CU upgrade

[safedepth]

I've been asked to upgrade a CU. It's a small 4 way unit, 40A Cooker, 32A Sockets, (Up and Down on one cct), 6A lights up, 6A lights down. Down has had an alarm piggy backed on to it. I'm intending to replace with a RCD protected MK unit. Separate the downstairs lights and alarm so having 5 ways.

Am I right to think this is acceptable. I have a nagging feeling it should have some discrimination, maybe lights on separate sides of RCD, this just seems a little excessive on a small 2 bed house with only 2 downstairs rooms. I can find no definitive regs in the BRB on this matter. It appears to be at my discretion. Any views out there?

 

[NozSpark]

I'd either use an ISO CU and RCBO's

or

a 6 way dual RCD CU

Preference is ISO CU and RCBO's though!

 

[safedepth]

Sorry, showing my inexperience here but what do you mean by ISO cu and would you go this route simply to provide discrimination?

 

[NozSpark]

I mean a CU with a main switch and not a with a main switch RCD covering all circuits

 

[NozSpark]

Just think what would happen if there was a L-E or N-E fault on the socket circuit and there was a RCD main switch,,,, everything would go OFF!!

If you used RCBOs then only the socket circuit would go off!

 

[safedepth]

Thanks,

Sounds arse now I know but I thought so.

I think cost comes into it. I need to justify to the customer the cost of a RCBO protecting the lights for up or down. All this on top of the

 

[NozSpark]

Thanks,Sounds arse now I know but I thought so.

I think cost comes into it. I need to justify to the customer the cost of a RCBO protecting the lights for up or down. All this on top of the

 

[batty]

You're not wrong there..just give the customer the options and tell them the benefits/pitfalls of each and let them decide...

Ask the audience.

 

[sellers]

If you run it by the customer then at least its their choice! I know that I'd rather have RCBO's.

 

[batty]

If you run it by the customer then at least its their choice! I know that I'd rather have RCBO's.

Me too.

 

[safedepth]

Thanks all,

I think this is another aspect of my inexperience. My previous CU changes have all been at my properties. I decide what I want and the subsequent cost. I am finding it hard to justify the costs to a customer, when if it was me I would fit RCBO's.

As you all say, put the ball in his court.

Many thanks again. Guinness

 

[spinlondon]

Have you considered the following:

"314.1

DIVISION OF INSTALLATION

Every installation shall be divided into circuits, as necessary, to:

1. avoid hazards and minimize inconvenience in the event of a fault

2. facilitate safe inspection, testing and maintenance (see also Section 537)

3. take account of danger that may arise from the failure of a single circuit such as a lighting circuit

4. reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation

5. mitigate the effects of electromagnetic interferences (EMI)

6. prevent the indirect energizing of a circuit intended to be isolated.

314.2 - Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of the other circuits, and due account shall be taken of the consequences of the operation of any single protective device."

 

[safedepth]

Have you considered the following:"314.1

DIVISION OF INSTALLATION

Every installation shall be divided into circuits, as necessary, to:

1. avoid hazards and minimize inconvenience in the event of a fault

2. facilitate safe inspection, testing and maintenance (see also Section 537)

3. take account of danger that may arise from the failure of a single circuit such as a lighting circuit

4. reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation

5. mitigate the effects of electromagnetic interferences (EMI)

6. prevent the indirect energizing of a circuit intended to be isolated.

314.2 - Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of the other circuits, and due account shall be taken of the consequences of the operation of any single protective device."

Hi, Yes.

I did read this, it was some help but left me a little in the dark still.

But having re read it here a number of times I think I see light at the end of the tunnel.

 

[spinlondon]

To my mind, minimizing inconvenience in the case of a fault, would entail not having an RCD cut off all circuits when only one has caused the RCD to trip.

Safe inspection etc. would be facilitated if only the faulty circuit was tripped.

Danger could be caused if the lights went out as you were comming down stairs, or were in the middle of cooking something.

Having all circuits on one RCD could mean that cumulative earth leakage from each circuit would nuisance trip the RCD, whereas there might not be enough leakage in each circuit to trip individual RCDs.

 

[safedepth]

To my mind, minimizing inconvenience in the case of a fault, would entail not having an RCD cut off all circuits when only one has caused the RCD to trip.Safe inspection etc. would be facilitated if only the faulty circuit was tripped.

Danger could be caused if the lights went out as you were comming down stairs, or were in the middle of cooking something.

Having all circuits on one RCD could mean that cumulative earth leakage from each circuit would nuisance trip the RCD, whereas there might not be enough leakage in each circuit to trip individual RCDs.

Cheers Spinlondon.

I agree with you completely, it was the cost implication which had me worried. Justifying the extra expense when there were only 4 (soon to be 5) cct's on the board. However after having a very restless night mulling it over whilst the wife suffered with a cold next to me, I have decided on the cheaper of the two new options. A dual RCD split load board. Slightly cheaper than all RCBO's.

Many thanks to all for their guidance and thoughts.GuinnessGuinness:Y:Y

 

[ianmacd]

See if you can split the downstairs/upstairs into either 2 rings or 2 radials so split them over the 2 rcds' too.

Ian.

 

[safedepth]

Well, after all that worrying I went with the split load dual RCD option. Incidentally the board was very reasonably priced. Anyway customer was very happy with setup, it's on view at the the bottom of the stairs so had to look discreet.

Installed, inspected, tested, arghh. Borrowed neutral on lights. Ended up having to put lights on same MCB to solve problem. I've done some research on here and whilst a rewire might be preferred option that would be too messy for customer so shared MCB is the answer, unless told otherwise by my learned friends on here.

In addition. Main earth is 10mm on 25mm tails and 100a fuse. No earth cable in van, so back soon to upgrade main earth cable to comply.

 

[Subneural]

The good old borrowed neutral for the landing light eh ?? Classic !!

Pop a floor board and run a fresh neutral from the nearest downstairs light through the airing cupboard up to the landing light. Easy money

 

[Lurch]

To my mind, minimizing inconvenience in the case of a fault, would entail not having an RCD cut off all circuits when only one has caused the RCD to trip.Safe inspection etc. would be facilitated if only the faulty circuit was tripped.

Danger could be caused if the lights went out as you were comming down stairs, or were in the middle of cooking something.

I've stopped using that argument now though as the lights are still covered by an RCD. It was easier to explain it when the lights weren;t on an RCD and the sockets were. Now everything is on an RCD, and I've noticed a lot of people mix sockets and lights across 2 RCD's so really you might as well just have 1 30mA RCD covering the lot. Big step backwards IMO there, from that point of view.