Please ensure your electrics are up to date!!!!!!!!!

Mary_Hartnell

That is "earth" in 20th century speak.

gromituk

It's not earth - it's ensuring that all metal that you can touch in the bathroom is at the same voltage, but that voltage isn't necessarily at earth potential. In fact you should not take the equipotential bonding back to the earth at the consumer unit.

mttylad

Technically yes - but it's done with an "Earth wire"

gromituk

Indeed. But earth wires traditionally connect to earth; these don't. The strange-sounding term isn't entirely a pointless invention to make things more opaque (and I used it precisely because if I hadn't, someone would have chimed in telling me that it's not earth bonding).

dwarvenassassin

gromituk wrote: »

Surely an RCBO is comparable in price to an RCD but the overall cost is greater because you need them for every circuit?

No, I actually mean that a new Consumer Unit with RCBOs on each circuit is comparable in price to a Consumer Unit with twin RCDs and MCBs for each circuit.
The cost of RCBOs has dropped significantly in the past 12 months.

zax47

dwarvenassassin wrote: »

No, I actually mean that a new Consumer Unit with RCBOs on each circuit is comparable in price to a Consumer Unit with twin RCDs and MCBs for each circuit.
The cost of RCBOs has dropped significantly in the past 12 months.

No way! I'd never fit a board fully populated with RCBO's. They are nothing like as cheap as 2 x RCD + 10 MCBS.

Look at TLC Wholesale for a good comparison;

MK
2 x 60A 30mA RCD @ £41.50 ea. + 10 x MCB @ £2.50 ea. = £108

10 x RCBO @ £ 24.95 ea = £249.50

Wylex
2 x 63A 30mA RCD @ £23.55 ea + 10 x MCB @ £2.99 ea = £77.00

10 x RCBO @ £25.00 ea = £250.00

Hager
2 x 63A 30mA RCD @ £14.95 ea + 10 x MCB @ £2.75 ea = £57.40

10 x RCBO @ £21.95 ex = £219.50

Contactum
2 x 63A 30mA RCD @ £14.50 ea + 10 x MCB @ £1.99 ea = £48.90

10 x RCBO @ £18.99 ea = £189.90

Cost per circuit with all RCBO's is at least 2.3 times as much as using RCD/MCB, and up to 3.8 times - using my examples above.

Comparable? - my !!!!!! (with all due respect ) Similar price difference at all my suppliers/wholesalers.

Mary_Hartnell

gromituk wrote: »

Indeed. But earth wires traditionally connect to earth; these don't. The strange-sounding term isn't entirely a pointless invention to make things more opaque (and I used it precisely because if I hadn't, someone would have chimed in telling me that it's not earth bonding).

Thank you, I stand corrected.

I think I understand that the (say) copper water pipes may connect to a plastic blue main. And I do remember the "Gas Board" trying to fit a plastic washer to their supply pipe so that it could not be used as an earth, back in the 1970's.

Please educate me, what is achieved by linking (say) the gas pipe to the hot and cold water pipes and the pipe that feeds the central heating radiator with green and yellow wire if none of them are earthed?
What if one of them is?

gromituk

I think a web search by you will achieve about the same as a web search by me. It's not a simple subject, because it takes into account not just shock protection but fire protection from faults, and the characteristics of protective devices which can detect different fault conditions, and I can't pretend to understand the whole thing. "Equipotential" just emphasises the fact that you can only get a shock by touching two conductive objects at different potentials, which then cause current to flow through your body. If those parts of your body are wet then the connection you make is much better so the shock is much worse, and any water you are in contact with itself becomes part of conductive objects it is in contact with. Hence the special attention placed on bathrooms and outdoors. Running an earth wire back from an equipotentially-bonded bathroom to the main bonding in the house will not improve how well the metal objects in the bathroom connect together, and I presume has some disadvantages which someone with more knowledge than me can explain.

gromituk

One thought: if there is a live-earth fault at one end of the equipotential bonding system in your bathroom, which connects all the metal objects together and then has a wire back to a good earth at the consumer unit, you could get a substantial potential difference between metal objects in the bathroom until the MCB trips or fuse blows. If that wire back isn't there, the majority of the potential difference is likely to be between the bathroom and the main earth, as this will have proportonately greater resistance than the equipotential bonding within the bathroom.

Mary_Hartnell

Thanks, I think I can understand this is in the aged of almost instant circuit breakers. Could be interesting if one pulled oneself up using the two metal bath taps if both were fed by copper pipes and one had become live and the other had not.

I must admit I have never felt insecure in my 1970 bathroom, with none of this protection (just one big slow clunky breaker on the company side of the fuse box, probably stops the house burning down but might not save someone with a serious shock through their body. (When I moved in a found someone had put hair pins in the 4 fuses that serve the whole house !).

In my previous house of 1950's vintage, we nearly had a widow next door: hubby had a bit of a dodgy drill (they were metal in those days). He was up a ladder, drill in one hand trying to fit plugs to take a curtain rail. In those days retro fitted central heating nearly always had the two pipes running down behind the curtains.
So he used the other hand to get extra purchase by pulling on the pipes.

Wife found hubby, with tongue sticking out, in a pool of water - husband supercharged by electricity running to earth from drill to pipe, had performed a bear hug manoeuvre and ripped the radiator pipe off the wall.

:eek:

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:eek: