Selective Coordination Realistic?

[don_resqcapt19]

For systems with OCPDs in that size range, the only real way to comply with the selective coordination requirements is to use fuses and not breakers.....again, Bussmann wrote these rules.

 

[paulengr]

The fact that the 20's and 40's won't coordinate makes having the 40A breaker on the load side of the ATS even worse.

If there is any short circuit on any 20A LS branch, there is a very good chance the 40A on the load side of the ATS will also trip, which will completely disconnect the LS panel.

The generator will never get a chance to do its job or to provide power to the LS branch. There will be an open circuit breaker right in the way.

Panels on the load side of ATS's should not have main breakers if it can be avoided. If it can't be avoided, they should be coordinated so they never trip before the upstream breakers.

So it’s a pure sub panel, MLO?

 

[mbrooke]

For systems with OCPDs in that size range, the only real way to comply with the selective coordination requirements is to use fuses and not breakers.....again, Bussmann wrote these rules.

Question is, does Bussmann have ground to stand on?

 

[don_resqcapt19]

Question is, does Bussmann have ground to stand on?

They made a very strong case that selective coordination for Article 700 and 701 systems is serious safety issue. In the event of a fault on those systems, the system must limit the outage as much as possible and selective coordination accomplishes that.

 

[steve66]

So it’s a pure sub panel, MLO?

If it were my design, both LS and DP-ES would be MLO.

If someone insisted on a local disconnect in LS, I'd probably put in a 100A main breaker and make sure the entire curve was to the right of both 40A upstream breakers.

Of course we would also have to fix the issue Don is referring to with the branch breakers not coordinating. So there are actually a couple of different problems with the one line as shown.