Series Rating - Class J / R Fuses

[nda38189]

Hey all,

I'm trying to figure out if my current set-up series rates or not. Per GE's series rating documentation "UL Component Recognized Series-Connected Ratings and CSA Certified Series-Rated Combinations" a GE THQL breaker will series rate with a Class J 400A (or less) fuse at 200kAIC. Currently I have a Class R fuse at 300A which means it does not series rate since it isn't a class J; however, the third note in GE's documentation makes me think otherwise: "3. Lower ampere-rated Class J, T, R, or L fuses may be substituted for listed fuse. Class J fuses may be substituted for Class R fuses, if acceptable for the application."

Does anyone have any experience with this rule and series rating? What would permit the class R fuse in this case to be "acceptable for the application" and make it acceptable to series rate with the GE THQL breakers?

Thanks in advance for any help!!

 

[steve66]

I don't think you have a series rated combination.

From the chart, you can use up to a 200A class R fuse. But not a 300A class R.

I believe (and I could be wrong) that the first note you refer to allows you to use a lower rated fuse of the same class, but doesn't allow substitutions between classes.

The second note about subbing a class J for a class R doesn't apply to your situation, since you have a class R fuse that is larger than 200 amps.

But just for the sake of discussion, say you had a 200A class R fuse. I believe the note would allow you to use a equal or lower rated class J fuse, if there weren't any circumstances that made class J "non-acceptable". In other words, you can use the class J if it meets the needed voltage and current ratings, and any other conceivable ratings, and isn't prohibited by any equipment installation instructions or other listings or similar items. In other words, the note about being "acceptable for the application" is a CYA note.

 

[Jraef]

I don't think you have a series rated combination.

From the chart, you can use up to a 200A class R fuse. But not a 300A class R.

I believe (and I could be wrong) that the first note you refer to allows you to use a lower rated fuse of the same class, but doesn't allow substitutions between classes.

The second note about subbing a class J for a class R doesn't apply to your situation, since you have a class R fuse that is larger than 200 amps.

But just for the sake of discussion, say you had a 200A class R fuse. I believe the note would allow you to use a equal or lower rated class J fuse, if there weren't any circumstances that made class J "non-acceptable". In other words, you can use the class J if it meets the needed voltage and current ratings, and any other conceivable ratings, and isn't prohibited by any equipment installation instructions or other listings or similar items. In other words, the note about being "acceptable for the application" is a CYA note.

I think your interpretation is dead on.

"Lower amperage" refers to the SAME class; i.e. 300A Class J is OK when a 400A Class J was specified.
Substituting Class J works as long as the original class works; i.e. 200A Class J is OK when a 200A Class R is OK.

 

[nda38189]

That's where I was leaning toward - it was just one of those situations where the note was a bit confusing. I will go ahead and recommend they replace with a class J if they want a series rating or else fully rate the panels downstream.

Thanks so much for your responses!!

I think your interpretation is dead on.

"Lower amperage" refers to the SAME class; i.e. 300A Class J is OK when a 400A Class J was specified.
Substituting Class J works as long as the original class works; i.e. 200A Class J is OK when a 200A Class R is OK.