Main Breaker or Sub Panel Breaker

[Big T Bear]

Hi Ya'll hope you all can help me with this. This is my first post.

Heres my dilema. At work the other day there was a discussion on wether we needed to install a breaker on a sub panel feeding the building. The service is 3 phase 400 amps and the 2 service panels (main lug) is rated at 200 amps each 3 phase. My question is do we need to install a 200 amp breaker at the service panels or do we need to change the service breaker (main breaker)?

 

[Dennis Alwon]

If these panels have more than 6 breakers (combined) to disconnect the structure then you would need either a 400 amp dissco or 2- 200 amp breakers.

If the panels can take a 200 amp breakers then you may install the breakers in the panel. Some panel have main breaker conversion kits (not sure about 3 phase panels).

 

[augie47]

panels

panels

sorry, I'm a lil lost in the post...are these main lug panels fed directly from the service conductors or are there overcurrent devices ahead of them ?

 

[Dennis Alwon]

sorry, I'm a lil lost in the post...are these main lug panels fed directly from the service conductors or are there overcurrent devices aheasd of them ?

I wasn't sure either that's why I responded generally.

 

[Big T Bear]

The 400 amp breaker and service wires are feeding the two 200 amp service panels. The question raised was do we need to install a breaker in the service to protect the service panels.:-?

 

[Big T Bear]

I wasn't sure either that's why I responded generally.

There are only 400 amp breakers at the meter service that feed the main lug service panels.

 

[Big T Bear]

sorry, I'm a lil lost in the post...are these main lug panels fed directly from the service conductors or are there overcurrent devices ahead of them ?

Yes the 2 main lug panels are fed by that 400 amp service breaker. My question is do I need to install 200 amp breakers into the service panels for protection.

 

[don_resqcapt19]

My question is do I need to install 200 amp breakers into the service panels for protection.

You need to protect the panels at or below their rating, so unless the panels are rated at 400 amps you need overcurrent protection on the line side or in the panels. Also the conductors between the 400 amp main and the other panels will need overcurrent protection. It might be possible to use the main in the subpanels to provide the required feeder overcurrent protection. 240.21(B)
Don

 

[infinity]

So what you have is a 400 main service disconnect which feeds 2-200 amp MLO panels. The conductors between the 400 amp OCPD and the two 200 amp panels are feeders. Since the two panels are only rated for 200 amps they will require a 200 amp OCPD to protect them. The feeders could be rated for 200 amps if they are installed under the provisions of the 25' tap rule. If not then each 200 amp panel would require 400 amp conductors from the 400 amp service disconnect.

 

[Big T Bear]

Thanks guys your help is greatly appreciated.