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Hello and thanks for the interest. I have a little dilemma and was unable to get an answer anywhere.

I'm trying to fit a SPD and an over/under voltage protector to my existing "Main Switch" and "RCD" setup. my question: is the location of the SPD and surge protector correct? thanks
 

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Hello and thanks for the interest. I have a little dilemma and was unable to get an answer anywhere.

I'm trying to fit a SPD and an over/under voltage protector to my existing "Main Switch" and "RCD" setup. my question: is the location of the SPD and surge protector correct? thanks
What is the current rating rating of your surge protector? I have fitted Dehn SPD’s at a factory this year and to simplify matters the units are rated for 125A with big terminals so you can fit them without going through a Mcb first and Just off the main switch. If you use smaller cable to connect them then they come off a suitable rated mcb. 232EBF9E-9FA7-4C35-93CD-9B69FA8D68D0.jpeg
 

pc1966

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It looks like your main switch is in fact a double-pole MCB, is that correct?

Nothing wrong with doing that provided it is appropriate for the load, etc, but it would make selectivity with any down-stream MCB/RCBO very difficult to achieve (unless its instant trip point is above the PFC/PSSC of your supply at that point).

As already said above, many of the SPD are designed to be safe with supply fuses of up to 125A (or more) so you can normally get away with the supply's own fuse and use a simple DP switch. However, if your choice of SPD specifies a smaller breaker then you need to look at the design more carefully.
 
It looks like your main switch is in fact a double-pole MCB, is that correct?

Nothing wrong with doing that provided it is appropriate for the load, etc, but it would make selectivity with any down-stream MCB/RCBO very difficult to achieve (unless its instant trip point is above the PFC/PSSC of your supply at that point).

As already said above, many of the SPD are designed to be safe with supply fuses of up to 125A (or more) so you can normally get away with the supply's own fuse and use a simple DP switch. However, if your choice of SPD specifies a smaller breaker then you need to look at the design more carefully.
thanks for the detailed explanation. yes the diagram is of a double pole mcb but as per the text its just a main switch (a manual on/off). the switch is rated as 40a and the spd is rated at up to 60a. the spd is the one below:
 

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pc1966

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That is 60kA peak surge current, almost certainly for a 8/20us waveform.

You need to look up the data sheet to see what the maximum over-current protection is, and check that is above the incoming supply fuse.
 
That is 60kA peak surge current, almost certainly for a 8/20us waveform.

You need to look up the data sheet to see what the maximum over-current protection is, and check that is above the incoming supply fuse.
thx for the reply. yes the spd is as you said. the incoming supply is 40a, so it should be enough. may i ask if you can advise if the components are positioned properly in relation to one another? (in particular the rcd position and the relay? should their position be swapped maybe?)thanks
 

pc1966

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The basic layout is OK, though you would get slightly better protection by having the power cables connect through the SPD (known as as Kelvin or V-wiring).

However, doing they way you have drawn is fine so long as you keep the cable lengths to the SPD down to a reasonable minimum, no more than 25cm for each live wire and ideally less for the earth wire to the main earth terminal bar of your enclosure. Also it is better if the cables are run close together to reduce inductance (i.e. less total "area" formed by the loop of switch L or to SPD and back to switch N).

Check the SPD data sheet for the minimum wire size. It should be at least 4mm section, but more often is specified at 10mm minimum so in the event of a fault in the SPD it can safely take out the supply fuse. However, if you have say a length 16mm wire for the rest of the power wiring and the switch terminals can properly clamp 2*16mm then just use the same 16mm size for all.
 

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