On 18/11/2019 19:54, Andy Burns wrote:
ARW wrote:

When I went to the ElexShow this year the CU manufactures were all
showing of their new CUs (obviously not MK) with SPDs built in at the
head end next to the main switch.

Yes, from looking at them there, and from various youtube sparky
channels, the SPD seems to be wired between the L & N output sides of
the main switch and earth ... not seen one in a CU connected to L via a
32A MCN as the leaflet shows.

The other option apart from putting them in the CU, is to put them in an
separate isolator switch, e.gÂ* Wylex REC2SPD, Fusebox F1M2SPD, Lewden
SRG1VCU-RM

https://www.tlc-direct.co.uk/Products/WYREC2SPD.html

https://www.gil-lec.co.uk/fusebox-f1m2spd-inline-surge-protection-unit-with-100a-main-switch


https://www.medlocks.co.uk/lewden-retrofit-type-2-surge-protection-unit-32a-mcb-100a-2p-main-switch


The last one *does* seem to include a 32A MCB to connect the SPD to.

I think that is because the last one is a different approach from the
previous 2.

The first 2 are wired /in series/ with the CU; have a switch which
isolates the whole supply; and for overcurrent protection rely on what's
upstream of the tails - usually the main fuse.

The last one is wired /in parallel/ with the CU; has a "main switch"
which isolates /only/ the supply to the MCB and SPD; and needs the MCB
because it can be connected with 6mm cable.

--
Robin
reply-to address is (intended to be) valid