# 100% Rated Breaker and Feeder



## electricista (Jan 11, 2009)

tkb said:


> I have a job that we will be using a 1200 amp circuit breaker that is rated 100%.
> Do our feeder conductors need to be rated at 1200 amps or 125% of 1200 amps for continuous duty?


If your calculated load is 1200 amps and the loads are all continuous duty then I would say yes you need to add 125%


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## tkb (Jan 21, 2009)

electricista said:


> If your calculated load is 1200 amps and the loads are all continuous duty then I would say yes you need to add 125%


That is what I thought, but my engineer seems to think that 1200 amps of conductor is good without upsizing.


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## electricista (Jan 11, 2009)

tkb said:


> That is what I thought, but my engineer seems to think that 1200 amps of conductor is good without upsizing.


What is the feeder supplying? A panel or a piece of equipment? Is the load actually 1200 amps?


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## william1978 (Sep 21, 2008)

electricista said:


> What is the feeder supplying? A panel or a piece of equipment? Is the load actually 1200 amps?


 I was thinking the same thing need a little more info.


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## tkb (Jan 21, 2009)

This is a feeder for a 750kVA UPS for a data center and we want full load capability.


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## lectricboy (Mar 11, 2009)

tkb said:


> This is a feeder for a 750kVA UPS for a data center and we want full load capability.


At what voltage?


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## brian john (Mar 11, 2007)

750 kva, 600 kw? Assuming .8pf

or
750 kva 750 kw at 1.0 pf?

First it is BAD practice IMO to operate a UPS at full load.
Second at 480 VAC the load is 902 amps and if it is a .8 pf full load is 772 amps at 480 and 1,666.00 amps at 208 at .8 pf.


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## tkb (Jan 21, 2009)

brian john said:


> 750 kva, 600 kw? Assuming .8pf
> 
> or
> 750 kva 750 kw at 1.0 pf?
> ...


We know that the UPS should not be at 100% but we need the feeder to be rated for it. This is a 480 volt system.

What we have now is a 100% rated 1200 amp breaker with a 1000 amp rating plug feeding a 1200 amp panelboard. This panelboard feeds two 300kVA PDU'. 

The 1000 amp feeder is 3 sets of 4-500 & 2/0g.
We are going to change the 1000 amp rating plug to 1200 amp and add a 4th run to make this a 1200 amp feeder at 125%.

For the ground we will be eliminating the neutral wire and use it for the ground because the 2/0 is sized for the 1000 amp feeder.

The UPS is a Liebert 610 750kVA/600kW 0.8pf, 908 amp nom input, 1135 max input.


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