Upgrade consumer unit, rcd rating question

[orionrockyhe]

I have replaced an old fuse style consumer unit with a MCB type. Lights and Fridge/freezer MCBs have been fitted. I need to connect RCD and MCB for shower and ring main. Shower is rated to be at 40 Amps with 40 Amps MCB and the ring main 32 Amps. What rating RCD should I be using?

The ring main is inside a small flat with no garden attached. Could I supply the ring main with a 32 Amp MCB only and use a 40 Amp RCD for the shower only?

 

[securespark]

Not clear what your situation is exactly.

If your board is a split-load type, it should already have a 63/80/100A RCD fitted.

If your CU has no RCD protection built-in, then you need to fit RCBO's for the ground floor ring and shower (usually recommended by manufacturer)

A 32A 30mA RCBO for the ring(s), not sure about shower as you don't mention it's electrical rating?

 

[Albert]

Just to add that the most important value on the RCD is the 30mA, and for a single circuit that it will be lower than the wires current carrying capacity, the latter one is correct for the MCB's as well.
As mentioned if it is a shower with a high load value I would recommend to find out this value and you can get a dedicated MCB/RCD unit for a shower.
BTW if you changed the consumer unit (the box), this is a notifyable job apparently not the fuses change, this depends on the council, in my area you would have to notify for the box but not for the MCB's.

Sorry to be the bad news carrier but this is for your safety, when you change the MCB's all the relevant circuits have to be tested and a PIR has to be field in.

 

[orionrockyhe]

Not clear what your situation is exactly.

If your board is a split-load type, it should already have a 63/80/100A RCD fitted.

If your CU has no RCD protection built-in, then you need to fit RCBO's for the ground floor ring and shower (usually recommended by manufacturer)

A 32A 30mA RCBO for the ring(s), not sure about shower as you don't mention it's electrical rating?

Reply
Thank you securespark, it is split load with one RCD 40A 30mA it was intended that this would supply the shower only. I understand that the RCD will trip in a fault condition if current ( 30mA) is detected on the neutral. As the RCD is rated at 40 Amps do I need to add a 40 Amp MCB?
Ok that takes care of the shower questions please let me know your answer.

Presently there is a 32A MCB on the ring main. Any tools would be used with a adaptor RCD. so I am less worried about RCD for the ring main is it nessesary to have one?

 

[Adam_151]

it is split load with one RCD 40A 30mA it was intended that this would supply the shower only.

thats going to be fine if the only load on the rcd side is the shower, and the shower is less than 40A, seems a bit strange to have an RCD that small though, the cheaper boards usually have a 60A, and better ones come with an 80A

I understand that the RCD will trip in a fault condition if current ( 30mA) is detected on the neutral. As the RCD is rated at 40 Amps do I need to add a 40 Amp MCB?

Yes, you will need an MCB for the shower circuit

Presently there is a 32A MCB on the ring main. Any tools would be used with a adaptor RCD. so I am less worried about RCD for the ring main is it nessesary to have one?

#

Only if its reasonably expected to supply equipment outside of the equipotential zone, how likely is it that someone would run an extension cord out to use a vacuum cleaner to clean a car? Other than that (using stuff outside), there is no requirement, but it is a good idea to RCD protect general purpose sockets

 

[orionrockyhe]

[/quote]
thats going to be fine if the only load on the rcd side is the shower, and the shower is less than 40A,

Yes it is 40 Amps
[/quote] Yes, you will need an MCB for the shower circuit

Thank you Adam that is what I needed to know. Will go today and install a 40Amps MCB on the RCD protected supply to the shower.


[/quote]seems a bit strange to have an RCD that small though, the cheaper boards usually have a 60A, and better ones come with an 80A

Yes it is a low value 40Amps RCD.
The main Breaker on the cunsumer unit is 100Amps but does not have RCD so I thought it wise to RCD protect the shower at least


[/quote]Only if its reasonably expected to supply equipment outside of the equipotential zone, how likely is it that someone would run an extension cord out to use a vacuum cleaner to clean a car? Other than that (using stuff outside), there is no requirement, but it is a good idea to RCD protect general purpose sockets

It is four stories up so no out door us would be expected. Thank you for clarifying that too.

