2 fuses and branch breakers series rating

[electrofelon]

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

I dont get it either. What are the numbers after the = sign?

 

[jim dungar]

I dont get it either. What are the numbers after the = sign?

In my example they are the series u combination short circuit rating in kA.
The letter combinations are the breaker identifiers we have been using in this discussion.

 

[electrofelon]

In my example they are the series u combination short circuit rating in kA.
The letter combinations are the breaker identifiers we have been using in this discussion.

I have never seen series ratings like that. The series rating is always the actual AIC rating of the upstream device. I've never seen, say, an A-B combination where A is a 65KAIC device but you only get an A-B combination when you have 42K available. That's why I don't get this "same interrupting level" thing.

 

[jim dungar]

I have never seen series ratings like that. The series rating is always the actual AIC rating of the upstream device. I've never seen, say, an A-B combination where A is a 65KAIC device but you only get an A-B combination when you have 42K available. That's why I don't get this "same interrupting level" thing.

It was an just an example, you can choose different numbers.

Note the series rating is not an AIC value it is a Series Equipment Rating typicaly expressed in kA.

 

[electrofelon]

It was an just an example, you can choose different numbers.

Note the series rating is not an AIC value it is a Series Equipment Rating typicaly expressed in kA.

Ok I'm still lost. Can we look at this specific example?


Say AFC is 60K everywhere (for simplicity, no conductor impedance). 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.

Let's be very precise and define all the terms, make sure we are all using them correctly.

What exactly is the series rating of A-B? I say it is 65K as that is the max allowed fault current at the terminals of B. Correct?

Now that term used in the Eaton publication, "interrupting level", what is the interrupting level of A-B?

What exactly is the series rating of A-C? I say it is 65K as that is the max allowed fault current at the terminals of C. Correct?

Now what is the "interrupting level" of A-C?

Isn't the interrupting level of both 65k?

 

[wwhitney]

As someone uninitiated, I infer from reading this thread that it is possible that a 65 kAIC breaker followed by say a 22 kAIC breaker has a series rating that is between 22 kAIC and 65 kAIC, not necessarily the full 65 kAIC. That would be what "option 4" is covering.

Cheers, Wayne

 

[electrofelon]

As someone uninitiated, I infer from reading this thread that it is possible that a 65 kAIC breaker followed by say a 22 kAIC breaker has a series rating that is between 22 kAIC and 65 kAIC, not necessarily the full 65 kAIC. That would be what "option 4" is covering.

Cheers, Wayne

Ok, I am just confused because I have never seen that. I am most familiar with Siemens and haven't delved into other manufacturers series rating tables. Maybe that is a thing and I just haven't come across a real world example.

 

[wwhitney]

Ok, I am just confused because I have never seen that. I am most familiar with Siemens and haven't delved into other manufacturers series rating tables. Maybe that is a thing and I just haven't come across a real world example.

I have no idea, but I can imagine that if you're doing some destructive testing, and the 65 kAIC / 22 kAIC combination in my example passes at 45 kA but blows up at 65 kA, it is worth recording that 45 kA is OK rather that just saying that there is no series rating.

Cheers, Wayne

 

[electrofelon]

I have no idea, but I can imagine that if you're doing some destructive testing, and the 65 kAIC / 22 kAIC combination in my example passes at 45 kA but blows up at 65 kA, it is worth recording that 45 kA is OK rather that just saying that there is no series rating.

Cheers, Wayne

Certainly, I guess comes down to how much time and money the manufacturer wants to spend testing these "in between" ratings.

 

[Tainted]

I would literally pay good amount of cash for a program that does series rating for me.

Is there anyway to make a triple series rating with 2 series rated overcurrent protections?

For example lets say I have a 200kAIC fuse, 65kAIC breaker and 22KAIC breaker. How can I make it a triple series rated circuit?

 

[Tainted]

If I have overcurrent protection A, B, and C

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

Does this make it a triple series rating? or you can't really do that? is there any way to make your own series rating.

 

[JoeStillman]

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

Where's the third breaker in a EZM meter center? Does that include the one downstream in the dwelling unit?

 

[jim dungar]

Where's the third breaker in a EZM meter center? Does that include the one downstream in the dwelling unit?

Yes.

 

[jim dungar]

I would literally pay good amount of cash for a program that does series rating for me.

