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

[mainline]

Not 100% selectivity no, but better than with SP.
Also DP or SPSN RCBOs would allow the upstream RCD to be reset after it trips on a N-E fault whereas with SP RCBOs you could be stuck with the whole installation being off.

Nobody is arguing that DP isn't a better option.

You could also have the whole installation off using DP rcbos, dependent on where the N to E fault was, I've seen N to E faults cause random rcbos to trip.

Also, regardless of whether Dp, Sp TT or Tn is used the fault will still remain.

Are DP rcbos a requirement ? NO

Are DP rcbos needed ? NO

 

[OLDBOY]

Nobody is arguing that DP isn't a better option.

You could also have the whole installation off using DP rcbos, dependent on where the N to E fault was, I've seen N to E faults cause random rcbos to trip.

Also, regardless of whether Dp, Sp TT or Tn is used the fault will still remain.

Are DP rcbos a requirement ? NO

Effectively they ARE a requirement where a 'back up' upstream S type RCD is employed on a TT system with final circuit rcbo protection as is general and good practice in the UK. It is not possible on such a system to completely design out all nuisance tripping of the up front RCD, but the only way to design out a known cause is to use dp rcbo's. To not do so would not be compliant.

 

[pc1966]

Thanks all for the advice and varying perspectives. So, bottom line is that none of this is really clear-cut, but open to interpretation.

Given the various opinions and info, I've taken another look at all this....

1) EICR - seems the way to go, but a valid point that if a lot of testing is done upfront then the CU replacement costs should be lower.

2) DP RCBO - actually the DP & SP are not too different in price, so why not go with DP, besides I have an electric car charger and would need a DP RCBO for that, I believe.

I think most folks will agree with you here.

3) Smoke/Heat alarms - on the positive side it got me to check the dates on my alarms and just added a Heat alarm to the kitchen.

Go for Aico if you can, less trouble than other brands but slightly more expensive. Here in Scotland they now mandate a linked alarm system, but RF is fine for home use, and a great thing to get with Aico is the separate test/silence button for wall mounting.

Ei450 RadioLINK Alarm Controller | Aico

Ei450 RadioLINK Alarm Controller. The Ei450 is used to control all the alarms in a system from one place.

www.aico.co.uk

No more flapping towels or climbing on chairs to deal with a false alarm!

4) No earth bonding to Gas currently. The Water Supply pipe is the blue plastic for the incoming mains, so gathering that means no earth bonding required for the water.

The gas supply must be bonded if metallic pipe (almost always the case?) but if water main is plastic then not required as you say.

5) For the isolator switch the DNO was not interested unless it was to be installed prior to the main fuse, however, British Gas surprised me by saying they could do it for £109 + tails cost extra. Will determine if the isolator will go between the fuse and meter or between the meter and CU. Given it's a smart meter probably the latter.

They will always put an isolator switch between the meter and the CU. It makes tampering with the meter (and living) harder that way!

The quoted price looks reasonable enough to me.

 

[mainline]

The only way to design out a known cause is to use dp rcbo's. To not do so would not be compliant.

A dual CU with a pair of rcds and sp rcbos would be compliant.

The use of Dp rcbos is still not a requirement, you can't call it a requirement or say it's needed if there are other ways of doing things.

 

[mainline]

A dual CU with a pair of srcds and sp rcbos would be compliant.

The use of Dp rcbos is still not a requirement, you can't call it a requirement or say it's needed if there are other ways of doing things.

 

[nicebutdim]

A dual CU with a pair of rcds and sp rcbos would be compliant.

The use of Dp rcbos is still not a requirement, you can't call it a requirement or say it's needed if there are other ways of doing things.

There's a strong argument against this position from the perspective of potential nusiance tripping. It's one of those areas I'd raised where regs can be considered open to interpretation. I'd be happy to defend my position and I'm sure you'd be happy to do the same. Where our positions differ is that you'd likely be happy to install DP RCBOs at the insistance of a client, whereas I might refuse to install a dual RCD board if I felt there was good reason to do so.

 

[mainline]

There's a strong argument against this position from the perspective of potential nusiance tripping. It's one of those areas I'd raised where regs can be considered open to interpretation. I'd be happy to defend my position and I'm sure you'd be happy to do the same. Where our positions differ is that you'd likely be happy to install DP RCBOs at the insistance of a client, whereas I might refuse to install a dual RCD board if I felt there was good reason to do so.

I haven't fitted a dual rcd board for many years and am not likely to do so

I always fit dp rcbos
But I'm not required to do so

 

[nicebutdim]

I haven't fitted a dual rcd board for many years and am not likely to do so

I always fit dp rcbos
But I'm not required to do so

You're not required to do so in the circumstances in which you fit them or you believe there's no circumstance in which they need to be fitted?


My limited experience has already involved a couple of faults in which N-E issues caused subsequent problems on other circuits. I like the idea of knowing a future problem should be isolated with the circuit on which it occurred, thus further avoiding the possibility of nuisance tripping.

Most customers have the means to cover an additional few % on the overall job cost and also have the ability to understand a basic explanation for those costs. Customers who have to shave every penny from a job often aren't going to like my proposals anyway (and I'll seek to avoid them) and for customers who are of limited means I'll obviously aim to find a sensible accomodation that involves keeping costs low, while incorporating as much future convenience as possible.

No customer is ever going to thank me for the power not going off on more circuits than necessary, but I'm content knowing my ears won't burn too much if only one circuit goes off.

 

[OLDBOY]

As this is in danger of going round in circles I will finish up. The usual and preferred arrangement with a small tt installation is a 100ma or above S type rcd main switch and rcbo's. With this arrangement dp rcbo's are effectively a requirement IMO . Other arrangements may be devised,as above,in which dp rcbo's would not be a requirement. ( A dual rcd board AND rcbo's...).Remember....main bonding is a requirement....except when it isnt.

 

[mainline]

As this is in danger of going round in circles I will finish up. The usual and preferred arrangement with a small tt installation is a 100ma or above S type rcd main switch and rcbo's. With this arrangement dp rcbo's are effectively a requirement IMO . Other arrangements may be devised,as above,in which dp rcbo's would not be a requirement. ( A dual rcd board AND rcbo's...).Remember....main bonding is a requirement....except when it isnt.

Why would you have an rcd main switch with a full dp rcbo board ?

 

[OLDBOY]

Not a main switch in a db, I use a separate RCD main switch which provides back up fault protection in case of rcbo failure, and protects the metal frame of the db rather than relying solely on mechanical protection to the tails.

 

[newfutile]

I guess your mean a s type (RCD) Residual Current Device in a tt system,otherwise there in no selectivity and little point in having rcbos,I have never had an rcbo fail only the rcds seem to fail for some strange reason

 

[mainline]

Not a main switch in a db, I use a separate RCD main switch which provides back up fault protection in case of rcbo failure, and protects the metal frame of the db rather than relying solely on mechanical protection to the tails.

If the db isn’t remote from the cut out and tails are properly installed a main switch with dp rcbos is compliant adding an upfront rcd is going to reduce selectivity

 

[OLDBOY]

If the db isn’t remote from the cut out and tails are properly installed a main switch with dp rcbos is compliant adding an upfront rcd is going to reduce selectivity

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.

 

[mainline]

Not a main switch in a db, I use a separate RCD main switch which provides back up fault protection in case of rcbo failure, and protects the metal frame of the db rather than relying solely on mechanical protection to the tails.

If the db isn’t remote from the cut out and are properly installed a main switch and dp rcbos is compliant

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.

sp rcbos on a tt with a main switch would have no selectivity with a N to E fault.

I think the issue is making a statement saying Required or Needed means that there are no other options.

 

[mainline]

edited double sent

 

[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.

You just said it again “ dp rcbos are required”.

Dp rcbos are not a requirement they are an option.

 

[OLDBOY]

I think you are rather mis-interpreting. I have only ever stated that where an upstream s type rcd is used in front of a db with rcbo's single pole rcbo's would not be compliant and therefore by default are required in that situation.I stand by that.

 

[mainline]

I think you are rather mis-interpreting. I have only ever stated that where an upstream s type rcd is used in front of a db with rcbo's single pole rcbo's would not be compliant and therefore by default are required in that situation.I stand by that.

Look at the definition of Required.

Your post @ 34 says sp rcbo with main switch would be compliant?

 

[OLDBOY]

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.