Question on maximum demand (load)

[Goody]

Hi, the maximum demand (load) in a property is as follows:

(4x32+4x6)0.40 = 60.8 amps and the main fuse rating is 60 amps.

Does this comply, taking tolerance into consideration? What is the tolerance in this kind of situation? Should I ask DNO to upgrade the fuse and the tails? Many thanks!

 

[Sparky Ninja]

You've multiplied the whole installation by 40%? Why is that?
4x6? Does that mean 4 x Light circuits? Do you know the individual circuit demand?

 

[JUD]

The formula is actually 100% current demand of largest circuit + 40% current demand of every other circuit.

In your case it would be..

32A (Largest circuit) + (3 x 32 x 0.4 = 38.4A) + (4 x 6 x 0.4 = 9.6A)

32 + 38.4 + 9.6 = 80A

 

[simpson93]

examples:

6amp lighting circuit -66% of total current demand
i=p/v
6 lamps at 100w=600w
600w/230=2.6amps
2.6amps = 100% 2.6/100 = 0.026= 1% 0.026x66
= 1.71 amps

20 amp genaral socket = no diversity
=20 amps

32amp rfc= 100% of largest point of utilisation and then 40% of current demand on any additional rfc
=32 amps

40 amp cooker = take 10 amps away and then 30% of whats left +10 amps
40-10 =30
30x0.3=9
10=9=19amps

maximum demand=
1.71a+20a+32a+19a= 72.71amps

 

[sparks_114]

Maximum demand calculations are bit of a gray area, the formulas outlined above are recognised and found in the IEE books but also note that "The use of other methods of determining maximum demand is not precluded where specified by a competent person" (Guidance Note 1, Selection and Erection). If you (as a competent person, well versed in the aspects of maximum demand and know what kind of maximum current can be used at any one time) can calculate and alternative method with good reasons then the figure you come out with can also be used. Usually your proof of competency is the old 2400 which is now 2391-2. If anyone has anything to add or correct me I'll be happy to hear them out. Cheers.

 

[JUD]

32amp rfc= 100% of largest point of utilisation and then 40% of current demand on any additional rfc
=32 amps

Not quite right.

Socket outlets -- 100% current demand of largest point of utilisation and then 40% current demand of every other point of utilisation

Largest point of utilisation being 13A and then 5.2A (13 x 0.4) for every other point of utilisation.

 

[IQ Electrical]

Maximum demand calculations are bit of a gray area, the formulas outlined above are recognised and found in the IEE books but also note that "The use of other methods of determining maximum demand is not precluded where specified by a competent person" (Guidance Note 1, Selection and Erection). If you (as a competent person, well versed in the aspects of maximum demand and know what kind of maximum current can be used at any one time) can calculate and alternative method with good reasons then the figure you come out with can also be used. Usually your proof of competency is the old 2400 which is now 2391-2. If anyone has anything to add or correct me I'll be happy to hear them out. Cheers.

I agree with the other methods of determining maximum demand but don't look upon proof of competency as being one particular qualification-it's a combination of qualifications and experience.

In this case, if it's an existing installation, a better assessment of maximum demand could be made just by talking to the client regarding use of the installation.

 

[Superspark23]

Ive done the 2392 course and we were told to simply add up each breaker and that number is the maxium demand for the installation, if its an 3phase board you record the highest one. We were shown this in the regs but i cant find it.

 

[telectrix]

Ive done the 2392 course and we were told to simply add up each breaker and that number is the maxium demand for the installation, if its an 3phase board you record the highest one. We were shown this in the regs but i cant find it.

if you did that, there'd be thousands of houses wanting 200A supplies.

 

[Engineer54]

Ive done the 2392 course and we were told to simply add up each breaker and that number is the maxium demand for the installation, if its an 3phase board you record the highest one. We were shown this in the regs but i cant find it.

That's because it's not in there!!!

 

[Kay]

if you did that, there'd be thousands of houses wanting 200A supplies.

Yes but that is maximum demand without diversity or design current/actual circuit loading taken into account.