SPD Location In this setup.

Your link doesn't work. But as a general comment - it's hard to achieve 0.5m max paths (L+N and L+E and N+E) when the SPD is in a separate enclosure, unless the supply is rerouted to pass through that enclosure rather than the enclosure being a spur.

Hi,


Sorry. How about this link?

https://ibb.co/19hDFHB

Personally I would reroute the supply (inc PE) so it goes from the output of isolator, into the SPD enclosure,  then out again and off to the Henley blocks. Bear in mind that shorter is always better; if you can get below 0.5m, then you should.

The only place physically seems to be to the left of the main isolator, so quite tight; but what a pleasure to see such tidy work! ?


(Not sure about Mrs Mop's bucket though.)

Many thanks for the replies.


So where are we actually saying the 0.5m rule applies too? Is it max 0.5m off the load side of the meter or 0.5m away from any point in the tails?


Chris, yes it is a lovely job they have done, lovely to see some one take pride in their work. I know who did it and I’d love to employ them but I think they are happy with the current company they work for. There are sadly a few things that don’t comply but I’ll be correcting them to the same standard. Like it is TT but there is a lot of metal bits the tails come into contact with before any RCD. I plan to fit and adjustable setting, adjustable delay main RCD before that main isolator.

Think of an SPD and its leads as a temporary jump lead that you use to briefly short together a L&N or whatever in a circuit where there is a transient. You would imagine this would bring the voltage at that point in the circuit to zero; however due to inductive effects etc and the fast nature of the spike, there will be in the region of 1.5kV across the SPD itself, and in the region of 1kV/m across its leads. So if the total length of the SPD's leads is 0.5m, then you're only reducing the spike in the circuit to 2kV. Generally, the electronics being protected downstream is supposed to be able to cope with 1.5kV.


The point where the "jump leads" attach to the normal path of the circuit being protected is where the length should be calculated from. So for example if the supply is at slot 1 on a bus bar, a circuit is at slot 2, and the SPD is at slot 10, then the length of the busbar between slots 3-10 contribute to the SPD's length as regards protecting that circuit. If you spurred the SPD from the Henley blocks, the total L+N path would be the tails x 2, plus a bit of busbar in the Henley blocks x 2, plus all the internal wiring in the SPD enclosure. For L+E protection, the length would include the E connection from the SPD to whatever point in the earthing system which is on the normal earth path for the circuit(s) being protected.