mutiply or divide

[stafelectric@yahoo.com]

If I had a total load of 200amp's and i ran it at 100%=200amp's and used a 200amp panel 120/208 three phase and divide 200 by 3 giving me 66.6 amp's per phase,but i'm using 3/0 thhn but the 75 degree colum that's good for 200 amp's per phase in the 200 panel. Don't this seem like over kill for a total connected load of 200 amp's? Do you think there is a alturnitve?

 

[jwr570]

A 3 phase 200 amp panel has 200 amps on each phase, so you have to use 3/O.

 

[John Paul]

Multiply not divide

Multiply not divide

The wiring supplying the panel is sized for the panel. The wiring supplying your load is sized per the load.

A 200A load run at 100% has 200A on all three phases unless there's more information you need to tell us.

The 200A load being fed from a 200A panel is not right. Overcurrent protection for the load should be sized at 125% of the load.

125% x 200A = 250A

 

[Dennis Alwon]

When you say total load that means that each phase is drawing 200 amps. If each phase is only drawing 66 amps then that's another story.

 

[raider1]

The 200A load being fed from a 200A panel is not right. Overcurrent protection for the load should be sized at 125% of the load.

125% x 200A = 250A

Welcome to the forum.

The branch circuit overcurrent device or feeder overcurrent device is sized on 100% of the non-continuous load plus 125% of the continuous load so unless the load is all continuous you don't need to always take 125% of the load to size the OCPD.

Chris

 

[John Paul]

Welcome to the forum.

The branch circuit overcurrent device or feeder overcurrent device is sized on 100% of the non-continuous load plus 125% of the continuous load so unless the load is all continuous you don't need to always take 125% of the load to size the OCPD.

Chris

Thanks for the welcome and you're technically right-on, I appreciate the clarification.

Great forum by the way. I'm very familiar with forums of a religious nature. This is a wonderful discovery for me and am enjoying the various discussions. There's not many people out there who speak EE or NEC.

 

[stafelectric@yahoo.com]

yes,ofcorses commercial 200amps

 

[stafelectric@yahoo.com]

why?IT's all non-continus

 

[stafelectric@yahoo.com]

total as in 200amp's total on the panel

 

[daleuger]

You're reading a little too much into this. Like said before 200A means 200A on each phase. If you're installing a 200 A panel according to table 310.16 you will still need a 3/0 copper for a 200A OCPD even if each phase was actually reading 66.6A and not your incorrect assumption based on 200A divided by 3 phases.

You didn't mention if this is new construction or an existing panel you are replacing. Have you done a load calc on everything fed from the panel? Perhaps a smaller OCPD and smaller wire is an option to be explored. If it's an existing panel why you would want to DOWNGRADE is beyond me but I"m just saying.

 

[brian john]

If the total connected load is indeed 66 amps (per phase) NOT 200 amps, then you could reduce the feeder and panel, over current protection and feeder sizes to accommodate the 66 amp load.