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Topic Title: Metal Work
Topic Summary: Should it all be bonded
Created On: 28 September 2012 08:07 PM
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 28 September 2012 08:07 PM
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Ampman

Posts: 1010
Joined: 06 February 2006

evening ,

I have been testing in a food production area with machines etc.....

My question is that some of themachines have either metal railings around them or metal steps that lead up to higher vantage point on the machine ,

now the machines are metal and earthed through either there 3 phase plug tops or are hard wired into the local fuse boxes .

The steps and fences are free standing and are not bolted to the machines but you can be either standing on the steps or leaning on the fence and touch the machine ,

the fences and steps are just free floating on the tiled floor

should these be bonded to the machines ????

cheers
 28 September 2012 08:17 PM
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daveparry1

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If they don't actualy go into the floor I would say bonding not required.

Dave.
 28 September 2012 08:50 PM
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Ampman

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no they dont go into the ground ,

I just get a bit paranoid about worse case scenarios !!!!!
 29 September 2012 06:05 AM
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ebee

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I did once work in a basement full of CH pumps and Iron pipes with three boilers in in the room.
There was a metal screen free standing and fabricated from sheet metal.
My initial thought was that BS 7671 does not require earthing or bonding as it is.
However I did watch an employee using a portable drill initially drape the flex over this sheet metal then realising the implications that no matter how well rounded this sheet was the thiness meant the edge remained nearly sharp and subsequently moved the flex to the floor.
Secondly, the proximity of the sheet metal to the pumps meant that it was conceivable that a person might lightly lodge themselves in the gap and therefore reminded me slightly of a restrictive conductive location.
Therefore bonding to pipework might be more appropriate in this instance.

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

Knotted cables cause Lumpy Lektrik
 29 September 2012 07:55 AM
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Jaymack

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Originally posted by: Ampman
the fences and steps are just free floating on the tiled floor ........... should these be bonded to the machines ????

Measure the ohmic value to a good earth, .......... Resistance = ?. If they can't introduce an earth potential, no bonding is required.

Regards
 29 September 2012 01:13 PM
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sparkingchip

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Flaming hell Ebee!

Do you realise how your post could be interpreted!!!!!!!

Andy
 29 September 2012 08:07 PM
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stateit

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Originally posted by: sparkingchip

Flaming hell Ebee!



Do you realise how your post could be interpreted!!!!!!!



Andy


That's nothing, I was working in close confines with some strippers the other day.

-------------------------
S George
http://www.sg-electrical.com
 29 September 2012 08:40 PM
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Ampman

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Can someone please confirm the reding i require to confirm these dont need bonding ,

I think its 23k ohms to the MET of the building or is it to the local fuseboard ?

Also what will my meter digits read on the lcd 23,000 ?


cheers

Ps if i have got the right figure ? I can not find this reading in the regs book , I remember reading a thread on forum about this ages ago and the figure sticks in my head ,
 29 September 2012 11:18 PM
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Parsley

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22K to the MET with everything else disconnected+1K human body
=10ma.
22K on IR setting of your tester.

Regards
 30 September 2012 11:20 PM
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Fm

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Ah i remember those days when consultants insisted everything within arms reach had an earth conductor going to it.
 01 October 2012 10:11 AM
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OMS

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Well not quite everything -

Handrails can be difficult - they have a nasty habit of exporting step and touch potentials way beyond where you'd expect them to be - similar to warehouse racking systems and mezzanine storage solutions.

So bonding or otherwise needs a bit of thought - particularly if they are earthy anyway due to machine contact or containment fixings - and what the floor structure is.

regards

OMS

-------------------------
Failure is always an option
 01 October 2012 08:29 PM
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Fm

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Ah i didnt mean everything, i meant in arms reach of the electricalmequipment.

But those werethe days when suspended metal legs on floor would have a tenby clamp, and a ceiling grid would have a crimp and nut and bolt as well

The good old days
 02 October 2012 08:47 AM
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OMS

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Ah i didnt mean everything, i meant in arms reach of the electricalmequipment.


I know - that's why I suggested handrails, crash barriers and racking present specific problems - it may be arms reach from a particular piece of kit but the other end of that metalwork could be a long way from the machine - but it will still rise to the machine potential under fault - you wouldn't want to be standing on a nice earthy floor touching the hand rail when a machine 25m away goes into a 5 second fault shutdown

Regards

OMS

-------------------------
Failure is always an option
 02 October 2012 10:10 AM
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zeeper

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I have had this dilemma before and discussed it with OMS and others on this forum.
For me I took it back to basic's.First of all,I dont want to introduce a potential danger or risk of electric shock . Second what does the regs say about earthing and bonding and when do we have to do it. Is the hand rail a exposed conductive part no, is the hand rail a extraneous conductive part. It might be,but its not introducing a potential that does not already exist, ie the floor. So by sticking a green and yellow on it you could be introducing a difference in potential between the hand rail and the floor as the MET is unlikely to be at the same potential as the floor,which is probably laying on the general mass of earth.
 02 October 2012 12:02 PM
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Parsley

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I was asked why we hadn't bonded the metal cable tray on an install.

I said show me in the regs where it states it needs to be bonded and asked how he thought bonding the tray and exporting touch voltages would make the installation safer. He walked away muttering something about the 15th.

Regards
 02 October 2012 12:06 PM
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OMS

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I was asked why we hadn't bonded the metal cable tray on an install.


Isn't it earthed ?

Regards

OMS

-------------------------
Failure is always an option
 02 October 2012 12:48 PM
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Parsley

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OMS

The tray wasn't an exposed conductive part and it wasn't extraneous either.

Regards
 02 October 2012 12:54 PM
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OMS

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Well I'm suprised at that - I'm assuming by your comment "not exposed conductive part" that you are making a claim of double insulation on the PVC oversheath of armoured cables and relying on the swa to act as the earthed metallic barrier between live parts and the tray then ?

Regards

OMS

-------------------------
Failure is always an option
 02 October 2012 01:03 PM
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AJJewsbury

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Well I'm suprised at that - I'm assuming by your comment "not exposed conductive part" that you are making a claim of double insulation on the PVC oversheath of armoured cables and relying on the swa to act as the earthed metallic barrier between live parts and the tray then ?

Isn't that what GN 8 says? (at least I think the old one did). If the cables themselves are safe to touch (either insulating sheath - deemed class 2 equivalent, or earthed metal sheath), then the tray should be just as safe without any additional precautions. Presumably no-one is putting unsheathed singles on steel tray?
- Andy.
 02 October 2012 01:33 PM
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Parsley

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Originally posted by: OMS

Well I'm suprised at that - I'm assuming by your comment "not exposed conductive part" that you are making a claim of double insulation on the PVC oversheath of armoured cables and relying on the swa to act as the earthed metallic barrier between live parts and the tray then ?



Regards



OMS



10.11 GN8 page 157.

As always I would appreciate your thoughts.

Regards

Regards
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