Split Load CUs

[phykell]

Can someone explain to me what split-load CUs are and why they're necessary or recommended?

Also, what are the best arrangements for fitting an RCD? Should I have a separate RCD for the shower, the garage and the rest of the power and lighting circuits?

Thanks

 

[ban-all-sheds]

Split-load boards have some circuits with RCD protection, some without. Do a search for split-load, RCBO, RCD, CU etc - loadsa info

In ascending order of cost:

1) RCD only board
2) Split load board
3) Non-RCD board with RCBOs
4) Non-RCD board with individual RCD sockets.

 

[ZenStalinist]

Split load CUs split the load so that you can have some circuits on an RCD, and others not, all in one CU. It is tidier than having two CUs, with RCD and non RCD.

As for what the RCD is it depends whether or not you have a 'TT' supply.

Identify your supply type.

As you can see, for a 'TT' install, you should have all circuits protected by an RCD of some sort, and others by a more sensitive RCD on the split load board. I reccomend a 100ma RCD before the CU, protecting lighting, water heater, oven etc., and a 30ma RCD protecting all socket circuits and nonessential fixed appliances, and shower, and outdoor circuits.

The other supply types: I reccomend you RCD protect socket circuits, and nonessential fixed appliances, the shower, and anything going outside with a 30ma RCD. The latter one is required, and all sockets that could possibly be used to supply something used outside must be RCD protected. Don't protect the lighting circuits, or alarm circuits or the immersion with the RCD.

 

[securespark]

S/L boards are used in most refurbs/ rewires these days as a convenient solution to the problem of giving rcd protection to several circuits.

They have a main isolator (usually 100A) which isolates the whole unit, both the non-protected side and the protected side) and then an RCD unit that protects only a given number of ways.

The RCD "looks" for earth faults and if it detects one, then it will isolate the supply in a very short time (varies according to mfr). 30mA is the current at which it is agreed injury can ocur, so that it the cut-off point, above which an rcd will trip.

The following circuits are usually included in rcd protection:

Rings (esp ground floor)

Showers

Anything powering any equipment used outdoors (shed garage etc...)

The following are wired to the unprotected side of the CU, as these circuits need to remain on in the event of an RCD tripping fault.

Lighting

Burglar Alarms

Smoke Alarms

Some wire Fridges/Freezers seperate so they are unaffected by tripping.


Whether the following circuits are rcd protected or not seems to be down the individual spark or the age of the appliance sometimes:

Immersion Heater

Cooker

 

[phykell]

Thanks for all the replies - much appreciated

Currently (no pun intended - or did I use that one already?), I'm looking at doing my kitchen. I have a 10 way CU with the following MCBs:

Shower 45A
Cooker 45A
Power 32A
Lighting 6A
Alarm 6A - and it's also on an FCU
HiFi 32A - some sort of hi-fi nut owned the house previously
Garage 45A

The garage circuit leads to another CU with the following:

Power 32A
Lighting 6A

I was planning to run my kitchen's power and lighting circuits off the garage circuit (not the oven/hob though) as you may remember from a previous thread.

However, I don't have any RCD protection at the moment and I now fully intend to fit RCDs as required. I thought about fitting one to the main CU and to the garage CU as a minimum but now I think I should also replace my CU with a split load one which would then allow me to also split my current power and lighting circuits into separate ones for the upstairs and downstairs. I'm hoping this will be relatively easy (as though *anything* ever is!)...

 

[ban-all-sheds]

Yo - you do not want lighting or fridge/freezer on RCD.

You may find you don't want the cooker on it either.

Is "alarm" burglar or fire? AFAIK you must not have fire alarms on RCD circuits.

 

[phykell]

Yo - you do not want lighting or fridge/freezer on RCD. You may find you don't want the cooker on it either. Is "alarm" burglar or fire? AFAIK you must not have fire alarms on RCD circuits.

Good points!

It's a burglar alarm and I won't have the cooker on the garage's RCD circuit but the kitchen sockets and lighting would be if I went ahead with my plan!

I just wish I knew how difficult it will be to separate the upstairs and downstairs lighting and power circuits. I guess it's just down to where the upstairs cable return meets the downstairs, assuming that such a thing is possible. The wiring may of course run from room to room, vertically meaning it would be very difficult to separate the circuits!