Supplementary bonding

[sevuk]

I've seen a sink recently which has copper pipe goes out of the toilet to a connection under the floor which is supplied in a non conductive material back to the main shut off valve. The same method is used from the toilet. To me this doesn't require bonding if there is rcd protection, but it did get me thinking. If the pipe work is supplied in copper then changes to plastic then changes to copper again, how long must the copper are we talking before it is deemed an extraneous conductive part that needs to be bonded?

 

[Leesparkykent]

You would test it to see if it's extraneous.

 

[Pete999]

I've seen a sink recently which has copper pipe goes out of the toilet to a connection under the floor which is supplied in a non conductive material back to the main shut off valve. The same method is used from the toilet. To me this doesn't require bonding if there is rcd protection, but it did get me thinking. If the pipe work is supplied in copper then changes to plastic then changes to copper again, how long must the copper are we talking before it is deemed an extraneous conductive part that needs to be bonded?

 

[sevuk]

Thanks, that clears it up.

So if it is above 20,000 ohms to earth its just a piece of metal. Below that it's extraneous, and needs to be bonded if above 1667 ohms.

 

[Pete999]

Thanks, that clears it up.

So if it is above 20,000 ohms to earth its just a piece of metal. Below that it's extraneous, and needs to be bonded if above 1667 ohms.

The 20,000 and 1667 are derived from 2 different calculations.

 

[sevuk]

Yep.

I think I get it. 1667 is the maximum allowed for rcd protection of an extraneous conductive part

The 20,000 ohm rule is based on ohms law allowing meaning you won't get more than a 10mA shock under fault conditions between the bonded pipe work and the "piece of metal"

 

[Ian1981]

To put it simply it’s 50v / 0.03= 1667 ohms
50v is the touch voltage and of course 0.03 is 30mA for the said rcd if that’s what protects the circuit

 

[sevuk]

Thanks guys.

I think I fully understand the calculation that gets the 1667, it would be 50v/0.01 if it was a 10mA RCD for instance. (I've only heard of the like integrated into sockets for use in areas used by small children such as nurseries and this wouldn't apply as it only provides protection for the use of portable appliances not the circuit).

What I want to make sure I'm totally clear on is defining a pipe as either extraneous or not.

Reason being is going back to my college days, if a part of a metal water pipe installation went to plastic then back to metal it would need to be bonded again. Which I expect would be still true, but only if the IR test between the pipe and a local known earth was below 22,000 ohms - the assumed 1000 ohms resistance of the human body. Is that correct? Am I mad?

 

[telectrix]

that's correct. the 22k added to the 1k gives a current through the body as 10mA. similar principal to the neon screwdriver that we all love.

 

[Pete999]

Yes correct

 

[sevuk]

Thanks, this clears it all up.

That reminds me I need to replace my missing volt stick.

I got my 2391 coming up and I'm sure I'll find more electrical theory to drive myself mad over.

 

[Ian1981]

Thanks, this clears it all up.

That reminds me I need to replace my missing volt stick.

I got my 2391 coming up and I'm sure I'll find more electrical theory to drive myself mad over.

Best of luck with it

 

[Midwest]

I quite like John Wards videos, like this one on this very subject;

Plus he's a bloody nice bloke

 

[westward10]

Looks like a serial killer.

 

[Midwest]

Looks like a serial killer.

Why 'cos he's wearing tinted glasses and flashy tee shirts

 

[westward10]

Why 'cos he's wearing tinted glasses and flashy tee shirts

Partly and he sits in darkened rooms making videos for You Tube, bet he was a premature baby that is a list topper for serial killers.

 

[westward10]

Why 'cos he's wearing tinted glasses and flashy tee shirts

I just clicked with that

 

[sevuk]

Nothing wrong with any of the blokes in the videos. Haha.

By the way the IR test at 500v or 250v?

 

[Midwest]

Partly and he sits in darkened rooms making videos for You Tube, bet he was a premature baby that is a list topper for serial killers.

Nice little earner apparently, depending on how many views you get. Beats working in someone's itchy, dusty loft

 

[cprfenom]

Nothing wrong with any of the blokes in the videos. Haha.

By the way the IR test at 500v or 250v?

Depends what you are testing.