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Topic Title: too much bonding?
Topic Summary: bonding everything to everything else
Created On: 23 February 2013 04:03 PM
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 23 February 2013 04:03 PM
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Littletrev

Posts: 6
Joined: 22 February 2013

Hi all a question for you all,the industrial factory where I am the sole engineer failed its I & T with insufficient bonding (TN-C-S), along the main factory wall there are a dozen or so isolators for the machinery from 100a to 20a wired in swa and under this 2 paralell 2in cooling pipes so i have bonded all isolators and structural steel to these pipes as they are embedded into concrete at the end .and the structural steel at the intake and also too the compressor pipework can you over bond ?im just concerned that a p.d could occur as all cabling come from the same db over the other side of the factory but different ampages so different resistances at the machine end.also can i put all the remidial bonding work on 1 minor works cert
 23 February 2013 04:14 PM
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daveparry1

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I don't see how you can have too much bonding from an electrical point of view, addmittedly it's probably wasteful but not a problem electrically. The MWC cert. is supposed to be for only one circuit but I think you could put it all on the one cert, there won't be much ellse to put on the cert. if you're not altering the circuit's in any way,

Dave.
 23 February 2013 05:04 PM
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MrOther

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I had an interesting discussion when doing my Mum's Bedroom recently. She has this big disco ball like thing hanging from the cieling, decorative and nice.

The patress is from an old light.

Testing it to MET it doesn't need bonding and by the regulation is doesn't need bonding.

But I know for a fact that cables run not to far away from the patress in the cieling, in fact maybe over it. So it is quite concievable that if a fault occured up their for it to become live.

So, as Dave said, I think the only negative is maybe cost. If you can deduce a solid reason why to or why not to bond then why not if it makes you sleep at night?
 23 February 2013 05:33 PM
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Martynduerden

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Not like this?

-------------------------
Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
 23 February 2013 05:56 PM
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ebee

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In an ideal world the earths crust would be several metres thick conductive metal say copper for instance.
But it`s not, so we keep adding and adding to make it nearer so.
Lovely bonding you can`t have too much, just some or none but never too much.



-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 23 February 2013 10:42 PM
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geoffsd

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Originally posted by: MrOther
Testing it to MET it doesn't need bonding and by the regulation is doesn't need bonding.

Should not be bonded, then.

But I know for a fact that cables run not to far away from the patress in the cieling, in fact maybe over it. So it is quite concievable that if a fault occured up their for it to become live.

That would be earthing - to be done if you consider the possibility likely.

So, as Dave said, I think the only negative is maybe cost. If you can deduce a solid reason why to or why not to bond then why not if it makes you sleep at night?

As long as it is necessary and done correctly.
 24 February 2013 06:58 PM
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Littletrev

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Joined: 22 February 2013

thanks for the replies guys i thought so,its such an old system and new bits added everywhere,there are 50 reccomendations on the test for me to work through from lack of bonding to missing grommets it will keep me busy for a while and a laser to fix too...what joy and i am even going through the code 4 ones too
 24 February 2013 09:06 PM
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MrOther

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Geoff it's extraneous and was to keep to extend the potential zone, therefore I treated it as supp. bonding.
 24 February 2013 09:37 PM
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geoffsd

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No - you said it wasn't extraneous (how could it be?) - now you are treating it as exposed.
 25 February 2013 10:34 AM
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AJJewsbury

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i am even going through the code 4 ones too

How old is this report? Code 4s disappeared from the regs a long time ago (just C1 - C3 these days).

- Andy.
 25 February 2013 11:39 AM
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Littletrev

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the test was completed on 5 12 12
 25 February 2013 11:56 AM
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OMS

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Originally posted by: Littletrev

the test was completed on 5 12 12


The tester didn't realy have a grip on the new amendment then - it was available on 1st July 2011 and came into force on 1st Jan 2012 - so nearly a year later, he was still using entirely the wrong "coding" system.

Based on the above and your original post, I would have a lot of trouble believing what the report said in terms of bonding - and the solution to those 2" chilled water pipes is questionable as well - i ametal framed building with a bond to the structure (ideally 2) then anything hanging off that structure is effectively bonded unless clearly isolated by AV mounts or insulating sections between the pipework and clamp.

Effectively, you have now made the CPC's of multiple circuits the bonding to the pipework - as you swap and change the installation over time, you expose more or less circuits to potential diverted neutral currents (or the installation neutral current or even the network current).

The 100A supplies may be OK - the 20A ones are highly questionable.

