maximum demand

[jonnyboy1]

Hi guys having been out of college for 4 years some of my knowledge was left there I think

Looking to do a few maximum demand calc's but I'm insure where to start. I know all about maximum demand and diversity, just the calculation and formula I'm lacking.

Commercial property ze = 0.055
Amb temp 25 degrees V = 400/230v.

I have various motors for car ramps etc maximum demand needs to be apied. 12 x 0.5 3 phase induction motors PF = 0.8 with 95% efficiency.

How do I work this out? Is it

(0.5 x 12 x 0.8) divided by 400v then square root of 3 the answer??

Then how do I add the efficiency into that.

I'm working away from home and don't have any access to my books

 

[telectrix]

very unlikely that more than 1 or 2 motors will be running at the same time. where's the 12 and the 0.5 come from?

 

[jonnyboy1]

12 0.5kw motors mate

 

[telectrix]

i'd allow 20A at most, allowing for diversity.

 

[Knobhead]

100% FLC for the largest motor + 80% of the second + 60% of the rest.

Another way of looking at it. How many people work there and how many buttons can they press at the same time?

 

[jonnyboy1]

It's an project assessment which I'm starting. To complete the approved grading. I have to work out the maximum demand of this plus other circuits. So I can then determine main cable and switch disconnector size.

I will need to show how I got to these figures rather than giving a figure of 20 amps.

It's more the formula/equation I'm looking for as once I have that I know what im doing.

Thanks for all help to date much appreciated

 

[Knobhead]

Look in the OSG

 

[wade88]

It's more answer to your homework your looking for really

 

[Engineer54]

Follow the BGB, and it's guides if this is to conform to BS7671. It'll be totally wrong mind, but in this case you need to follow the laid out procedures i'm afraid!! ...lol!!

 

[jonnyboy1]

Osg is in Scotland I'm in London haha

Not really answers to homework wade was only asking for an equation!!

I will wait untill I get home to get started on this where I'll have all the books to sort me out

Cheers fellas

 

[Knobhead]

Follow the BGB, and it's guides if this is to conform to BS7671. It'll be totally wrong mind, but in this case you need to follow the laid out procedures i'm afraid!! ...lol!!

I was so tempted to say that but thought better of it