SPD's & Submains

[Danny124]

Hi Everyone.

After being out of the trade for a little while due to injury, illness & then COVID, I'm due to dust the tools off.

Since my time away, SPD's have picked up momentum.

Currently looking at a large Manor house rewire, in a semi rural area. It has a college at back of property with bucket loads of air con units, and by doing my research, this college teaches welding, joinery etc, so big machinery is suspected.
Along with that, this house is next to a set of new build houses, and at the end of the close, there seems to be a possible substation of some sort.
So my immediate recommendation is SPD's.

As this Manor house is large, it will need 1-2 separate consumer units (circuit calculations pending). Looking at consumer units with built in T2 (Type2) SPD's.
Obviously these extra consumer units will be supplied by SWA via dedicated isolators, but looking through the BIG BLUE BIBLE I can' t seem to find or have missed it (very late at night) whether the SWA Submain will need the to have the surge protection too.

Am I ok with built in Type 2 Surge Protection devices at each consumer unit and over thinking this, or am I right to think the submains need the protection too.

Sorry if this has been talked about before, been searching for hours and can't seem to find the answer to my question.

Take care all, and thanks in advance for your guidance.

regards

Dan

 

[Lucien Nunes]

Is there any reason not to put just one SPD at the origin?

 

[timhoward]

After being out of the trade for a little while due to injury, illness & then COVID, I'm due to dust the tools off.

Glad you are bouncing back - sounds like a prolonged difficult era.

Am I ok with built in Type 2 Surge Protection devices at each consumer unit and over thinking this, or am I right to think the submains need the protection too.

Sorry if this has been talked about before, been searching for hours and can't seem to find the answer to my question.

I've actually been wondering exactly the same thing this week and I'm glad you have raised the question.
My use-case was a little unusual as one of the sub-mains is suspended from (earthed) overhead catenary wire of about 10m and lightening strikes to this were also in the back of my mind. I was never going to convince the customer to fit an expensive type1+2 though.

All that to say I'm also interested what others are doing with new consumer units on sub-mains, if anything. My tendency has been to "just fit one" but maybe I should be taking a more educated approach!
(One manufacturer does mention fitting type 2's on sub-mains more than 10-15m from the incomer. )

 

[Strima]

Only needed where services enter the building. i.e. the point of supply.

 

[pc1966]

It kind of depends on just how serious the risk is.

Typically you just need on at the entry point, and that might be a Type 1 (1+2) if there is a lot of lightning, or if the property has a lightning protection system in use (i.e. it might get hit and a significant portion of the direct surge appear on the service cables).

Many of the suppliers suggest a type 2 at sub-boards if they are over 10m away on the basis the internal cables can pick up induced surges and so end protection is less than the entry point. That to me at least makes sense if there is a LPS so massive internal fields possible, less so for a typical home in light risk area.

Many CU now come with a type 2 SPD as stranded so you might as well make use of them for all CU. If there is a high risk then look at a type 1+2 at the entry point splitting arrangement (I doubt you are looking at a MCCB board, but you might have some sort of TPN if feeding individual CU off separate phases).

 

[pc1966]

the BEAMA guide has a lot of background info, etc:

BEAMA Guide to Surge Protection Devices (SPDs) – Selection, Application and Theory

www.beama.org.uk