borrowed neutral??

[pmac10]

can some of you installation guys enlighten me a little on borrowed neutrals?
i was changing a rcd socket outlet in the factory today which was spurred from a water metering control panel, switched the mcbs in the panel and the supply from dist. board, checked for dead, ok, but when the wires were diconnected from the old socket i found out the hard way, 230V appeared between neutral and earth?
could this be supplied from a lighting circuit? ideas please.

 

[DurhamSparky]

potentially! only way to tell is kill the lights as well, see if it disapears...! but why would you suggest lights?? with out physically looking at the set up it would be hard to tell you any more correct info!?

 

[Kamikaze]

Is the water metering control panel 3 phase?

 

[pmac10]

steve, as im sure you know i couldnt plunge productions lines into darkness, when i got the job done (don't ask!), this voltage disappeared, i remembered ( i think) reading on here about borrowed neutrals on lighting circuits in domestic premises meaning having to kill 2 circuits to make safe? i might have dream't that though?

 

[pmac10]

Is the water metering control panel 3 phase?

no mate, red lion counter, 230v supply, 12VDC metering

 

[DurhamSparky]

ask no questions get no lies!! hahahaha!

i would have turned them off just for a laugh!
yes 2 circuits need to be killed to fully isolate borrow neutral!

 

[Kamikaze]

Problem does not sound like a borrowed neutral. I will have a bit of a think about this.

 

[DurhamSparky]

MAYBE!! Just Maybe

you have a faulty MCB (that did not turn off) and the supply is crossed at some point!!!

just making it up as i go along now!!

 

[pmac10]

MAYBE!! Just Maybe

you have a faulty MCB (that did not turn off) and the supply is crossed at some point!!!

just making it up as i go along now!!

funny you should say that, thats what i thougt and found 50 odd volts at the wrong side of one of the mcbs, so told myself to man up, then got the good news again!

 

[Kamikaze]

No sorry, can't think of anything sensible, but something must have still been turned on.

 

[Deleted member 26818]

Is it possible that polarity is incorrect, and that the MCB is actually switching the neutral?

 

[Paul.M]

Long shot in the dark but could it be that in the control panel you have got another energized circuit not being fed from that dis. board? It has to be coming from somewhere. Or does the neutral come from another dis board and polarity is crossed over? Pity its not a house, just turn the lot off, back on one at a time.

 

[SKY]

Sounds like you did not follow the correct procedure in the OSG for safe isolation - LOL
Only joking anyhow! we are continually being drummed in about safe isolation at college.

 

[Paul.M]

Sounds like you did not follow the correct procedure in the OSG for safe isolation - LOL
Only joking anyhow! we are continually being drummed in about safe isolation at college.

Sounds like he did follow safe isolation procedures, tested dead when shut down but then got a bolt from the natural to cpc/earth. That's the puzzle.

 

[blackiel]

Got an Apprentice...???

 

[Hawk81]

can some of you installation guys enlighten me a little on borrowed neutrals?
i was changing a rcd socket outlet in the factory today which was spurred from a water metering control panel, switched the mcbs in the panel and the supply from dist. board, checked for dead, ok, but when the wires were diconnected from the old socket i found out the hard way, 230V appeared between neutral and earth?
could this be supplied from a lighting circuit? ideas please.

A borrowed neutral does not only happen or come from lighting circuits. some one could have borrowed a neutral for another socket or anything really. When you had the panel isolated that fed this socket did you test for this voltage between neutral and earth at the panel?

 

[Kamikaze]

I’m with you Paul. The most logical explanation would be a remote control or monitoring circuit which is feed from somewhere else. There would be no sense in borrowing a neutral for some lights or a socket from a water metering control panel. Well now that he’s got all our juices going, I believe he should go beyond the call of duty to track the gremlins down so we can sleep easy at night….lol

 

[eckersecker]

I work in a factory and have often noticed when working on lighting circuits that if you touch neutral to an earth there is a spark. [despite having the breaker out for that circuit] Never had a belt, though I am cautious not to touch the neutral ! Assumed it was either capacitance in the circuit or a circuit that was still on was using the same neutral.

 

[GT1]

Have noticed sparking neutrals myself. Have always assumed it to be the passage of electrons. (as opposed to charge).

 

[pmac10]

A borrowed neutral does not only happen or come from lighting circuits. some one could have borrowed a neutral for another socket or anything really. When you had the panel isolated that fed this socket did you test for this voltage between neutral and earth at the panel?

yes of course i tested neutral/ earth, like i said, it only appeared once the wires were disconnected, and disappeared when reconnected (all still isolated i thought). i have encountered a live neutral a few times before and it is always the result of an open circuit, ie, a neutral out of its termination further along the line, i'm now wondering have i disturbed something from another circuit which shouldn't be connected to this?
as for further investigation, will do if i ever get the time!