Replacing old consumer unit

[glider2]

JohnD,

Thanks for a very helpful post. I've just purchased a MEM fuse you refered to on Ebay.

Yes there is a green/yellow Earth cable that enters the flat with the supply cables (thankfully). You should be able to see it on the pic I inserted in a previous post. There is however no cable between the water supply and the MET, though the incoming water and central heating pipes have been cross-bonded. What needs to be done please? Cable size, clamps etc please.

You said

All circuits entering a bathroom should be supplementary-bonded to all metallic services entering the bathroom, so the fan supply needs to be bonded wherever you put it. But SELV downstream of the transformer must not be earthed or bonded.

What if the fan is SELV and the transformer is outside the bathroom in the airing cupboard? Any sup bonding required, if so how?

Thanks. If you have a minute have a look at my other thread regarding installing a bathroom fan, specifically the wiring question.

 

[JohnD]

I think you mean the G&Y seen in the bottom right of this pic

Untitled

• glider2
• 14 May 2008
• 2

It looks undersized to me, I would guess it might be 6mm size. this is a lot better than nothing (depending what it is connected to at the other end) but not to current standards.

Tip: If you are in a DIY shed or electrical supplier, have a look at the cables and see how thick a 6mm one is compared to a 10mm or 16mm. You might get them to let you take an inch off the reel as a sample. you can also use cable Clips as a handy gauge as they are made to fit different sizes. use a permanent marker to write the size on each sample in case you forget or they get mixed up.

Modern domestic installations usually need a 16mm earth (you can calculate it, but the size always seems to come out to 16mm)

I expect you are going to say it will be difficult to run a larger earth cable to the meter. It would be very useful to get access to your meter and take the pics.

The incoming water pipe, gas pipe, oil pipe, metallic air con ducts etc entering your home all need to be bonded back to the MET with 10mm G&Y and BS pipe clamps. If the earth bar in your CU is not big enough, you can use an earth block adjacent to it (I suggest an 8-way rather than a 4-way) with a durable label on it.

Boiler manufacturers usually ask for all the pipes around the boiler to be bonded, I presume this is so a gas engineer cannot be shocked if he is touching two pipes, even if he has just unjointed one of them. But it is not an electrical regulation.

The pipe clamps come with labels, that is the easiest way to get one.

there is a lot about earthing and Bonding on //www.diynot.com/wiki/electrics

have a browse.

Bearing in mind that circuits entering the bathroom must be bonded, if you have a SELV fan transformer, it will usually come off the lighting circuit. The lighting circuit will doubtless enter the bathroom so it needs to be supplementary-bonded.

 

[streetlighter]

If you can get into the mains room there may alredy be an isolator switch for the submain feeding your flat which would make the job of replacing the unit easier.

 

[glider2]

Thanks.

I checked the links and found them useful in explaining the idea behind sup bonding and main earthing as well as the various earthing set-ups (TN-S etc).

How can I check whether the bathroom lighting circuit has been bonded to the metallic components of the bathroom? How am I supposed to carry out sup bonding if it hasn't? The bathroom is tiled, the ceiling is concrete...

I'd like to run a 3-core and earth cable from the ceiling rose in the bathroom (covered in trunking) throught the wall to the old airing cuboard, through a 3P isolator switch, tranformer, and back out across the ceiling to the wall-mounted SELV timed fan. Does this sound reasonable?
Thanks.

ps: thanks Streetlighter but unfortunately I checked and there's no isolator switch there.

 

[JohnD]

How can I check whether the bathroom lighting circuit has been bonded to the metallic components of the bathroom? How am I supposed to carry out sup bonding if it hasn't? The bathroom is tiled, the ceiling is concrete...

If you can't see G&Y clamped to the pipes (including iron soil pipe or galvanised waste pipe if you have it) and test its continuity back to the circuit, then you haven't got it. Supplementary bonding has to be accessible for test and inspection.

It is quite common to take the lighting circuit earth from the ceiling switch.

If you have an adjacent airing cupboard that the pipes pass through you can do the bonding on that side of the wall. This is also a convenient place to bond to the immersion heater circuits and possibly the CH pump and cylinder stat if you have them.

UK bathrooms don't usually have socket circuits or electric heaters. Shaver sockets are mostly taken off lighting circuits, if not, you have to bond them as well.

 

[glider2]

Thanks. There's no immersion heater as that was taken out a while back and replaced with a combi boiler in the kitchen (no tank).

Q: is it ok to run cable along the bathroom ceiling (surrounded by self-adhesive trunking)? I'd like to spur off the ceiling rose to feed the wall mounted fan. The fan would be in zone 3, as would the wiring.

 

[JohnD]

you can do that, but wiring in bathrooms is subject to Building Regulations notification.

the fan should have an isolator for cleaning and maintenance.

p.s. you have strayed off the original topic so should be starting new questions separately.

 

[securespark]

MEM?

Tis indeed! 10/10!