Prospective short-circuit current?

GreySquirrel

What value would the "Prospective short-circuit current" be on an ordinary domestic supply? (63 Amp incoming fuse)

Steve

It would depend on the sub station capacity and the distance from it.

Incoming fuse should be at least 50kA. (I think)

Interesting question, why do you ask?

GreySquirrel

Getting SPDs for house. The DIN-rail ones I've look at specify MCBs with breaking capacity equal to that at head of installation. My background is in PCs, so the only time I really deal with mains (230V) voltage is in swapping out PSUs.

The Irish regs and manuals say breaking capacity at incomer 10kA. Irish and British ones say Distributors overspecify by quite a lot, minimum 16kA.

I'll measure the impeadence and use the forulas to see.

Steve

SPDs Surge arrestors?

I don't think you should worry about actually measuring the impedance.

Most domestic MCBs are 3kA / 5kA. If you want HBC ones, Merlin Gerin C60H breakers (or equivalent) would be more than adequate.

This article might also interest you.

You could also wire in MOVs on the load side of your existing breakers as a cheaper solution.

GreySquirrel

Sorry about that. SPD - Surge Protection Device.

I'm getting conflicting advice on same. Some say they are an expensive "con" job.

I'll read up on that article.

The one in the Hager.ie catalogue seems to be a poor translation from the French. And having looked at French Circuit diagrams all their MCBs seem to have to be Single pole and Switched Neutral, so it's unclear if the MCB protecting the SPD has to be Single pole and Switched Neutral or if in a Tn-C-S system a Single pole will suffice.

Steve

Have you got a link to the devices that you're looking at?

Irish power system is TNC so single pole is fine.

The only time you use switched neutral here is when using RCDs on socket circuits.

I would agree that they are expensive items to install and wouldn't really recommend them unless you are having specific problems with power spikes.

GreySquirrel

http://www.hager.ie/files_download/hager/ProtectionDevices.pdf

On Hager.ie's page 55, the diagram for the surge protectors seems to come from the French edition but I can't find my link to the French one.


Found link

http://hager.fr/files/download/0/51_1/0/guide_technique_parafoudres_ZD234e_05.pdf

Steve

Which one were you looking at (part#).

Steve

OK, looked at the diagrams - what are you trying to protect against?

A lightening strike to the mains or general spikes?

GreySquirrel

Both. Had a lightning strike in the vicinity which took out a modem and wireless video link. Also outages in area which popped some lightbulbs when supply came back. Dundrum Town Centre the culprit? I don't know enough about mains supplies to really point the finger. Global warming seems to be giving us a lot more thunder storms than I recall when I was younger.

Looking at Part SPN240D and SPN208S

The Irish version of the catalogue seems to be a translation from the French. French systems seem to be TT, which I suppose is where the T comes from. (Captain Jack Sparrow: "That would be the French")

I couldn't get through to Hager

Steve

Ah OK, now I understand what your trying to do.

It's been a while since I've been in this game but Reg Farrell Engineering would be the place I'd start looking. I used to deal with them a lot for this type of thing.

Here's their surge protectors:
http://www.rfe.ie/Products/panel%20acc/erico/surge.htm

If you can get talking to Ian or Stephen, they should be able to suggest the best solution for you.

The other place I'd try is Barb Electrical , they used to do this type of thing years ago, don't know if they still do. They do, however, know all there is to know about power system faults / spikes / surges / harmonic distortions.

Either of those places will be able to give you a lot more advice than me.

GreySquirrel

Thanks for the link