Series rating combination

[Tainted]

I know in some circumstances you cannot combine series ratings.

But what about this scenario, is this an exception:

Fuse A = 300kAIC
Fuse B = 200kAIC
Breaker C = 65kAIC
Breaker D = 65kAIC

Fuse A and B are in series and feed breakers C and D as shown below. Let's pretend breakers C and D are in a standalone panelboard labelled red.

A is series rated with C at 100kAIC
B is series rated with D at 100kAIC
A does not series rate with D
B does not series rate with C

Is it correct to say that the red panelboard is series rated at 100kAIC?

 

[petersonra]

The answer to your question is yes.

 

[don_resqcapt19]

Breakers and fuses are series rated with each other only when part of a tested and published combination.

 

[petersonra]

Breakers and fuses are series rated with each other only when part of a tested and published combination.

While true it does not answer his question. I don't believe there is any prohibition on having multiple fuses in series and still being able to use the series rating of one of the fuses.

 

[wwhitney]

I don't believe there is any prohibition on having multiple fuses in series and still being able to use the series rating of one of the fuses.

So the fuse B does not represent a dynamic impedance that would interfere with the tested series behavior of A with C? That only applies to circuit breakers, not fuses?

Cheers, Wayne

 

[petersonra]

So the fuse B does not represent a dynamic impedance that would interfere with the tested series behavior of A with C? That only applies to circuit breakers, not fuses?

Cheers, Wayne

As best I understand the rules on such things.

 

[Tainted]

So the fuse B does not represent a dynamic impedance that would interfere with the tested series behavior of A with C? That only applies to circuit breakers, not fuses?

Cheers, Wayne

I think only breakers experience dynamic impedance because they have contacts that tend to arc when immediately opened.

With fuses it's quite different, there are no contacts and that the elements within the fuse just burn away

 

[petersonra]

So the fuse B does not represent a dynamic impedance that would interfere with the tested series behavior of A with C? That only applies to circuit breakers, not fuses?

Cheers, Wayne

The diagram shows a feeder. It does not show what is upstream of the feeder. There is some kind of ocpd upstream not shown. Does that negate the series rating?

 

[Tainted]

The diagram shows a feeder. It does not show what is upstream of the feeder. There is some kind of ocpd upstream not shown. Does that negate the series rating?

In this scenario, fuse A is a service fuse

 

[jim dungar]

With fuses it's quite different, there are no contacts and that the elements within the fuse just burn awa

At short circuit values the fuse elements arc enough to met the sand filler.

 

[Tainted]

At short circuit values the fuse elements arc enough to met the sand filler.

I would assume it would be very marginal compared to breakers arcing? Obviously it depends on voltage applied

 

[don_resqcapt19]

While true it does not answer his question. I don't believe there is any prohibition on having multiple fuses in series and still being able to use the series rating of one of the fuses.

It appears to me that the question is to a series rating between the fuse and the breaker.
There is no problem with the use of the fuses in series, and if either of the fuses is part of a listed and tested series combination with the breakers that would be fine, but the OP did not provide any indication of a listed fuse/breaker series combination rating.

 

[electrofelon]

So the fuse B does not represent a dynamic impedance that would interfere with the tested series behavior of A with C? That only applies to circuit breakers, not fuses?

Cheers, Wayne

There is document on applying series ratings by Eaton. And it states the following:

Any FULLY RATED breaker can be applied upstream, downstream, or in the middle of any of the series ratings stated in the tables.

Note it specifically says "breaker". I kind of have a feeling that's just an oversight and wasn't meant to exclude fuses but you never know.

they also state this which I believe covers the OP, but again note the word "breaker":

Breakers A, B, and C are in series respectively from main to branch. Breakers A and B series rate together. Breakers A and C series rate at the same interrupting level (or higher). It is allowable to use A, B, and C together at the A-B series rating.

 

[Tainted]

Breakers A, B, and C are in series respectively from main to branch. Breakers A and B series rate together. Breakers A and C series rate at the same interrupting level (or higher). It is allowable to use A, B, and C together at the A-B series rating.

However in my case, A and B are fully rated at 200kAIC, not series rated together (guess it doesn't matter).

 

[electrofelon]

However in my case, A and B are fully rated, not series rated together (guess it doesn't matter).

I was thinking about it with the Eaton example shifted over so A is your B, B is your C, etc, then per the first quote, a fully rated device in front of everything which doesn't matter (assuming there is actually not a restriction for fuses).

 

[Tainted]

I was thinking about it with the Eaton example shifted over so A is your B, B is your C, etc, then per the first quote, a fully rated device in front of everything which doesn't matter (assuming there is actually not a restriction for fuses).

Eaton's quote: Any FULLY RATED breaker can be applied upstream, downstream, or in the middle of any of the series ratings stated in the tables.

I think maybe this quote above matches my case better.

The fact that in my case both A and B are fully rated, it can be applied to series rating downstream, in my case C and D are downstream of fully rated fuses A and B