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SPD(s) for an outdoor TT install

psychicwarrior
Good morning


I am trying to get my head around surge protection - the *basic type and positioning* really- and taking an example situation please where surge protection may be added:


A moorland, overhead supplied, residential property; TN-C-S.


Outdoor regular wall meter cupboard in which is the DNO head, meter and some existing consumer switchgear (been as it is for over a decade with RCDs, MCBs from when the supply was TT) in an enclosure fed via a supply splitter block [henly] , which is there to supply two consumer units each at either end of the property.


Also fed from the splitter block, a supply to another nearby enclosure in which resides switch gear for TT outdoor services - lamp columns and electric gate 30ma RCBO final circuits and a  RCD type s distrib circuit to a 'garden work pod' which has a little sub-board.


(rough block diag attached to help description)


1) What would be the positioning and type of any surge protection  (where there is no LPS on the building rightly or wrongly)   ?


my questioning thoughts on this:

- near the origin (as in the source of energy) a  Type 1 as it is overhead fed, but not sure if CT1 or CT2 connection 

- in the consumer units a type 2  CT1 connected

- for the TT outdoor final circuits a type 2  , does this have to be upfront of RCBO being TT and  CT1 or CT2

- for the TT pod  distrib circuit, a type 2 and none  in the 'pod' sub board, or  none and type 2 in the pod subboard


- does the outdoor TT install even require SPD; can a 'surge' propogate back uptream into other parts

- future considerations, if alterations made e.g.


2) Lastly, is SPD simply about protecting connected equipment, or is it also about protecting  conductor insulation from voltages that might damage it ?


It does seem that adding type 1 SPD at the 'origin' (in meter box - other one is possible)  into this situation is nigh impossible without major works, so unless its possible to simply add it to each consumer unit/subboard as such... it seems academic, but still   it would be interesting to know where it should go ideally.


Regards

Habs


(perhaps one's ambition outweighs one's abilities)

7b9cf34fb3da18dccd3044d711131e43-huge-ietwrforumspd1.png


(last para edited for clarity ... well that was the intention)
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  • 0
    I think its reasonable to assume that earth connections entering a building (whether in the downstream or upstream direction) could briefly have a very high voltage induced on them relative to the live conductors in that building due to lightning, so you'd ideally want an SPD between line/cpc in both buildings at a point before that spike could reach sensitive equipment.


    An SPD is really about restricting spikes to the overvoltage category supported by the equipment it protects (see table 443.2). So this will include insulation (and test equipment!). So DBs, sockets, and the cabling and connectors between them are class III equipment, so should all be capable of handling 4kV spikes. So the SPD at the DB needs to reduce spikes to at least that. But if class II equipment like domestic appliances will be plugged in, then you need to be < 2.5kV at the sockets, and for electronic equipment (class I), then < 1.5kV at the socket.

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  • 0
    I think its reasonable to assume that earth connections entering a building (whether in the downstream or upstream direction) could briefly have a very high voltage induced on them relative to the live conductors in that building due to lightning, so you'd ideally want an SPD between line/cpc in both buildings at a point before that spike could reach sensitive equipment.


    An SPD is really about restricting spikes to the overvoltage category supported by the equipment it protects (see table 443.2). So this will include insulation (and test equipment!). So DBs, sockets, and the cabling and connectors between them are class III equipment, so should all be capable of handling 4kV spikes. So the SPD at the DB needs to reduce spikes to at least that. But if class II equipment like domestic appliances will be plugged in, then you need to be < 2.5kV at the sockets, and for electronic equipment (class I), then < 1.5kV at the socket.

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