Bonding

[fencer]

Hello all,
What is the score with bathroom bonding if all the copper pipe work has been joined together using plastic push fit connectors, surely the connectors will break any continuity to earth.
Thanks for any help.

 

[brown-nought]

No it is not isolated if you use plastic Push Fit fittings to join Copper to copper.

If you test continuity with a meter it may appear to be isolated – however the few mm of plastic is not enough to ensure isolation when full of water with 240v potentially present. See the Hep20.co.uk website – there Paul Cook of the IEE writes an excellent article on bonding with plastic pipe. (The article applies to all plastic pipe including Speedfit as well as Hep.)

 

[wonderdust]

so does that mean if i have added a towel rad using plastic pushfit i have to earth the rad as well

 

[andy]

there has to be an earth link between each connector so the pipe id earthed. even tho the plastic is insulated the water is not

 

[plugwash]

remember what you are trying to achive with bonding

you should bond all the copper pipes that leave the bathroom there is no need to bond the sections that are only inside the bathroom

 

[ban-all-sheds]

But if you've bonded the pipes, then you've turned a radiator at the end of a few inches of pushfit into an E-C-P....

 

[josey]

i thought i knew what i was doing with regards to bonding untill i read this,
our shower is piped in plastic form the cold tank, but changes to chrome in the attic and aprox 4" of the chrome pipe comes down the bathroom wall into the top of the shower, are you saying the chrome pipe should be bonded

 

[wonderdust]

whats an E C P

 

[Lectrician]

ECP - Exposed conductive part.

A short length of copper pipe with in the bathroom, fed via a length of plastic doesn't require bonding.

 

[wonderdust]

so are you all saying that if a towel rad or radiator in a bathroom that has been spured of the main ch pipework in plastic that the towel rad should be earthed backe to the main ch pipes

 

[andy]

yes. the idea is that everything is earthed, so there can be no potential diference between 2 metal parts so if you touch them you wont get a shock (since the resistance thru the bonding will be lower than that of your body)

 

[wonderdust]

so as well as using plastic supply and return pipes you would have to run an earth cable to every radiator or is there another way round this

 

[ban-all-sheds]

so are you all saying that if a towel rad or radiator in a bathroom that has been spured of the main ch pipework in plastic that the towel rad should be earthed backe to the main ch pipes

It depends.

I don't think there is a defined length of plastic pipe, with less than which a radiator becomes an extraneous-conductive-part. If you look at the document mentioned above, 15mm pipe with inhibited water in it has a resistance of approx 20kohms/m, so a short length is going to leave you with the possibility of a semi-decent earth path, i.e. the worst of all possible worlds.

With all-plastic installations, or ones which are all plastic apart from a few cm of chromed pipe used for æsthetic reasons it's cut and dried - no bonding.

For all-metal ones it's cut and dried - bonding.

For the situation you describe? Guess you could pick a value for the resistance of the human body, decide on a maximum current, and therefore a minimum total resistance, and then measure from the rad to earth to see if it should be bonded.

At the end of the day, I guess it's safer to bond when you don't need to than vice-versa...

 

[ban-all-sheds]

so as well as using plastic supply and return pipes you would have to run an earth cable to every radiator or is there another way round this

Plastic rads, if only they were available.

Or plastic piping throughout, not just odd bits.

Or nothing but SELV in the bathroom, with the sources outside. Quite realistic for lights and fans.

Not so good for power showers, but you might well be able to position the pump and all of its switchgear outside.

For electric showers you'd have to use a split-unit one with the heater outside.

For electric or dual towel warmers you'd be have to ensure that they were Class II.

So it is do-able.

 

[plugwash]

the main point of bonding is to stop potentials ENTERING a special location from faults elsewhere in the system.

so the inportant thing is that metal pipes leaving the specail location are bonded

if a section of pipe is only within the equipotential zone then there is no reason to bond it