20 or 40 KA SPD

[Tradie]

Another topic that creates a ton of confusion, there is no grey area, just a lot of unskilled people doing installations.

I have heard people say you have to use a 40 ka SPD, which is correct, however the majority of type 2 SPD's being installed at the moment look like they are 20 KA which is also correct.

You need to read the label on the SPD.

Looking at a Chint for example:

NU6-11G

40/275
50/60 Hz
In : 20 KA
UC : 275
I max : 40 KA (T2)
Fused at 125A

What does this all mean, it is a T2 SPD, suitable for AC installations.
In 20 KA, stands for Nominal Discharge Current.
UC 275 being the continuous voltage rating
I max 40 KA, being the max discharge current.

IF the circuit is higher than 125 amps, it must be fused with a 125 amp fuse.

IF you are installing the SPD in a domestic property for example, then no fuse protection is required, provided you use the correct gauge wire for the circuit, IE 60 amp, 16 mmsq wire.

If installed on the output of an 8 KVA inverter, rated at 32 amps, 4 mm wire would not require a fuse.

It is very important to select the the correct SPD for AC and DC circuits, something many dont seem to understand.

[Derlyn]

Just an enquiry. Isn't 16 sqmm wire an overkill for 60A ?

[Tradie]

1.0 mm - 10 amp
1.5mm - 16 amp
2.5 mm - 20 amp
4 mm 32 amp
6 mm - 40 amp
10 mm - 50 amp
16 mm - 60 amp
25 mm 80 amp

[Tradie]

You could use table 6.2 (a) on page 94 of the regs to consider various types of installation methods, but generally speaking the numbers shared in the previous thread would keep you in the CYA club.