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

[Dartlec]

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:



and this behind the door:



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!

 

[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 )

 

[timhoward]

Regarding point 2 - that is your choice and not the only way to do it.
An up front / time delayed RCD is not needed if every circuit has RCBO protection as this provides the fault protection.
Things evolve and a metal CU with a tails clamp is deemed to be safe enough these days, making tail faults upstream of the CU’s protective devices extremely unlikely.

 

[Robert2254]

Regarding point 2 - that is your choice and not the only way to do it.
An up front / time delayed RCD is not needed if every circuit has RCBO protection as this provides the fault protection.
Things evolve and a metal CU with a tails clamp is deemed to be safe enough these days, making tail faults upstream of the CU’s protective devices extremely unlikely.

agreed, you can do that, it clearly states in the guidlines that you can.
you have answered your own question, why ask it?

 

[timhoward]

agreed, you can do that, it clearly states in the guidlines that you can.
you have answered your own question, why ask it?

Neither myself or @nicebutdim asked any questions including the original one!
This thread was actually resolved in August 2020. You decided to add a comment yesterday, and one of your statements that every TT install needs an up front 100ma S type or 300ma RCD was a bit misleading as it's only one way to comply, hence the further debate to clarify things a bit.
Anyway, I think we are all agreeing so it can probably rest again now!

 

[nicebutdim]

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 )

Tim has summed matters up fairly well in the above post and I don't wish to be drawn into protracted argument that digresses from the point at hand.

Your original comment is below, please read it again.

"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"

There are indeed circumstances where it would be appropriate to fit an upfront 100mA type S RCD.

There are many circumstances where it would not be required, although fitting one would be perfectly acceptable. I see nothing wrong with this belt and braces approach and would generally agree with it, but with the proviso that the upfront unit incorporate type A sensing.

As for the suggestion that a 300mA RCD is acceptable place of 100mA type S? This may not be appropriate, depending on the installation in question.

I hope this clarifies my 'disagreement' with your original comment. I'm a learner who still has much to learn. I don't think it helps anyone when statements are made that don't align with regulatory requirements and when regulations are quoted to back up an argument at odds with the regulation quoted.

To answer your question; I would not fit a 10mA MCB in the circumstances you describe as doing so would be absurd, not to mention being at odds with the regulations we generally work to.