Main Switches

[GerryB]

Do fused discos, back fed breakers work both ways? I know power would have to go both ways if they are closed, but will they open on overcurrent or a short on the solar side? Probably a dumb question.Also trying to remember the terminology for a backfed breaker going both ways, thanks. I thought the were called something specific.

 

[chris kennedy]

A fused safety switch with line and load reversed will leave the fuses energized in the open position.

 

[jaggedben]

Do fused discos, back fed breakers work both ways? I know power would have to go both ways if they are closed, but will they open on overcurrent or a short on the solar side? Probably a dumb question.

If there's an AC short on the solar side of the fuse or breaker then fault current from the utility will still open the breaker or fuse. From this point of view, it is not necessary for them to work 'both ways'. Looking at it differently, they do work both ways in the sense that if there was too much current from an inverter then the fuse or breaker would also open. But if properly sized and installed that would never happen.

(One issue to be aware of on larger systems is that ground fault protection (GFP) on a feeder or service does not work both ways, and there are restrictions on connecting to feeders that have it. See 705.32.)

Also trying to remember the terminology for a backfed breaker going both ways, thanks. I thought the were called something specific.

Not that I can think of.

 

[kwired]

Do fused discos, back fed breakers work both ways? I know power would have to go both ways if they are closed, but will they open on overcurrent or a short on the solar side? Probably a dumb question.Also trying to remember the terminology for a backfed breaker going both ways, thanks. I thought the were called something specific.

They respond to overcurrent no matter which way it is "flowing".

As has already been mentioned some breakers have a definite line and load side because of things like ground fault protection or other accessories, and a fused safety switch would leave the fuseholders hot if you didn't connect the supply to the "line" terminals.

Solar equipment that backfeeds into the utility typically needs to sense incoming utility voltage or it doesn't produce any "output", so those can be used without creating such problems.

If you had a fault on the "solar side" it would still trip the overcurrent device if the fault ends up drawing high level of current through the device, like say you had two conductors fault to one another - because they are connected to the utility supply fault current will flow from utility source through the fuse/breaker to the fault location and back on the other conductor involved.

 

[ggunn]

Do fused discos, back fed breakers work both ways? I know power would have to go both ways if they are closed, but will they open on overcurrent or a short on the solar side? Probably a dumb question.Also trying to remember the terminology for a backfed breaker going both ways, thanks. I thought the were called something specific.

OCPD operates without regard to the direction of current flow, but an inverter is incapable of causing an overcurrent event if the conductors and OCPD are specified correctly.

 

[GerryB]

Thanks guys for those responses, very helpful.