Sizing a Circuit Breaker

Diversity factor - Wikipedia, the free encyclopedia

Start here. Then get some text books on the subject and learn how to perform the calculations yourself, in case you need to do this when you don't have a PC handy.

If the machine is 130kW, it will draw power of 130kW when running won't it? The diversity here may mean that it runs only 35% of the time maybe? not logical though.

However, if it ever runs at 130kW power, the Circuit Breaker will have to be sized to that only, since a smaller CB will nuisance trip.

If there are multiple machines which total 130kW, and only a third of them run at any time, the 35% diversity factor makes sense.

regards,

kvsridhar

Diversity factor is used when someone is calculating for a large installations and distribution which include so many individual equipment,especially in large domestic installations.

It is expected that all the loads will not be used at thesame time,so it will not be necessary using oversized switching or protective equipment for that installation,but only that size of equipment which can conveniently handle the very loads that are in use at any given time.This will save u cost and proper protection of yr installation.This is what is known as diversity.Pls read yr textbooks on electrical installation and u will get a better understanding.

For yr cct breaker size,calculate the total sum of yr installed loads in amps,multiply it by yr diversty factor and record yr value.If yr value is say 615.51Amps,select a closer breaker range in the market say 630Amps ABB make.

But it seems u hv a small workshop with a few installed machines or motors,here u may not need to apply diversity factor,but to do yr normal overcurrent or short cct protection calculation to get the right sizing of yr protection breaker for yr wkshop.

Patrick Whowha

The diversity factor is always greater than 1.0, where as you have referred as 0.35. Refer any standard electrical engg. text book. The full load current at a p.f of 0.8, will be 245.5 amps for 135 KW.

You have not given the motor load details, care to be taken for the higher KW motor, since starting current issue will come in to picture. The circuit breaker should be capable of handling this transient state till it reaches normal current.

45.5 KW breaker is not sufficient and selection is not correct, the current for 45.5 KW is 82.7 Amps where as for 130 KW as stated by you, the full load current is 245.5 Amps, and no way sufficient since kick load and short circuit for 1 second is not taken care for this 45.5 KW.

You consider diversity factor of 2.0 and the current rating will be 490.9 amps which will take care for all transients

Further the short circuit current to with stand for one second is also to be considered, and which ever higher rating comes, follow that.

Dhayanandhan.S