Demand Factor 'v' Diversity Factor - which is your preferred method

[esparks]

I thought I had better add to welchyboy's post.

The 1.8 factor is not applied to the connected load of the fluorescent luminaires, it is applied to the protection device. It is applied to the circuit protection device to ensure that the circuit breaker will not trip when the lights are switched on.

Also as another poster has indicated the connected load is not 30 x 2 x 58w. You need to account for control gear losses, which can be in the region of between 5% to 10% of the lamp rating. It's best to take the manufacturers details for an accurate total luminaire watts.

 

[GT1]

Forgive me if I'm in incorrect but my OSG is in the van and I'm on my second glass of red, thus can't be ars*d to go get it.
But I noticed that OSG didn't give any diversity for RFC's. ?
So 32amps straight into the total demand figure.
Or am I talking rubbish again.?
hic..

 

[malcolmsanford]

Forgive me if I'm in incorrect but my OSG is in the van and I'm on my second glass of red, thus can't be ars*d to go get it.
But I noticed that OSG didn't give any diversity for RFC's. ?
So 32amps straight into the total demand figure.
Or am I talking rubbish again.?
hic..

It does 2a sockets in table A1 on page 110, it asks for us to assume 0.5 amps at each point. So 10 2amp sockets = 5amps.

It does not give any diversity for 5amp or 15amp sockets and it then refers us to Table H7 where we are given a recommended number of BS 1363 sockets in certain areas, but just for homes.

Diversity for sockets is virtually impossible to advise on. You could have 2 identical houses in one a single person and in the other a family of 5 with 2 teenagers, so the demand will be so diverse.

Bottom line really is we know from experience that though a RFC is recommended to have a 32amp protection device, I would lay my pension if 95% of RFC in use today in British homes, draws at any one time 12-15 amps.

I'm sure that within 10-15 years there will be a major overhaul on RFC and how they are used. Certainly for domestic, and may even be for industrial/commercial though with High protective conductor currents, especially in offices, I would think RFC in 4mm is going to become more prevalent.

I always have used the old DNO method for diversity. Add your protection device up and then multiply by 0.4 for domestic, 0.5-6 for commercial and 0.8 for industrial. Never let me down yet.

 

[GT1]

So yes. Like I said, no diversity is given for a "standard" domestic RFC.

I appreciate what your saying about the old rule of thumb method, and I've used it myself quite successfully. However it's something of a blunt instrument. There's a thread elsewhere with someone asking for help with max demand figure on a new build. It has 3 RFC's !
So the method will give 38amps for those alone. I totally agree with you that most RFC's rarely come anywhere near their full capacity.
So in the above example I would be reducing the demand below the figure that the .4 of the total gives.
To the OP of this thread I think the short and tall of it is that the current situation has come about due a combination that the "old rule" allows a significant amount of spare capacity and the fact that most modern appliances consume less energy now than before, thus increasing the margin.

As an experiment (when I bought my first clamp meter) I went round my house and turned every appliance on the house I could find.
Washing machine
Kettle
Oven
Micro
Tv
Dryer
Etc etc
The max demand I measured at the tails was about 42 amps...

The electric shower mind... Pulled 38amps on its own..!!!!

 

[HandySparks]

As an experiment (when I bought my first clamp meter) I went round my house and turned every appliance on the house I could find.
...
The max demand I measured at the tails was about 42 amps...

The electric shower mind... Pulled 38amps on its own..!!!!

By way of contrast, I did the same thing when I bought my current clamp meter and got up to 65A without adding the dishwasher and clothes washing machine, which I recon could add about 10A each if heating. So 85A max.

We have gas CH, gas hob and no electric shower. From memory, loads included: 1x fan heater, 4x PCs, TVs, HiFi, double oven, tumble dryer, toaster, microwave, iron, shower pump, immersion heater, all lights, all the kids electric gadgets, etc. Anything I could find was plugged in. Ordinary 4 bed house, but I was trying quite hard.

The average load is about 18kWh per day, which is only 3.2A.

 

[GT1]

Haha. You wouldn't want to be pulling that amount of load every day
You'd need another mortgage...!

 

[just add water sparks]

By way of contrast, I did the same thing when I bought my current clamp meter and got up to 65A without adding the dishwasher and clothes washing machine, which I recon could add about 10A each if heating. So 85A max.

We have gas CH, gas hob and no electric shower. From memory, loads included: 1x fan heater, 4x PCs, TVs, HiFi, double oven, tumble dryer, toaster, microwave, iron, shower pump, immersion heater, all lights, all the kids electric gadgets, etc. Anything I could find was plugged in. Ordinary 4 bed house, but I was trying quite hard.

The average load is about 18kWh per day, which is only 3.2A.

is my maths bad ???? should it not be 7.8 amps????

 

[Welchyboy]

I know I am a bit late commenting but for information only.

1/. I would not put 30x58W Twin Fluorescents on one circuit. The maximum circuit protection for lighting would normally be 16 Amp or 10 Amps.

2./ Therefore the normal lighting connected load for a 16 Amp circuit would be around 8 Amps, for a 10 Amp circuit the connected load would be 5 to 6 .

The lighting was split over 5x 10a type C mcb's

I was aiming at calculating a figure for the maximum demand as a whole not for one lighting circuit.

 

[HandySparks]

is my maths bad ???? should it not be 7.8 amps????

It's your maths (I think).

18kWh per day, average.
Divide by 24h: = 18/24 kWh per hour = 0.75kW
Divide by nominal supply voltage: = 0.75kW/230V = 3.2A average.

 

[Guitarist]

I know that I have mentioned this before, but the instructor on my 17th ed course was talking to a power network design guy not long ago, and he said that when they work out demand for new housing estates they allow 12A per house as an average.