400a switch feeding 50a panel

[Alwayslearningelec]

Is this possible. The drawings say that a 400a switch in the dist. board is fedding a 50a panel. Is this possible and if so why would you have such a large switch feeding a 50a panel? Is the feed sized of that switch or the 50A panel? Thanks a lot.

 

[Mayimbe]

It can be possible if the 400A switch is feeding a couple more of 50 A panels, not just one. If it is just one as you said, I believe something must be wrong. Problems with protection selectivity.

 

[Alwayslearningelec]

It can be possible if the 400A switch is feeding a couple more of 50 A panels, not just one. If it is just one as you said, I believe something must be wrong. Problems with protection selectivity.

Thanks very much Mayimbe. Would the feeder be sized off the switch size or the 50a panel? I am pretty sure it is of the panel.

 

[Mayimbe]

No problem. Yes, the feeder should be sized for the 50 A panel.

 

[zog]

Is this possible. The drawings say that a 400a switch in the dist. board is fedding a 50a panel. Is this possible and if so why would you have such a large switch feeding a 50a panel? Is the feed sized of that switch or the 50A panel? Thanks a lot.

Is this a switch or a breaker? Fused switch?

 

[roger]

Thanks very much Mayimbe. Would the feeder be sized off the switch size or the 50a panel? I am pretty sure it is of the panel.

Are you talking about a 400 amp OCPD in the DB or a fusible switch?

Roger

 

[Alwayslearningelec]

It actually does not say. it only says 400s/400f...the 'F' is for the frame....right?? Thank.

 

[zog]

It actually does not say. it only says 400s/400f...the 'F' is for the frame....right?? Thank.

Sounds like you got that off a print, what is the real info off the device?

 

[Alwayslearningelec]

Sounds like you got that off a print, what is the real info off the device?

I did. There is only a panel schedule for the new panel. Nothing on the extg. switchboard that the new panel is being fed from. Why, is there more info that is needed. It is just an existing feeder to an existing to be removed panel. The existing feeder to now be connected to the new panel. So it has to be cut back/spliced and extended to the new location along with the branch circuits. Also, When this work is being done the switch feeding the existing to be removed panel NEEDS to be shut off obviously, correct. And if it is feeding other panels not in this scope I would assume this should be done on OT so as not to affect other panels/circuits to remain. Cause it is a 400a switch feeding a 50A panel so In assume it is feeding other stuff?? Thanks

 

[zog]

I did. There is only a panel schedule for the new panel. Nothing on the extg. switchboard that the new panel is being fed from. Why, is there more info that is needed. It is just an existing feeder to an existing to be removed panel. The existing feeder to now be connected to the new panel. So it has to be cut back/spliced and extended to the new location along with the branch circuits. Also, When this work is being done the switch feeding the existing to be removed panel NEEDS to be shut off obviously, correct. And if it is feeding other panels not in this scope I would assume this should be done on OT so as not to affect other panels/circuits to remain. Cause it is a 400a switch feeding a 50A panel so In assume it is feeding other stuff?? Thanks

Usually an AF on a print refers to a breaker, not a switch. Just because it has a 400A frame does not mean that is where it will trip. Different CT's and/or trip settings can be used to achieve proper protection of your 50A panel. Or is it really is a switch you can change the fusing.

 

[Alwayslearningelec]

Usually an AF on a print refers to a breaker, not a switch. Just because it has a 400A frame does not mean that is where it will trip. Different CT's and/or trip settings can be used to achieve proper protection of your 50A panel. Or is it really is a switch you can change the fusing.

Zog, why would I change the fusing? If this switch is feeding multiple other panels and I am only concerned with the exisiting feed to a exisiting to be removed 50A panel that will be rerouted to a new 50A panel in approx. the same location there should be no work at the dist board/existing 400a switch feeding that panel mentioned above. Right?

 

[augie47]

Under the 10 ft tap rule {240.21)(B)(1)} you could have a 50 amp panel with #8 feed from a 400 amp feeder

 

[Alwayslearningelec]

Under the 10 ft tap rule {240.21)(B)(1)} you could have a 50 amp panel with #8 feed from a 400 amp feeder

I am reading it now and I am not sure what you mean Augie. Why woundn't I have a #8 feed? That sounds right. Also, reading that 10' tap rule is a bit confusing. Can you sum it up in lamens terms? Thanks Augie.

 

[augie47]

I may not fully understand your situation, but, in general you protect a conductor at it's ampacity.
If you had a breaker of fuse providing 400 amp protection, the 10 ft tap rule would allow you to tap onto the 400 amp feeder with a conductor with an ampacity less than 400 amps if you comply with the tap rules.The 10 rule allows a conductor with 10% of the OCP rating to extend to a overcurrent protective device sized to protect the smaller conductor.

I picture a wireway or j box with 400 amp conductors and one or more 50 amp taps to overcurrent devices.
It is pure conjecture on my part, but I would assume the customer is providing for future load and this would be the 1st of many taps.

 

[Alwayslearningelec]

I may not fully understand your situation, but, in general you protect a conductor at it's ampacity.
If you had a breaker of fuse providing 400 amp protection, the 10 ft tap rule would allow you to tap onto the 400 amp feeder with a conductor with an ampacity less than 400 amps if you comply with the tap rules.The 10 rule allows a conductor with 10% of the OCP rating to extend to a overcurrent protective device sized to protect the smaller conductor.

I picture a wireway or j box with 400 amp conductors and one or more 50 amp taps to overcurrent devices.
It is pure conjecture on my part, but I would assume the customer is providing for future load and this would be the 1st of many taps.

I got it, thanks for the clarification Augie. But like you said there could be #'8 right from the 400a switch to my 50A panel.

 

[augie47]

There might be room for debate so I'd check with your AHJ.
In any event, your length would be limited by the tap rules.

 

[Alwayslearningelec]

There might be room for debate so I'd check with your AHJ.
In any event, your length would be limited by the tap rules.[/QUOTE

Thanks Augie.

 

[Alwayslearningelec]

Is what I mentioned before correct though. Id there is a 400A switch in the dist. board feeding my existing to be replaced 50a panel(with new 50a panel). If that 400a switch is feeding other panels not in my scope I would assume that this work should be done on OT because the 400a switch has to be turned off to do the swap.

Thanks.