Bathroom earth bonding

[Ivor Nastychestikov]

Bathroom has hot and cold water pipes, electric towel rail and an electric shower, what bonding is required?

[Alan]

Is everything RCD protected? Has the incoming water pipe (and gas/oil) got bonding in place? If so, then it is likely that there is no need for any Supplementary Bonding.

If no RCD, or not all circuits in the bathroom are RCD protected, then you should have Supplementary Bonding between exposed conducitve metalwork, and the CPC of the circuit(s) in the bathroom.

[John Rumm]

Firstly, no such thing as "earth bonding" - the phrase makes no sense.

You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding).

That depends...

If the main equipotential bonding[1] is in place, and all the circuits that feed the bathroom are RCD protected (with 30mA trip devices), then since the 17th edition of the wiring regs, none is actually required.

If the above requirements are not met (say the lighting circuit is not RCD protected), then you will need to equipotential bond the earth conductors of all the circuits that feed anything in the bathroom, along with any other metalwork that is capable of introducing a potential into the room (and that includes an earth potential).

So typically that would include hot and cold water pipework, and possibly central heating pipework.

You don't need to bond pipes that are plastic, or are just isolated bits of metal "show" pipework feed from plastic pipes. Nor do you need to bond radiators, baths or any other lump of metal that by itself is not able to introduce a potential into the room.

You may need to bond waste pipes if they are metal and ultimately connected to earth. (if unsure measure the resistance between them a a known good earthing point)

For more information see:

[1]

[Ivor Nastychestikov]

Yes.

The hot and cold water pipes are bonded to each other. The incoming water supply enters house by a pvc pipe. There is a 4mm earth cable back to the consumer unit, but that is not connected at the moment. There is no oil or gas.

[F Murtz]

I have a strange situation in my bathroom, all the copper water pipes are bonded to earth externally but I sometimes get a tingle to taps when standing in the shower, (About 5 volts measured from metal round drain to taps) I can only assume that when the house was built(on concrete slab) the reo steel in the concrete was not bonded to earth which is a requirement today

[tabbypurr]

You need to fix that.

NT

[Scott]

Using a JCB :-)

[F Murtz]

I can not be bothered at the moment am not the slightest bit worried that it is ever going to electrocute anyone, Some day I may jackhammer a bit of concrete to expose some reo and bond it,

[Brian Reay]

The 5V isn't but it is a sign of something more serious- it looks like you may have a PME earth and have 'imported' an external (real) earth.

PME earths are fine but rely on your not 'mixing' a PME earth and a real earth in case there is a earth neutral fault- specifically a break in the combined Neutral and Earth conductor which supplies your property.

[tabbypurr]

It is indeed a hazard. A nearby strike would also put a massive voltage gradient across anyone in the shower.

NT

[Dave Plowman (News)]

Is it a wet room? I'd not expect the metal drain to be connected to anything other than a plastic waste pipe.

I'd be inclined to check the potential between your copper pipes and true earth. I've be surprised if you could feel 5v.

[Adam Funk]

But they're both done with green & yellow striped cable!

[John Rumm]

Hence why they call it a Circuit Protective Conductor (CPC) and not an "earth conductor"

You have what are classed as "fortuitous effects"; in that equipotential bonding (by inclusion of multiple CPCs) may also lower the earth impedance at the point of a fault and hence improve disconnection times. Likewise earthing may add additional conductors that will also function as eq bonding, and hence lower the touch voltages.

However these effects (while not unwelcome) may not be relied upon[1], and each system needs to function independently.

[1] e.g. your main eq bond to the incoming water main may provide a good additional path to earth. However it would be unwise to rely on that as an earth since the water supplier may change it to plastic etc. So when testing your main earthing terminal, you disconnect any bonding connections to it for the duration of the test. Likewise eq bonding conductors in a bathroom, don't actually need any connection back to the main earth terminal to function correctly.

[Adam Funk]

I was just joking that using the same cable makes it easy for people to confuse the two.

[ARW]

I would not bother.

If anything you bond the metal waste pipe (UK regs)

[ARW]

I have said it before, and I'll say it again.

Bathroom electrics will one day need supplementary bonding fitting again.

RCDs are not good enough.

[John Rumm]

It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics.

[Adam Funk]

I'm struggling to imagine how it could do any harm to have more bonding than required, as long as it's sound (i.e., not connected to anything "bad").

[tabbypurr]

just a waste of money, some of which is used for useful purposes.

NT

[John Rumm]

Depends on your definition of more than required... if you mean including bonding in a bathroom which meets the 17th edition exception and hence could in theory do without, then yup no harm, and not expensive.

However some places take it to the extreme and festoon every bit of pipework with bonding cables in places where there is not an elevated shock injury risk. In those cases, there are probably other things you could do with an installation to get a better return on the investment.