Bonding a bathroom fan

[Richard C]

Regarding local supplementary equipotential bonding in the bathroom; the mirror & ceiling lights are connected into the supplementary bonding loop running from the water/CH pipe work, through the mirror light up to the ceiling light & then looped over in the general direction of the ceiling fan. The fan is fed from a separate spur in the same loft mounted junction box that feeds the ceiling & mirror light spur.

The lights are class 1 & no problem as they have E feeds & terminals but the fan, fed from a double pole, fused switch on the wall outside the bathroom, is class 2 & doesn’t have an earth terminal; although there is an earth tail insulated & tucked back which is connected back to the external fan switch! The regs. say both class 1 & 2 equipment circuits must be bonded but what am I supposed to connect the bonding cable to?

 

[JohnD]

I take it that the fan is fed from the upstairs lighting circuit? Then you bond with 4mm G&Y to the earth of that circuit at any convenient place. This is usually at the bathroom light switch. You can bring the wire down in any pipe duct you may have or the airing cupboard if it is adjacent to the bathroom.

You do not have to bond to every fitting; just once to every circuit that enters the bathroom and to every metal pipe that enters the bathroom (including cast-iron soil pipes, or lead drains, if present).

If you have 20 lamps, 3 fans and a shaver socket all fed from one circuit in the one bathroom, you only have to bond to that circuit once (not 24 times). You also have to bond to the Immersion circuit, and the circuit that runs your shower or jacuzzi, if present.

 

[Richard C]

John D
Thanks for the reply. The fan is fed from the upstairs radial circuit as is the mirror light & main light; the mirror light & main light are wired in series from a spur off a loft junction box & the fan is wired on a separate spur from the same junction box.

So, the bonding loop from the pipe work up to the mirror light is all that is required (as all the equipment is on the same radial circuit) & the bonding loop from the mirror light to the main light & onto the fan is superfluous & not required; can you confirm I’ve understood correctly? It certainly makes sense that you only need to bond each circuit once but, if this is so, why do all the wiring examples I’ve looked (including the NICEIC one which many say is the easiest to understand) show separate bonding on items which will almost certainly be wired into the same (lighting) circuit); rather confusing!

 

[JohnD]

When you say Radial, you mean a 20A 2.5mm or 32A 4mm circuit usd for sockets? Yes, you can take lamps and fans off these, with a FCU fused to 3A (or 5A).

You do not need to link to each fitting on the circuit. One is enough. The connections should be accessible so not hidden, so it is often more elegant to run the wires into the airing cupboard.

There is a good diagram on page 3 of http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf


//wiki.diynot.com/electrics:sp...l_bonding:supplementary_equipotential_bonding

 

[Richard C]

John D
The upstairs circuit is mainly loop in/loop out between each light but the bathroom lighting (mirror & main) & the fan are each on individual spurs taken from a junction box (in the lighting circuit) located in the loft; as is the lighting for the master bedroom; but I thought this was normal? The fan is wired through a double pole fused switch (3A). The supplementary equipotential bonding connections are all present, accessible & seem to be as per regs. Thanks for the links but I’ve already seen both (along with several others); what was a little confusing was why there should be an earth bonding tail floating around in the loft adjacent to the old fan unit (also class 2). But from what you’ve said, bonding isn’t necessary here, or indeed the main light, as the circuit is already bonded via the mirror light.

The house electrics were more or less condemned last year due to crappy old fuse wire, insufficient main earth, no main or supplementary equipotential bonding & no protective earth on the majority of lighting circuits & so the whole lot had to be upgraded (contractor) to current spec due to other building work. I’m now replacing some of the old equipment & doing some good housekeeping checks & maintenance.

The lighting circuits, 1 up/1down, are 1.5mm twin & earth - I assumed they were 15A? They circuits do not loop back to the consumer unit which is why I refer to them as radial but I thought this was normal with lighting circuits? The 2 socket outlet circuits (up/down) are on separate 2.5mm ring mains, which is what I would have expected.

The earthed lighting spurs for the bathroom, main bedroom & an exterior security light were not part of last years upgrade & look to have been done during a previous partial re-wire intended to upgrade these spurs for a bathroom light/shaver, some metal wall lights in the main bedroom & an exterior security light.

Sorry for what seems a lot more questions but you’ve got me thinking about some of the other stuff & any advice would be greatly appreciated!

 

[JohnD]

yes - it is normal for lighting circuits to be radials (rings are only used for UK socket circuits). Lighting circuits should be fused (MCB) at 6Amps. Radial circuits are also used for sockets in some cases, and always for immersion heaters and large cookers.

If it is fed from a lighting circuit you don't need to fuse it down again for the fan, light or shaver socket, and you can feed the mirror light from the shaver socket if you want (it might be a little more usual to come straight down from the ceiling, though.) It is very important to run cables vertically to the outlets (or horizontally between two) and never in diagonals and curves. This is so people can forecast where they are when drilling e.g. for a shelf or towel rail.

 

[Richard C]

Thanks again for the input; although not a spark I always endeavour to make myself aware & comply with the regulations & am familiar with safety zones & general points of good practice - I’ve already changed a few in here that aren’t! It’s just that the requirements for main/supplementary equipotential bonding seem a little confusing & misunderstood by many, including some sparks; hence the redundant bonding tail lurking in the loft space adjacent to the fan unit with nowhere to go! Thanks again for your help.