Adding a Shower RCD unit at fuse board

[Mike2007]

I told a long time served electrician about my problem of adding an RCD to a shower circuit and no form of isolation of the tails which presently supply an add-on double fuse box (BS3036 30A + 40A Wylex B40).
He said he would probably pull the cut outs or put them in live!
Surely its not possible to even handle the tails live without getting some current discharge??

 

[Softus]

Surely its not possible to even handle the tails live without getting some current discharge??

Certainly not to be recommended with bare wet hands, but do you class the tails differently to, for example, touching the grey sheath of an energised 2.5mm² T&E cable?

Granted, the T&E might be protected by an RCD, and the tails not, but the voltage is the same, so how much current do you think would "discharge"?

 

[Mike2007]

Surely its not possible to even handle the tails live without getting some current discharge??

Certainly not to be recommended with bare wet hands, but do you class the tails differently to, for example, touching the grey sheath of an energised 2.5mm² T&E cable?

Granted, the T&E might be protected by an RCD, and the tails not, but the voltage is the same, so how much current do you think would "discharge"?

Umm I don't know, I guess in perfect circumstances none! Maybe carefully gripping them with 1000v VDE pliers would be safe but not your hands. One conductor at a time, no two conductors bare at same time. They are 10mm I think?

 

[Adam_151]

If you have a second fuse box, then the likelyhood is you have a couple of henley/service connector blocks splitting the tails.

There are many sparks in this world who would be tempted to open the service connector blocks up and drop the tails out of there, and reconnect/insert new tails when the job is done (downstream isolators open of course), its not right but some sparks would feel comfortable doing it (and of course a few just have wood for brains!)

Live terminals and dead tails is always going to be less risky then dead terminals and live cables (because its the cables you actually have to move)

^^^For information only, I'd much rather you didn't electrocute yourself!

 

[Mike2007]

If you have a second fuse box, then the likelyhood is you have a couple of henley/service connector blocks splitting the tails.

What do the regs state what is acceptable practice? I would not want an electric shock at any time and reducing risk at all time is very important!
WHY are isolators (lockable) not fitted after the meter on ALL domestic installations, they know work will need to be done on consumer units at a later stage??
Plumbers have service valves, stop-cock at mains source and a cock in the street.......3 lines of isolation. When you work with something more dangerous like electricity.......umm very little

 

[Steve]

Plumbers have service valves, stop-cock at mains source and a cock in the street.......3 lines of isolation. When you work with something more dangerous like electricity.......umm very little

Water does more harm more quickly when it goes wrong. And there are no safety stops on a typical supply, what you'd call fuses with electric. So isolation is very important.

With electricity the emphasis is on protection with fuses, so when it goes wrong it is quickly put right by automatic disconnection.

 

[Mike2007]

Plumbers have service valves, stop-cock at mains source and a cock in the street.......3 lines of isolation. When you work with something more dangerous like electricity.......umm very little

Water does more harm more quickly when it goes wrong. And there are no safety stops on a typical supply, what you'd call fuses with electric. So isolation is very important.

With electricity the emphasis is on protection with fuses, so when it goes wrong it is quickly put right by automatic disconnection.

Quick disconnetion if its been installed right and not tampered with too much over the years. Also with water, it may cause structural damage but not a sudden loss of life in a faulty situation! Its true, there are no devices for too much water being used suddenly as a flood?

Anyway, back to my shower unit, RCD or RCBO??

 

[Adam_151]

It depends on what you are doing with it

an RCD provides earth fault protection and supplimentary protection against direct contact

a fuse or MCB provides overload, short circuit and (except on TT installs) earth fault protection

An RCBO is quite simply an MCB and RCD in one unit.

If you are taking a supply directly from the henley blocks, you are going to need both MCB and RCD, or two pole RCBO

If you have an existing circuit, thats already got an MCB on, and you want to add rcd protection to it, then an RCD is all you need

*basically a circuit must not be protected by RCD alone*

I'd be worried about that B40 breaker, does it sit a bit sideways? I'm not comvicned that board is meant to take anything bigger than a 32A, you might be best having that board replaced (and it might be wise to have the other one done and have it all as one big modern board)

 

[Mike2007]

It depends on what you are doing with it

an RCD provides earth fault protection and supplimentary protection against direct contact

a fuse or MCB provides overload, short circuit and (except on TT installs) earth fault protection

An RCBO is quite simply an MCB and RCD in one unit.

