Borrowed Neutrals ! (gotta be careful)

[muzza1]

Hi Lads, how are you all? Was just wondering if any you have come across "the hidden killer" (borrowed neutrals)? Thought it would be a good idea just to raise awareness. Thanx.

 

[Brightspark2]

Ha ha raise awareness eh...is this a new campaign...

I'm sure we've all come across it a few times...especially the domestic lads...

 

[chrish_1977]

Nothing better than turning of a lighting circuit, then finding out the neutral still have voltage, keeps you on your toes

 

[dan86]

keeps you on your toes

and sometime across the other side of the room flat on your back...

 

[TAZ]

Alarms bells should ring when you isolate the upstairs lighting circuit & the landing light stays on, Had this not that long ago & ended up rewiring the two way switching

 

[telectrix]

if that were the case, then the alarm installer has got it wrong again.

 

[bigbaddave]

The dreaded shared neutral.. Don't we just love em

 

[TAZ]

That's what i like a sparks with a good sense of humour (telectrix)

 

[shanky887614]

and sometime across the other side of the room flat on your back...

one of the sparkies on the firm got a better shock.

they put head above ceiling and got a belt, next day they had a mark on centre of forehead.

they got shocked by a hanging cable that was still live

 

[Deservices]

I had one on some three phase. Had 3 banks of lights all 240v, isolated the bank I was changing fitting on. Went up ladder tested for dead all seemed good. As I disconnected the neutrals one side touched my thumb one my finger, lights went out then was fed via my hand. Shock of my life muscles froze, slowly fell back off the ladder, ended with third degree burns on 2 fingers and a few grazes from falling. Lucky escape.

 

[muzza1]

I had one on some three phase. Had 3 banks of lights all 240v, isolated the bank I was changing fitting on. Went up ladder tested for dead all seemed good. As I disconnected the neutrals one side touched my thumb one my finger, lights went out then was fed via my hand. Shock of my life muscles froze, slowly fell back off the ladder, ended with third degree burns on 2 fingers and a few grazes from falling. Lucky escape.

Blimey, that sounds like a nasty one! Note to self, test again ! and again...

 

[Darkwood]

Hi Lads, how are you all? Was just wondering if any you have come across "the hidden killer" (borrowed neutrals)? Thought it would be a good idea just to raise awareness. Thanx.

If you make anyone aware of this that wasn't before and they claim to be electricians then they are kidding themselves IMHO ... its part of your college work and can be a killer if you didn't pay attention.... for all the other out there that receive a nasty supprise this way then thats why we spend yrs learning how to do our trade safely , treat every circuit that you haven't wired yourself --- though it may have a borrowed Neutral and work accordingly and you wont fall foul of this set-up.

 

[muzza1]

To true, Darkwood. I can't remember covering this in college. Even if it makes just one youngun stop and think before he chops (and grabs) it's well worth chatting about. Just reiterating the need to stop and think, only for a minute. could well save a nasty shock.

 

[Darkwood]

I always give Neutrals a wide birth regardless unless ive persoally designed and wired the circuit ... too many DIY jobs out there it isn't just a case of domestic crossover of stairwell lighting...
You can really only get a shock if you complete a circuit with your body, best way to work is to pretend every cable is live when you make them off this way you never touch the conductors thus greatly reduce the risk of finding a borrowed neutral its not just a case of borrowed neutrals but N/E faults, poor earthing systems etc can create a hazard voltage on a multiple cable joint even if you follow correct isolation procedures....

Its ironic that all the emphasis is to test/test again before working on a circuit but little is taught to make you aware of the fact you break a circuit open at say a joint it can create a voltage that wasn't there to start with due to unrelated conditions.

 

[Guest111]

Had one on a school some years ago,fitted a new rcd board which tripped occassionally turned out to be a neutral on the wrong bar,so came up with this test to find it,leave rcd to that side of board off and using a tester pull each neutral in turn until offending one is found.This was fine as I soon found one that was "live",returned this to correct side of board thinking happy days job done,I then touched the "dead" neutral bar and received a right belt which caused me to fall off the ladder,turned out there were 2 crossed neutrals feeding lights in store rooms that were only used occasionally.Hell of a way to learn a lesson that was.

 

[Estimator]

Borrowed Neutrals, they're always treated as a bit of a joke....
I knew a spark who got killed by one in a commercial setting around 20 years ago...
From what I can remember he was working on a lighting circuit in a false ceiling, he'd tested everything was isolated and started work. Unfortunately, he touched the neutral after he disconnected it... That was it he was DEAD.
The HSE were never really convinced that he had tested everything... They didn't get that he completed the circuit...
This sticks in my mind as he was about the same age as me...
Killed because some idle spark saved an hour or two, by not installing one wire...

 

[Darkwood]

I got similar to borrowed N lesson in a unexpected way... was taking some Galv trunking lid off and as i pulled it away from the trunking i got a belt of the lid.... turned out after scratching my head that a socket neutral had come out of a connector and rested on the lid which gave a return path and i come along and get a right belt... although not a borrowed N it does highlight the dangers... i now always pull lid off from one end first looking behing as i do..... now they dont teach you these senerio's but just one of those things.

 

[KoFi]

Came across this recently 70w CDM-T fittings wired in multicore SWA 5 core 2.5mm TP&N Dis board time clock controlling contactors core 1=L1 ,2=L2 ,3=L3 ,4=N ,5= CPC. Armoured went into unit unknown location then re appeared in a 230v rated fitting where joints were made the three phases being linked (in singles) out so that every other two fittings were on a different phase via the contactors sharing the one neutral. one fitting had 400v across phase conductor and neutral break some where. not good practice.

 

[Leshark]

I just did a CU change, and found the hall upstairs pendant taking its live from downstairs & neutral from the upstairs circuit, being wired this way in the 70's with no RCD its likely it would not have reared its head, luckily, I could rewire without too much disruption

 

[Darkwood]

N break over 3ph systems can create floating star points giving voltages up to 400v across single phase points L/N.... common situe should be avoided in design of final circuits, hard to avoid if incomming N is lost because of gypo's nicking su station E/N tap.