Joys of "Park" homes - Can an RCD be described as "Earth Leakage Circuit Breaker" ?

[Dartlec]

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Ah, it gets even messier

All you can really do here is deal with your customer's safety and inform the site owner (in writing, of course) of the potentially serious issues facing the main supply arrangements.

If you fit a replacement CU, for example, that has proper protection for the high Zs TT system then they should be OK. While not strictly necessary if they have all-RCBO or dual RCD board, my own preference is still to have a 100mA or 300mA delay RCD up-front as then there is no single point of failure in the future that would prevent safe ADS on a fault.

That just leaves the sub-main SWA armour as a risk if it is not earthed in a manner that can result in the supply ADS working within the regulation time for shock protection. You or the customer would need to inquire about the responsibility for that.

I presume there is a billing meter? Where is it located?

Usually the demarcation of ownership would be at that point, with the site owner responsible for the supply to the meter and the meter itself, and the customer from the meter's output downstream.

Yes I can see a can of worms but may leave that to others to worry about once I've made things clear in writing. I didn't do enough of a site survey of the supply to be sure either way whether it's perfectly OK or a complete lash up...

From what I gather the site owner has a single meter for the site from the DNO, but that is not something I saw. I'd assume it's a 3 phase incomer for a site that size - he then supplies his own meters for each home and charges them based on their usage. Presumably he does quite well out of it as he's just moved into an 8m pound house....

It may be that all the meters/isolators in the cupboard I saw were on one phase and that the other properties are split that way, but that would purely be speculation.

I've followed some of the issues that changing CU to metal brought up with TT installations, though I don't see them that often around here now. As I understand it the NICEIC consider a cable gland as acceptable to minimise the risk of incoming tails touching metal enclosures, though several of the manufacturers seem to provide or sell cable clamps internally too.

Do you install the Time delay RCD in a separate insulated enclosure before the board such as the Wylex one often used for isolators, or replace the main switch?

 

[pc1966]

I've followed some of the issues that changing CU to metal brought up with TT installations, though I don't see them that often around here now. As I understand it the NICEIC consider a cable gland as acceptable to minimise the risk of incoming tails touching metal enclosures, though several of the manufacturers seem to provide or sell cable clamps internally too.

Do you install the Time delay RCD in a separate insulated enclosure before the board such as the Wylex one often used for isolators, or replace the main switch?

I think the risk of an input to metal CU short in a properly installed CU is negligible:

• Using a gland avoid both the sharp edge of the case and keeps down any strain on the tails from external movement
• Using the 19-strand Doncaster tails are more flexible and less likely to strain the internal connections (than traditional 7-strand double sheathed cable)
• Checking the incomer terminal screws (and others) with a torque screwdriver as a final once-over after fixing stuff in and pull-testing the connection, just before replacing the cover, should avoid anything coming loose in the first place
• Having an up-front delay RCD means the busbar is already protected (unlikely to short to case anyway)

Others on here might have more inputs on this to take in to account!

 

[Dartlec]

I used the Doncaster tails on my most recent install, and I don't think I'll be using anything else now - they make the bends in the board so much easier!

 

[Robert2254]

Seems to be my month for finding odd bodges by supposed professionals.

Installing an external socket in a shed today at a park home (non-mobile home) and find this label on the consumer unit:

View attachment 60297

and this behind the door:

View attachment 60298

It looks like the CU was installed at the factory and then shipped with the house to site, where someone installed it on a TT and left it like it.

A more recent electrician apparently put a bigger earth rod in (8 feet rather than the 2 feet - Ze of 22 Ohm so fairly good as earth rods go) and the gas people discovered a 'reverse polarity' that was fixed.

But (according to the client at least) at no point did anyone tell him that none of the lighting, Central Heating or Oven circuits were protected by anything other than MCBs with a Zs that would certainly not meet any disconnection times.

The label is just plain confusing though. I know in the 16th there was a regulation that socket outlets needed RCD protection, and that's fine. But it ignores the fact that I've never seen a TT system where some sort of upfront RCD wasn't required for all other circuits to meet disconnection requirements. I'd have expected them to have fitted an S type RCD as the main switch at least, but no doubt this saved them some pennies.

