Wylex SPD

[JohnW2]

Hi Folks,
In contrast with most other brands, the standard Wylex Type 2 SPD (NMT2SPD3W/1) seems not to 'require' external overcurrent protection (i.e. an MCB).

It clearly has no such internal protection (or, at least, none which could be 're-set') and the nearest the documentation seems to get to saying anything about this is:

FULLY RATED 100A
No need for additional back up device in the consumer unit

Does this mean that it is not felt necessary to 'protect' the device with anything other than the DNO fuse (and, if so, why do most other manufacturers seemingly think differently?) - and, probably more to the point, does it mean that a surge of sufficient magnitude/duration would blow the DNO fuse? ... or what?

Kind Regards, John

 

[sparkwright]

I believe the Lewden ones now no longer require a 40amp mcb.

 

[JohnW2]

I believe the Lewden ones now no longer require a 40amp mcb.

Fair enough - but, as I wrote, most brands do call for an MCB (and the 'with SPD' CUs they sell come with the MCB installed).

When manufacturers explain 'why', they invariably cite the two issues I mentioned - protecting the SPD itself and avoiding the DNO fuse blowing under certain (albeit very improbable) circumstances.

 

[ericmark]

The original fusebox 2 modules wide did not have an MCB, the later single module wide did. Not a clue why the change?

 

[blup]

The oVer current seems to be diverted within a few millionths of a second, before the damage is done. The lightning strike chooses its own path.

 

[JohnW2]

The original fusebox 2 modules wide did not have an MCB, the later single module wide did. Not a clue why the change?

I'm becoming increasingly confused. In terms of what TLC are currently offering this single-module SPD plus a separate MCB ...

...and also this ("Type 1, 2 and 3") 2-module wide one plus a separate (63 A) MCB - so they seem to think (like most other manufacturers that an external MCB is required - so why not Wylex?

Can someone help to unconfuse me a little?

 

[ericmark]

I just fitted what came with the box, but some 4 year ago now.

 

[JohnW2]

I just fitted what came with the box, but some 4 year ago now.

Indeed, and I imagine that's what nearly everyone does. That means that almost everyone is fitting an MCB with the SPD, other than those using Wylex (and maybe also Lewden) ones - which doesn't make a lot of sense.

I think that my view of SPDs is probably 'deteriorating' Not only do I remain far from convinced that there is a significant 'need' for them in domestic installations, but it seems that not many people actually understand the implementation of this technology (so they are just blindly doing 'what they are told')!

 

[ericmark]

(so they are just blindly doing 'what they are told')!

Yep, I did, it was not a high cost, so fitted to be on safe side.

Now have two, as second fitted with solar panels, I do have far less LED lamp failures to my son who has non fitted, but no way to know if the SPD is reason why.

 

[JohnW2]

Now have two, as second fitted with solar panels, I do have far less LED lamp failures to my son who has non fitted, but no way to know if the SPD is reason why.

As you know, I am personally extremely doubtful that the SPD has anything to do with your LEDs' survival

 

[flameport]

but it seems that not many people actually understand the implementation of this technology (so they are just blindly doing 'what they are told')!

That is a summary of 90% of the electrical and other construction industries.

Can someone help to unconfuse me a little?

All SPDs require overcurrent protection.
What that is depends on the specific SPD and where it is installed.

When SPD operate due to overvoltage, they essentially short out the supply either L-L, L-N or L-E.
It's only for a tiny duration, but that current can affect overcurrent devices.
The magnitude of that current depends mostly on the supply characteristics. How long it lasts depends on the transient and how well the SPD can deal with the energy.

Overcurrent protection of too low a rating risks it disconnecting when a transient occurs.
Too high a rating risks severe catastrophic damage to the SPD if it fails due to a large transient.
Larger SPDs can be made to deal with much higher fault current and energy levels - but there is then a trade-off as to how effective they are, as they will pass more energy through to downstream circuits and devices.
Smaller SPDs can be more effective, but they won't be as capable at dealing with high energy levels and will therefore need a lower rated overcurrent protection device.

