I feel duty bound to fit SPD protection whilst I am modernizing an installation, but there are couple of issues which are vexing me so I would appreciate an opinion from the few learned colleagues who are still here please.
The part of the installation to be protected is served by an SP DB served by a 30 m long distribution circuit through a B63 MCB. Zs of the DB is 0.30 Ohms.
I have sought the advice of the manufacturer (Eaton) but they fell short of the service which I have obtained previously. The call centre is in Hungary and the operative's first language appears not to be English, so the combination of poor reception and the language barrier hardly helped.
I had 2 questions. First, although the SPD kit comes in its own enclosure, I would like to put it in the DB, which would be neater and minimize the length of the connecting leads. Quite reasonably, Eaton's response was that this would probably be fine, but because it has not been tested as such, they cannot recommend it.
My second question concerned the MCB for the SPD. The kit includes a C63 MCB. Clearly, this will provide no discrimination. The BEAMA Guide says that a 20 A MCB should be adequate. However, this is what Eaton said:
"Having said that, max. back-up provides highest possible voltage protection level (Up). Therefore, going below that is not an issue as long as this protection device does not affect the Up of the installation.
In UK we also suggest to use a 40A, 50A, or 63A type C breaker as long as above statement of Up is met. Since we cannot calculate the application and installation at a customer side, we could only recommend this."
So my question here is whether lowering the rating of the MCB might make the SPD pointless please? I might add that we have not had a damaging surge over the past 26 years so it all seems to be a bit hypothetical any way.
