Surge Protection Device

Am I correct in understanding that such devices are in general terms only required where there are overhead power lines between the sub-station and the premises that could potentially be struck by lightning?

That's what I thought when I was trying to invoke the get out clause but my BCO was not having it. There are three types of SPD the Surge Devices website does explain the difference and has a handy device selector. The one posted is the recommended one for domestic situations with underground cables for fitting into Domestic Distribution panels (CU). It does not protect against direct lighthning strikes as it does not need to, but does protect against other causes of surges that could damage delicate electronics. I meant to mention that at present Toolstation is the cheapest supplier I have found @ £44 but do not expect to find it in your local store only available online.

Richard

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. I believe that they were all type 2 SPDs as I believe you can only use a type 1 with the additional protection of a type 2 (for domestic properties). I should have taken more notice, but I was actually there for info on the AFFDs.

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

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

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

Those AFDDs are quite expensive although on a par with the more expensive brands of RCBOs like MK. Using those double modules is going to have an impact on the size of CUs to accommodate them.

Richard

Is this not a contradiction:

"Connect to a 32A MCB b or c curve" and "You only need one arrester per board and all your outgoing circuits on that board will be protected"

I thought the device relied on tripping a 32A MCB to disconnect that specific circuit? Or will it take the company fuse with it?

Am I missing something? What has happened to MK?

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.

Thanks. I was missing something.

Will this affect MK's status as (arguably) the market leader for electric wiring equipment?

No, neither of those. The SPD would function even without the MCB. The way it works is to "snub" the transient (either L to N or L/N to E) - i.e. it passes a current limiting the rise in voltage. The downstream equipment should be none the wiser, and carry on operating as normal.

The purpose of the MCB is just for the protection of the SPD - should it fail short, or attempt to act on a significant surge that would result in its destruction. With a 32A C Curve MCB, it can pass up to 320A for a very short duration to effect the suppression (or <=160A for a type B), and beyond that the MCB would operate removing from the supply.

And

Quite expensive?

AFDD, MCB and RCD in one single module unit.

I went down to the show partly to get info on them as we had a quote to do that specced over 20 of them. That's the first £4K plus CU we have quoted on.

Thanks for the explanation.

Looking at some more info and their characteristics at raised voltages I do wonder how effective these are at preventing high voltage transients.

ISTR clive did an SPD teardown, and it relied on overload melting the solder on a spring loaded contact ... maybe that's just the Lucky Golden Hedgehog ones?

Not very, they are simply 3 voltage dependent resistors which "prevent" transients by failing (much as "surge protected" extension leads. Having failed they sit there being completely useless until someone spots the little light on them and remembers this means you have to go out and buy a replacement cassette (or a completely new device at about the same price.

Any lightning near bye will destroy them long before they have done any good so they are a triumph of rules for the sake of rules.

Fortunately they are not required in singe dwelling houses (Section

Does that include those with electric cars being charged ?.

There is no mention of electric cars.