Is a neutral needed

[Alwayslearningelec]

2000a 480v board feeding a 300kva step down xfrmr that feeds a 800a dist. board. Would there be three phase, neutral and ground to the xfrmr? And what about leaving the xfrmr? I thought a neutral was not needed for the xfrmr thus the reason for the question. Thanks.

 

[bob]

Neutral not needed to the transformer but you do need an EGC. Usually Tr is connected delta on the primary side. As far as the secondary, You need a neutral if there is load is connected phase to neutral. If not then you only need the phases and the EGC.

 

[Alwayslearningelec]

Thanks Bob. Just curious, why is a neutral not needed on the primary side?

Also for a 400a feeder what determines whether you use 500mcm or 600mcm? Thanks again.

How is the secondary feeder size calculated?

 

[jumper]

Thanks Bob. Just curious, why is a neutral not needed on the primary side?

Not needed.

Also for a 400a feeder what determines whether you use 500mcm or 600mcm? Thanks again

.

Calculated load, is it more then 380A?

How is the secondary feeder size calculated?

240.21(C) for protection and 220 calcs for size

 

[Alwayslearningelec]

Not needed.

.

Calculated load, is it more then 380A?



240.21(C) for protection and 220 calcs for size

Thanks jumper...the 400a feeder is feeding a 800a dist panel via a 300kva transformer. What would the calculated load be? The loads the 800A panel is feeding? Thanks.

 

[augie47]

240.21(C) does not allow the provisions of 240.4(B). If you are feeding a 800 amp M/B Panel from a transformer, your conductors have to be rated 800 amps (no "next size up"), normally parallel 600 kcmil Cu

 

[Alwayslearningelec]

240.21(C) does not allow the provisions of 240.4(B). If you are feeding a 800 amp M/B Panel from a transformer, your conductors have to be rated 800 amps (no "next size up"), normally parallel 600 kcmil Cu

Thanks Augie. Question- so when parallel sets terminates in main breaker switchboard do two phases(hots) terminate under each lug?

 

[ActionDave]

... Question- so when parallel sets terminates in main breaker switchboard do two phases(hots) terminate under each lug?

If they are on the same phase they do.

 

[Alwayslearningelec]

If they are on the same phase they do.

Ty

 

[Strathead]

Thanks Bob. Just curious, why is a neutral not needed on the primary side?

Also for a 400a feeder what determines whether you use 500mcm or 600mcm? Thanks again.

How is the secondary feeder size calculated?

For this part of your question I assign you homework. Do and internet search for a delta wye transformer diagram. Remember that physically each delta coil is lined up with one of the wye coils. Electrically they are wired in the configuation shown. That is why a 480v delta to 120/208 wye is actually 3 sets of coils with a 4-1 ratio that are 480 volt to 120 volt coils. While I can't imagine why you woul do this, you could theortically have a Wye Wye transformer. In that case the coils would be 277 volts to 120 volts and you would run the neutral.

 

[Besoeker]

Thanks Bob. Just curious, why is a neutral not needed on the primary side?

If, as Bob has suggested, the primary is connected in delta, there would be nowhere to connect a neutral.

 

[Alwayslearningelec]

For this part of your question I assign you homework. Do and internet search for a delta wye transformer diagram. Remember that physically each delta coil is lined up with one of the wye coils. Electrically they are wired in the configuation shown. That is why a 480v delta to 120/208 wye is actually 3 sets of coils with a 4-1 ratio that are 480 volt to 120 volt coils. While I can't imagine why you woul do this, you could theortically have a Wye Wye transformer. In that case the coils would be 277 volts to 120 volts and you would run the neutral.

Thanks Strat I will....I'll get back to you.

 

[Besoeker]

Thanks Strat I will....I'll get back to you.

Here's one I did earlier. Any help to you?

The delta primary is on the left. As I said, there's nowhere to connect a neutral on the delta.

 

[ActionDave]

Here's one I did earlier. Any help to you?

Your diagram is monochromatic and, as such, is no help to me at all.

 

[Besoeker]

Your diagram is monochromatic and, as such, is no help to me at all.

Squint at it a bit and imagine colours......

 

[iwire]

Thanks jumper...the 400a feeder is feeding a 800a dist panel via a 300kva transformer. What would the calculated load be? The loads the 800A panel is feeding? Thanks.

How the hell would Jumper know the calculated load? :roll:

 

[Alwayslearningelec]

How the hell would Jumper know the calculated load? :roll:

What I meant is what loads are the calculated loads he's referring too? The ones the 800a panel is feeding?

 

[Alwayslearningelec]

Thanks Strat I will....I'll get back to you.

Got it Strat. Thanks


http://www.google.com/search?q=wye+...diagram&ie=UTF-8&oe=UTF-8&hl=en&client=safari