Wylex SPD

[ericmark]

Thank you, @SUNRAY and also @JohnW2 yes if the window turns red, you know the SPD needs changing. But when a MCB trips some do only move half way, and have to be switched off, before switching on again, so one can see if tripped or switched off. But many, no way to know.

Many commercial consumer units have a locked lid, so a MCB powering a SPD would not be seen if it did trip. I know where I worked, electrical panels had to be locked, and I got ticked off by HSE inspector for leaving a key in a panel.

 

[JohnW2]

Many commercial consumer units have a locked lid, so a MCB powering a SPD would not be seen if it did trip. I know where I worked, electrical panels had to be locked, and I got ticked off by HSE inspector for leaving a key in a panel.

Isn't that dangerous (unless there is some other isolator upstream of the CU/DB (which is not the case in a substantial proportion, probably the majority, of UK domestic installations)?

I would certainly not want to be in a building in which I didn't have immediate and free 'unhindered access' to a means of killing the electricity supply to the building, would you?

 

[ericmark]

Isn't that dangerous

The isolator is not under the locked cover, so not dangerous, it has caused problems, as only authorised people can reset a trip, but that was the whole idea, if something is tripping, want to know about it.

 

[JohnW2]

The isolator is not under the locked cover, so not dangerous,

Are you referring to some sort of isolator external to the CU/DB? The photo you posted (to illustrate a Cu with a locked cover) seemed to show a locked cover which was covering everything.

 

[ericmark]

Are you referring to some sort of isolator external to the CU/DB?

Yes, HSE rules are you must isolate elsewhere, so having an isolator in the CU/DB is pointless, even when that's the norm.

 

[JohnW2]

Hi folks,
I'm still not really much closer to understanding this situation regarding OPD protection of SPDs, particularly the fact that Wylex, but few (if any) other brand suppliers seem to feel that the DNO's fuse is adequate protection. I suppose the bottom line question is whether 'we' (and, in particular, I) should feel comfortable having a Wylex SPD protected only by the DNO fuse?

Another question has occurred to me - I wonder what the DNOs view is in relation to an item of connected equipment in the installation which is reliant on the DNO's cutout fuse for its overcurrent protection.

Has anyone got any thoughts about any of this?

Kind Regards, John

 

[flameport]

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

Yes, and have done many times. Likewise with Hager.
I have also installed a few others such as Lewden where an MCB was required for the SPD.

 

[JohnW2]

Yes, and have done many times. Likewise with Hager.

Interesting . That's reassuring, but I was at least half-expecting you to have a different view from that!

The Hager one says that "each cartridge incorporates its own thermal disconnect mechanism" (and "No secondary back-up protection required" - although it also says "Max backup fuse 125 A" !). If "its own thermal disconnect mechanism" is some internal OPD, I would not have thought that a thermal mechanism would be anything like fast enough to prevent the SPD being destroyed by a transient overvoltage that resulted in an (probably extremely brief) very high current, would it?

The Wylex one says nothing about any 'disconnect mechanism' but merely says "Fully rated 100A: No need for additional back up device in the consumer unit" - which I presume means that they believe it will not come to any harm if protrected by a 100 A (or smaller) fuse.

This all still leaves me a little confused/uncertain. As you've said, there are very few manufacturers of SPDs, and even that few are very probably producing extremely similar devices, so most of the brands available are probable the same or very similar. That being the case (and ignoring Hager which, as above, may be rather 'different') is there a reason why Wylex feel that SPDs bearing their brand name are adequately protected by the DNOs (100 A max) fuse, whereas all the other brands seem to feel that external (32 or 40 A) external protection is required.

Whilst, as above, your view is certainly reassuring, I have to say that I would be much more comfortable if I understood (and 'agreed with') the reason why Wytlex appear to take a different view than do most/all other companies who sell identical or similar devices.

Also, as I recently mentioned, do we know what is the view of DNOs about one having a device protected only by their cutout fuse - and particularly when that device is actually designed to create L-N or L-E 'short circuits' (albeit usually of very short duration) ?

I have also installed a few others such as Lewden where an MCB was required for the SPD.

