Feeder Size

[Alwayslearningelec]

If I have a 800A 277/480 panel fedding a 277/480 225A panel. What do you base the feeder size off of? The 225A rating? Thanks.

 

[Dennis Alwon]

What size load do you anticipate. Do you want 225 amps. If so, then use T. 310.16. Just because the panel is rated 225 does not mean you have to run wire rated 225 amps.

 

[raider1]

I agree with Dennis, the feeder should be sized off the calculated load and not necessarily the maximum ampacity rating of the panelboard.

Chris

 

[augie47]

Probably just show my dumbness here, but I'm unclear. Do you have an overcurrent device in the 800 amp panel supplying a 225 amp panel. If so what size OCP ?

 

[Alwayslearningelec]

Here is the schedule

Here is the schedule

What size load do you anticipate. Do you want 225 amps. If so, then use T. 310.16. Just because the panel is rated 225 does not mean you have to run wire rated 225 amps.

How do you calculate the load....I assume based on what that panel(attached) will be feeding.

 

[Dennis Alwon]

How do you calculate the load....I assume based on what that panel(attached) will be feeding.

Absolutely -- but you may want to leave a little extra for expansion.

 

[Alwayslearningelec]

Here we go

Here we go

Absolutely -- but you may want to leave a little extra for expansion.

I apologize. Here is the other schedule and it shows a 3p 200 frame 150 trip to feed the other 225A panel. So I assume it should be sized for 150. What is the frame/trip exactly. The frame is like the housing???? Thanks.

 

[Dennis Alwon]

I would guess, not sure, I don't work with this type of equipment, that the frame is the style of breaker and the trip is the amperage but I have never seen anything referred to in that way. Hopefully someone else will help out.

 

[ksmith846]

I apologize. Here is the other schedule and it shows a 3p 200 frame 150 trip to feed the other 225A panel. So I assume it should be sized for 150. What is the frame/trip exactly. The frame is like the housing???? Thanks.

Yes you follow what the Engineer of Record put on your plans. You should have a riser diagram depicting the wire and conduit size from your main panel to the sub panel. You are not responsible for the calculation in this case. Don't you have a complete set of "E" drawings?

 

[mwslo]

Feeder Size

I apologize. Here is the other schedule and it shows a 3p 200 frame 150 trip to feed the other 225A panel. So I assume it should be sized for 150. What is the frame/trip exactly. The frame is like the housing???? Thanks.

Yes, the frame is like the housing. The feeder needs to be sized per the trip unit. If you need more than the 150A, some breakers have an adjustable trip unit that can be changed out.

 

[Alwayslearningelec]

Yes you follow what the Engineer of Record put on your plans. You should have a riser diagram depicting the wire and conduit size from your main panel to the sub panel. You are not responsible for the calculation in this case. Don't you have a complete set of "E" drawings?

Yes, I know that but is was not on there hence the reason for the question. But you are correct, usually it is on the riser/one-line or the wire soze will be give on the schedule.