Service Disconnect to Panel

[quantum]

This is a hypothetical question, not an actual installation.

If I have a 200A Service and a 200A Service Disconnect and I want to feed a 100A panel from this Service Disconnect. Does the feeder cable between the Service Disconnect and the 100A Panels Main Breaker need to be rated for 200A (like the disconnect), 100A (like the panels main breaker), or do I need to fuse down the service disconnect to 100A's first?

 

[iwire]

This is a hypothetical question, not an actual installation.

If I have a 200A Service and a 200A Service Disconnect and I want to feed a 100A panel from this Service Disconnect. Does the feeder cable between the Service Disconnect and the 100A Panels Main Breaker need to be rated for 200A (like the disconnect), 100A (like the panels main breaker), or do I need to fuse down the service disconnect to 100A's first?

In general the conductors would be required to be 200 amp rated however you might be able to use one of the feeder tap rules found in 240.21 so that you could run 100 amp conductors to the 100 amp panel.

 

[quantum]

This is a hypothetical question, not an actual installation.

If I have a 200A Service and a 200A Service Disconnect and I want to feed a 100A panel from this Service Disconnect. Does the feeder cable between the Service Disconnect and the 100A Panels Main Breaker need to be rated for 200A (like the disconnect), 100A (like the panels main breaker), or do I need to fuse down the service disconnect to 100A's first?

Side question, if I have a 200A service drop going to a Service Disconnect with 200A fuses, can I fuse it down to 100A or 60A if I am feeding a device outside of the footages for tap rules?

Another way to ask this, if your service is 200A can I have a disconnect rated for 200A with smaller fuses installed?

 

[iwire]

Side question, if I have a 200A service drop going to a Service Disconnect with 200A fuses, can I fuse it down to 100A or 60A if I am feeding a device outside of the footages for tap rules?

Another way to ask this, if your service is 200A can I have a disconnect rated for 200A with smaller fuses installed?

Sure but a smart inspector would want to see the load calculations that support the fuses you choose.

 

[quantum]

Side question, if I have a 200A service drop going to a Service Disconnect with 200A fuses, can I fuse it down to 100A or 60A if I am feeding a device outside of the footages for tap rules?

Another way to ask this, if your service is 200A can I have a disconnect rated for 200A with smaller fuses installed?

A final question if you don't mind. As for the feeder between the service disconnect and the panel, which OCPD is actually protecting the feeder? Is it the fuses on the disconnect or the main breaker in the panel it is running to, or to both?

 

[don_resqcapt19]

A final question if you don't mind. As for the feeder between the service disconnect and the panel, which OCPD is actually protecting the feeder? Is it the fuses on the disconnect or the main breaker in the panel it is running to, or to both?

The line side OCPD is providing the short circuit and ground fault protection for the conductors, and the load side device, if smaller, will provide overload protection for the conductors.

 

[wwhitney]

A final question if you don't mind. As for the feeder between the service disconnect and the panel, which OCPD is actually protecting the feeder? Is it the fuses on the disconnect or the main breaker in the panel it is running to, or to both?

See 240.21. Generally conductors needed to protected by properly sized OCPD at their point of supply. The tap rules in 240.21 are an exception, where the OCPD providing overload protection is permitted to be downstream of the point of supply, when additional conditions are met.

Cheers, Wayne

 

[kwired]

Side question, if I have a 200A service drop going to a Service Disconnect with 200A fuses, can I fuse it down to 100A or 60A if I am feeding a device outside of the footages for tap rules?

Another way to ask this, if your service is 200A can I have a disconnect rated for 200A with smaller fuses installed?

If you had a really long service drop or lateral you may oversize the conductors for voltage drop reasons, you probably would still call it a 100 or 60 amp service even though the supply conductor "base ampacity" is more then that. Something to think about - though this is not a branch circuit, branch circuit ratings are based on overcurrent device setting and not the conductor size.

A final question if you don't mind. As for the feeder between the service disconnect and the panel, which OCPD is actually protecting the feeder? Is it the fuses on the disconnect or the main breaker in the panel it is running to, or to both?

As mentioned the supply side provides short circuit and ground fault protection, the load side provided overload protection. This is called a feeder tap conductor, a true feeder has overcurrent protection on the supply side that doesn't exceed allowed ampacity of the conductor.