Wylex 3rd Amendment CU - TT recommendation

[Midwest]

I've picked up my first 3rd Amendment CU, a Wylex one. Inside was a sheet containing recommendations for maintaining IP ratings for cable entries and when using a TT supply, bottom right in attachment. Now I thing I'm right in saying that the pictured 100ma RCCB's are manufactured in insulated plastic, of the type to be 'outlawed' by reg. 421.1.201. Would you say that these RCCB's are 'switchgear assemblies', as described by said reg?

 

[Richard Burns]

I would say that they are certainly similar assemblies and also likely to catch fire (well as likely as the CU anyway!) and so they must be in metal boxes, therefore you still need another RCD to protect those tails..... until you can get the RCD outside the property and do a risk assessment that says a fire in this will not affect the building structure.!!
Well thought out IET idiots.

 

[Midwest]

Chicken & egg thing, perhaps someone can come up with a double insulated RCCB enclosure, with a surrounding metal casing! Have Wylex dropped a boo boo?

 

[Dave OCD]

It seems to be getting a bit ridiculous, even on a TT install if the tails come in through a proper gland correctly fitted surely they'll be fine ? I bet a time delayed 100ma RCD won't leave you much change from £60+ on top of the more expensive board and extra work.

 

[drzsta]

Yes they did mess up there. I would probably put a 100mA type S in place of the main switch and use apprpriate glanding with double insulated tails going directly into the terminals of the RCD.

 

[Midwest]

Yes they did mess up there. I would probably put a 100mA type S in place of the main switch and use apprpriate glanding with double insulated tails going directly into the terminals of the RCD.

I can see that using an RCD as a main switch will prevent the metal CU becoming live, should the bus bar somehow become shorted out. There is still a possibility of a short between metal case and tails after they have entered the CU, even if you use a stuffing gland. There's a good video by John Ward (someone else posted before) which highlights the issue. Can't cut & paste here for some reason, just google 'TT supply to metal consumer units.

Like the idea of the consumer unit pattrass, dunno how much they cost though?

 

[drzsta]

It would be very unlikely of the tails being damaged and touching the metal case of the DB if you use the appropriately sized gland and carrying the double insulation of the tails directly upto the termination point. There is little possibility of severe damage to the tails once inside the C.U.

 

[Midwest]

It would be very unlikely of the tails being damaged and touching the metal case of the DB if you use the appropriately sized gland and carrying the double insulation of the tails directly upto the termination point. There is little possibility of severe damage to the tails once inside the C.U.

Just playing devils advocate, although unlikey, it is possible, depending on how the cables are routed inside the CU. That's why prior to the 3rd Amendment, insulated CU's or external 100ma RCD (with metal CU's) were recommended for TT supplies. Just using a plastic bush was not enough. So now because we will have to fit metal CU's, we can suddenly forget about the prior recommendations for TT supplies, that does not make sense to me. It is possible to have a highly dangerous situation to exist, when using a metal CU with TT supply. The onus is on us to resolve this. Seems no thought has been given by IET/BSI to this conundrum.

 

[sammyshooter]

Bit of a side step, but have you noticed how heavy that wylex unit is? I was shocked!

 

[Midwest]

That's cos it's made of metal

 

[Midwest]

Rang Wylex TechSupport. They hadn't seen recommendation sheet supplied with their CU. They gave me the mobile number of their sales operations manager (or something like that). So I rang him. He was bit surprised. He suggested that a ‘common sense approach should be made, and that using a plastic RCCB before a metal CU is a lessor of the two evils. If the RCCB was to catch fire as opposed to the metal CU becoming live, that would be less hazardous. But we are the manufacturer and I should seek advice from whom I’m registered’.

Waiting for a response from my scheme,......but its been a while!

 

[NDG Elecs]

Waiting for a response from my scheme,......but its been a while!

It probably will be a good while longer yet, as the schemes don't seem to know any better either! As RB says: Well thought out IET idiots!

 

[Midwest]

Well had my reply. Apparently the answer is on page 32-34, in the new yellow On-Site-Guide. Various diagrams with different CU arrangements on TT system, 'all of which are acceptable'.

Now I haven't got round to buying one of them yet (Xmas present possibly!). Anybody got one and can enlighten us with the basics?

 

[Richard Burns]

Thems the pages, a lot of good it will do you!

 

[Midwest]

Thanks Richard. Having had a quick look, seems the only viable option suggested by the new yellow OSG, is figure 3.6.3 (ii) with a 100ma time delayed RCD as main switch. There's nothing to protect the incoming tails supplying this RCD as it enters the metal CU. Does not suggest the option recommended by Wylex. I understand Wylex offer a plastic stuffing gland and Hager a tails clamp.
Prior to Amendment 3, and I quote 'The enclosures of RCD's or Consumer Units incorating RCD's in TT installations should have an all-insulated or Class II construction. Otherwise additional precautions recommended by the manufacturer need to be taken to prevent faults to earth on the supply side of the 100ma RCD' unquote.
Seems that this paragraph has been deleted from the yellow OSG.

 

[Dave OCD]

No more dual RCD with main switch or main switch/RCBO's on a TT either, think it's time to take up plumbing.

 

[PaulG]

I know this is a bit old now, but been to look at a job today which needs a cu change and is TT, so been doing some looking at this. Noticed in the OSG, figure 3.6.3 page 33 that it says for the enclosure 'for TT installation insulated enclosure or further mechanical protection to meter tails'

There you have it OSG says insulated enclosure is fine...

 

[Deleted member 9648]

I know this is a bit old now, but been to look at a job today which needs a cu change and is TT, so been doing some looking at this. Noticed in the OSG, figure 3.6.3 page 33 that it says for the enclosure 'for TT installation insulated enclosure or further mechanical protection to meter tails'

There you have it OSG says insulated enclosure is fine...