If the structire is bonded to the MET, and you have confidence in the continuity of the shed frame, then just bond any pipework, compressed air lines etc etc to that frame.

Can you have too much bonding - yes - if you start connecting up stuff that clearly is neither extraneous of exposed then it too will have the potetial at the MET when under fault when it need not - that introduces a shock risk that wasn't present before.

Be very careful of things like compressed air lines with external compressors - grasping bonded pipework whilst standing on a re- bar slab with no DPC at true earth potential isn't funny - people fall over or off things and get hurt - badly sometimes.

Regards

OMS

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Failure is always an option
 26 February 2013 08:34 AM
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Littletrev

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I see your point hence asking on here , and all the structural steel is into the concrete base as well as all pipework so it is connected .I wandered round with my tester and all steelwork and pipework has a res of under 0.10 ohms before i added bonding so there was a connection to the MET and steel/pipework so why did the report say "no apparent MPB to structural steel or compressor pipework "as i proved a connection with my test instrument so i bonded to make sure the connection was a permanent one.this place is a real electrical nightmare, old and new circuts blanks missing ,no charts,screws missing trucking not bonded and lids missing there are 49 items on my list ! multiple feeds from single MCBS you get the idea and i bet its not the only factory like this.

thanks for the reply
 26 February 2013 08:54 AM
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zeeper

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Its almost like your treating it like a bathroom.

Also you need to take so time and study the difference between main protective bonding and supplementary bonding.

The other week I used this regulation 415.2.2. To rule out the requirement for supplementary bonding between a socket and compressed air pipe.

Its all about the touch voltages.

Edited: 26 February 2013 at 09:04 AM by zeeper
 26 February 2013 09:15 AM
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Littletrev

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well its not a special location but the installation is worn and dodgy in places and the swa cables arnt bolted through the isolators either and as all pipework is sunk into the concrete and attached to the steel anyway via loose brackets.all the large machinery have cpc fly leads as well as the swa.I know the difference between MPB and SEB . its such a complecated place and unsure what to do for the best,if i dont bond the compressor pipes they will still have a potencial but if just relying on the loose brackets and the fact they are sunk into the concrete could give them a different potencial than the MET and steelwork plus they are jointed all over the place that will also alter the potencial (well that was my thinking anyway) so if they are bonded all will have the same potencial .....am i right and i am only bonding pipework and steel that has a poor attempt at supp bonding (jubilee clips with earth wrapped around it lol)
sorry to go about this you are very understanding

Edited: 26 February 2013 at 09:28 AM by Littletrev
 26 February 2013 09:29 AM
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OMS

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Originally posted by: Littletrev

well its not a special location but the installation is worn and dodgy in places

Sounds like a typical factory

and the swa cables arnt bolted through the isolators either

Not uncommon

and as all pipework is sunk into the concrete and attached to the steel anyway via loose brackets.

OK - so if it's in concrete that makes it extraneous

all the large machinery have cpc fly leads as well as the swa.

Quite usual - a lot of designers don't trust electricians do make off a gland properly - and it sounds like they are right

I know the difference between bonding and earthing its such a complecated place and unsure what to do for the best,

You have a big metal shed - effectively everything inside that shed, that either comes from outside or comes via the concrete slab is extraneous including the shed - as long as it's all connected together you still have a credible zone of protection. The metalwrk of the shed, is going to be a far better bonding conductor that anything you could install - make good use of it.


if i dont bond the compressor pipes they will still have a potencial but if just relying on the loose brackets and the fact they are sunk into the concrete could give them a different potencial than the MET (well that was my thinking anyway) so if they are bonded all will have the same potencial .....am i right

Yes - but as I said, you also have a PME system - so any MET voltage caused from the neutral potential will be present on those pipes - if you are outside on a earthy slab, you may well experience some voltage (low usually but can go high) - if there are no seperated inserts then so be it - just be aware of the risk that bonding can create when taken outside the zone of protection (ie the shed)


sorry to go about this you are very understanding



regards

OMS

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Failure is always an option
 26 February 2013 09:45 AM
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Littletrev

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Joined: 22 February 2013

thanks for all that sounds like im going the righ way about it

regards
littletrev
 26 February 2013 10:14 AM
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zeeper

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.I know the difference between MPB and SEB


My point was that things like water , gas , structrual steel, air pipes, would normally have a main protective bonding conductor connected at or near where they enter building.

This is important to confirm, you can then use supplementary bonding where necessary to reduce touch voltages. However it is supplementary to the main protective bonding not instead of.
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