Full load versus demand factor result

[keynotez]

Hi Engineers, just want to clarify something. I have a computation of Total Full Load Current of 195 Amperes.
My client gives me a demand factor of 0.70, multiplied to my Full Load Current 195 Amperes results to 136.5 Amperes. My decision is to use a 200 Amperes Main Breaker, am I right with that decision? Please help and judge me with my decision. Thank you and more power to all of you! By the way, my client is an Industrial Type Building. Thanks to all!

 

[malcolmsanford]

Where as this demand factor come from ?

 

[Electro-tech]

demand factor: is the ratio of the sum of the maximum demand of a system (or part of a system) to the total connected load on the system (or part of the system) under consideration. Demand factor is always less than one.It essentially acknowledges that not every load is likely to be running at the same time.

 

[telectrix]

so it's just a term for guys who can't spell diversity.

 

[mattmoo1974]

I think malcom is asking where the 0.70 bit comes from Tech, Not what it is!
IE How was this demand figure(diversity) calculated?

 

[mattmoo1974]

Tele ever 1 knows Diversity!

 

[telectrix]

got it. there's 7 of them and 2 are 70% fullsize, ssiimples

 

[mattmoo1974]

Keynotz full load current might not be any where near running current ie Large induction motors/ Banks of lights 1.8 x running current(from memory)
Then the fact that everything mite/wont be all on at the same time(diversity)
And the MCB is there to protect the cable.
Food for thought.

 

[keynotez]

The demand factor 0.70 was given by my client, since loads are not running 24/7 and not at the same time. Diversity factor was not given so I assumed that it is in unity, 1.00....

 

[mattmoo1974]

I personnely would get more info from him ie what its running and you can make a better judgement on MCB sizing etc.

 

[keynotez]

Mattmoo, thanks... but where can I get my running current? From my full load current or from my full load current multiplied by the demand factor? Did I oversized my MCB which is 200 Amperes? Thanks! ^_^

 

[keynotez]

Ok, well then.. I just have to analyze the system using a power analyzer by tomorrow in order to get the running current..thanks again mattmoo...

 

[Electro-tech]

diversity factor ::clap: The ratio of the sum of the individual maximum demands of the subdivisions of the system to the maximum demand of the complete system. Note: Since maximum demand of a system cannot be greater than the sum of the individual demands, the diversity factor will always be equal to or greater than unity.

 

[mattmoo1974]

Just read max load and running current of said equipment. It will be in the spec/Instrutions/ stamped on a plate some where.
And no probelmo

 

[i=p/u]

yes depends on equipment ,will be on the data and if no data its time to role the sleeves up and check. if there is alot of equipment or full building, sytem analyzer is what is needed, id say. which can prove to be really low at times. day/night

 

[malcolmsanford]

Thanks Matt that is what exactly I meant. If your client as given you this factor then that is what you design the installation to, though in a commerical situation a rule of thumb is 0.8 for me.

As Matt as quite rightly said it is dependent on the installation use, an industrial processing plant would be a totally different design say to a manufacturing plant. You have to decide as the designer what diversity/factor you will use, and I'm afraid that is something that can not be taught.

Bottom line if the client wants 70% diversity that is what he gets.

 

[mattmoo1974]

Mattmoo, thanks... but where can I get my running current? From my full load current or from my full load current multiplied by the demand factor? Did I oversized my MCB which is 200 Amperes? Thanks! ^_^

Start up current and run current are 2 diff things. There stamped on the spec plate of the motors
All the information you need should be on the equipment (Fingers crossed)
Your MCB should be ok, Use a type c This will allow for "Inrush current"/Full load current.
Full load on a motor is the current it takes to get the thing spinning up, IE if if needs alot of torque to get something moving.
The current will drop back alot. If the guy giving you the spec is clued up you should nt have any problems.