SUPPLEMENTRY BONDING

[snowplough]

CAN SOMEONE EXPLAIN TO ME IF SUPPLEMENTRY BONDING WHEN CONNECTED TO PIPES AND RADIATORS SAY IN A BATHROOM ALSO NEEDS TO BE CONNECTED TO THE CPC IN THE SHOWER UNIT WHICH RUNS TO THE MAIN EARTHING TERMINAL IN THE CONSUMER UNIT.
IM A BIT CONFUSED I SEEM TO READ DIFF THINGS ON THE INTERNET , SOME SAY SUPP BONDNG SHOULDNT BE CONNECTED TO THE MAIN EARTHING TERMINAL IN THE CONSUMER UNIT ,YET OTHER SUGEST IT IS CONNECTED.
SURELY IF ALL THE METAL WORK IS CONNECTED TO A CPC IN THE BATHROOM , SAY THE METAL WORK INSIDE THE SHOWER OR SHAVER UNIT WHICH IN TURN IS CONNECTED TO THE CPC AND THEN TO THE MAIN EATH IN THE CONSUMER UNIT THEN IT IS ALL EARTHED WITH THE ELECTRICAL SYSTEM.

PLEASE HELP IM CONFUSED

 

[Spark123]

STOP SHOUTING!

The idea of supplementary bonding is that it connects together all metalwork which can introduce a potential to the location so that no dangerous voltages can appear between two metal parts.
There is no need to deliberately connect it back to the MET, it will as you say be connected back to the MET via CPCs of circuits but there is nothing you can do about that.

In contrast, under the 17th edn regs in certain circumstances supplementary bonding may be ommitted altogether.

 

[snowplough]

thanks for repling to me ,
so surely its better to be connected in some way to the main cpc if thats wot your saying because if all metalwork was supp bonded together in a bathroom but not connected to the met either by the cpc in a socket outlet box or run directly back from bathroom and that metal work became live then surely someone touching it could get a serious electric shock i assume if the fault current can get back to earth to complete its circuit.

so i can see why all metal parts need to be bonded together but surely they need to be connected to earth in the met some how so fault current can flow and blow a fuse rather then making mtal live waiting for someone to touch it .

am i right thinking this its interesting as i am starting my electricians city and guilds so imtrying to understand.

 

[rebuke]

Your supplementary bonding should connect to any extraneous conductive parts (i.e. CPCs of lighting and shower circuits etc), in addition to the exposed conductive parts (pipework), so there will be a route back to the MET - what Spark123 was saying is you don't have to run a separate earth cable directly back to the MET, you can just rely on the CPCs...

 

[snowplough]

thanks for that i seemed to have read diff things on the net ,one saying S.B SHOULD BE CONNECTED BACK TO MET THEN OTHERS SAYING IT SHOULDNT.
I ASSUME THEN IT IS A MUST THEN THAT ALL SUPP BOND MUST BE CONNECTED TO THE MET IN THE CONSUMER UNIT.

IF THE SUPP BONDING RUNS THROUGH ALL METAL PIPE WORK IN BATHROOM AINCLUDING THE COLD WATER PIPE GOING TO THE ELECTRIC SHOWER WHICH I ASSUME IS CONNECTED TO THE CPC IN THE SHOWER UNIT IT SELF , JUST BY CONNECTING THE SUPP BOND TO THE SHOWER COLD WATER PIPE WOULD MEAN IT IS ALL CONNECTED BACK TO THECPC SO YOU WOULDNT HAVE TO RUN THE SUPP BOND INTO THE SHOWER UNIT ITSELF IF U GET ME DRIFT, AM I RIGHT

 

[rebuke]

No, as a lot of showers don't actually connect the incoming pipework to earth, as they go through plastic fittings inside (e.g. my shower uses a compression fitting to connect incoming copper pipe to plastic bits)...

 

[Spark123]

OK, look at it from a different point of view.
What if the only electrics in the bathroom were SELV lighting and metallic pipework to the radiator and hot/cold water?
Under the 16th edn regs you would supp bond the hot to cold to radiator. As there is no electrical appliances to bond to that is it, no need to connect to MET.