If you are taking a supply directly from the henley blocks, you are going to need both MCB and RCD, or two pole RCBO

If you have an existing circuit, thats already got an MCB on, and you want to add rcd protection to it, then an RCD is all you need

*basically a circuit must not be protected by RCD alone*

I'd be worried about that B40 breaker, does it sit a bit sideways? I'm not comvicned that board is meant to take anything bigger than a 32A, you might be best having that board replaced (and it might be wise to have the other one done and have it all as one big modern board)

What was in was a 10.5kw shower on a 6mm t&e cable! Now has a 10mm t&e cable but finding a suitable protection device seems much more difficult. Are you also saying the RCD alone should be ran through a fuse or MCB. I don't recall seeing the Henley blocks, can I get an 40amp RCBO as detached unit like RCD's are now made? Its a 9kw shower now, so should just scrape under 40amp's?

 

[Anteaus]

Not sure I quite envisage the setup here - Is it that tails run direct from the meter to a small CU containing an isolator and two breakers?

If so, the correct approach would be to tap into the shower cable itself downstream of the breaker, and fit an RCD into a 2-module or 4-module DIN enclosure. These are only a few pounds.

If OTOH you want to disconnect tails from a meter, or from Henley blocks on the supply side you MUST contact the supply company first. Otherwise they are likely to suspect you of tampering with the meter, in which case they may get very shirty with you! The correct, safe way to do this is to remove the supply fuse from its sealed holder (again you MUST contact the supply company)

Some electricians may work 'live' on Henley blocks, but bear in mind they have a great deal more experience than you, working live on a 100A circuit is most definitely not for beginners. The issue here isn't so much shock, but an accidental short which could leave you with burns or even eye damage from the flash. Basically... if you're at all unsure leave this kind of thing to the experts.

Might also add that it's not mandatory to have an RCD ona shower feed. Personally I like to see one, but many electricians don't fit one. The main point is to ensure that the shower and its feed pipe (if metal) are well-earthed (use 6mm earth wire) and that all touchable metal within the vicinity of the shower (bath-taps etc) is cross-bonded together and linked to the shower earth. Principle here is to ensure that a fault in the shower cannot create a voltage between adjacent metal fittings.

 

[Mike2007]

Not sure I quite envisage the setup here - Is it that tails run direct from the meter to a small CU containing an isolator and two breakers?
Yes thats right.

If so, the correct approach would be to tap into the shower cable itself downstream of the breaker, and fit an RCD into a 2-module or 4-module DIN enclosure. These are only a few pounds.
If an RCD is mid-stream then how can I test the installation to varify the installation integraty? How do I get 500vac through an RCD mid-stream?

If OTOH you want to disconnect tails from a meter, or from Henley blocks on the supply side you MUST contact the supply company first. Otherwise they are likely to suspect you of tampering with the meter, in which case they may get very shirty with you! The correct, safe way to do this is to remove the supply fuse from its sealed holder (again you MUST contact the supply company)

Some electricians may work 'live' on Henley blocks, but bear in mind they have a great deal more experience than you, working live on a 100A circuit is most definitely not for beginners. The issue here isn't so much shock, but an accidental short which could leave you with burns or even eye damage from the flash. Basically... if you're at all unsure leave this kind of thing to the experts. Don't intend putting myself in hospital, I have had arc-eye off a welder before so could guess at what 60-100amp's would give me!

Might also add that it's not mandatory to have an RCD ona shower feed. Personally I like to see one, but many electricians don't fit one. The main point is to ensure that the shower and its feed pipe (if metal) are well-earthed (use 6mm earth wire) and that all touchable metal within the vicinity of the shower (bath-taps etc) is cross-bonded together and linked to the shower earth. Principle here is to ensure that a fault in the shower cannot create a voltage between adjacent metal fittings.
I am well familiar with supplementary bonding of supplies.

 

[plugwash]

Maybe carefully gripping them with 1000v VDE pliers would be safe but not your hands.

Touching the plastic sheath of the tails should be no more dangerous than touching the plastic sheath of any other cable, you just have to make sure you don't touch the bare metal ends when you have them out.

Afaict the big risk with handing live tails is not so much the shock risk (which is no worse than with any other live cable) as the kind of burns you could end up with if you accidently shorted them out.

afaict most electricians just cut the seals and pull the fuse even though they aren't meant to.