Cirquit breaker for electric shower?

I have a 7 kw electric shower fed by 6 sq.mm T&E cable from the main fusebox. What is the correct circuit breaker or (or other device) to use? Can I obtain one for a Hager fusebox? Here is a photo of the fusebox:

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also need some extra circuit breakers for this fuse box, and would like to know where I can get them...

Thank you.

Jeff

Reply to
Jeff D
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Reply to
Dave Plowman (News)

Is it much better to use an RCD in place of a MCB for a shower? Can 32 map ones be obtained? The Hager ones at the above site seem to start at 63 amps...

How about for an electric cooker?

Cheers,

Jeff

Reply to
Jeff D

40A is sufficient as that is what I am using here and have done for years.
Reply to
Bob

I don't know of anyone ever electrocuted in a shower or by a cooker protected by an MCB.

32A for cooker and 40A for a shower of 7KW. It depends on how paranoid you are. A shower will blow when first switched on if there is a fault, and how many people get in before switching it on!
Reply to
Bob

On Fri, 27 Apr 2007 19:10:42 +0100, Jeff D mused:

it, and you're thinking of wiring the shower and the cooker, I'd stop there and get someone else to finish the job off.

Reply to
Lurch

On Fri, 27 Apr 2007 20:35:06 +0100, Jeff D mused:

An RCD is not a replacement for an RCD, they both perform different functions. An RCD is for fault protection and an MCB is for overcurrent protection, you need both.

Reply to
Lurch

On Fri, 27 Apr 2007 20:49:06 +0100, "Bob" mused:

That's not really the point. Whether or not you know of someone being killed by an electrical fault on a shower doesn't mean you should not fit the required equipment to the circuit.

ITYM competent. 40A for a shower of 7kw is way OTT.

You are just too dangerous.

Reply to
Lurch

On Fri, 27 Apr 2007 20:46:26 +0100, "Bob" mused:

40A could well be the incorrect rating, and probably is. Guessing isn't the way to do it.
Reply to
Lurch

Thanks. I should mention that the 6mm cable curently runs inside a cavity wall which at some point may be injected with insulation. Could this cause the cable to overheat with a 40 amp fuse? I now note that others recommend 32 amp fuses.

Jeff D

Reply to
Jeff D

On Fri, 27 Apr 2007 21:29:07 +0100, Jeff D mused:

I would imagine 40A is too big anyway. 32A is what I would normally fit to an 8.5kW shower run in 6mm. If your cable is in a cavity full of insulation then you may need to decrease the MCB rating, and get a new shower, or run a larger cable in.

Reply to
Lurch

So you nominal maximum load at 230V is 30A. So the correct breaker would be a 32A type B.

Next question, is the cable to the shower ok? For that we need to know how long is it in total? How many meters of that are buried in the insulated wall? How is the rest fixed along the route? (I.e. surface wired, buried in plaster, in conduit etc). Does the cable route pass through unusually hot areas (like an airing cupboard?). Is the cable tightly bunched with any others along the way? Finally what type of earthing does your main consumer unit provide?[1]. Once we know all of that we can do the design calculations to see if the cable choice correct, and also what additional protection (if any) will be required.

(Electric showers appear simple enough to install, however there are quite a number of (sometimes quite subtle) bits of detail that need taking into account)

Before you go much further, what is the wire feeding the consumer unit? Again same questions as above. If that is for example also 6mm T&E you may not have any spare capacity for other circuits.

[1] for information on answering this question see here:
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Reply to
John Rumm

Even I can see bare conductors showing and I'm no expert on electrics .

Reply to
Stuart B

Good - thanks!

12 metres, 3 mtrs of which are in the cavity wall, which is, as yet, uninsulated, but I may want to add insulation at some time soon. I am wondering if I could feed some sort of flexible 3" dia tubing up the cavity, inside which the cables will run (to pevent them becomeing caked with insulation. Anyone know of any such thing? (I'm envisaging something like a flexible vacuum cleaner hose, but about 3 inches in bore.

It runs underneath the upstairs floorboards, the underfloor space has no insulation. It is not bunched with other cables anywhere. There are no hot areas.

At the main electric meter there is what looks like 16 sq.mm earthing wire fixed to the metal casing of the Electric Board's armoured rising main cable. This earth cable goes to a type of connector block. From this, earth cables (I think 10sq.mm), go to the main switch. From the main switch, there is a 5 mtr lenth of 16 sq.mm T&E cable going to the fuse box from where the 6sq.mm T&E shower cable runs.

I don't have any earth cable running to the bathroom taps, etc. The water plumbing is all grey plastic. There is one copper gas pipe going from the gas meter to the attic where the boiler is located. I don't know if that pipe is earthed or not. It doesn't go near ant electric cables.

