Spd specifications

[gazdkw82]

Iv been tasked with upgrading a 16th edition board with a schneider 6 + 8 way acti9 board with spd protection.

SPD was specified for me so I dont have to perform the calculation, however, I am stuck with the specifics of the devices themselves.

Firstly, can the device hang of the back of an rcbo or is rcd protection not a requirement for them? Is mcb for overcurrent protection sufficient?

I have ascertained the SPD will be a type 2 with a replaceable cartridge, however there are so many other figures that are listed on Schneider website and such there are numerous different type 2 devices. I'm a little baffled.

Do I need to factor into account Imax? Limp?

Am I over complicating it?

 

[pc1966]

The SPD should be before any RCD/RCBO (except sometimes in it is a delay RCD for TT incomer). RCD don't enjoy carrying the surge current and the RCD impedance means parallel circuits (off the supply) have poor protection.

All SPD need some form of OCPD but the device specks should tell you want. Often it is a fuse in the 125-315A sort or range and then the incoming DNO fuse is adequate. Others require a MCB for it, but that should be low inductance so something like a 32A D-curve is probably a good choice. Again, check the manufacturer's recommendation.

So generally the SPD is directly off the busbar or a MCB dedicated to it.

The actual surge handling is usually a minor issue unless you have a type-1 for a building with lightning protection and then you have a handful of categories of protection level that give acceptable probabilities that the SPD is big enough.

 

[gazdkw82]

Thanks pc1966. I think that pretty much covers it all