Sockets Close to Sink and other related electrics

[TheScullster]

Hi all

Kitchen wiring works again. Am trying to "predict" where sockets will be required/desirable (even though SWMBO hasn't signed off on my layout plans yet!).

This brings a few questions to mind which would be useful to resolve (don't have on-site-guide to hand unfortunately).

Some time ago ISTR, the permitted distance between a wall socket and the sink was something like 1 metre. Also IIRC this was found to be generally unworkable.

So my questions are:

How close can a socket be to a sink? Are there specific requirements re depth of buried power/lighting cables? Am I right in thinking that cooker cable has to be buried 50mm or put in earthed conduit? Can an electric hob be above a dishwasher or above to one side of said dishwasher?

Are there any other proximity issues to be wary of?

Does sink need an earth taking back to the CU or is equipotential local bonding the order of the day in kitchens?

TIA

Phil

[Guy King]

The message from "TheScullster" contains these words:

At least twice as many as you first think you'll need is a good rule of thumb.

[John Anderton]

This can't be true (or the building inspector who signed off my kitchen extension wasn't aware of it), my sockets are about 50cm from the sink and I've got an extractor fan switch within 25cm.

See above

Not that I know of

No idea on this one.

Don't see why not. The only concern would be liquid dripping down from the hob, surely and my dishwasher is under the sink/draining board so that concern doesn't seem to be a showstopper

Don't think so, just make sure there's lots of them !

Can't say. A Corian sink and plastic pipework makes the point moot :-)

Cheers,

John

[Tournifreak]

Not sure offhand.

No as long as they are in vertical or horizontal runs. 50mm otherwise. Best to keep to horizontal or vertical runs though.

No, same as above.

Yes. No probs.

Height of sockets above worktop. Google this group for more info. 150mm I think. Height of sockets/lightswitches. 450mm to 1200mm from floor.

Eqi local bond is fine. Arguably using a short length (1m?) of plastic pipe to insulate the sink from the rest of the copper pipework is safter though. Then your sink has a high-impedance connection to earth rather than a very low one. There are good arguments on both sides. I have a plastic sink and all plastic pipework FWIW.

Regards, Jon.

[Nigel Molesworth]

I still think all this bonding lark is old hat.

But I did wonder what I should do in the case of my stainless sink, it isn't connected physically to the taps, and has no bonding tag.

[Owain]

As close as you like, subject to the "suitable for intended location" ie if in a location likely to be splashed it should be a splashproof socket.

You can put a socket *in* the sink if you want, subject to appropriate IP rating :-)

Cables should run in permitted zones (horizontally or vertically from visible accessory), or 50mm (although I dislike that in walls as plenty of fixings will penetrate >2" into a wall) or protected.

Don't see why not

Switch for hob/oven Does sink need an earth taking back to the CU or is equipotential local

Kitchen sinks do not need any bonding.

Owain

[John Rumm]

As in easy, or not required?

IIRC there is no actual regs requirement to bond the sink. However many sparks will swear blind that there is since it is stated as a requirement in one of the popular wiring books (Whitfield)

[Nigel Molesworth]

Not required. Why would running a bit of wire to a tap make the slightest difference to the resistance to earth.

[John Rumm]

Certainly less than that, as little as 30cm may be acceptable, although you need to exercise good judgement based on the particulars of the install.

See:

Are there specific requirements re depth of buried power/lighting cables? Not if they are in the permitted zones.

Am I right in thinking that cooker cable has to be buried 50mm or put in

No

It would depend on clearance under the worktop.

Sockets to hob, flues to windows etc?

The latter (if fitted)[1].

[1] Not required:

[John Rumm]

It wouldn't... but then again that is not the point of the exercise is it!

The intention is to create an equipotential zone (i.e. a Faraday cage).

that in the event a fault, the voltage *difference* between any bits of accessible metalwork can not rise to a significant level with respect to each other.

Think through the following scenario:

Say your dishwasher develops a fault that causes its casework to become live. Since it is earthed, a massive fault current will flow for a short time before its protective device operates (fuse in the plug, or MCB on the circuit).

However since the case of the dishwasher may be on the end of a long ish cable run back to the CU there will be a very small but tangible resistance of this path to earth. Which may mean that the voltage of the earth near the dishwasher rises significantly toward mains voltage until the fault is cleared.

If you were simultaneously touching the case of the dishwasher and a tap for example, then you could be in for a potentially fatal shock. By bonding everything together you won't necessarily lower the resistance to earth, and hence the voltage on the metalwork may still rise. However you help to ensure that it all rises *together* to the same potential so that there is no risk of you ending up as part of a circuit.

[TheScullster]

"John Rumm" wrote

Thanks to all respondents and for the links John

Phil

[Nigel Molesworth]

They *are* bonded together, where the water pipe enters the building.

[Guy King]

The message from Owain contains these words:

Just so long as you empty the sink before opening the casing!

[John Rumm]

And how many compression fittings with PTFE tape or Boss white on them are in the pipe run?

Is there a difference in length of the pipes?

Any other equipment in series with one perhaps (combi?)

A fortuitous parallel earth on another (electric shower) perhaps?

Are you sure no one at any point in the *future* will end up inserting a bit of plastic pipe?

With the size of fault currents we are talking about (100s or even 1000s of amps), fractions of an ohm make a *big* difference to the voltage rise at a distance from the main bonds. Hence why equipotential bonding is carried out *locally* to the potential point of contact, and repeatedly.

This is of vital importance if you have a TN-C-S supply (PME), since a fault outside your property like an open circuit neutral will leave all the exposed metalwork on earthed appliances sitting at 240V indefinitely! (since your "earth" is connected to the disconnected neutral and the cable head end in your property - a neutral that is connected to 240V by all the appliances that your neighbours currently have connected). So you want to be really sure that anything you can touch is also at the same potential.

[Lobster]

Mm. I was a bit peed off when the sparks I got to vet my rewiring job failed it on account of no bonding on the sink (didn't feel it would go down too well to argue the toss, so sink was duly bonded!)

David

[Owain]

There must be plugs / sockets rated for connection / disconnection whilst submerged surely?

Owain

[Guy King]

The message from Owain contains these words:

I can't think of any.

[Alistair Riddell]

Of course, but hardly for domestic use -

mateable down to 3000 metres - they cost a couple of hundred quid a pop IIRC

[Owain]

Surprisingly reasonable. I suggest stocking up before wet-mateable sockets are mandatory on all ground floors under the Building (Global Warming) Regulations 2012.

Owain

[Guy King]

The message from Owain contains these words:

Did you see their "Flight qualified" Sub-D connectors - for sattelites. Bet they ain't cheap.