Never assume that what one reads in an Internet forum is necessarily correct (see post #2)

Kind Regards, John

 

[davelx]

The MK SPD datasheet says:

"MAX. MAINS-SIDE OVERCURRENT PROTECTION 125AgG
SHORT-CIRCUIT WITHSTAND CAPABILITY FOR MAX. MAINS-SIDE. OVERCURRENT PROTECTION (ISCCR) 50KA"

and their CUs supplied with ready fitted SPD have them connected directly to the main switch

 

[JohnW2]

The MK SPD datasheet says:
"MAX. MAINS-SIDE OVERCURRENT PROTECTION 125AgG
SHORT-CIRCUIT WITHSTAND CAPABILITY FOR MAX. MAINS-SIDE. OVERCURRENT PROTECTION (ISCCR) 50KA"
and their CUs supplied with ready fitted SPD have them connected directly to the main switch

Yes, that's true - so essentially the same as Hager. In fact, the MK (2-module) SPDs look as if they may well be the same as the Hager ones.

We have therefore established that three major brands (Wylex, Hager and MK) are happy for their SODs to be protected only by the DNO fuse - which I suppose reassures me enough to make me fairly comfortable to use them like that. However, I still don't really understand:

1... Why do most/all of the other brands require a 32/40A MCB protecting the SPD.​

​

2... Although the tails as far as the CU will probably be 25mm², the N and E connections to the SPD within the CU will almost certainly be a lot smaller than that - so theoretically not adequately protected by a 100 A fuse. It is presumably not impossible that a fault could arise within the SPD which resulted in 100A (or a bit more) flowing, not enough to blow the DNO fuse but overloading one of those conductors to represent a potential fire risk?​

​

3... As I've ask, I wonder what the DNOs feel about their fuse being the sole protection of a device within the installation, particularly when it's a device designed to produce 'short circuits'under some circumstances?​

Kind Regards, John

 

[plugwash]

Every SPD I've seen has some form of overcurrent/overheat protection built-in. It really has to, even a few amps flowing continuously through the surge protection element would be a major problem.

So the main question is whether that built-in protection has enough breaking capacity that, when combined with the upstream protective device all reasonablly likely faults are adequately handled.

 

[JohnW2]

Every SPD I've seen has some form of overcurrent/overheat protection built-in. It really has to, even a few amps flowing continuously through the surge protection element would be a major problem.

That would all make sense, but ...

(a) how did you ascertain that, since I don't think I've yet to see the documentation for any SPDs which make any mention of any such built-in protection?​

​

(b)... if what you say is true, what is the difference between those which do and those which don't say that protection by an external MCB is required? ... and why do those said to need the protection of an MCB actually need that?​

​

So the main question is whether that built-in protection has enough breaking capacity that, when combined with the upstream protective device all reasonablly likely faults are adequately handled.

Since, as above, the documentation for most of them doesn't even mention any built-in 'breaking', they don't usually give any figure for 'breaking capacity' (only 'maximum, discharge current', which is usually/always 40 kA).

 

[morqthana]

Curious - Hager CU and SPD

Afternoon All, Purely a curiosity question this but - Hager and most other CU manufacturers in the past had a secondary protection device (MCB) upstream of the SPD. The RCBO board I've bought now takes directly from the 100A incomer and their literature states no upstream protection is...

www.diynot.com

 

[plugwash]

The ones I've seen teardown videos of use a spring-loaded fusible element if the surge protection element gets too hot the element melts and the spring pulls the connection apart. This also causes a failure indication to appear on the SPD.

Any SPD without such protection would be dangerous as heck in the event of a sustained overvoltage that was sufficient to cause significant current flow in the surge protection element, but not so high as to cause a current flow that would trip the overcurrent protective device.

As for the differences between ones that are ok with 100A upstream protection, and ones where the manufacturer suggests smaller I don't know, but I would speculate that it comes down to the details like how big the contact gaps are, how good the case is at tolerating arcs until the upstream overcurrent protection blows and so-on.

 

[JohnW2]

Curious - Hager CU and SPD

Afternoon All, Purely a curiosity question this but - Hager and most other CU manufacturers in the past had a secondary protection device (MCB) upstream of the SPD. The RCBO board I've bought now takes directly from the 100A incomer and their literature states no upstream protection is...

www.diynot.com

Thanks - but all that seems to indicate is that people were just as confused and uncertain about all this two years ago as I am today