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Topic Title: Cables in trunking space factor
Topic Summary: PIR code for over stuffing
Created On: 04 September 2006 07:52 PM
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 04 September 2006 07:52 PM
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deleted_johnwoods

Posts: 997
Joined: 05 September 2005

2 questions in one night, sorry about this.

Just something that is about to come up, we have 150mm sq. trunking which is less than half full so no problem. But at one point this goes down to 75mm sq and is pretty packed. This is all older cable in an old installation.

What code would you give this, tricky for me to be subjective as I don't think anyone will do anything about it. One option I did think of was just to swap the trunking for 150mm but this would mean disturbing the cables and I would rather not do that. Like me they aren't that flexible anymore.

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 04 September 2006 08:19 PM
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dlanders

Posts: 311
Joined: 20 May 2005

John,
I suppose initially it would have to be Coded 3 - further investigation required - without knowing overcurrent protective device ratings. But have no doubt Code 1 would pertain once derating factors are applied to circuit conductors.
 04 September 2006 08:33 PM
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deleted_johnwoods

Posts: 997
Joined: 05 September 2005

I have a nasty feeling you are right.
Hopefully we can derate some circuits using smaller mcbs and remove others which are now unused to sort this out in the short term. Or increase the trunking size.
But we will have to do something more permanent in the near future.

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You must be the change you want to see in the world - Mahatma Gandhi
 04 September 2006 09:03 PM
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mikespark

Posts: 307
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Without evidence of deterioration or overheating due to the overstuffing it can't possibly be a Code 1. That effectively condemns the installation and is just not a practical state. Code 3 isn't any good either because you can't rectify it whatever investigaton you do, without upgrading the trunking, which is really the only option. That's a Code 2, "requires improvement". If, and I stress IF, there is really no evidence that the overstuffing is having any impact at all, I would even consider a Code 4, just a non compliance with BS 6761. I've seen many instances like this, where over a period of years more and more cables have been drawn in but the loadings have been nowhere near cable limits. Measuring the temperature inside the trunking would quickly determine if it was a problem.
 06 September 2006 01:54 AM
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dlanders

Posts: 311
Joined: 20 May 2005

mike,

Measuring the temperature inside the trunking would quickly determine if it was a problem.


Surely this measurment is "further investigation" Code 3.

Code 3 isn't any good either because you can't rectify it whatever investigaton you do, without upgrading the trunking, which is really the only option.


You could also derate the overcurrent protection but that doesn't change the next point.

I would even consider a Code 4, just a non compliance with BS 6761


and,

That's a Code 2, "requires improvement".


I would have thought this obvious, as space factors have to be taken in to account.

Without evidence of deterioration or overheating due to the overstuffing it can't possibly be a Code 1. That effectively condemns the installation and is just not a practical state.


This is about safety, not practicalities.

So there are you four codes, ALL relevant to this install. Take your pick any one of 2 to 4 will definitely apply and Code 1 as I stated earlier MAY apply dependant on the others. If carrying out a PIR you will be the one in the dock if it all goes wrong.

Dave
 06 September 2006 08:19 AM
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mikespark

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dlanders
Very nicely put. Just goes to show that PIR's are all about judgement calls.
You cannot rectify the situation by derating the OPD's. It's still overstuffed!
You can't rectify it by measuring the temperature, but that helps to establish if, in your judgement, there is a safety issue. I reiterate my first point that if there is no evidence that the cabling has is in any way unsafe due to the overstuffing it cannot possibly be a Code 1.
I would be very happy to defend that in court having made the professional judgement.
OK, you could put down Code 3, requires further investigation, and walk away but I would think you're more likely to get sued if there was a subsequent problem unless you have followed that up with a detailed recommendation for further action which had been ignored. Same goes for Code 2, requires improvement.

Code 4, non-compliance, has a lot going for it. Gives you the opportunity on the face of the report, to give the client useful information without being alarmist.
A PIR is intended to be a report on the condition of an installation at the time of the inspection and a list of non-compliances does just that.
 06 September 2006 08:39 AM
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jimroberts

Posts: 272
Joined: 23 January 2005

Good point; Cables in trunking space factor

Spoke with IET the other day apparently the 45% guide, in general is to allow for additional future circuits

If design the of circuits is correct you could near fill the trunking (I am told)

(came across many a stuffed trunking, albeit not cool to stuff however feels & runs cool)

In that case would the code be 0?


Jim
 06 September 2006 08:50 PM
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deleted_johnwoods

Posts: 997
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Just caught up on this and would go along with the code 4 if the cables could be proven to be ok. I believe they will be in good condition (IR tests will tell) and I do not believe the last PIR showed any hot spots, they apparently used a heat camera.

I would still recalculate based on no of conductors in one enclosure and derate as required, there shouldn't be too many requiring derating.
These were put in, mostly, with the standard non derated mcbs/fuses for the cables. I would think the original installation was fine, or would like to think so, but over 40 years various people have done stuff and not been too bothered.

Problem here is that looking at summer and winter loads gives different readings. Also machines keep getting moved around, a local sport it seems, so loads shift. I will err on the side of caution and derate as appropriate as we will be reviewing / replacing most DBs over the next 2 years.

Thanks for the input everyone

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You must be the change you want to see in the world - Mahatma Gandhi
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