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Hello All,

Iv been asked to pick up the remedials on someone else's EICR that was done last year on a school for Deaf Children. One of the items listed on the report is the conductors leading to the sub mains from the main panel are undersized. I popped the cover off to have a look and sure enough 4 out of 5 submains have a 16mm XLPE SWA (3 Phase) on a 100 amp MCCB, ok so initially I'm thinking this may need looking into.

But after looking at the sub mains, and there actual loading from the final circuit charts, it would be suffice to say that 2 out of the 4 submains wouldn't be able to even get close, and the other 2, once diversity was applied, would never be able to achieve a loading to surpass there capacity either. I haven't done the exact calc's yet and would like to quote for my time to do an accurate assessment of the loading alongside some of the more straight forward parts which im going back for anyway, but it looks like this would have been why they were installed as such 15 years ago.

The reason I am trying to find this out is the MCCBs are discontinued (willrose don't have any in stock either, Hager HD149 I would need the HD147 or possibly the HD149U rated to 80 amps instead of 100) and the last resort would be to rip the panel out and put a new one in with the correct amperage switches.

Now I'm all for doing what's necessary to be safe, bugger the cost, but surely this should have good reason for having being installed this way originally and as such if I can prove it to be fit for use then I shall do, they are a good client and I don't want to milk them unnecessarily. Should these calculations fall under the CCC would this be justifiable for me to omit changing anything and negate the C2 that was coded for it?

Thoughts and opinions welcome.
 
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telectrix

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if they been in there for 15 years and show no signs of thermal damage, I'd downgrade to a C3 with the caveat that regular inspection should be undertaken. you never know what future loads may be added. FWIW, i's had 16mm carrying 110A for 30 minutes and it never got above 40 deg.C.
 
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if they been in there for 15 years and show no signs of thermal damage, I'd downgrade to a C3 with the caveat that regular inspection should be undertaken. you never know what future loads may be added. FWIW, i's had 16mm carrying 110A for 30 minutes and it never got above 40 deg.C.
Yeh I would agree but as its been noted in a report I want to be able to justify my reasoning according to the regs, just incase the school does burn down next week! :D
 
BS7671 permits departures and modifications if properly designed and recorded. All you need to do is to set out your calculations in writing, demonstrating that the circuits are OK, noting this as a departure from BS7671. You can then support that with a simple risk assessment. Also worth placing a notice somewhere conspicuous so that someone following you can understand your reasoning - in the same way that having done the calculations you did so to the original design. The paperwork should be attached to the test certs and retained in the customer's records so that it is available for inspection.
 

Charlie_

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I don’t even think it should be coded..

CCC of 99 amps
Make an adjustment for ambient air temp of 20 oC (x1.09)

107.91 amps..
 

James

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I agree with Charlie, didn't pipe up earlier because I thought I was missing something and didn't want to look a fool.
 
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Thanks guys, kind of confirmed what I thought really. I don't want to make a mountain out of a molehill but as the previous inspector has flagged it I just needed to be sure that my justification of not carrying out remedial action was valid. Thanks again all.
 

Charlie_

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I will be posting up some beauties soon..
Just in the process of going through nearly 600 observations from a recent pi carried out by another company..
 

James

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Thanks guys, kind of confirmed what I thought really. I don't want to make a mountain out of a molehill but as the previous inspector has flagged it I just needed to be sure that my justification of not carrying out remedial action was valid. Thanks again all.
I have seen a lot of companies, normally the larger ones, pricing inspections cheep with the hope of a blank cheque for the remedials.

not a practice I agree with.
 
How long are the submains? I'm assuming it's not a huge building, but worth checking that Volt drop isnt an issue?
 

Ian1981

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Xlpe has a ccc of 99 amps reference method E if the cable is running at a maximum temperature of 90 degrees only.
The ccc should be determined using the 70 degree temperatures as specified by bs7671 unless the switchgear it connects to and manufacturers instructions allow their products to be connected to a higher temperature which I doubt they will.
 
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How long are the submains? I'm assuming it's not a huge building, but worth checking that Volt drop isnt an issue?
Maximum of about 25 Meters for the longest, there well in.
 
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Xlpe has a ccc of 99 amps reference method E if the cable is running at a maximum temperature of 90 degrees only.
The ccc should be determined using the 70 degree temperatures as specified by bs7671 unless the switchgear it connects to and manufacturers instructions allow their products to be connected to a higher temperature which I doubt they will.
So we would be looking at a CCC of 83 Amps?
 

Ian1981

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So we would be looking at a CCC of 83 Amps?
Yes, without taking into consideration any correction factors.
The cable can run more current at a maximum operating temperature of 90 degrees however the switchgear and associated accessories will most likely not, meaning that the possibility of overheating is then likely.
Put it this way a Schneider mccb panel board fitted the other day has a maximum temperature at the terminals of the switch disconnector of 75 degrees So it will not be advisable to size the distribution circuit for a 90 degree operating temperature for ccc
 
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