SCCR series rating

[Clay S]

Hi,

I am confused how a fuse that is inside a fused disconnect switch can increase the SCCR rating of the disconnect itself. Based on what i am reading here in this design guide from Eaton it appears as though it doesn't really matter whether the fuse is upstream of the disconnect switch or inside the disconnect switch.

https://www.eaton.com/content/dam/e...ty-switch-general-design-guide-dg008001en.pdf

Page 25

My understanding before seeing this was that for a series rating to be applicable the protective device had to be upstream in the circuit.

Any help in explaining this would be appreciated!

Thanks,
Clay

 

[LionelHutz]

It's all relative to the current the device will withstand as the protection clears. If the disconnect switch part failed before the fuses opened then that'd be a problem that cascades to the upstream protection. But, if it withstands the current until the fuses open then it's fine. If it fails internally then the protection upstream would have to do the protecting.

A breaker couldn't have a SCCR if having the SCCR required it to protect it's internals against failure. That's the job of the upstream protection.