So, again, where is the evidence that these things are actually guaranteed to 'save' your equipment? After all, if we are now required to 'sell' the concept to the customer, and then rely upon the outcome of their decision we need hard evidence that the things are actually capable of saving that "£4000 television"?
I'm not sure there are any guarantees that apply in all possibly circumstances - a bit like seatbelts I suppose - they just weight the odds a bit more in your favour. I would have thought it self-evident that electronics and even very short pulses of high voltage aren't a good mix (as those of us who grew up playing with unbuffered CMOS ICs learned the hard way, as an extreme example), so anything that reduces the likelihood or magnitude of spikes reaching equipment sounds like a good idea to me, in principle. The cost-benefit is always a bit variable, but given the amount of electronics about these days (from the washing machine to the hob through the TV and boxes to RCBOs, never mind the EV and charge point) it wouldn't take much of a percentage increase in average lifespan to pay for a few SPDs.
More of a challenge to me is co-ordinating the placement of SPDs - across all incoming services - including TV, phone, PV etc. so that we're not inadvertently making things worse rather than better.
- Andy.
I am hampered in this discussion by having to wait until next week before I get my new big brown book, but I am pleased to see that the topic has been greatly simplified.
If I understand briefings elsewhere correctly, SPDs should be provided unless the owner of the installation declines them, which seems very reasonable. One might draw an analogy between mandatory vehicle insurance and SPDs where their absence might give rise to a risk to life on the one hand; and optional domestic insurance and a risk which is limited to a few bits of equipment on the other hand.
I must say that I would have preferred opt-in to opt-out as we do for most aspects of our lives.
Back to the technical ...
Where is the best place to put SPDs? Does one at the origin cover everything? And if it is difficult or impracticable to install one at the origin, is it sufficient to install one at any final distribution boards? My thinking here is that if a CU is to be changed, it is both easy and cheap to buy one with an SPD already fitted so why would you not do so?
Where is the best place to put SPDs? Does one at the origin cover everything?
Not necessarily - if the distribution circuits are long (>10m) the benefits of can be much reduced. Likewise the benefits of having one in some local DBs but not others or at the origin can be undermined by any cross-connections that by-pass the SPD - c.p.c.s, bonding conductors and extraneous-conductve-parts being one obvious example, data/signal cables being another (e.g. multiroom TV aerial wiring).
Likewise I reckon main SPDs need to be co-ordinated with those on other metallic services entering the building - phone lines, TV aerials, perhaps PV wiring - otherwise the sensitive equipment in between might actually be worse off if the mains side SPDs pull that side closer to Earth during a spike.
- Andy.
Shall be provided when?
When a new consumer unit is installed?
When a new circuit is added?
When a new expensive fixed appliance is installed?
When minor electrical work is carried out, such as adding an additional plug socket?
I presume it's on the same basis as everything else (e.g. bonding or 30mA RCDs) - only your new work necessarily has to benefit from the new requirement, but achieving that in practice often means upgrading some or all of the existing installation. So all of the above with the possible exception of the fixed appliance, as if that's connected to an existing point, it's unlikely to be in scope of BS 7671.
- Andy.
So does adding a new circuit to an existing plastic consumer unit a non-compliance?
Not to my mind - the addition didn't require the selection or installation of the consumer unit, so the new regulations wouldn't apply to that. The new work doesn't need to be fed from a metal clad CU in order to be safe of itself.
The old CU might be missing some features that your new circuit might need - be it 30mA RCD protection or SPDs or AFDDs - in which case you'd have to consider how to meet that need - it might be a new CU or is might be something extra in a separate enclosure.
- Andy.
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