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.

 

[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!

 

[pushrod]

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

electrons are charged

 

[GT1]

Yes they are. They are negatively charged.
What I meant to say was flow of electrons as opposed to voltage.

 

[SKY]

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.

we are taught on the 2330 that safe isolation consists of testing:

between phase and neutral
between phase and earth
between neutral and earth.

(also the standard testing of the known and accurate device and using a proving unit)

 

[pmac10]

we are taught on the 2330 that safe isolation consists of testing:

between phase and neutral
between phase and earth
between neutral and earth.

(also the standard testing of the known and accurate device and using a proving unit)

as paul.m pointed out, i tested dead, which is what you describe as being taught in class, and this would still not have highlighted my painful experience. the voltage appeared after testing and only when neutral and earth where disconnected from their terminations, the very reason i'm asking for suggestions.

 

[jaresquire]

Just to clarify, pmac10, you killed the supply and found 230V between neutral and cpc when the rcd socket was dissed?

 

[pmac10]

jaresquire,that is correct, i also made and installed the panel a few years ago (utilising the supply from the old panel) so i know its wired proper and there is no polarity issues as the electronics wouldn't work.

 

[jaresquire]

Bit of a head scratcher, why were you changing the rcd socket - any other issues?

 

[pmac10]

water damage, couldn't reset the trip coil, have troubleshooted this panel in the past with no issues, if i get the time i'll figure it out, probably wont be til next time someone gets a blast, the joys of industry, thanks for all the replies.

 

[Marvo]

It's a long shot but is there a sneaky UPS incorrectly installed somewhere? You would usually hear a squealing noise though when the power goes off.

 

[pmac10]

all this 'borrowed neutral' discussion reignited my interest in a painful problem i experienced earlier this year, here i believe was the cause,Electrical Times - Features, second last paragraph, test for dead ok, disconnect conductors shock!:cuss: