After a New Consumer Unit, now I need EICR & 100A DP Isolation Switch

[mainline]

A main switch....not an rcd main switch. A db with a main switch and sp rcbo's would be compliant. It is not the way i would do it though.
Add a s type rcd main switch and the sp rcbo's are no longer compliant.

I wouldn’t add an upfront rcd at all

Dp rcbos with main switch would be much better although not a requirement
The use of an upfront rcd should be avoided if possible.

 

[DefyG]

And - just to throw a spanner in the works!

Regulation 411.5.2 (Just refreshing memory on TT systems) states;
One of the following i) RCD OR ii) Overcurrent Protective Device shall be used, with;

Note 1 "An appropriate overcurrent protective device device may be used for fault protection provided a suitably low value of Zs is permanently and reliably assured."

Now we know in the real world a 'permanently and reliably low value of Zs' is unlikely, but hyperthetically, installing a RCD is not necessarily a god given!

 

[OLDBOY]

And - just to throw a spanner in the works!

Regulation 411.5.2 (Just refreshing memory on TT systems) states;
One of the following i) RCD OR ii) Overcurrent Protective Device shall be used, with;

Note 1 "An appropriate overcurrent protective device device may be used for fault protection provided a suitably low value of Zs is permanently and reliably assured."

Now we know in the real world a 'permanently and reliably low value of Zs' is unlikely, but hyperthetically, installing a RCD is not necessarily a god given!

Irrelevant.
All I have stated is that where an up front rcd is used sp rcbo's would not be compliant. I have not suggested any of the above is required, only the requirements where they are used.

 

[DefyG]

Its all totally irrelevant to the OP's original post!

 

[OLDBOY]

Its all totally irrelevant to the OP's original post!

True, so what was your thinking posting something totally irrelevant?

 

[DefyG]

Thought I'd join the party, - as the previous 20 or so posts debating RCD's RCBO's in a TT system were all irrelevant to the OP's query!

 

[7029 dave]

Before the birth of rcbo's it was standard practice to fit an upfront 100ma S type RCD on a TT earthing arrangement. I still would old habits die hard as they say.

 

[mainline]

In that instance sp rcbo's would be compliant. I have never said otherwise, and I have always stated an s type rcd main switch which will give selectivity. But many, myself included prefer to have the added insurance of an up front(s type) rcd on a tt, and in that case dp rcbo's are required. I have never stated that is the only option.

If something is REQUIRED then that would mean that you MUST use DP rcbos when using an up front rcd, but that's not the case as there are other options to having to use dp rcbos.

Meaning that it's not a requirement.

 

[nicebutdim]

 

[OLDBOY]

If something is REQUIRED then that would mean that you MUST use DP rcbos when using an up front rcd, but that's not the case as there are other options to having to use dp rcbos.

Meaning that it's not a requirement.

I have never stated dp rcbo's MUST be used where an upfront rcd is in service, if you read back through my posts I clearly agree other options are compliant such as a dual rcd board.
What I do state (very clearly I believe) and stand by is that wherre rcbo's ARE used......they must be dp where there is a upstream s type rcd and in that arrangement are effectively a requirement, you seem incapable of understanding that I am only refering to where rcbo's ARE used. I believe i have been quite clear that with other arrangements sp rcbo's are compliant.
Perhaps you would be good enough Mainline to answer this.

Lets say you have a job where the designer has specified DB's with rcbo protection to all final circuits. A main switch of s type rcd is also specified. Its a TT earthing system.
Would you install sp rcbo's and provide an EIC on completion?

 

[mainline]

I have never stated dp rcbo's MUST be used where an upfront rcd is in service, if you read back through my posts I clearly agree other options are compliant such as a dual rcd board.
What I do state (very clearly I believe) and stand by is that wherre rcbo's ARE used......they must be dp where there is a upstream s type rcd and in that arrangement are effectively a requirement, you seem incapable of understanding that I am only refering to where rcbo's ARE used. I believe i have been quite clear that with other arrangements sp rcbo's are compliant.
Perhaps you would be good enough Mainline to answer this.

