Spds - multiple consumer units

copey84 · Jul 13, 2023

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.

littlespark · Jul 13, 2023

In parallel with existing boards, as close as possible to the source (main fuse)

The SPD is to protect internal devices from an external influence… So you want the SPD to work before that influence can reach the devices.

copey84 · Jul 13, 2023

Thanks for the reply.
Was thinking about configuration of spd in meter cabinet.
Should I have the spd before the s type rcd, or will the delay in rcd operating time allow the surge to clear.
Probably hard to determine.
If the rcd was before the spd then I could use a metal enclosure if not will have to be plastic. It's a tricky one, trying to incorporate rcd protection overcurrent protection and spd protection within the meter cabinet.

mainline · Jul 13, 2023

copey84 said:
Thanks for the reply.
Was thinking about configuration of spd in meter cabinet.
Should I have the spd before the s type rcd, or will the delay in rcd operating time allow the surge to clear.
Probably hard to determine.
If the rcd was before the spd then I could use a metal enclosure if not will have to be plastic. It's a tricky one, trying to incorporate rcd protection overcurrent protection and spd protection within the meter cabinet.

SPDs should wherever possible be installed upstream of RCDs.

You can use a metal enclosure on a TT earthing system.

The meter cabinet is for the Dno equipment.

littlespark · Jul 13, 2023

when you get an spd built into a new CU off the shelf, its after the mainswitch, before any rcd and protected by a (usually) 32A MCB...
So in parallel with the supply side of the S type RCD, i would reckon....

oh... good point @mainline

So all the devices within the house will be fine, but the S type RCD could get a rough time....

To be honest... how likely is there to be a surge? Is the property in an area susceptible to lightning strikes, or from an overhead supply?

copey84 · Jul 13, 2023

To get spd as close to main fuse it will have to go in meter cabinet.
I was thinking the spd will have to go in plastic enclosure if it's before the rcd incase of a fault, if metal could come live, and only main cut out fuse for protection, which will not operate in a tt set up.

mainline · Jul 13, 2023

Table 534.5 Connection of the spd dependent on supply system

I'm assuming you have a Sp+n fused unit in the meter cabinet with a !00ma timed delayed rcd used as the main switch ?

Swa to the house ?

copey84 · Jul 13, 2023

Correct mainline.
It's a 20m run from meter cabinet to the house consumer units, then from the house to garage is a further 15m.

mainline · Jul 13, 2023

copey84 said:
Correct mainline.
It's a 20m run from meter cabinet to the house consumer units, then from the house to garage is a further 15m.

Something like this at the house end would do.

[ElectriciansForums.net] Spds - multiple consumer units

copey84 · Jul 13, 2023

Problem is I have two consumer units in house and one in detached garage.
I want to cover all three with one type 2 spd, so customer doesn't have expense of another two spds.

mainline · Jul 13, 2023

copey84 said:
Problem is I have two consumer units in house and one in detached garage.
I want to cover all three with one type 2 spd, so customer doesn't have expense of another two spds.

Are the two Consumer units in the same place at the house, and tails from henleys ?

A bit more information as to the layout etc would be useful.

copey84 · Jul 13, 2023

Hi mainline, are you using the consumer unit to serve final circuits or are they feeding other consumer units?
I had the idea of taking supply to a separate consumer unit in house above the two for final circuits.
Fit the surge in it and treat the out going circuits as feeds to the three consumer units.
That way all are covered by one surge.
It's basically a parallel connection where ever its fitted, be it at origin or in house.

copey84 · Jul 13, 2023

Yes the two consumer units are in same location.
The supply from meter to house is 20m. In the house the supply is split on henly blocks or as we call them Iscos.
From here both consumer units are feed in house then a single way consumer unit supplies the garage 15m away.
Basically can I configure the spd to cover all consumer units, less expense.
It's a parallel connection, so in theory what's to stop me fitting it in house in either a stand alone 2 way consumer unit or as I mentioned in previous post a consumer unit with the spd and mcbs feeding the three consumer units, two in house one in garage.

mainline · Jul 13, 2023

copey84 said:
Hi mainline, are you using the consumer unit to serve final circuits or are they feeding other consumer units?
I had the idea of taking supply to a separate consumer unit in house above the two for final circuits.
Fit the surge in it and treat the out going circuits as feeds to the three consumer units.
That way all are covered by one surge.
It's basically a parallel connection where ever its fitted, be it at origin or in house.

It feeds 2 Dbs and a few final circuits via rcbos.

Btw they are main switches not rcds

mainline · Jul 13, 2023

copey84 said:
Yes the two consumer units are in same location.
The supply from meter to house is 20m. In the house the supply is split on henly blocks or as we call them Iscos.
From here both consumer units are feed in house then a single way consumer unit supplies the garage 15m away.
Basically can I configure the spd to cover all consumer units, less expense.
It's a parallel connection, so in theory what's to stop me fitting it in house in either a stand alone 2 way consumer unit or as I mentioned in previous post a consumer unit with the spd and mcbs feeding the three consumer units, two in house one in garage.

I would 100ma time delayed rcd at the Fused switch.
Then as per pic.

Only CT2 is permitted upstream of the first RCD on TT systems.