Bathroom Electrics

[bernardgreen]

I suppose that bonding in a bathroom would have a purpose if the "Eathing" on a bit of exposed metal failed to remain conductive.

 

[EFLImpudence]

I'm not sure what is happening.

 

[flameport]

If Metal bit A is connected to "Earth" and Metal bit B is also connected to "Earth" then Metal bit B will be at the same potential as Metal bit A

Only if they are connected to the same earth, and by a low impedance.

The bonding of Metal bit A to Metal bit B would only serve a useful purpose if "Earth" was not at the same potential as "Earth"

That's the whole point - a metal part in a bathroom could have a substantial voltage on it when a fault occurs, but without bonding, another metal pipe entering from outside would not have that same voltage, and a dangerous potential would exist between the two items.
Connecting them together keeps those two items at or very near the same potential.

 

[JohnW2]

Basic electrical theory seems to be excluded from the matter of bonding, If Metal bit A is connected to "Earth" and Metal bit B is also connected to "Earth" then Metal bit B will be at the same potential as Metal bit A .... The bonding of Metal bit A to Metal bit B would only serve a useful purpose if "Earth" was not at the same potential as "Earth"

Exactly. If "Earth" were not in inverted commas, but were just a 'single point', then everything connected to it would be at the same potential (if no current were flowing through the 'connections').

However, as you know only too well (since you are always going on about it in relation to TN-C-S), when those inverted commas are in place (which they often are) then there is plenty of scope for there to be ' "Earth" and "Earth" ' (i.e the two not necessarily being the same, or at the same electrical potential).

Kind Regards, John

 

[bernardgreen]

a metal part in a bathroom could have a substantial voltage on it when a fault occurs

Two faults really, (1) a live conductor comes into contact with the metal part and (2) the connection of that metal part to "Earth" has also failed.

 

[frank999]

Thanks, so, in a bathroom 1.5x2.4mt (so a small size), there exists:

a chrome water towel rail
a porcellain sink with metal taps.
a shower with metal mixer taps.
an electric ceiling fan 240v or 12v (to be decided, most likely 12v)
a 240v ceiling light on loft floors lighting loop.
a glass wall mirror with metalic back box, with 240v suppling an LED lighting driver, to power recessed LED lighting in the mirror.

This 4mm earth bonding cable cable connects:
to the earth of the fan
celing light earth
wall mirror supply earth
then onto earth straps:
clamped onto the hot and cold copper pipes feeding the sink
then same on shower copper pipes
then onto clamps around a bare section of the towel rail copper feed pipe

... all run as one uncut continous section of cable, but not necessarily in that order of strapping/connecting.

I have had 3 bathrooms installed, mostly complete, all with the same above configuration,.
I cannot see any 4mm earth cable sticking out of the wall where a 240v 1.5mm² cable end stick out, reasdy for the lit wall mirrors to be hung, in fact I do not beleive there is any earth bonding in the bathrooms ... as I supplied all the materials, and know the builders did not request a drum of 4mm earth.
Would it be legitimate for the bonding to have been omitted, all circuits in the property go back to an RCD Protected CU.

 

[EFLImpudence]

Firstly, if all the circuits of the bathroom are covered by an RCD - and a couple of other requirements are met - then in the words of the regulations "supplementary bonding may be omitted".
In my opinion, this wording - 'omitted' meaning 'left out' - is misleading. It is just that, with RCDs, the circumstances where SB would still be required are virtually impossible to be the case.

Then:
"a chrome water towel rail
a porcellain sink with metal taps.
a shower with metal mixer taps."
are all irrelevant.
It is the pipes supplying them that must be considered.
Are they extraneous-conductive-parts? If they are then they must be bonded (without RCDs present).

and:
"an electric ceiling fan
a 240v ceiling light
a glass wall mirror with metalic back box,"
are also irrelevant.
It is whether they have any exposed-conductive-parts.
If they have then they must be bonded (without RCDs present).

Plus, which of these items are simultaneously accessible.

The regulations state that all CPCs of Class1 and Class2 equipment must be connected to the bonding but this is not an electrical requirement if they have no exposed-c-ps, merely a cover-all in case the equipment is changed in the future for equipment with exposed-c-ps.


To repeat, one cannot answer with a 'yes' or 'no' the question "There is a pipe sticking out of the bathroom floor: does it require bonding?".
There are measurements that must be taken to determine whether it is an extraneous-c-p to the room and then measurements to other extraneous-c-ps to determine if SB is necessary.

 

[frank999]

Thanks for the explanation.

The circuits are RCD protected, so supplimentary bonding in the bathrooms, being 'omitted' is not an issue, am i right to suggest that this is ... provided disconnection times happened within set times.

Before establishing whether RCD disconnection is within limits, would it be prudent to lay wiring in preparation for bonding any extraneous-c-ps and exposed-c-ps, in case it is needed and so walls can be closed.

 

[EFLImpudence]

The circuits are RCD protected, so supplimentary bonding in the bathrooms, being 'omitted' is not an issue, am i right to suggest that this is ... provided disconnection times happened within set times.

Yes, as well as the RCDs, the disconnection times must be complaint and Main Bonding must be satisfactory, again IF required.

Before establishing whether RCD disconnection is within limits,

It's also the MCB disconnection times - as RCDs are 'additional' protection, although they may be the only protection device.
I know that doesn't really make sense but that's how it is. If you can achieve the times with the MCBs then you should.

would it be prudent to lay wiring in preparation for bonding any extraneous-c-ps and exposed-c-ps, in case it is needed and before walls are closed.

I suppose it would, but that is up to you. Will there be any fixtures with exposed-c-ps, if not then complying with the so-called 'future proofing' is also up to you.


Bear in mind that SB for the bathroom doesn't have to be in the bathroom. It can be anywhere that achieves the necessary low enough impedance between the parts.

I used to manage a small flat which had all the services - water and electricity supplies, DHW cylinder, main bonding and the consumer unit on the other side of a wall of the bathroom. Whilst SB was technically required, all of the pipes and circuits were so short none actually needed to be fitted.