3 phase SPD MCB size

[newfutile]

Does anyone know what size cable to use for a MCG type 2 SPD (3 phase) and what MCB.the manufacturers instructions don’t state any values!

also should i use 3 x single phase or a 3 phase MCB?

 

[pc1966]

If it is anything like this one then 32-63A MCB:

https://pdg.cef.co.uk/downloads/pdg/mcg_sy2-c40x_datasheet/mcg_sy2-c40x_datasheet.pdf

There might be some figured in the new regs on SPD cable sizes but I don't have copies of any with me. I would probably look at 10mm as a typical value to go with.

Generally for good SPD performance you want minimum inductance, so C or D curve MCB if you can get them as well as short cables and cables all close together to keep loop area down.

Some of the smaller ones say 16-32A MCB so maybe 32A D-curve is a choice for all. I would go 3P as if you want to isolate for test you would want all poles off!

 

[newfutile]

That’s the exact one but in a metal enclosure, it seems a bit vague on sizes. I will see if i can get 5 x 10mm cables though the bushing, it will be installed touching the top of the 3PH DB with cables just long enough to connect .
thanks for the advice.

 

[Electro-tech]

I noticed CEF does SPD cable kits but they do not show sizes. Same with Contactum at TLC. I think the earth has to be a minimum of 6MM & any larger than 16mm will not fit the terminals.

 

[pc1966]

Just looked at 534.4.10 which has the CPC minimum size as 6mm for type 2, or 16mm for type 1 SPDs.

For the live conductor it has to be rated at prospective fault current (so I guess adiabatic for protection MCB) and also minimum of 6mm for type 1 and 2.5mm for type 2 SPD.

So in your case if you have 6mm cable then probably that will do all and neatly as data sheet shows it is OK.