For those devices intended for domestic use, assumptions have obviously been made regarding typical fault levels and what fuse will already be installed at the origin by the network operator.
There are plenty of different brands and labels of SPDs, but very few actual manufacturers.

 

[ericmark]

As you know, I am personally extremely doubtful that the SPD has anything to do with your LEDs' survival

I would agree, but we have no way of knowing. And at the end of the day, can't see a downside.
@flameport does make some valid points, what would be of interest, is how many times have people found the MCB supplying the SPD has tripped?

Maybe we need a pole? You or me?

 

[JohnW2]

That is a summary of 90% of the electrical and other construction industries.

As I implied, that's what I suspected/feared - and why, coupled with my doubts about the 'need' (benefit) in domestic installations, I remain very sceptical about these devices.

I was already familiar with most of what you go on to say (for which I thank you), but I'm still a bit confused .....

All SPDs require overcurrent protection.

Indeed. That seems to be little more than common sense.

What that is depends on the specific SPD and where it is installed. When SPD operate due to overvoltage, they essentially short out the supply either L-L, L-N or L-E. It's only for a tiny duration, but that current can affect overcurrent devices.

Quite so.

The magnitude of that current depends mostly on the supply characteristics.

... and, presumably the magnitude of the over-voltage?

How long it lasts depends on the transient and how well the SPD can deal with the energy.

Again, quite so - and the former of those will always be an 'unknown' (with no theoretical limit), so assumptions (about magnitude and duration of transient over-voltages) can presumably only really be guesses?

Overcurrent protection of too low a rating risks it disconnecting when a transient occurs. Too high a rating risks severe catastrophic damage to the SPD if it fails due to a large transient.

Agreed.

Larger SPDs can be made to deal with much higher fault current and energy levels - but there is then a trade-off as to how effective they are, as they will pass more energy through to downstream circuits and devices. Smaller SPDs can be more effective, but they won't be as capable at dealing with high energy levels and will therefore need a lower rated overcurrent protection device.

That all makes sense.

For those devices intended for domestic use, assumptions have obviously been made regarding typical fault levels and what fuse will already be installed at the origin by the network operator. There are plenty of different brands and labels of SPDs, but very few actual manufacturers.

So Wylex, but seemingly few, if any (maybe Lewden?), other brands feel that it is acceptable to rely upon the DNO's fuse to protect the SPD (hence regarding it as acceptable that a 'surge' could result in the DNO's fuse operating)? Particularly if Wylex-branded products are identical to those sold as other brands, why/how do you think this difference has come about, and what do you think about it? Have Wylex made different 'assumptions' from everyone else, or what?

Would you be comfortable installing a Wylex-branded SPD without any overcurrent protection other than the DNO's fuse?

 

[SUNRAY]

My local Church Hall had a CU change 3-4 years ago, the SPD MCB is regularly tripped, the electrician who conned them into the changeover (based on the existing 4 CU's being plastic) had made several tests and finds nothing wrong and suggests someone is turning it off as it is between the 3 RCBO's powering the stage lighting and the main switch, however no one should be touching the stage lighting RCBO's and they doesn't appear to any evidence of them being used. The twice I've known it to trip (I check beginning and end of any booking I have involvement with) the dishwasher has been used but I don't know at what point the MCB trips.

 

[JohnW2]

I would agree, but we have no way of knowing.

Indeed we don't - but, as I said, I definitely "have my doubts"!

And at the end of the day, can't see a downside.

Well, I'm sure that some people would suggest that, unless there was a fairly clear balancing 'upside', the massive cost (monetary and environmental etc.) of manufacturing, distributing, installing and 'maintaining' countless millions of these things constitutes a definite 'downside'

..... what would be of interest, is how many times have people found the MCB supplying the SPD has tripped?

Indeed - and, of course, if it tripped it's MCB, the chances are that it would not have served its intended purpose, at least not as fully as one would have hoped ... and, of course, if it were a Wylex (or whatever) one without an MCB, it could be the DNO fuse that was operating as a result of the SPD being present - which would again probably count as a 'downside'