What code is advised for the distibutors tails that are 16 mm2 with the main supply fuse being 100 Amps .

Thanks ........

None provided the maximum expected load is whithin the max rating for 16mm tails, (87 amps in free-air I believe) Also, how do you know it has a 100 amp fuse in place, are you just going by the label on the cut-out?

Dave.

The sticker on the cutout fuse says 100 A , without breaking the cutout seal and pulling the fuse , I have to presume that a 100 Amp fuse has been fitted , allthough a 60 or 80 Amp might be in its place .

I wouldn't code it unless it was a hell of a big installation or the tails were excessively long.

The maximum demand for the installation is appox 50 Amps

There you go then!

Code it as requires further investigation ..... You cannot not code a cable which is not adequately protected against overload (or short circuit) unless there is suitable protection downstream.....

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Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com

If we are talking about the tails between the cutout and the meter, you cannot code them against BS7671, as they do not have to comply with it. BS7671 begins at the outgoing (load) terminals of the electricity meter, or the outgoing (load) terminals of the isolator where this is provided by the electricity supplier / DNO.

Regards,

Alan.

Alan the EICR's covers metering & supply equipment....

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Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com

Yup EICR clearly asks about cable heat, meters, tails of DNO. I would code it prob 3 and note it under hereto g section of eicr

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Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!

I know it does. It is interesting how you are supposed to code it against a standard you probably don't have.

Regards,

Alan.

The form calls for comparison to bs7671....

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Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com

That is what is so strange about this one, as 110.2 (i) would specifically exclude it!

Regards,

Alan.

I'm just wondering what Regulation is being broken, that warrents a code?
Is there some new Regulation in BS7671 that prohibits this situation?
Since when did the DNO fuse start protecting anything other than the distributer's equipment?

433.3.1 (iii) ? - if we're talking about the tails after the meter/isolator.

If they're the DNO's property it's hard to tell. I've seen a couple of most-definitely 100A fused supplies that have what look for all the world to be 16mm tails (with blue/brown sheath) - I can only guess they're 90-degree rated - hence 16mm2 would be good to at least 109A.
- Andy.

Start with 433.3.1 (iii).

Determine Ib from 311.1 noting the bit about diversity.

Determine PSCC and evaluate the tails against a 100A fuse from 434.5.2. - or even do it non adiabatically from BS IEC 60287

Recognize the Annex ZA issue over the Consumer Unit, the assumption for 16kA compliance and what the standard tests against for that - ie the incoming tails size and outgoing cable size.

I'd be very suprised if 16mm tails proved to be a problem on a 100A domestic set up in the UK.

There is/are no regulation number(s) against the aspects for inspection listed in the EICR.

Unless there are inadequacies noted, I suspect a Code 3 isn't appropriate.

regards

OMS

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Failure is always an option

I discussed a similar situation with my registration bodies area engineer earlier this week, if a supply from a busbar to a DB has reduced CSA conductors compared to the busbar supply conductors should the DB supply be fused down, we were reviewing a commercial EICR.

The engineer basically said if the conductors aren't likely to be overloaded then no overload protection is required, he also mentioned the lengh of the conductors being less than 3m from busbar to DB and the conductors being adequately mechancially protected. However If a DB serves final circuits that are not fixed loads and also has spare ways how can you be sure the DB supply conductors couldn't be overloaded as per the requirements of 433.3.1. (ii)? Of course before any new circuits are added to the DB the submains current carrying capacity should be checked.

I always have installed switch fuses on outgoing busbar supplies.

Regards

I could show you thousands with no" local" overcurrent protection and a significant number with no isolation either - SWA or PILC straight into the bus bar chamber (or via a glanding box) out tothe DB's or panel boards - some of which also have no board isolators.

Usually supplies up to about 630A where it's pretty reasonable to size cables for short circuit protection and almost certainly end up with a size that can't be overloaded by the nature of the load (some of those even being loads that could easily be described as being subject to simultaneous overload).

Perhaps not fully aligned with current thinking, but certainly BS 7671 compliant. It's suprising what BS 7671 will let you get away with

I did one a little while back asa PJ for a contractor who had seriously undercooked the price on a D&B job for an office block. Caused a real row with the employer, his consultant team and TA and the clients FM guys. The employers requirements were pretty silent requiring only compliance with BS 7671, 20% spare capacity and provided stated design demands ripped off from the BCO guide. I was told the design was looked at in some detail by NICEIC via the FM guys and a few calls to IET for clarification via the consultants and ultimately no derrogations were identified.

The contractor then went back and offerd to "upgrade" based on the consultants now re-stated requirements at an additional cost - not sure who paid, but I wouldn't have wanted to be the one with the Beano down strides in the inevitable meeting with the employer that's for sure.


Regards

OMS

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Failure is always an option

Thanks OMS very interesting.

I guess sometimes we just get used to doing things in certain ways.

I wasn't suggesting fault current protection wasn't provided, rather overload protection of the submain wasn't as the outgoing loads from the DB weren't fixed and no design data being available.

Regards

regards

OMS

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Failure is always an option