2 fuses and branch breakers series rating

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Tainted

Tainted

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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 said:
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.
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I have seen triple device ratings used on multi-metering equipment, like Square D's EZM family.
 
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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
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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.
 
electrofelon said:
now granted they do say "breaker", but I believe that applies to fuses also.
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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?
 
Tainted said:
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?
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correct, a fully rated device can go ahead or in between the two devices that have a series rating.
 
electrofelon said:
correct, a fully rated device can go ahead or in between the two devices that have a series rating.
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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?
 
Tainted said:
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?
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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.
 
jim dungar said:
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.
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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?
 
Tainted said:
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?
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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
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Option 4 is not using a B-C series rating. Effectively it is using using two independent series combinations.
 
Tainted said:
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?
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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.
 
electrofelon said:
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.
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So in other words, there is no way to make your own triple ratings and that the manufacturer needs to provide the info?
 
Tainted said:
The wording from Eaton is a bit confusing and I have no idea what the 4th option is unless I see an example
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jim dungar said:
Option 4 is not using a B-C series rating. Effectively it Is using using two independent series combinations.
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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?
 
electrofelon said:
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?
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You're not alone, I got stuck there too
 
electrofelon said:
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?
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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.
 
jim dungar said:
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.
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I still don't get it. Maybe it's the wording
 
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