Can Someone Check My Diversity Calcs Please?

[ray-bentos]

Can someone please just check over my working & diversity calcs for the following CU change:
Supply is 100amp TNC-S with 25mm tails, 16mm Main earth & 10mm bonding so all good there.
Working from OSG Table A2: Working off number 9 (Standard arrangement of circuits in accordance with Appendix H):
100% of current demand of largest circuit + 40% of current demand of every other circuit. This is based on OSG stating current demand of a final circuit complying with Appendix H is the OCPD rating.

SO:

1x 32amp Cooker
1x 16amp Immersion Heater
1x 6amp Central Heating
1x 6amp Lights (upstairs)
1x 6amp Lights (Downstairs)
1x 6amp Outside Lights
1x 32amp Sockets (Ring)
1x 20amp Sockets (Radial - Utility Room)
1x 45amp Shower

Overall demand of circuit thus: 45+((32+16+6+6+6+6+32+20)x0.4) = 94.6amps

Divided circuits on a dual RCD board as follows:

RCD 1 (63amp):
45amp Shower
6amp Downstairs Lights
16amp Immersion Heater
6amp Central Heating
6amp Outside Lights
45+((6+16+6+6)x0.4) = 58.6amps

RCD 2 (63amp):
32amp Sockets (Ring)
6amp Upstairs Lights
20amp Utility Radial
32amp Cooker
32+((6+20+32)x0.4) = 54.4amps

I know having both sockets circuits on same RCD might be viewed as not ideal but the utility radial is only really sorting out what was originally a spur from the ring feeding 2 double sockets and an outdoor socket at the MCB. Wired in 2.5mm so made into own radial with 20amp breaker?
Does this look OK to you?

 

[telectrix]

swap the immersion and the utility sockets over. otherwise your diversity is a bit pessimistic. bet you'll never see anywhere near 94A. more kike 50A.

 

[ray-bentos]

Better to be pessimistic though?

Referring to the radial, its what OSG appendix H terms A3 radial (2.5mm with 20amp OCPD), section H2.4 spurs only mentions putting spurs on A1 ring & A2 radial circuits.

However in BGB appendix 15 (fig 15B) clearly shows 20A 2.5mm Radial with spurs connected to it, unfused spurs which don't have a one socket limit like on ring circuits.

The outdoor socket is a spur from one of the sockets on this radial, I assume by the BGB this is OK?

 

[telectrix]

a radial does not have spurs. as the circuit cable is 2.5mm and fused at 20A, then any additions are branches and there's no possibility of overloading the cable as with spurs off a RFC.

 

[Farmelectrics]

Your calc look ok to me

 

[alanl]

The only way you'd see 50 Amps being drawn would be if the shower, cooker, immersion and a whole load of appliances were on at the same time.

Have you got a clamp meter? If not, get one and monitor the usage at your own house, you'll be very surprised at how low the current used is - last time I did mine, typical appliances plugged in, TV and comp on etc, it was using less than 1 amp.
Of course you get the slight surge when the freezer/fridge etc kicks in, but our energy use is pretty low in a domestic house unless we are heating water or cooking.

 

[Octopus]

Add up all the breakers and multiply by .33

 

[telectrix]

which gives him approx. 66A. a bit more realistic.

 

[Octopus]

which gives him approx. 66A. a bit more realistic.

or multiply by 0.25 which would give about 42A !