When working on circuits do you isolate whole board or just the final circuits using MCBs ?

[newlearner]

When working on circuits do you isolate whole board or just the final circuits using MCBs ? Or is there any instances when the whole board has to be isolated even if you are working on few final circuits?

Thanks.

 

[Mikegh]

Depends what you're doing really and whether other circuits need to stay on

Sometimes I prefer the rcd off , DP isolation and you might be shorting an N-E which will trip it anyway

You need to be making sure what you're worku on is dead obviously

 

[freddo]

I usually work on commercial and industrial installations so switching off the whole board would be impractical. For a DIYer like yourself I would always recommend isolating the whole board, make sure you are aware that the supply cable and terminals will always be live.

Some older industrial boards are a nightmare with exposed, closely spaced busbars, it's good to switch those off before installing MCBs and so on. The old Crabtree C50 boards have exposed 3phase terminals all down the sides, not fun to install new circuits with the power on.

 

[littlespark]

You would need a very good reason not to isolate the whole board. Risk assessment and all that.
Domestic, there’s no excuse.
10 minutes without the broadband router powered isn’t a good enough reason for not doing the work safely.

 

[Pete999]

When working on circuits do you isolate whole board or just the final circuits using MCBs ? Or is there any instances when the whole board has to be isolated even if you are working on few final circuits?

Thanks.

Hi Mate no disrespect intended, but I feel it would be wrong and unprofessional to offer such advice to a DIY person, so end of my involvement in this post, leave it to those who know what they are doing. Sorry if I sound abrupt , but it's your life we are talking about here.

 

[Mikegh]

You would need a very good reason not to isolate the whole board. Risk assessment and all that.

Domestic, there’s no excuse.
10 minutes without the broadband router powered isn’t a good enough reason for not doing the work safely.

Switching off all the lights in an installation can create risk for the homeowner and the electrician

If it's unnecessary

 

[ChipFanDave]

I usually work on commercial and industrial installations so switching off the whole board would be impractical. For a DIYer like yourself I would always recommend isolating the whole board, make sure you are aware that the supply cable and terminals will always be live.

Some older industrial boards are a nightmare with exposed, closely spaced busbars, it's good to switch those off before installing MCBs and so on. The old Crabtree C50 boards have exposed 3phase terminals all down the sides, not fun to install new circuits with the power on.
View attachment 88040

Do you have any form of documentation to permit the working on or near live conductors ?

 

[littlespark]

Switching off all the lights in an installation can create risk for the homeowner and the electrician

If it's unnecessary

Head torch.

There is an argument that the live tails into the mainswitch, even with the mainswitch off, is still working on a live board.

I learned quickly not to cut corners as an apprentice.
Working in a 3ph board in a warehouse, some of the circuits were live and I was told to strip the cables coming into the board.
Pulled the cpc on a twin and earth, as I’d been shown to to seperate the sheath….. the bare cpc decided to curl itself back into a circle and the end fell perfectly in between the mcb’s and the busbar……

 

[Mikegh]

Well that's a little more dangerous of a scenario

A trained electrician shouldn't need to switch off an entire installation in every circumstance when working on circuits imo

 

[freddo]

Do you have any form of documentation to permit the working on or near live conductors ?

I'm hoping an electrical permit to work covers this.

 

[littlespark]

Well that's a little more dangerous of a scenario

A trained electrician shouldn't need to switch off an entire installation in every circumstance when working on circuits imo

We’re not assisting a trained electrician here. OP is tagged DIY, so advice is geared toward non-experienced.

Even a trained, well experienced spark can have the odd accident concerning working on a circuit within a live board.

Another story I heard about 3 older guys, decades of experience, pushing new cables along conduit into a busbar chamber. Cables kept catching on the bush, so one guy stuck his head into the live chamber to get a better look….

He lost his life, his two mates lost their jobs.

 

[timhoward]

Just remember any mistake might be the last one you make.
Work on circuits connected to a live board is never risk-free and assumes that the installation is exactly as you expect it to be.
I've been caught out by a circuit fed from two boards before now, and a single circuit fed from two breakers. In both cases the wiring was live when it logically shouldn't have been. On one of them I was tired and stupidly didn't test it and grabbed some bare conductors. I just remember a blinding light and opening my eyes standing somewhere else with painful burns on thumb and finger.

Or is there any instances when the whole board has to be isolated even if you are working on few final circuits?

On an unknown installation I would anyway. Also, if doing work that warrants a certificate, then the whole board needs isolating before it's possible to safely and accurately test the earthing arrangements.

Whatever the hype - and whatever you see some youtubers do when fault finding, most sparks do actually turn things off.
Stay safe!

 

[Straker]

So from my little corner of the industry, working live events rather than fixed installations, no arguments; isolate, lock off and preferably disconnect and bag as well (easier when everything is on connectors rather than hard wired.) The systems we put in have too much potential to be installed not as designed or mislabelled.

It just isn't worth working with potentially live parts of the system accessible apart from the obvious exception for testing. Having said that I'm yet to find a BS7909 testing scenario in the real world that couldn't be done with made up testing adaptors.

 

[Mikegh]

We’re not assisting a trained electrician here. OP is tagged DIY, so advice is geared toward non-experienced.

Even a trained, well experienced spark can have the odd accident concerning working on a circuit within a live board.

Another story I heard about 3 older guys, decades of experience, pushing new cables along conduit into a busbar chamber. Cables kept catching on the bush, so one guy stuck his head into the live chamber to get a better look….

He lost his life, his two mates lost their jobs.

Fair point

In terms of domestic, working on sockets I would usually DP isolate at an RCD if available

Otherwise I expect my training to protect me checking dead and avoiding contact


We're using single pole main isolation up to now here in the ROI and we're now switching to DP main isolation


My inspector mentioned a kitchen fitter who had been killed at work working on a cooker

Turned off the MCB only and the installation was reverse polarity so the SP main isolator wouldn't have saved him


Moral of the story I reckon

You're just never safe unless you know what you're doing

 

[MJPD29]

I dont do domestic work, but in a commercial and industrial environment it simply isn't practical to always isolate the board. Yes, there are times when it is nessecary but 9/10 times I am happy to add an mcb ato a live board. If I turned off every board i was working on, I doubt I'd be back to half of the places. The domestic environment is a lot more simple, and i cant think of a valid reason why the board could not be isolated.