Lets say you have a job where the designer has specified DB's with rcbo protection to all final circuits. A main switch of s type rcd is also specified. Its a TT earthing system.
Would you install sp rcbo's and provide an EIC on completion?

You said There is no specific regulation stating that a dp protective device is required for a tt with an upstream s type rcd.

Which was my point from the start.
That it’s Not a requirement.

@westward posted the same statement as I was typing saying dp rcbos aren’t a requirement and your reply was yes they are and proceeded to try and find a situation where they would be an actual requirement which has now come down to a designer telling you to fit them

You can go through all the scenarios you like where the use of them is going to be the sensible thing to do but That would still not make it a requirement.


If a main switch rcd is within the enclosure I would be questioning the competence of the designer

 

[mainline]

I work a lot on a rural converted estate with 21 holiday cottages which were wired by the owner over the last 40 yrs tails running 20 Mtrs through 3ft thick walls and attics.

Added over the yrs is wind/solar and now comes the batteries and more solar along with ev points and bore hole pumps.
There is a mixture of Pme/tt along with stables swimming pools and spas.

To have an upfront rcd for no other reason but to be a backup wouldn’t be very sensible especially in the above situation.

I do everything i can do to avoid the use of them.

 

[OLDBOY]

You said There is no specific regulation stating that a dp protective device is required for a tt with an upstream s type rcd.

Which was my point from the start.
That it’s Not a requirement.

@westward posted the same statement as I was typing saying dp rcbos aren’t a requirement and your reply was yes they are and proceeded to try and find a situation where they would be an actual requirement which has now come down to a designer telling you to fit them

You can go through all the scenarios you like where the use of them is going to be the sensible thing to do but That would still not make it a requirement.


If a main switch rcd is within the enclosure I would be questioning the competence of the designer

Unfortunately you have chosen to ignore the fact that I am only referring to a situation where an up front s type rcd is used with rcbo final circuit protection, a common arrangement but not the only one. In that case sp rcbo's are not compliant. At no point have i suggested other compliant arrangements are not possible.
Clearly you have not answered my question because you know you cant without admitting that for the specified arrangement sp rcbo's not compliant.

 

[mainline]

Unfortunately you have chosen to ignore the fact that I am only referring to a situation where an up front s type rcd is used with rcbo final circuit protection, a common arrangement but not the only one. In that case sp rcbo's are not compliant. At no point have i suggested other compliant arrangements are not possible.
Clearly you have not answered my question because you know you cant without admitting that for the specified arrangement sp rcbo's not compliant.

why would I say that they were compliant when they are not ?

Dp rcbos would do the job but that doesn’t mean it’s a requirement and that’s what you have to fit. You said yourself that there is No specific requirement to fit them.

If you believe there is a requirement to fit dp rcbos on upfront rcds then carry on.

 

[i3_happy]

Just a follow up on the original questions I posted.

The 10 way main CU (all MCBs) has this.....

1) one dedicated MCB for the back garden where there is a small CU that feeds a garden lights, outside socket and a car charger. This external CU has all RCDs.
2) one MCB for the lounge sockets. This has a fused spur in the lounge that then feeds a single outdoor CU to the front and has an a single RCD.

Photos of the outdoor CUs attached.

The question is, if I get the main CU replaced with 10 RCBOs gather this will impact the outdoor RCDs?

Or can I have an RCBO and RCD on the same circuit?

For the back garden (1 above), it has a dedicated circuit on the main CU so we could just have an MCB rather then a RCBO on the main CU?

For the front garden (2 above), would it be wise to have an RCBO at the main CU, but replace the outdoor old RCD with a MCB?

Appreciate any thoughts.

It's never straightforward!!!

 

[i3_happy]

One more....

My gas mains is earth bonded with a 10mm cable, this is near the CU (understairs cupboard).

Can the water (hot/cold) and heating flow pipes be cross bonded (interlinked). This cross bonding would happen under the comobi boiler with is not near the CU.

