Finding the correct neutral to pull in a DB

[Gurnatronics]

So, I can’t turn off the board, can’t really turn off circuits except the one I am replacing with an RCBO. It’s all singles in trunking no sheaths to trace back to find the appropriate L and CPC, and obviously, nothing is labelled and they definitely aren’t in the correct neutral terminals.

Normally I would link out L&N and bell out neutrals as I pull the neutrals out the bar but that is no good on critical live systems.

Anyone got any hacks or tricks? I don’t want to tell them it’s a no go without a shutdown

Cheers

 

[telectrix]

Unless you solely work in the domestic sector realistically it is unavoidable at times. You assess and minimise the risk according to each job.

and always test for live using the back of your hand/fingers.

 

[TJ Anderson]

According to the EAWR regulation 14 it’s ok as long as certain precautions are taken Besides how would you ever get a ZE or PFC/PSCC without working live?

I appreciate what you're saying but live working and live testing are two different things.

People of quote Reg 14 EAWR to justify live working but you would very rarely meet the conditions of it. It justifies live testing because you need it to be live and you have suitable precautions e.g. Training, GS38 leads and PPE etc.

You will never justify changing devices live in a DB unless it was for example, a distribution board in a hospital with other circuits supplying life critical equipment. You would also have a very well documented method statement, risk assessment and likely an Authorised Person involved.

The main reason is usually financial, e.g. they don't wish to pay for out of hours working to isolate a DB just to replace one MCB or RCBO so would rather work live instead. Money over safety. That would never be a defence if it went wrong as it is not unreasonable in all circumstances for it to be dead.

Work on or near live conductors​

14. No person shall be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless–

(a)it is unreasonable in all the circumstances for it to be dead; and

(b)it is reasonable in all the circumstances for him to be at work on or near it while it is live; and

(c)suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury


It is not a criticism of you in any way and I appreciate the real world pressures we are put under to get things done. 99.9% of the time you will probably get away with it but if it goes wrong you very likely won't have a defence.

 

[Ron Sparks]

Board can't be shut down out of hours?

 

[pc1966]

If there is enough length then you could use a clamp meter that goes down to leakage levels (like @timhoward suggested one) to clamp both L and suspected N as that way you should get near-perfect cancelling of the currents (so long as wires routed same way!) which is more reliable than trying to subtract values that might by time-varying.

The suggestion by @telectrix to check with the MCB on/off is also excellent, though if the circuit has no load at the time you are trying to test it that wont not tell you much.

 

[Gurnatronics]

Board can't be shut down out of hours?

No unfortunately it’s a 24/7 monitoring do-hickey

If there is enough length then you could use a clamp meter that goes down to leakage levels (like @timhoward suggested one) to clamp both L and suspected N as that way you should get near-perfect cancelling of the currents (so long as wires routed same way!) which is more reliable than trying to subtract values that might by time-varying.

The suggestion by @telectrix to check with the MCB on/off is also excellent, though if the circuit has no load at the time you are trying to test it that wont not tell you much.

Brilliant idea to clamp both, if they are long enough I’ll attempt it next time I’m there.

Was just wondering though. Would popping a resistor of say, 10ohms between live and neutral in a plugtop create an artificial draw of approx 2.3A? (I=V/R) Or would that just be risking it going bang?

Assuming a 10ohm resistor can survive 2.3A obviously

 

[westward10]

Use a kettle or fan heater.

 

[ipf]

Use a kettle.

I like that.........another good reason/excuse found for having a brew.....

 

[Gurnatronics]

I like that.........another good reason/excuse found for having a brew.....

Use a kettle or fan heater.

I was thinking that but didn’t want a search party mob with pitchforks and torches hunting us

 

[littlespark]

Using a kettle encourages you to do the test quickly…. It’ll boil and cut off within 5 minutes.

 

[padawan]

TJ Anderson is correct especially if its commercial environment. RAMS protect the client
in exceptional circumstances for live working, i would get written instruction from client as evidence, let them assess and manage the risk
you may also need special PPE
if the circuit earth is not identified, will you certify the work?
days of working live on busbars are gone

 

[Rockingit]

and always test for live using the back of your hand/fingers.

It's stupid, I know (in the hopefully unneccesary sense), but I always as a sub-conscious 'drilled into me as a nipper' kind of thing, always do tap the back of the finger onto ANY metal enclosure or panel that I have to engage with.

 

[pc1966]

It's stupid, I know (in the hopefully unneccesary sense), but I always as a sub-conscious 'drilled into me as a nipper' kind of thing, always do tap the back of the finger onto ANY metal enclosure or panel that I have to engage with.

Indeed, touch before you grip, just in case you can never un-grip!

Also old-timers working on valve gear would try and keep one hand in pocket so any shock would be largely confined to a hand. Going to hurt, and possible made worse by cutting the back of your hand whipping it out against any metalwork, but less chance of fibrillation death.

 

[Rockingit]

Indeed, touch before you grip, just in case you can never un-grip!

Also old-timers working on valve gear would try and keep one hand in pocket so any shock would be largely confined to a hand. Going to hurt, and possible made worse by cutting the back of your hand whipping it out against any metalwork, but less chance of fibrillation death.

It's also because a burn injury will heal faster on the back of your hand than the palm. I also was taught (and still do!) to work one handed in some situations - and the number of times I've opened up a panel and it all comes tumbling out where there's no dressage and too much untidy slack......

 

[Rockingit]

back to the OP - again, not 100% guaranteed - but if you think you've narrowed it down with a clamp meter, see if you can get the live/s in as well as the neutral - theoretically should be solid zero under a full load (unless there's a earth fault).

 

[loz2754]

back to the OP - again, not 100% guaranteed - but if you think you've narrowed it down with a clamp meter, see if you can get the live/s in as well as the neutral - theoretically should be solid zero under a full load (unless there's a earth fault).

As also suggested in post number 19