the panel as well as any 3-wire circuits leaving it - if you had a service or sub panel with only one 3-wire in it - that cable or circuit had to carry ALL of the current of any connected load in series. If there were FIVE 3-wire circuits they carried portions of the connected load in series.... They may not have carried it equally - but they may have carried far more than designated in 310.16. And possibly more than required to break down insulation. And yes - the breaker may not have tripped... The operational characteristics of a 120 breaker are different at both 30 volts, and also at 210V...

 

[jjhoward]

High voltage when neutral is removed

High voltage when neutral is removed

I have seen 600 volts from ground to hot leg when the neutral was broken.

That has happened in 2 different houses. Both times just about everthing plugged in was broken. CF bulbs smoked in their sockets.
GFI breakers smoked in the panels.

I haven't seen any damaged wires but lots of damaged TVs, clock radios, dishwashers, garage door openers......etc.

Maybe the customer needs an insurance adjuster?

 

[casey100]

The wiring should be fine. Amps heat up wires, not volts. That's why the overcurrent protection is designed to monitor amps, not volts. Pretty sure anyway..

 

[Den]

As long as the grounding was still on the trans and the neutral was cut going to the house, you would have some high voltage but if the ground was cut to the trans you can have basically extremely hi voltage up to the distribution line voltage and thats when things blow out of the wall and really melt down stuff. I have seen a transmission (69K) line drop onto our distribution system (7200 )and that really caused problems. We were changing transformers all night and everything in the houses were blown up.

 

[LarryFine]

Amps heat up wires, not volts.

True, but voltage can damage insulation without heat (at first. )