Chaps,

Just checking stuff prior to changing a CU. The main cutout is a BS88/60A. No other marking apart from "Q".

PFC comes in at 15,7kA. Obviously this is over the 6K limit of the MCB's.

Table 7.2.7(i) in the LGB states BS88-3 type 1 + 2 and BS88-6 are all good for at least 16k.

My question is, does my Q type fuse comply?

Many thanks,

S.

In a domestic???
- Andy.

Indeed it is.....!

That might make things "interesting" from a c.p.c. sizing point of view - even if you assume that the cut-out fuse effectively limits the fault current to the equivalent of <=6kA. See table A5 in GN3 (I think there's an equivalent in the current OSG, but don't have it to hand).

There might be a case for not replacing fuses with MCBs if the existing wiring is in T&E....

As for the cut-out fuse, as long as it's a reasonably modern cut-out on a domestic supply, I think I'd probably just assume it's the equivalent of the old BS 1361 house cut-out types (or better) and so the 16kA rating for the CU applies.

- Andy.

See table A5 in GN3 (I think there's an equivalent in the current OSG, but don't have it to hand).

Help > Where is table A5 in Guidance Note Three?

Appendix A - it's on page 114 on the version I'm looking at, but might be slightly different on paper.
- Andy.

The same table is listed here: http://electrical.theiet.org/w...ata-2008.cfm?type=pdf
- Andy.

--its highly unlikely you have that level of fault current, what is the
distance from the main to the cut-out?

Regards.

UKPN

The installation may be located next door to the transformer!!!

Keith

LoL - sitting right next door to a 0.8MVA TX with a 25mm2 split con service straight off the distributor - happy days

regards

OMS

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Failure is always an option

The Standard for a Consumer Unit (BS EN 60439-3) has an additional bit written for the UK, which is known as "Annex ZA". This gives a Consumer Unit a conditional rating of 16kA (the maximum allowable for a domestic supply), provided that the installation has a BS1361 type 2 supplier's fuse and the Consumer Unit with its Protective Devices have been type-tested as a complete assembly. In general, this means that an MK board (for example) must only be populated with the MK protective devices it was designed for.

The new BS88 fuse links (that replaced the withdrawn BS131 type 2) also allow the conditional rating to apply. I can't remember the exact marking - I fit cutout fuses so rarely these days that the ones in my van are still all BS1361 type 2.

Once you get any distance from the CU, the PSCC will drop dramatically. It should of course be noted that the "Annex ZA" test relates to breaking the current flow without a destructive failure of the CU assembly, it doesn't necessarily mean that the mcbs are suitable for continued service!

Regards,

Alan.

PFC comes in at 15,7kA
In a domestic???
- Andy.
Is the substation in the back garden

What test instrument have you used?

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http://www.niceic.biz

I have a TP 80A supply, 100ft from the substation and have a PFC of 1.4kA.

Raining and bad year for Hawthorn this spring and PV this summer, Butterflies and Bees forget them. Toolbox thoughts:

BS88 must have been around a long time only 88 down the line since start of BS, and never given much thought. In big old switchgear, and fusegear some BS88 fuses are 660volt, and then you get 415volt and 240volt. A 415volt, version is a quarter the volume of the 660volt. While it is obvious that it would be 415 volt versions in a three-phase switch-fuse or main- switch and 240volt in single-phase fusegear. What is to stop you using different voltage rated fuses because even a 63A or 100A can have the same bodies. What criteria used, what specification, and who is responsible in selecting the voltage rating of BS88 fuses?

Why is PV protection 1000volt fuses?

http://docs-europe.electrocomp.../0900766b80e17cad.pdf

http://uk.rs-online.com/web/p/...ed-tag-fuses/7038263P/

Some inverters (e.g. see http://www.sma.de/en/products/...0hf-2500hf-3000hf.html Technical Data tab) expect d.c. input of up to 700V - allow a bit of margin for safety and 1000V doesn't seem unreasonable.
- Andy.

Thanks for that reply, did not know that about PV inverters do cater for up to 700volt. (One leg almost out of BS7671, hope they do not climb any higher). Maybe that is the answer to the other question, why 600V as against 415V just being over cautious, the big-bodied 600volt HRC fitted to industrial fuse gear.
And talking about BS88, and Breakers long time ago had one MOD senior engineer (us being contractors) would only allow German or Europe screw type called Diazed type fuses in Bomb dump stores, when pointed out that these also had a fine wire suppose in parallel with the fuse element holding a flag at one end . When the fuse ruptures the wire also brakes and releases an indicator forced out with a spring. Never got an answer but suppose HRC also has an indicator on the outside body of the fuse and the little burn mark which is suppose to let know it is blown would make you wonder are these suitable for switchboards just outside hazard areas.

Again thanks for the reply
jcm