high pfc

[sb_89]

Hi guys

I'm currently doing a eicr on a house. It's a Tncs ( PME sticker ) supply, protected by a 100A 1361 (33KA) main service fuse.

I did a ze test at the consumer unit, all parallel paths disconnected, and it came back at 0.01 ... I know its Very low

I then carried out a pfc which came back at 13.5KA

Now the breakers are only rated at 6KA, so my question is, other than write it down on my sheet, what course of action should be recommended ?

Got it never mind, the bs1361 provides the protection, even to the upstream devices, so it complies

 

[Zeespark]

The PFC at the head I am lead to believe is 16KA, so it should be within safe limits if I have read the question properly.

AndyGuinness

 

[springcrocus]

Unmodified consumer units have a blanket cover of 16.5 KA (or so I am led to believe). Something to do with type-testing.

 

[steptoe]

but MCBs dont!

 

[ElectekAir]

I thought that the pfc should not be greater than the rating of the MCB's the main fuse may be able to take it but the MCB's can't

 

[batty]

What meter are you using?

 

[sb_89]

megger 1502 was what I used, recently calibrated and I carried out the test at least 4 times with the same result.

I was under the same impression as you, that the breakers were only rated at 6ka, so the pfc shouldn't be greater, but upon speaking with the nic tech line today, it's fine. So long as there is 'back up' protection, that is capable of breaking the pfc it compliesu. I need to look in to it further though as it stumped me today

 

[ParkySparky]

I was under the impression the mcb's had to be rated accordingly! Why else would they give them a rating?

It's all well and good the DNO's fuse being capable of coping with the fault current but the fault still has to pass through the mcb and I don't think there will be much left of it with that fault current!

I wouldn't like to try be looking at it if it tripped anyway!!!

 

[OnOff]

16kA MCB's are available if your that worried........................

 

[sparkytim]

The BS1361 Service fuse gives BACK UP protection up to 16 kA IF Consumer Unit is to BS EN 60439 so no need to do anything.

See Part 3 of BS EN 60439 1991 annex ZA June 2006.

 

[user 15807]

I thought the service cutout fuse was rated at 16Ka therefore giving protection to downstream devices IE con unit and MCB/RCBO's

 

[sb_89]

Ok guys I think we cleared that up, but just a side thought, if a system did have a fault of 13.ka, even though the main service fuse can handle it, would it damage the mcb's rated at 6ka , I think it possible could, but I've been wrong before lol

 

[Ash]

I had an issue similar to this. I had my Kewtech calibrated, it failed on Loop, so they "repaired" it.

When I was testing I was getting readings in the 0.0x range on Ze in domestic houses and PSCCs over-ranging.

long story commenced and in the end had to send it to Kewtech to fix.

Kewtech told me that it's all software and no one but them can do "repairs" so god knows what the other people did to it.

Long story short: get you meter checked out

 

[Sidewinder]

IF you fault current is as you say, and you CU is a type tested assembly to the relevant standard then you are OK, however if an MCB trips it must be replaced as it may well have been subjected to a fault current in excess of that which is acceptable for the MCB to be used in further service.

So unless the client can guarantee that none of the MCB's have ever tripped then they may be damaged beyond use.

The only way you will know is if they fail to disconnect and burn the place down or kill someone before the main fuse goes as backup protection.

 

[Manator]

I agree, if any mcb trips under such faults the mcb maker will always tell you to replace the breaker, unless they can guarantee its safety in continued use.

 

[apprentice87]

Hi Sb89,

What you are supposed to do, is, when you are relying on an "upstream" device, [such as your BS1361] as "backup" protection for devices that cannot in themselves disconnect the full fault current, is to either consult the makers of the upstream device, or, in any case, by whichever means, discover the "let through" energy of the upstream device, and then make sure, again by asking the makers, that this amount of energy will not damage the "downstream" devices. [Or at least that is my understanding of things!!]

No doubt Sidewinder and Manator will be able to comment further on the correct procedure, but in any case, as has already been said by Sparky Tim and Sidewinder, if it is a proper approved CU for the purpose, all will be well..

I think i should point out here, that i think i am right in saying, that this ONLY applies if the MCB's are in such a type approved CU. If you just stuck them in any old enclosure, the the very same MCB's would not be approved for the very same job.....

john.

 

[wozz]

I agree, if any mcb trips under such faults the mcb maker will always tell you to replace the breaker, unless they can guarantee its safety in continued use.

Isnt this down to the Icn rather than what the manufacture says. If Icn is exceeded it gets replaced?

 

[apprentice87]

Hi Wozz,

So far as i know, Icn is the ultimate breaking capacity of the thing, even if it destroys the breaker in the process, and Ics, is the current it can break without sustaining damage to itself.

Problem is, in the event of a fault, i suppose it would be hard to know exactly how much current it has broken. Just be easier to replace the thing!

john

 

[wozz]

my understanding also, also the same point i was making.

the way i remember Icn 'n' being No good anymore.

 

[apprentice87]

Hi Wozz, Yes!!! I think of the Ics as "continued service" and the Icn as "completely knackered" !!!!!!

john...