Under the 17th supp bonding in the above may not be required at all.

 

[snowplough]

SO I ASSUME THEN ALL S.B CABLE SHOULD BE TAKEN FROM ALL PIPE WORK ETC STRAIGHT TO INSIDE THE SOWER UNIT CONNECTED TO THE SAME SCREW AS THE CPC CABLE GOING BACK TO THE MET VIA THE MAIN ELECTRIC SHOWER 6MM CABLE.

IN MY BATHROOM I CANT SEE THE SUPP BOND CABLE GOING FROM THE PIPEWORK ETC INTO THE SHOWER UNIT AS DISCUSSED, WILL IT BE HIDDEN BEHIND THE PLASTER DO U THINK OR MIGHT THERE NOT BE ONE IF SO DOES ONE NEED CONNECTING TO IT?

 

[rebuke]

Please stop shouting (writing with caps lock on) - it makes your posts very hard to read.

I'm not sure of the exact regs as to how it could be connected to your shower, I'll leave that to someone else. What I will say, is if all circuits in your bathroom are RCD protected (this includes the lights), then under the 17the edition of the wiring regs as long as any exposed conductive parts are 'effectively' connected to earth (i.e. you measure the resistance, and it's less than a certain amount - don't have the figure to hand), you don't need supplementary bonding. I've not got any in my bathroom for example, as it would have been a pain to do such that it looked OK, and since I replaced the CU with everything on RCBOs, it's allowed...

 

[snowplough]

Sorry for shouting

i know my shower is on an rcd, lights are not, so i assume it should be supp bonded and all light cpc only should be connected to the supp bond cable from the extraneous conductive partsi.e pipe work.

spark123 comment about 16th edition saying none required back to the met , surely theres a chance of electricution then in the unlikly event of a live cable coming into contact with the radiator and pipe in the bathroom because its not connected to the met a fuse might not blow keeping the metal work live,

im slowly coming to conclusion that supp bonding isnt required if all bathroom exposed conductive parts are on rcd so they should trip straght away u hope meaning no mealwork will become live, but even then i suppose rcd can fail so why dont they combine the two, am i thinking logically

 

[Spark123]

The idea of supplementary bonding isn't to provide a path to earth, it is equipotential bonding i.e. ensuring everything in the location which can introduce a potential is at (or about) the same potential.
If everything is at the same potential then when you touch 2 metal parts no current can flow.
If they are at a different potential then you may recieve a shock, the magnitude of the shock being increased as in special locations such as bathrooms as you will have a lower body resistance when wet and naked.

 

[snowplough]

Sorry for sounding thick spark123 im just learning

so what would be the pointof bonding the radiator and pipe together because are u saying with no cpc in location theres no chance of touching a cpc and a extraneous cond part at the same time .

Surley even if all metal work is at the same poetential u can still get a fatal shock if u create a circuit back to earth by touching it hence an earth connection back to the met required to blow fuse and eliminate this , am i thinking right

 

[Spark123]

Fault currents don't necesserally have to originate from inside the location hence bonding the radiator to the water pipes will reduce the risk associated with say the immersion heater in an adjacent room faulting.

If the pipework is effectively bonded together anyway then under the 17th by implementing RCDs to all circuits in the bathroom and ensuring there is a path back to the MET via the main bonding for all extraneous conductive parts.
This way it ensures the fault on a piece of equipment in the bathroom does not exist long enough to cause danger.
Doesn't really help much with the immersion heater scenario above though!

 

[snowplough]

Sorry spark 123 not sure wot u mean re the immersion in an adjacent room do u mean if it and its pipe work became live through fault it would make the pie in the bathroom live if connected?.
even if this happened surely if it was not connected to the met it would be a sitting live fault ready to cause an electric shock so even if all metal is at thesame potential surely its just as dangerous if its not connected to the met so it can blow the fuse. "i think"

 

[Spark123]

The pipework may have a voltage existing on it whilst the protective device on the immersion heater clears the fault.
In order for a current to flow you need 2 different potentials. If everything in a room is at 230v with respect to mother earth then touching 2 parts should not result in a fatal shock, though it might get a little bit tingly.