I've also never seen a modern RCD described as an Earth Leakage Circuit Breaker - I thought that only applied to the old voltage ones which were considered obselete in the 80s.

Currently putting something in writing to the client so they can brandish it to the site owner, who is apparently not known for his adherence to regulations, and will quote for a new board.

Anyone seen a label like this before?

I'm thinking I'll quote for a Fusebox RCBO board with SPD as they seem good at the price. Though even a Screwfix special dual RCD would be an improvement!

The TT supply must have an RCD of 100mA Time Delay or a 300mA rcd. The circuits downstream must have an RCD of 30mA for Discrimination ( now called Selectivity )
The RCD is an Earth Leakage Device the older types now banned and obsolete were Voltage operated circuit breakers

 

[westward10]

The TT supply must have an RCD of 100mA Time Delay or a 300mA rcd. The circuits downstream must have an RCD of 30mA for Discrimination ( now called Selectivity )
The RCD is an Earth Leakage Device the older types now banned and obsolete were Voltage operated circuit breakers

Where does it state a TT earthing system must have rcd protection.

 

[Robert2254]

Where does it state a TT earthing system must have rcd protection.

in the Regs 411.5.2. Fault Protection. if your Earth Rod Impedance is low then you can rely on a overcurrent device but the Earth Rod changes all the time depending on the ground conditions, always err on the side of safety. ( my motto ) you do as you like my friend but I am devout RCD man on TT

 

[nicebutdim]

You previously stated

The TT supply must have an RCD of 100mA Time Delay or a 300mA rcd

Given the OP states they had an RA of 22Ohms, I see nothing in 411.5.2 that justifies the above statement.

Don't get me wrong - I'm not suggesting an upfront RCD shouldn't be fitted, but pointing out your suggestion that one 'must' be fitted is erroneous.

 

[Robert2254]

You previously stated



Given the OP states they had an RA of 22Ohms, I see nothing in 411.5.2 that justifies the above statement.

Don't get me wrong - I'm not suggesting an upfront RCD shouldn't be fitted, but pointing out your suggestion that one 'must' be fitted is erroneous.

If you had a high Rod impedance is what I am referring to. If you did have ( for instance 99 ohms )
or less and an overcurrent device would not suffice in protecting your install , how would you have fed a Ring and a Cooker Circuit ?
lets just say it was 20 ohms would you feed the supply through a 10A mcb?, knowing that as soon as you turn on the cooker or the ring had a kettle on or toaster or something similar it would trip. so.......RCD time delay as I already stated

 

[nicebutdim]

If you had a high Rod impedance is what I am referring to. If you did have ( for instance 99 ohms )
or less and an overcurrent device would not suffice in protecting your install , how would you have fed a Ring and a Cooker Circuit ?
lets just say it was 20 ohms would you feed the supply through a 10A mcb?, knowing that as soon as you turn on the cooker or the ring had a kettle on or toaster or something similar it would trip. so.......RCD time delay as I already stated

Perhaps it is a failure to understand on my part, but I'm struggling to see the point you're making here.

 

[Robert2254]

Perhaps it is a failure to understand on my part, but I'm struggling to see the point you're making here.

OK
1.Instead of an RCD you can use a MCB as FAULT PROTECTION "IF" the Rod Resistance is low enough to do so.
BUT supposing your Rod Resistance was 50 ohms? 230/50 =4.6A on Fault. This wouldn't be enough to trip a 5A Breaker or fuse.
Answer? Fit a Time Delay RCD Type S ( time delay 100mA ) as FAULT PROTECTION. Even if you used a 5a Breaker as soon as you turn on a cooker or use some other device above 5A load you will lose your supply.
Short Circuit protection ( L-N ) would be protected by the service fuse ( assume 63A or similar ) Fault Protection via the time delay RCD

2. you answered your own question on your original post.
22 ohms on the rod ( which will change in different seasons according to ground conditions )
230/22 = 10.45A.
Again I ask you, would you put a Low rating MCB on the supply as Fault Protection? NO
I would use a Time Delay or Type S RCD.
I hope this clarifies the matter.
I would fit the RCD to CYA ( cover your arse )
All the circuits in the board would be 30mA rcd protected. ( dual RCD or RCBO's )