Remember that the requirement for fire proof enclosures only applies to domestic installations.....the OSG is not exclusively about domestic installs,there is no reason why an insulated CU could not be installed in a commercial situation for example.

 

[Midwest]

I know this is a bit old now, but been to look at a job today which needs a cu change and is TT, so been doing some looking at this. Noticed in the OSG, figure 3.6.3 page 33 that it says for the enclosure 'for TT installation insulated enclosure or further mechanical protection to meter tails'

There you have it OSG says insulated enclosure is fine...

Don't think so Paul. I haven't got a copy of the yellow OSG yet, but Richard posted a copy of pages 32-35 at #14. No mention of insulated enclosure there, as far as I can see. I've emailed my scheme on this, and they referred me to those pages. Also watched a 'webinair' by NIC/ELECSA, and that nice young Darren Stantinforth said for TT, using double insulated tails and protect them, when entering the metal enclosure, with a dedicated plastic gland (such as Wiska sprint tail kit, or the Wylex gland), would be suitable for a TT supply. Hager have also introduced a cable clamp for the tails. Are you in a scheme? If so ask them. In the past the, we were always told to use insulated for TT, now I don't think they have properly thought this through. Even the new OSG say's the chance of internal cable links/bus bars touching the metal enclosure are 'minimal', so still possible. You could consider a time delay RCD as main switch?

 

[Midwest]

..........or put a plastic one in before next year!

 

[Midwest]

Take a look at these two vids; https://www.youtube.com/watch?v=Bj_plR6lU3o for the wiska gland

and this one from Wylex; https://www.youtube.com/watch?v=XjaEQJBDhts

Interestingly, if you watch this vid' at 4 mins, you'll see that Wylex suggest you can use a 'plastic' time delayed RCD to protect the tails prior to the CU on a TT. My scheme - Elecsa - says NO, and when I rang Wylex (it was in that flyer I posted at the start of this thread), their Tech Support quickly bated me off to some sales person, whom I rang. After a bit of discussion on 421.1.201, he said using such a insulated RCD was the lesser of 'two evils'. I don't think this reg. is going to be completely ironed out for a while.

 

[darkside]

Sorry for late reply, I was thinking about this recently. The wording of 421.1.201 is "Within domestic (household) premises, consumer units and similar switchgear assemblies...".

I think you can make a strong case that a standalone RCD is not a "similar switchgear assembly". It is not an OPD and it is not associated with a reduction in current carrying capacity of cables. It performs a totally different function to a CU.

A switchfuse or isolator plus OPD is effectively a one-way CU so does need to be non-combustible.

If you take this new reg as banning RCDs in plastic enclosures, then it also bans Wylex REC series isolators (and the Hager equivalent) where these are owned by the consumer.

 

[Midwest]

Here's the reply from Elecsa, when I asked about Wylex recommendation for using a 100ma time delayed RCD prior to metal CU with TT supply (I forgot to post it here,sorry);

'Regulation 421.1.201 does indeed state “consumer units and similar switchgear assemblies”.

However, what regulation 421.1.201 states in full beforehand is “within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439-3 and shall: 1) have their enclosure manufactured from non-combustible material or, 2) be enclosed in a cabinet or enclosure constructed of non-combustible material complying with Reg 132.12”.

Whilst the data sheet you provide seems to indicate a domestic installation when you first look at it, whether or not it’s actually showing a domestic installation is something that the manufacturer needs to clarify.

However, if t is a domestic installation shown in the data sheet, I would agree with you that the separate RCCB unit would have to be in accordance with points 1 or 2 of Regulation 421.1.201'.

 

[YoungScud]

Sorry for late reply, I was thinking about this recently. The wording of 421.1.201 is "Within domestic (household) premises, consumer units and similar switchgear assemblies...".

I think you can make a strong case that a standalone RCD is not a "similar switchgear assembly". It is not an OPD and it is not associated with a reduction in current carrying capacity of cables. It performs a totally different function to a CU.

A switchfuse or isolator plus OPD is effectively a one-way CU so does need to be non-combustible.

If you take this new reg as banning RCDs in plastic enclosures, then it also bans Wylex REC series isolators (and the Hager equivalent) where these are owned by the consumer.

I work as a metering trainer for a REC and this has raised an interesting question. For some time now, our company has talked of making the isolator the property of the consumer, thereby making them responsible for replacement of faulty isolators. However, I can't for the life of me see how this is possible, and I have two main reasons for saying this. Firstly, the REC seals the top end of the isolator, making it impossible for the consumer to legally replace the isolator. Secondly, the top of the isolator is live at all times and the consumer would have no legal way of isolating this. With this being the case, I feel the isolator would have to remain the property of the REC and so would be essentially part of the supply, not the installation. That would mean that the requirements of the regs would not apply to the isolator.

 

[Midwest]

That's what I've been told by Elecsa (think it was them) regarding the aforementioned plastic isolators not forming part of the 'domestic' installation. Doesn't make sense though, when sometimes these isolators are in the same location as the CU. Perhaps the DNO's can be more trusted than your domestic electrician

 

[YoungScud]

That's what I've been told by Elecsa (think it was them) regarding the aforementioned plastic isolators not forming part of the 'domestic' installation. Doesn't make sense though, when sometimes these isolators are in the same location as the CU. Perhaps the DNO's can be more trusted than your domestic electrician

I do agree with you. It seems odd to me that an isolator placed at almost exactly the same point as the CU wouldn't be subject to the same safety concerns as far as fire risk is concerned. I suppose it's possible that at some point the ESQCR will catch up with BS7671, but don't hold your breath.