split load across RCDs

[sm_jamieson]

OK, I have a large 3-way split CU with space for some non-RCD / RCBO circuits and two RCD groups. Space for about 18 circuits. I could have used all RCBOs but already decided the 3-way split. Unless I chuck out my two RCDs ... Anyway, assuming two RCDs, what is the best way to split the circuits between 2 RCDs ?

For the record, this was the mad maxed-out circuit plan I made up a while ago :-

• lights downstairs C6A MCB (typeC reduces nuisance trips)

• lights 1st floor C6A MCB

• lights loft C6A MCB

• sockets downstairs (not kitchen) B32A MCB

• sockets 1st floor B32A MCB

• sockets loft B32A MCB

• sockets kitchen ring B32A MCB

• kitchen cooker circuit (B32A ? - separate RCBO, or non-RCD, often earth leaks)

• kitchen fridge/freezer sockets radial 16A (non-RCD (needs reinforced cable))

• kitchen B32A radial (4mm/6mm) with remotely switched sockets for fixed kitchen appliances (washing machine/dishwasher etc).

• lights outside (separate B6A RCBO so no trip inside)

• sockets outside (separate B20A RCBO)

• power to garage/shed (mini-CU in there eventually - double-pole RCBO reqd ?)

• electric shower (10kW, B50A MCB)

• light in meter cupboard (non-RCD, surface wired)

• interlinked alarms B3A RCBO (or off lighting circuit ??) =========================

Thanks, Simon.

[js.b1]

1. Put the loft lights & sockets on SFCU off the upstairs unless you have a loft-conversion (and even then to be honest unless huge, lots of equipment, electric heating etc).

1. Put the outside shed on sub-main, with SFCU for outside sockets & lights suitably placed.

2. Put hall lights on smoke, so if you lose lights-up you still have hall lights.

1. Forget the dedicated no-RCD run to freezer, it is pointless.

2. Forget the light in the meter cupboard, you are building a reliable install not rewireable fuses in ceramic carriers installed by "I used to wire DC, all this AC stuff is new to me". Go to Amazon etc, buy a

2AA Maglite and fit Lithium batteries, remove the front to turn it into a candle.

1. If you have 2 kitchen circuits, a ring ideally should be balanced or use 4mm FTE. I would use a single isolator for each unless you have inbuilt appliances (Elec Guide to BR suggests only built-in need switches above the counter).

SFCU = DP Switched Fused Connection Unit

[John Rumm]

Fair enough - but don't put them on the same RCD as that which protects the sockets on the same floor.

32A for a loft may be excessive.

RCBO to avoid cable protection issues.

Or RCBO again

Do you actually need two 32A circuits in the kitchen? 14kW of appliances is quite alot!

They could probably share the same RCBO - can give a bit more flexibility adding extra lights / sockets when there is just once socket to worry about.

Do you need to avoid losing the lights on a RCD trip? If so then use a MCB on the non RCD side so that you can have the garage CU sort out the split between circuits to maintain lights on a socket trip etc.

45A would be enough

Put it on the same lighting circuit as that adjacent to the meter cupboard, but fit a non maintained emergency light. (or a maintained one if you want it to be manually switchable). That way it comes automatically when you lose power to the lighting circuit for whatever reasons.

Either. Most have LEDs to indicate mains presence, and also backup batteries. Some have a remote control capability so that you can remotely test / hush / identify the alarms. Remote hush is good if you have high ceilings.

[John Rumm]

Non RCD is arguable, but it being discrete from other circuits can be advantageous.

(same could apply for the central heating if you often away in the winter)

I would say that depends much on the cupboard. Having a usable light in a large but otherwise dark cupboard is quite handy.

IMHO you need to be able to isolate under counter appliances easily without needing to pull them out. So either above counter switching or their sockets being accessible at the back of the adjacent cupboard.

[NT]

ishwasher etc).

If I were doing a new install I dont think I'd group things by room, better to have different circuits each side of each room so in case of fault you still have power everywhere.

Ditto with lights, losing half the lights on one floor is far less bother than losing all downstairs lighting.

There are many little tricks you can do to improve such an install, eg

[js.b1]

Oh, whilst I remember, Loop-In switch can be handy because it means you have a neutral at the switch.

I have a suspicion this might be useful someday if we have smart light switches which require a neutral (occupancy stuff, intelligent stuff). It does mean you need a supply & return drop to the light-switch so double oval/round makes it easier.

[sm_jamieson]

ine/dishwasher etc).

Thanks, some of the items there are for a loft conversion that is not done yet ! I guess it would be best to have lights up / sockets down on one RCD, vice versa on the other RCD. Simon.

[sm_jamieson]

/dishwasher etc).

p://wiki.diyfaq.org.uk/index.php?title=3DRewiring_Tips

I guess the only thing with that is the expectation that a whole room would be isolated with a single switch. I think you'd want to clearly indicate the situation somewhere. Although obviously you should always check for live circuits, not assume anything. Simon.

[NT]

ne/dishwasher etc).

ttp://wiki.diyfaq.org.uk/index.php?title=3DRewiring_Tips

yes, a notice by the CU for the unaware.

NT

[ARWadsworth]

Thanks, some of the items there are for a loft conversion that is not done yet ! I guess it would be best to have lights up / sockets down on one RCD, vice versa on the other RCD. Simon.

Yes. I also tend (on such big CUs) to put the kitchen ring on an RCBO or two is there are two rings. On the 17th edition setup I usually put the smokes with the upstairs lights on an RCBO. Don't always believe that a C type MCB will stop nuisamce trips on the lights:-) I usually put the shower on an RCD not an RCBO. If the shower fails then it can be isolated via it's double pole switch. The same applies to a cooker. Fridges usually go on RCBOs (unless the customer wants to pay for extra way of making the circuit not RCD)

As long as all the lights are not on 1 RCD and all the sockets are on another RCD then things are usually OK. Then just use common sence as to the RCBOs with things such as fridges, central heating and smoke alarms.

Cheers

Adam

[george [dicegeorge]]

[ARWadsworth]

Sometime it does:-) eg this reply.

It depends on the message that I am replying to. Something to do with OE and the way the -- sig is used I believe.

Cheers

Adam

[Huge]

Like we give a shit what some shouty top poster "thinks". Let your Mum have her computer back.

[John Rumm]

Have you got OE quotefix installed?

[ARWadsworth]

No. And I cannot seem to be able to download from that site at the moment. I'll give it a day or so and see if the site has a proplem

Cheers

Adam