 

[pc1966]

The question is, if I get the main CU replaced with 10 RCBOs gather this will impact the outdoor RCDs?

Or can I have an RCBO and RCD on the same circuit?

You can but it is not good design practice. It also depends on the cable between the CU and the outdoor blocks:

• If that cable needs additional RCD protection then you need RCD/RCBO at the CU.
• However, if it is something like SWA, adequately glanded to earth the armour and with a low enough end of circuit Zs to disconnect on a MCB alone, then you would be best to have just the remote RCD and feed from a MCB.

MCB feeding MCB+RCD or RCBO is still not ideal as selectivity on high faults is rather poor, but slightly less troublesome than upstream 30mA RCD and acceptable for non-critical areas like a shed, etc.

If loss of lights from the common upstream MCB/RCBO presents a hazard then you need to look at feeding off a suitable switched-fuse for better selectivity, or better still install emergency lights (i.e. internal battery sort) so they come on when power fails due to any reason.

 

[i3_happy]

Thanks.

I'm thinking....
1) replace the Protek RCB for a MCB.....
2) replace the GE RCD switch for a non-RCD one....

Then get an electrician to put in RCBOs on all circuits on the main CU.

I'd hate to spend all the money on a new CU and end up with the odd MCB within it.

 

[pc1966]

I'd hate to spend all the money on a new CU and end up with the odd MCB within it.

Why?

If that is the best overall design option then you should accept that.

If it is better to have RCBO at the CU and replace ageing RCD at the outdoor locations then fine, but that is not an argument for/against MCB at the CU as such.

 

[littlespark]

One more....

My gas mains is earth bonded with a 10mm cable, this is near the CU (understairs cupboard).

Can the water (hot/cold) and heating flow pipes be cross bonded (interlinked). This cross bonding would happen under the comobi boiler with is not near the CU.

No cross bonding required if rcd protected.

 

[davesparks]

Can the water (hot/cold) and heating flow pipes be cross bonded (interlinked). This cross bonding would happen under the comobi boiler with is not near the CU

They can be, but it wouldn't achieve much as they will already all be electrically connected together via the metalwork of the boiler.

 

[i3_happy]

Why?

If that is the best overall design option then you should accept that.

If it is better to have RCBO at the CU and replace ageing RCD at the outdoor locations then fine, but that is not an argument for/against MCB at the CU as such.

Thanks for the feedback.

My comment was related to a point made earlier....by going the MCB route there would be no RCD protection on the cable between the indoor and outdoor CU. It's probably at least 10m long and just a normal cable - not SWA.

 

[davesparks]

Thanks for the feedback.

My comment was related to a point made earlier....by going the MCB route there would be no RCD protection on the cable between the indoor and outdoor CU. It's probably at least 10m long and just a normal cable - not SWA.

What type of cable is it and how is it installed?

Does it need RCD protection and would it actually be achieving anything if it was provided?

 

[i3_happy]

Just seems like a standard cable out of the CU, chunkier then the others.

Not sure how it gets outside, possibly behind the kitchen units.

 

[pc1966]

Just seems like a standard cable out of the CU, chunkier then the others.

Not sure how it gets outside, possibly behind the kitchen units.

If you are not certain it is safe from DIY nailing, etc (i.e. if it could be hidden less then 50mm from the surface of a wall/flooring/etc) then it will need RCD protection. Here your best choice is an RCBO at the CU and then whatever at the out buildings.

Leaving the existing RCD there is not a big deal, not ideal perhaps, but not such an issue as worth a lot of work to change it unless you are making changes anyway.

 

[i3_happy]

If you are not certain it is safe from DIY nailing, etc (i.e. if it could be hidden less then 50mm from the surface of a wall/flooring/etc) then it will need RCD protection. Here your best choice is an RCBO at the CU and then whatever at the out buildings.

Leaving the existing RCD there is not a big deal, not ideal perhaps, but not such an issue as worth a lot of work to change it unless you are making changes anyway.

Thank you, that's a really helpful post, nice & clearly stated and helps me clear up a lot of confusion on this matter.