New SPD Regs for Sub Main

Initforthemoney · May 28, 2023

Now that SPD's must be fitted regardless, how does this stand from a sub-main perspective?

Went to look at a job and they want a supply to a pre wired Shepherds hut 50M away with no SPD as it has been sat unconnected for a couple of years.

The main incoming is entering an old barn that has a recent-ish Hager 3 phase board that is separate from the main house with its own meter.

So, the question is, do i need to somehow get an SPD on the single phase sub main in the old barn to feed the hut? Should i be replacing the existing mini 2 way garage board in the hut to incorporate an SPD at the use end?

pc1966 · May 28, 2023

Does the old barn have any equipment of value and/or that the loss of it would significantly impact on their business?

In terms of protecting the shepherd's hut then an SPD at the feed end of the sub-main is not terribly great as 50m of cable could pick up some energy if the strike is quite local. You would be better with an SPD at the its own garage board for protection of it.

Is it really just a 4-slot one so main switch/RCD and a pair of MCBs? If the sub-main is only 32A or so then you won't need protection for any SPD at the hut, or you can get an SPD that is OK to 100A sort of DNO fuse like the compact Wylex one.

pc1966 · May 28, 2023

I just noticed the BG do a 5-way pre-populated "EV CU" with RCD/MCB/SPD, in both internal and IP65 versions. Probably you would just need to change one of the MCBs for 6A for the lights.

Initforthemoney · Jun 4, 2023

Sorry for the reply delay!

No, there is nothing of value connected in the barn, just a few socket outlets and lights etc.

I think due to the sort of complexity I’ll skip it as you say, it wouldn’t be much help at the barn end and the hut has similar, a couple of sockets and a light so nothing of value.