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

 

[7029 dave]

clamp meter on L and N under some load, the values should match.

 

[Gurnatronics]

clamp meter on L and N under some load, the values should match.

Genius!

 

[littlespark]

It’s a no go without shutdown.

It says you’re a trainee, so you shouldn’t be poking about in a live db without supervision

And the suggestion above, clamping the L and N for load won’t help finding the cpc.

 

[Gurnatronics]

It’s a no go without shutdown.

It says you’re a trainee, so you shouldn’t be poking about in a live db without supervision

And the suggestion above, clamping the L and N for load won’t help finding the cpc.

Not a trainee I’m gold card qualified but still everyday is a school day. I need to find out how to get that tag removed

I just assume he meant clamp the L to get a reading, then clamp each N sequentially till you get a matching reading

 

[7029 dave]

Not a trainee I’m gold card qualified but still everyday is a school day. I need to find out how to get that tag removed

I just assume he meant clamp the L to get a reading, then clamp each N sequentially till you get a matching reading

You assumed correct, but as @littlespark states you wont be able to ID the cpc with a live board.

 

[littlespark]

Not a trainee I’m gold card qualified but still everyday is a school day. I need to find out how to get that tag removed

I just assume he meant clamp the L to get a reading, then clamp each N sequentially till you get a matching reading

Sorry mate. I just assumed.

You can find the L and N by comparing current, but change the current and test a couple of times…. Just in case there’s another circuit pulling exactly the same.

Still won’t help with the cpc.

This is why we have numbered terminals to match the cct numbers

 

[Gurnatronics]

Sorry mate. I just assumed.

You can find the L and N by comparing current, but change the current and test a couple of times…. Just in case there’s another circuit pulling exactly the same.

Still won’t help with the cpc.

This is why we have numbered terminals to match the cct numbers

No bother pal alls well.

Im normally an industrial install spark and everything I did in boards were in the correctly numbered terminal and cable tagged. Going into remedials now and when you gotta swap an MCB for RCBOs in and nothing is ever identified it starts doing your nut in trying to find s**t after a while, especially after a 2 hour drive and once you swapped and certified it you can go home again grrrr

 

[Deleted account]

This is why we have numbered terminals to match the cct numbers

have you ever seen a board that matched the numbered sequence. Very rare.

unless you’ve done it yourself I wouldn’t rely on that method.

 

[telectrix]

an idea is to switch that 1 MCB off. clamp each N in turn till you get 1 or more with zero current. then identify the right one by switching MCB on and finding which N jumps up.

 

[Gurnatronics]

Brilliant ideas thanks very much for the sanity checks!!

On a related note, anyone got any recommendations for a clamp meter? Im half eying up a fluke t6 or even the Megger MET1000 that I could then use for safe isolation. The open jaw clamp would work for finding the neutrals no?

 

[timhoward]

The cheapest one worth having IMHO is this one: (£40 inc vat)

https://cpc.farnell.com/multicomp-pro/mp780050/mini-leakage-current-tester/dp/IN08364?mckv=sdUObAoH2_dc|pcrid|426684131405|

That is a rebadged Tek 775 which normally costs £75+

I'm not sure I'd want my 2-pole tester to become a more sophisticated and expensive item, it gets so much abuse day in day out I don't wanting to be forking out big money to replace it!

 

[hasel5]

Working live in a DB ? Is that ok

 

[Gurnatronics]

Working live in a DB ? Is that ok

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?

The cheapest one worth having IMHO is this one: (£40 inc vat)

https://cpc.farnell.com/multicomp-pro/mp780050/mini-leakage-current-tester/dp/IN08364?mckv=sdUObAoH2_dc|pcrid|426684131405|

That is a rebadged Tek 775 which normally costs £75+

I'm not sure I'd want my 2-pole tester to become a more sophisticated and expensive item, it gets so much abuse day in day out I don't wanting to be forking out big money to replace it!

Awesome I will check it out thanks. I just want to carry less stuff around so not having a 2 pole and multiple meters with multi batteries to keep track off would be ace, like you say though, more chance of breaking grrrr

 

[MJPD29]

Working live in a DB ? Is that ok

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

 

[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