Fuse for surge arrester protection

[Designmen90]

Hello everyone,
Is there any rule how to determine the size of fuses which will protect surge arrester. I have 3P+N surge arrester, 20kA, and I need to protect him with fuses. But, how to determine the correct size (amper) of those fuses.
tnx

 

[pc1966]

Check with the manufacturer's data.

They all need OCPD protection, but for many SPD that is a fuse in the range of 125A-315A so you don't need anything else with a typical 100A supply as the incoming fuses are enough.

Not sure if it comes off a MCCB though, they might have too high a fault let-through.

 

[Designmen90]

They all need OCPD pro

Check with the manufacturer's data.

They all need OCPD protection, but for many SPD that is a fuse in the range of 125A-315A so you don't need anything else with a typical 100A supply as the incoming fuses are enough.

Not sure if it comes off a MCCB though, they might have too high a fault let-through.

Tnx,
I have distribution board with 250A incoming circuit breaker NSX from Schneider. So if i took surge arrester 20kA and look at his datasheet, there is note that it should be protectet with 80A gG fuse. So It will be OK?

 

[pc1966]

I have distribution board with 250A incoming circuit breaker NSX from Schneider. So if i took surge arrester 20kA and look at his datasheet, there is note that it should be protected with 80A gG fuse. So It will be OK?

You will need to put in a fuse of 80A or less then. Or something like a 32A C/D-curve MCB to feed the SPD.

 

[pc1966]

If you can, go for the D-curve as lower inductance (smaller magnetic trip coil for the high instantaneous trip current).

SPD performance depends mostly on inductance, not cable resistance. Hence the guidance in the 18th regs on having the total cable less than 1m, and ideally less than 0.5m, from L--SPD--N/E

It also helps to keep the cables to/from the SPD together so you have a smaller "loop area" in the inductor formed by the cables.

 

[Designmen90]

If you can, go for the D-curve as lower inductance (smaller magnetic trip coil for the high instantaneous trip current).

SPD performance depends mostly on inductance, not cable resistance. Hence the guidance in the 18th regs on having the total cable less than 1m, and ideally less than 0.5m, from L--SPD--N/E

It also helps to keep the cables to/from the SPD together so you have a smaller "loop area" in the inductor formed by the cables.

Thank you for advices. I will go with fuses, because investor wants it. For him it's easier and cheaper to change fuse inserts than CB (in case of damage).

 

[pc1966]

You can get DIN rail holders as well, such as this:
https://uk.rs-online.com/web/p/rail-mount-fuse-holders/0482859/
Not clear if they fit the busbars of the Schneider DBs though, you would need to check (or put in an DIN enclosure along with the SPD).