I think the main problem has been the lack of slots(6) I larger unit would have been better. Hind sight is a wonderful thing!

 

[orionrockyhe]

Just to add that the most important value on the RCD is the 30mA, and for a single circuit that it will be lower than the wires current carrying capacity, the latter one is correct for the MCB's as well.
As mentioned if it is a shower with a high load value I would recommend to find out this value and you can get a dedicated MCB/RCD unit for a shower.

Thanks Albert, About the dedicated unit for a shower I assume this will still fit on the the same rail in the consumer unit and not have to be separately mounted. That being so how many slots wide are they two or three?

BTW if you changed the consumer unit (the box), this is a notifyable job apparently not the fuses change, this depends on the council, in my area you would have to notify for the box but not for the MCB's.

Sorry to be the bad news carrier but this is for your safety, when you change the MCB's all the relevant circuits have to be tested and a PIR has to be field in.

I will look into to rules about notifying. If I were to have cicuits tested and obtain a certificate what would be the best way to go about this?

 

[Albert]

Thanks Albert, About the dedicated unit for a shower I assume this will still fit on the the same rail in the consumer unit and not have to be separately mounted. That being so how many slots wide are they two or three?

I think that you might not fit it but it does not need to be complicated, from the dedicated MCB 40A or whatever the value has to be you can pull a cable to this dedicated unit which will have an RCD in it. It can sit just near the consumer unit.
If not, may be an RCBO could do the trick, you can get them single space or double, this will fit on the rail and do the MCB and RCD job.

 

[orionrockyhe]

Thanks Albert, About the dedicated unit for a shower I assume this will still fit on the the same rail in the consumer unit and not have to be separately mounted. That being so how many slots wide are they two or three?

I think that you might not fit it but it does not need to be complicated, from the dedicated MCB 40A or whatever the value has to be you can pull a cable to this dedicated unit which will have an RCD in it. It can sit just near the consumer unit.
If not, may be an RCBO could do the trick, you can get them single space or double, this will fit on the rail and do the MCB and RCD job.

Thanks very much for all your good advice. I will look into to rules about notifying. If I were to have cicuits tested and obtain a certificate what would be the best way to go about this?

 

[Albert]

I have replaced an old fuse style consumer unit with a MCB type.

Changing Consumer unit is notifyable, you have to notify the unit only.

Lights and Fridge/freezer MCBs have been fitted.

Changing MCB's is not notifyable.

I need to connect RCD and MCB for shower and ring main. Shower is rated to be at 40 Amps with 40 Amps MCB and the ring main 32 Amps. What rating RCD should I be using?

If the circuit exists and you add the MCB/RCD only, it is not notifyable if you have to add the cables as well it is notifyable.

Don't forget one thing, whether you have to notify or not "ALL MODIFIED CIRCUIT HAVE TO BE TESTED AND THE RECORDS KEPT IN A SAFE PLACE", and as you changed basically the whole consumer unit and the MCB's all have to be tested.

 

[ban-all-sheds]

I will look into to rules about notifying.

You are too late - you are now in contravention of the Building Regulations as you should have notified in advance.

//www.diynot.com/forums/viewtopic.php?p=286636#286636

And judging by your lack of adequate planning, and the questions you're asking, I fear you are also in over your head - hope you don't find any problems with any of the circuits.

If I were to have cicuits tested and obtain a certificate what would be the best way to go about this?

You can't get any sort of certificate. You should be able to get a Periodic Inspection Report carried out.

 

[securespark]

The main Breaker on the cunsumer unit is 100Amps

You may find this is an isolator only - it is not an MCB.