New CU question.

[AndyPRK]

EDIT

Ok I will agree with you John.

It would seam it shouldn't be installed like that, unless a Type S time delayed RCD is used.
Though obviously that isn't the solution in this case

 

[JohnW2]

These type 2 ones shunt between L & N it would seam. (good for TT installs) and therefore surges shouldn't activate the RCD

Are you sure about that (which differs from my understanding)? Why do you think they have earth connections.

Anyway, that wasn'r my point. If an SPD is downstream of an RCD in a dual-RCD board, then the 'live' circuits (protected by one RCD) do not have RCD protection if the SPD is downstream of the other RCD and that RCD has been 'switched off manually' or has tripped for some othercreason.

If one feels the need for SPD protection, it surely should be upstream of any RCDs, shouldn't it?

Kind Regards, John

 

[AndyPRK]

Ok John you are correct, but maybe not for the correct reasons.

It would seam sensible to have it before the RCD. (wonders if this is true for TT)

 

[JohnW2]

Ok John you are correct, but maybe not for the correct reasons.

Fair enough, but I'm not sure what you think are my 'incorrect reasons'. Admittedly we are (as so often!) talking about incredibly improbable scenarios, but if one feels the need to install some protective device it surely makes sense not to install it downstream of something which could, under some circumstances, disable that protection in relation to at least some 'live' circuits, doesn't it. As you say ...

It would seam sensible to have it before the RCD.

Quite so.

(wonders if this is true for TT)

I can't see why the earthing system, per se, makes any difference. If you are talking about a TT system with an up-front 'whole installation' Type S RCD then, as above, it would seem to me to make sense to have SPD protection upstream even of that.

Kind Regards, John

 

[plugwash]

SPDs failing and disconnecting themselves is definitely a thing, indeed many surge protectors have indicators of such. Whether this is down to surges that are too big for the surge protector to handle or whether it's down to simple random failures I could not say. There is no way though that any device should be connected across the mains without some consideration of what happens when it fails.

I'm dubious about the whole idea of parallel-connected surge protectors, but if you are going to have one then it doesn't seem like it would make a huge difference to the effectiveness whether the protection against the surge protector failing is entirely within the surge protector or is provided in whole or part by an external MCB.

 

[AndyPRK]

I believe Hagar and Wylex/Crabtree connect them direct to the main switch.

Wylex have a soldered joint in them, intended to disconnect if it all gets a bit hot and sets the replace flag.

 

[JohnW2]

There is no way though that any device should be connected across the mains without some consideration of what happens when it fails.

I can't disagree with that as a concept. There are, of course, a small number of things (like 'tails' and a Main Switch) in an installation which are protracted by nothing other than the cutout fuse and I suppose that is, at least electrically, fair enough (when essentially unavoidable).

I'm dubious about the whole idea of parallel-connected surge protectors ...

Same here. What interests/suprises/amuses me is that it is not so long ago that any mention of 'surge protection' invariably resulted in a barrage of disparaging comments, liberally interspersed with references to 'snake oil'

... but if you are going to have one then it doesn't seem like it would make a huge difference to the effectiveness whether the protection against the surge protector failing is entirely within the surge protector or is provided in whole or part by an external MCB.

Agreed. However, again "if you are going to have one", it seems to make no sense (at least, not to me) to have them downstream of something that can 'disconnect' them for reasons (e.g. manual 'switching off', or an unrelated fault elsewhere) unrelated to a 'failure' of the SPD

Kind Regards, John

 

[ericmark]

I know in my board the SPD connects to Line, Neutral and Earth so if after the RCD it would trip the RCD, so would have thought either two one for each RCD or it is wired before the RCD. It seems wrong to wire after the RCD.

 

[JohnW2]

I know in my board the SPD connects to Line, Neutral and Earth so if after the RCD it would trip the RCD, so would have thought either two one for each RCD or it is wired before the RCD. It seems wrong to wire after the RCD.

AS I've said, I agree.

Kind Regards, John

 

[SUNRAY]

Well to be quite honest I've seen a selection of SPD's in various CU's and as far as I can see most of them are inadequately incorporated.

With the format used in pro installations the circuit protected is always wired via the SPD, not the SPD wired by some random selection of hi Z switch gear connected to a random position within the circuit or even worse one of the circuits.

If we're going to add gratuitous devices into the regs, at least add them in a way that they are able to have some benefit.

 

[JohnW2]

If we're going to add gratuitous devices into the regs, at least add them in a way that they are able to have some benefit.

Agreed - but, on the basis of what (little) by way of hard facts I have managed to find so far, I probably would have been more inclined to write something like ...

"If we're going to add gratuitous devices into the regs, at least add them in a way that they are may possibly be able to have offer some appreciable benefit."

Kind Regards, John

 

[SUNRAY]

Some manufactures use an Mcb to protect the spd, rather than rely on the main fuse!

so what I said stands

Shame it was done by a Lewden salesman rather than a regular electrician.
Could have tried to line the devices up.
SPD as installed is pointless.

 

[SUNRAY]

Agreed - but, on the basis of what (little) by way of hard facts I have managed to find so far, I probably would have been more inclined to write something like ...

"If we're going to add gratuitous devices into the regs, at least add them in a way that they are may possibly be able to have offer some appreciable benefit."

Kind Regards, John

I'm happy with that too.

 

[ericmark]

I see a fridge or freezer without some display as a problem, as loose power, and you will not realise power lost until too late. It seems with my SPD there is a fuse-able link built in, and should it not be able to cope with the load it will rupture/melt, and a spring loaded flag will show it has failed. There seems little point in having a MCB feeding a device which already has a fuse-able link within the unit. All it means is it can be switched off in error.

 

[AndyPRK]

SPD as installed is pointless.

Why do you say that out of interest? I note the cables are less than 50cm