Maximum demand

[blenki]

Hi , when filling in the Maximum demand on the EIC do you guys work out everything based on diversity or do you add up all the MCB's then multiply by 0.66. I keep hearing different versions ,some people just put down the cut out fuse value

 

[ezzzekiel]

heard of 40% being used

 

[Spudnik]

The maximum demand will usually only be the fuse value as it cat pull anymore than that!

To be honest, i dont think there is a strict requirement to be spot on.

I know some sparks put down the biggest MCB size.

 

[kung]

Hi Blenki
What i do is turn everything off in the house and use a clamp meter on meter-cu line and turn everything on in the kitchen (cooker/hob/toaster/mike/lights/all sockets plug in something and switch on ) this should give you the total load of the property.
Regards
Kung.
norm find its about 54amps for a 3 bed house.

 

[blenki]

Thanks lads , ive got part p assessment coming up and i want to make sure i can answer him if he asks , il probably work out all the diversitys of each circuit then add them up. just wondered if you lads who have been in the trade a while have a quicker way of doing it

 

[sixfingers]

In General with domestic small house about 35 meduim 45 large 55 or there abouts!

 

[blenki]

problem i got is with 2x32a ring circuits (100% of first ring then 40% of second)
1x32a boiler circuit (assuming 100% diversity)
1x32a cooker circuit (cooker rated at 30a before diversity)
2x6a light circuits (around 8x 100w lamps on each circuit)


I GET JUST OVER 100A IF IM DOING IT RIGHT

 

[suburban]

problem i got is with 2x32a ring circuits (100% of first ring then 40% of second)
1x32a boiler circuit (assuming 100% diversity)
1x32a cooker circuit (cooker rated at 30a before diversity)
2x6a light circuits (around 8x 100w lamps on each circuit)


I GET JUST OVER 100A IF IM DOING IT RIGHT

If the boiler circuit is only doing a boiler,pump,controls could that be reduced to 16a or less.

 

[blenki]

yes your right suburban , i dont know what the boiler is so ive just allowed for the worst case scenario

 

[ezzzekiel]

x 0.4 = 56amps

 

[blenki]

what you get when you apply diversity on each circuit ezzzekiel

 

[pushrod]

I was under the impression that you should take account of diversity when working out maximum demand.(tin hat on). If you apply diversity to the cooker and 2nd ring your total is still less than 80A even if there is a socket on the cooker point.

 

[blenki]

hi pushrod , how did you work that one out mate

 

[pushrod]

Hi Blenki
cooker is first 10A then 30% of the rest of it (plus 5A if there is a socket outlet on the cookerpoint). Lighting is 66% of max. Ring is 100% of first one and 40% of second.

you said cooker was 30A so that is 10A plus 30% of 20 = 16A ( or 21A if there is a socket outlet)
first ring 100% = 32A
2nd ring is 40% of 32A = 12.8A
Lighting 800w/230V=3.5A x2=7A X 0.66% = 5A

total demand = 66A ( or 71A if there is a socket outlet on cooker)

(rounded figures up)

 

[blenki]

hi pushrod thats the way i worked it out , but you have missed out the boiler circuit (i allowed for 32a worst case scenario ) as i dont know what the boiler is taking. i cant see it taking 32a so it should be under 100a max demand. Thanks for the reply

 

[pushrod]

sorry didn't notice the boiler - what type is it ? I assume it is not a gas boiler as the current demand to that is tiny. If it is an immersion heater it is probs 3 KW with an approx 13A demand. It would probably be worth looking at it and seeing if you can find a power rating on it. Allowing 32A for it would mean that it was a 7kW+ heater (very unlikely unless it was a shower) You are right that there is no diversity allowed on a water heater.

 

[blenki]

cheers pushrod , got my part p coming up so i want to make sure i get it right . as long as the max demand comes under 100a il be happy

 

[maddfridge]

Hi , when filling in the Maximum demand on the EIC do you guys work out everything based on diversity or do you add up all the MCB's then multiply by 0.66. I keep hearing different versions ,some people just put down the cut out fuse value

hi there

i take it that you are the designer of the installation yes / no ?

Maximum demand is considered at the design stage and as such you should have to hand all the designers calculations for each circuit to be installed to ensure that you meet BS7671

If you are installing and testing etc if you stick to all the books then ok you will meet maximum demand etc.
It is really down to what you have installed at the time and in the design any future use which may take in expansion etc.

looking at each circuit in a common sense way ie lighting will the put a cooker on it ?
ie 32 amp ring final circuit its cold the heating's packed up outcome 15 3 k watt heaters etc.

i think you look at the whole of the installation and make a calculated common sense judgment on what you have and what you may be likely to expect in service use

there is a design guide by the iee electrical installation design guide isbn 978-0-86341-550-0 which give more details etc of maximum demand etc mainly aimed at designers

cheers alll

 

[dazza69]

Hi blenki cooker circuit is first 10A then 30% of the remainder + 5A if its a soket outlet on the switch.