16 sq.mm T&E, coming from the main switch. The main switch is fed by much thicker meter tails from the electric board's meter, etc.

Many thanks for the input.

Jeff D

Reply to
Jeff D

I quite agree. The picture shows poor workmanship and several violations of BS 7671.

  1. Is that a Hager housing which, when used with the switch- disconnector and MCBs fitted, constitutes a type-approved consumer unit assembly? Or have the Hager parts been fitted into a recycled housing from another manufacturer?
  2. The bare incoming CPC (earth) should of course be sleeved with green-and-yellow PVC sleeving.
  3. The crude great gaping hole in the bottom, convenient for connecting a finger to the live busbar, must be plugged. All enclosures must meet at least IP2x on the bottom and sides and IP4x on any accessible top surface.
  4. The neutral and earth conductors are not connected to the designated terminals, which won't help with correct identification of the conductors of outgoing circuits.
  5. The 6 mm^2 incoming cable is unlikely to be adequate for the loading of two outgoing 32 A circuits.
  6. No anchorage is visible for the incoming cable. Since the CU housing provides no anchorage all connected cables will need to be clipped or otherwise secured close to their exit points.
Reply to
Andy Wade

There are two shower ones that I know of in last ~5 years.

One was a relatively new shower, just installed by a qualified electrician. The very same electrician was brought back in to investigate the installation after the death, and unsurprisingly found nothing wrong. Any further inspection after that would have been invalidated due to the opportunity to tamper with the installation, although I'm not aware there was any further inspection. From the description in the press, the mode of death would have been impossible if the bonding was up to spec in the bathroom.

Second one was a bloke doing up his own house. There was no electricity, and he ran the shower off a cable from next door. As far as could be determinated afterwards, he must have been holding the shower unit in one hand whilst showering himself with the other, as it had never been installed or even fixed to a wall.

In some cases, you have to get in to switch it on. I've known a shower (at work) develop a fault whilst in use. The shower of sparks and popping sounds was a good clue to get out of the shower fast. However, a properly bonded installation represents no risk of electrocution even in this case with no RCD.

Reply to
Andrew Gabriel

Thanks for the comments. The housing is a Hager one. I think those MCBs were in there when it was new.

That will be done.

Point taken - thanks.

Are you sure?

It is actualy 10 sq.mm cable in the photo, but it will have 16 sq.mm cable when it's fitted.

I appreciate the advice - thanks.

Jeff D

Reply to
Jeff D

May I ask what constitutes 'proper bonding'? In my case, the shower unit housing is made of plastic and the only metal item touchable from the outside is the flexible shower hose. The 6mm T&E cable feeding the shower unit has its earth properly attached to the termonal provided inside the unit and the other end is connected to the main earth at the electric meter (clamped to the outside of the armoured rising main). Is that proper bonding?

I'd like to make sure it's correct, since electricity, water and a wet, naked human seems like a mix that warants time spent ensuring it's done right.

Thanks,

Jeff D

Reply to
Jeff D

Oh, OK. Is it being used as intended? There doesn't seem to be much wiring space above the main switch - might be tricky if you were trying to get 25 mm^2 tails in.

Maybe not. There are positions marked "N" and [earth symbol?]. I took those to be the incomer terminals, but maybe they're only fixing screws for the bars. In that case I'd put the neutral feed from the switch to terminal 1 or 2, so that the outgoing neutrals can correspond to their MCB positions, counting L to R.

What's the screw that seems to be wedged behind the incoming neutral, BTW?

Apologies, I guessed at 6. What's it being fed from, by the way. If it's off the meter (via a Henley block, etc.) you'll need a separate 16 mm^2 earth, since the 6 mm^2 earth in 16 T&E won't comply with Table 54G.

Also use of the old red & black colours are no longer permitted, of course.

Reply to
Andy Wade

On Sat, 28 Apr 2007 14:17:59 +0100 someone who may be Jeff D wrote this:-

That depends on the installation.

Is the bath or shower tray metal? If so it must be bonded to the shower.

Are there metal pipes in the bathroom, heating as well as water pipes? If so they must be bonded.

Is there an electric towel rail in the bathroom? If so it must be bonded.

The above list is not exhaustive.

The aim is to create a zone within which there is no potential difference between the metal parts (other than small things which are unlikely to introduce a potential such as coat hooks). Then in a fault it doesn't matter what the potential of the zone is (and the potential will vary during the fault) as this will not cause harm.

You may not be aware that in an instant water heater, including a shower, the electricity passes through a bare uninsulated heating element over which the water flows. That is why it is important to get it right.

Reply to
David Hansen

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