Spds - multiple consumer units

[copey84]

Hi all, what is the best way to configure surge protection in domestic dwellings when you have multiple consumer units?
Does each consumer unit need it's own spd, or can I fit one in parallel with all consumer units?
I have a 20m run from meter cabinet to two consumer units in house, then there's a detached garage a further 15m away.
The main supply to meter and garage supply are all underground. The earthing system is tt.
I was thinking of a few ways to do this install. Either fit a spd in meter cabinet which might be tricky with s type rcd and switched fuse isolator in there. Or fit an additional distribution consumer unit in house with spd and 50a type c mcbs for the other consumer units.
This way all have protection and less expensive than another 2 spds.
Anybody know of a better way?
If so appreciate a reply.

 

[Risteard]

In my opinion if you have distribution boards downstream a reasonable distance from the other distribution boards then these really should have their own SPD as well. One at the origin won't cut it.

 

[copey84]

Thanks mainline.
I think my contactum surge is a c1 so will have to go after the s type rcd.
Reading up on it c2 creates a short between live and neutral then shunts to earth preventing dangerous fault not clearing on a tt, think that's the way it works.
With that said the surge is a parallel connection, so is there anything preventing me from connecting the surge in a 2way enclosure from the henly blocks in the house, where the supply is split to feed the two house consumer units and garage. I'm thinking a 2way enclosure to house the spd will be a cheaper option than another consumer unit to house spd and mcbs to feed consumer units.
It's the same either way I think, if a surge comes into the house it will appear on live terminals, the surge reacts and sends voltage to earth.
Or is it more likely to go to earth if the supply coming into house goes directly to surge consumer unit that houses mcbs that serve house and garage consumer units.
Hope this makes some kind of sense, think I'm confusing myself now.

 

[copey84]

Hi Risteard, I'm thinking the surge will be placed in either a 2way stand alone enclosure or another consumer unit to house distribution to the three consumer units serving final circuits in house and garage. Do you know what would work best, this setup will be in house not meter cabinet however there will be a 15 m run to garage.

 

[davesparks]

I want to cover all three with one type 2 spd, so customer doesn't have expense of another two spds.

Is that what the customer really wants, to save a few quid by not having a well designed SPD setup?

 

[copey84]

They are expensive so why fit three if I can make one cover.

 

[mainline]

In my opinion if you have distribution boards downstream a reasonable distance from the other distribution boards then these really should have their own SPD as well. One at the origin won't cut it.

When a sub-distribution board is located more than 10m away from the mains SPD, additional SPDs are required.
Both his consumer units are close together.
It leaves the question of does the garage need one.

 

[tidytech]

Could someone kindly share why the SPD unit must be in parallel? I'm confused sorry! Hard to say without a basic wiring diagram of the current installation.
I assume a plastic 100A isolator switch with a built in SPD would work straight after the main supply incoming tails. Then anything downstream will be protected, including the time delayed RCD and all the other CCUs. . Though not strictly allowed (dno only), but could be placed in the meter cabinet. Here are examples:

Wylex type 2 SPD isolator, suitable for TT


There may already be an isolator after the main tails not sure. But that could be replaced with this.