Bonding

[Rob69]

Can someone explain to me when supplementary bonding is required in wet rooms and what type of asseccories need this cross bonding.

I find this confusing in the 17th edition

For example

LV vent fan

Shower pull cord switch

Shower unit

Normal light

Pull cord light switch

Main bonding (10mm) to services are fitted and all circuits are RCD protected.

Thanks Rob

 

[Andy™]

701.415.2 - if the 3 conditions are met, then no need for any bonding.

so if all MEB's done, and all circuits RCD'd, then your unlikely to need any bonding

 

[sparkytim]

Ditto

Fully 17th Edition compliant installations do not normally require supplementary bonding

.

 

[Rob69]

Is supp bonding required for pipes to sinks and toilets in bath / shower rooms if main bonding in place ?

Also, what about plastic water pipes from main stop cock as this wont be bonded but still got copper pipes in bathroom......what happens in this instance??????

 

[spinlondon]

You need to check for continuity between the pipes and the MET (Main Earth Terminal).

If the reading is between 0.05ohms and 22kohms, then supplementary bonding is required.

 

[sparkytim]

As said earlier if your Main Bonding is to current standard and all circuits RCD protected then NO supplementary Bonding is required.

 

[green-hornet]

Supplementary bonding was one of the most abused methods of earthing employed by the 16th edition, many times it was used when not required and introduced potentials that was not there before.

Now under the 17th edition it is abused by the fact that many people assume that because we have RCD protected circuits we do not need it.

If the conditions are not met by 701.415.2 you will still need supplemental or equipotential bonding.

Its a simple continuity test that now shows if it is required or not.

 

[Mark2spark]

A nice accurate post by greenhornet, saves my typing fingers

 

[Rob69]

Hi Spinlondon,

Those values you mentioned are between MET and any pipes anywhere????

Where does any docements mention these figures????

Cheers Rob

 

[davetheglitz]

As an aside - I've never understood what purpose supplementary bonding serves. To get a shock you are looking for a differential between metal parts of say a lighting circuit and radiator or towel rail in a bathroom. Assume R2 for the lighting circuit at about 1 ohm, towel rail 0.5 ohm - metal to metal 1.5 ohms. To get 50V differential voltage would need 33.3A to be flowing between them - and I can't see any mechanism for this to happen. Can someone explain what the supplementary bonding adds that main bonding doesn't?

 

[a1spark]

Isnt it in part, to ensure that if a Fault to Earth occurs on the Light fitting [mettallic] or any other exposed conductive part within the bathroom that they will all rise to the same voltage level simultaneously [ including any extraneous conductive parts ] therefore producing minimal shock risk....and the circuit protective device will then obviously operate and clear the fault as per any Earth fault

 

[davetheglitz]

That makes sense - thanks!

So what we are protecting for here is someone touching a metal light fitting/towel rail in the bathroom at the very instant that the appliance goes faulty whilst simultaneously touching the taps or other metal fitting. You are then in contact for the time it takes the MCB to trip. In the scale of things how likely is that to happen?

 

[ianmacd]

That makes sense - thanks!So what we are protecting for here is someone touching a metal light fitting/towel rail in the bathroom at the very instant that the appliance goes faulty whilst simultaneously touching the taps or other metal fitting. You are then in contact for the time it takes the MCB to trip. In the scale of things how likely is that to happen?

What if not enough current is flowing to Earth to trip the MCB or the path to earth is broken so the fitting is contantly at 230V?