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Topic Title: supplementry equipotential bonding
Topic Summary: do ya need to if
Created On: 31 January 2013 11:10 AM
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 31 January 2013 11:10 AM
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Avatar for zeeper.
zeeper

Posts: 1407
Joined: 11 July 2008

I got a metal air line next to a site that a metal clad socket will be installed.

By using a near by light switch cpc I measured 0.19 to pipe.

I would like to treat this as a extraneous-conductive-part for my argument. As this pipe could well be a water pipe (just not in this case).
There is no rcd protection of circuit.

So its less than 22K ,but it also meets the requirements of 415.2.2 . (20AMCB B type)

So im look at 50/100= 0.5

If pipe is less than 0.5 Ohms to socket then supplementry would not be required.

Or have I got me wires crossed.
 31 January 2013 11:44 AM
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Avatar for OMS.
OMS

Posts: 19457
Joined: 23 March 2004

Does it introduce a potential that's not already there - ie is the pipe bonded where it enters the building or is installation such that it's in intrinsic contact with bonded building steelwork, or does it connect to equipment that's already earthed

It almost certainly doesn't require supplementary bonding, but if you want to do it you need to pick up everything accessible - so that light switch for example.

From there determine which is the biggest CPD in play - ie is it the socket or is it the CPD to a local machine that the comp air supplies and is now included in the bonding scheme.

assuming it is the 20A device then you need a max of 0.5Ohm (as you've calculated) measured between all the accessible exposed and extraneous parts.

remember if it's a socket outlet, your zone of protection may need to extend to the limit of where an appliance flex on a class 1 bit of kit can reach.

Basically, what you are doing is ensuring the touch voltage doesn't exceed 50V for more than 5 seconds (or a higher voltage for shorter time) - ie you are effectively shortening R2 and from the equation Vtouch = If x R2 you can see as R2 gets smaller, so does Vtouch.

Regards

OMS

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Failure is always an option
 31 January 2013 11:50 AM
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Legh

Posts: 3472
Joined: 17 December 2004

Vtouch = If x R2 you can see as R2 gets smaller, so does Vtouch.


Or to put it another way

If R2 (csa) gets larger then R2 (ohms) get smaller

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 31 January 2013 12:12 PM
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Avatar for zeeper.
zeeper

Posts: 1407
Joined: 11 July 2008

The compressed air pipe is a long run branching off to all different parts of the site. At this point probably around 100m away from compressors.

Thanks for the help, I just dont like bonding things just because I know no better.
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