Consumer Unit - Circuit Loading & Allocation

[Pickup]

Hi,

Just bought a 1960's bungalow (2 bed, kitchen, lounge, bathroom, hall. All on one (ground floor level)). House was re-wired about 1992.

The existing consumer unit is a 100 A unit. the circuits are MCB protected and assigned as follows:

Heating 6A
Door Bell 6A
Lights 6A
Water Heater 16A
Ring Main 32A
Ring Main 32A (ie there are 2x 32A MCB's labelled Ring Main)

Total 98A

I'm refurbishing the kitchen and bathroom and intend to replace the 2 "Ring Main" MCBs with RCBOs but I also want to install extractors in the bathroom & kitchen, an electric oven (currently gas) & gas hob and run a supply to the garage.

Can the extractors, oven & hob be run from Fused Connection Units on the ring main or do they need to be separate supplies?

As the total capacity of the Consumer unit is 100A does this mean that tha load capacity of the MCBs added up must be less than 100A or can the total capacity of the MCBs exceed 100A provided the load doesn't exceed 100A ie can I add a 16A MCB for the garage giving a theoretical total of 104A.

Can any of the heating / door bell / water heater circuits be combined with the ring main circuits (ie install FCUs on the ring main to power these items) or can the 2 ring main circuits be combined into 1 to provide the "extra" capacity I need?

Thanks

F

 

[1john]

after applying diversity it should be fine as it is and proposed additions should be fine. Keep as many individual circuits as possible if you can, gives you more versatility and makes things convenient if things go pear shaped.

Also, more than likely, all circuits will need RCD protection if you are trying to comply with regs. is the main bonding and main earth the correct size too>?

 

[ricicle]

Diversity means that not all circuits will be pulling full or near full current at any one time. Sometimes units can be full of mcbs that have a total of 2 or 3 times the rating of the main switch. (imagine your electricity bill if you were pulling 98amps for even 8 hours a day !)

 

[flameport]

The fact the individual MCBs add up to 98A is of no relevance, since there is no way they will all be used at their maximum.

Gas hob and extractors can be connected via FCUs as you suggest.
Some ovens can be, although this depends on the rating.

Separate circuits for a door bell and heating (gas boiler?) are OTT, these could just as easily be supplied by FCUs if you need the space in the CU.

Probably better to keep the 2 rings as they are. Is one of them for the kitchen only?

 

[securespark]

Although it is handy to have the boiler on its own. If the RF RCBO trips, you've still got CH & HW.

 

[Pickup]

Folks,

many thanks for these responses. You've made my life a lot easier!!

F