sizing the switch on consumer unit

[GPack]

Just a quick one. When adding up all the MCBs in the consumer unit and applying diversity I work out the design current as 101.5A. This is not a large house. A 10.2kW electric oven, 7.2kWshower, 3kW boiler, ring final circuit, 2 x lighting circuit etc. If it were at the design stage I take it the DNO would have to provide a 125A fuse. Based on the fact that most fuses I see at the cut out are 60A-100A, are the providers using different rules of diversity to the OSG?

 

[albi]

You don't just add up all the total amps on the DB your diversity is applied to each circuit

Allowance for diversity to be applied to an individual household installation, including an individual dwelling in a block

Purpose of final circuit fed from conductors or switchgear to which diversity applies

Diversity factor to be applied to the distribution circuit

Lighting

66 % of the connected lighting load

Heating appliances

The first 10 A of the connected load plus 50 % of the remainder of the connected load

Cooking appliance(s)

The first 10 A of the rated current plus 30 % of the remainder of the rated current in excess of 10 A plus 5 A if a socket-outlet is incorporated in the cooker control unit

Instantaneous water-heaters

100 % F.L.of largest appliance plus 100 % F.L. of 2nd largest appliance plus 25 % full load of remaining appliances

Storage water heaters

No diversity allowable

Floor warming installations

No diversity allowable

Thermal storage space heating

No diversity allowable

Socket-outlets and stationary equipment supplied by a standard arrangement

100 % of current demand of largest socket-outlet circuit plus 40 % of current demand of every other socket-outlet circuit

F.L. full load

 

[ian.settle1]

Just a quick one. When adding up all the MCBs in the consumer unit and applying diversity I work out the design current as 101.5A. This is not a large house. A 10.2kW electric oven, 7.2kWshower, 3kW boiler, ring final circuit, 2 x lighting circuit etc. If it were at the design stage I take it the DNO would have to provide a 125A fuse. Based on the fact that most fuses I see at the cut out are 60A-100A, are the providers using different rules of diversity to the OSG?[/QUOTE]


Suppliers do not work to either the BS7671 or OSG but ESQCR when giving a supply you need to inform them off what your loading is.

 

[GPack]

Thank you for your responses. Yes, I didn't word things to well. I had applied diversity to each of the circuits on the board and added those amounts to come up with the 101A figure. By rights should the main switch on the consumer unit be greater than the usual 100A normally provided or is there a tolerance? I now appreciate the DNO works to the ESQCR. Do you know what rules they apply to establish the size of the Main Fuse? Thankyou for your help.