2 fuses and branch breakers series rating

[Tainted]

I have a circuit that will feed a MLO panelboard with branch breakers. The circuit goes like this:

400 amp fuses (200kAIC) -> 200 amp fuses (200kAIC) -> MLO panel with 20 amp branch breakers (10kAIC)

Must the 20 amp branch breakers be series rated with both 400 amp and 200 amp fuses? Must there be a triple series rating or can it just be series rated with the 200 amp fuses only?

 

[JoeStillman]

Just the 200 will do.

 

[jim dungar]

You do not need a triple rating if your breakers are listed with the 200A fuses.

 

[JoeStillman]

I think in this case you can be series rated with either one, but I know of no method where you get a rating from both at once.

 

[jim dungar]

I think in this case you can be series rated with either one, but I know of no method where you get a rating from both at once.

I have seen triple device ratings used on multi-metering equipment, like Square D's EZM family.

 

[electrofelon]

Eaton says this in this document: https://www.eaton.com/content/dam/e...ries-rating-information-manual-1c96944h02.pdf

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

now granted they do say "breaker", but I believe that applies to fuses also.

FWIW, it is highly unlikely there will be a series rating between a 400 fuse and a 10KAIC breaker. The ONLY fuse to 10KIAIC breaker rating Siemens has is for a class T, max 200A. Also keep in mind, going up to 22KAIC branches GREATLY increases the series combinations available. Another Siemens example as I am most familiar with their products, the largest main/feeder breaker that will series rate with a 10K branch is 250A. But go up to a 22KAIC branch and you can rate to a 1200 amp main/feeder breaker or as high as a 6,000 with a class L fuse.

 

[Tainted]

now granted they do say "breaker", but I believe that applies to fuses also.

So for example suppose I have overcurrent protection A, B, and C. Available fault current is 120kA

What eaton is saying is that breaker/fuse B needs to be sized at 100% or more of the available fault and that A and C are then allowed to series rate together?

 

[electrofelon]

So for example suppose I have overcurrent protection A, B, and C. Available fault current is 120kA

What eaton is saying is that breaker/fuse B needs to be sized at 100% or more of the available fault and that A and C are then allowed to series rate together?

correct, a fully rated device can go ahead or in between the two devices that have a series rating.

 

[Tainted]

correct, a fully rated device can go ahead or in between the two devices that have a series rating.

If I have all A, B, and C breaker at different AIC ratings. C has to be series rated with A and B, but what about B being series rated with A?

 

[jim dungar]

If I have all A, B, and C breaker at different AIC ratings. C has to be series rated with A and B, but what about B being series rated with A?

Not if B is fully rated.
If B is not fully rated, you cannot also use the A to C series rating. This would require a triple series rating.

 

[Tainted]

Not if B is fully rated.
If B is not fully rated, you cannot also use the A to C series rating. This would require a triple series rating.

If C is series rated with A and B
and B is series rated with A

Does that make it a triple series rating? or you cannot do it that way?

 

[electrofelon]

If I have all A, B, and C breaker at different AIC ratings. C has to be series rated with A and B, but what about B being series rated with A?

For OCPD's A B and C we would have the following options:
1. All three are fully rated for the AFC at their respective locations
2. IF A and B are fully rated, C could be series rated with either A or B (or both but thats not required) .
3. If only A is fully rated, you would need a triple rating OR B and C could be the exact same type

There is maybe a 4th option, from that Eaton publication. I have to think about it a bit more though:

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]

There is maybe a 4th option, from that Eaton publication. I have to think about it a bit more though:

The wording from Eaton is a bit confusing and I have no idea what the 4th option is unless I see an example

 

[jim dungar]

Option 4 is not using a B-C series rating. Effectively it is using using two independent series combinations.

 

[electrofelon]

If C is series rated with A and B
and B is series rated with A

Does that make it a triple series rating? or you cannot do it that way?

Say AFC is 65K everywhere (for simplicity). OCPD's A B C from main to branch. Ratings of individual devices are: A is 65KAIC, B is 42 KAIC, C is 10 KAIC. Say A and B have a series rating, and B and C have a series rating. You CANNOT combine these two rating into a make your own triple rating, because note the B-C rating is for B seeing 42 KAIC max, in other words it is assumed to be fully rated, but it is in fact seeing more than 42 KAIC.

 

[Tainted]

Say AFC is 65K everywhere (for simplicity). OCPD's A B C from main to branch. Ratings of individual devices are: A is 65KAIC, B is 42 KAIC, C is 10 KAIC. Say A and B have a series rating, and B and C have a series rating. You CANNOT combine these two rating into a make your own triple rating, because note the B-C rating is for B seeing 42 KAIC max, in other words it is assumed to be fully rated, but it is in fact seeing more than 42 KAIC.

So in other words, there is no way to make your own triple ratings and that the manufacturer needs to provide the info?

 

[electrofelon]

The wording from Eaton is a bit confusing and I have no idea what the 4th option is unless I see an example

Option 4 is not using a B-C series rating. Effectively it Is using using two independent series combinations.

Ok let me try:

Say AFC is 65K everywhere (for simplicity). OCPD's A B C from main to branch. Ratings of individual devices are: A is 65KAIC, B is 42 KAIC, C is 22 KAIC. Say A and B have a series rating, and A and C have a series rating. ......I get stuck on the "same interrupting level or higher" part. What is the interrupting level?

 

[Tainted]

Ok let me try:

Say AFC is 65K everywhere (for simplicity). OCPD's A B C from main to branch. Ratings of individual devices are: A is 65KAIC, B is 42 KAIC, C is 22 KAIC. Say A and B have a series rating, and A and C have a series rating. ......I get stuck on the "same interrupting level or higher" part. What is the interrupting level?

You're not alone, I got stuck there too

 

[jim dungar]

Ok let me try:

Say AFC is 65K everywhere (for simplicity). OCPD's A B C from main to branch. Ratings of individual devices are: A is 65KAIC, B is 42 KAIC, C is 22 KAIC. Say A and B have a series rating, and A and C have a series rating. ......I get stuck on the "same interrupting level or higher" part. What is the interrupting level?

If the A-C rating is at least equal to the A-B value then the three devices can be in series.

For example
If A-B = 42kA with 41kA available
Then if A-C = 46kA, the three devices can be in series
But if A-C = 40kA, the three breakers cannot be in series.

 

[Tainted]

If the A-C rating is at least equal to the A-B value then the three devices can be in series.

For example
If A-B = 42kA with 41kA available
Then if A-C = 46kA, the three devices can be in series
But if A-C = 40kA, the three breakers cannot be in series.

I still don't get it. Maybe it's the wording