Is there anyway to make a triple series rating with 2 series rated overcurrent protections?

For example lets say I have a 200kAIC fuse, 65kAIC breaker and 22KAIC breaker. How can I make it a triple series rated circuit?

You cannot.
Series ratings are only available from the manufacturer.

 

[electrofelon]

If I have overcurrent protection A, B, and C

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

Does this make it a triple series rating? or you can't really do that? is there any way to make your own series rating.

I would say that is acceptable based on the discussions we have had and the paper by Joseph Eaton. I would NOT call that a triple rating. A triple rating would be where either B is not series rated with A and/or C is not series rated with A.

 

[Tainted]

I would say that is acceptable based on the discussions we have had and the paper by Joseph Eaton. I would NOT call that a triple rating. A triple rating would be where either B is not series rated with A and/or C is not series rated with A.

Hmmm is that the only literature out there that says this is acceptable? Are other manufacturers in agreement? I know Eaton is very credible but I’d like to read it also from other sources for reassurance.

 

[electrofelon]

Hmmm is that the only literature out there that says this is acceptable? Are other manufacturers in agreement? I know Eaton is very credible but I’d like to read it also from other sources for reassurance.

It's odd but no one else seems to have a guide or instructions on applying series ratings.

 

[Tainted]

It's odd but no one else seems to have a guide or instructions on applying series ratings.

I still can't wrap my head around why it would be acceptable to combine 3 devices such that

B series rate with A
and C series rate with A
I mean, why are we not including B being series rated with C?

assuming 200kAIC, 65kAIC, 22kAIC respectfully.

I'm just still extremely baffled by this quote from Eaton "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"

Why is Eaton the only one saying this? This is suspicious to me.

I found a quote from a comment you had a long time ago: https://forums.mikeholt.com/threads/three-100-amp-panels.2551448/

you said "Another option is to rate A-B and A-C as long as A-C has the same (or higher) interrupting level as A-B."

Can you give me an example? I'm seriously desperate to figure this out lol

 

[electrofelon]

I still can't wrap my head around why it would be acceptable to combine 3 devices such that

B series rate with A
and C series rate with A
I mean, why are we not including B being series rated with C?

Like Jim said, I think it's just two single series ratings across three devices. Think about it, if C has a series rating with A, it's all good and there is no need for a rating with B. You don't need a series rating for every permutation.

I think I stated this earlier but here is an example of what you CAN'T do, maybe it will help to revisit it:. Devices A, B, C. A is fully rated, B and C are not so we need some series ratings for those two. We have a series rating for A-B. Now we say " ok now B is good, so I look at the chart again and see that B series rated with C.". But no, B is not fully rated so it's AIC is less than the available fault current, so you can't use that as the first device in a series reading.

 

[jim dungar]

I still can't wrap my head around why it would be acceptable to combine 3 devices such that

B series rate with A
and C series rate with A
I mean, why are we not including B being series rated with C?

assuming 200kAIC, 65kAIC, 22kAIC respectfully.

I'm just still extremely baffled by this quote from Eaton "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"

Why is Eaton the only one saying this? This is suspicious to me.

I found a quote from a comment you had a long time ago: https://forums.mikeholt.com/threads/three-100-amp-panels.2551448/

you said "Another option is to rate A-B and A-C as long as A-C has the same (or higher) interrupting level as A-B."

Can you give me an example? I'm seriously desperate to figure this out lol

You are making this much more complicated than it needs to be. Series ratings have been in existence for 30 years, with minimal changes to the rules and procedures.

The NEC requires the majority of series ratings to be tested.
Every manufacturer has published documentation showing the results of their testing.
Every manufacture says you cannot cascade series ratings in order to have more than two devices in series. Each manufacturer also has a few triple ratings available typically for residential type installations.

Do not look at the AIC rating of the individual devices, look at the device catalog numbers and the amount of available fault current. Specifics matter.

This is from the Schneider Electric publication: https://ckm-content.se.com/ckmContent/sfc/servlet.shepherd/document/download/0691H00000EEJp3QAH

A series-connected rating can be accomplished using a switchboard OCPD (A) and a panelboard main disconnect (B) (two-tier), or using a panelboard main OCPD (B) and a panelboard branch OCPD (C) (two-tier). In order for all OCPDs (A, B, C) to be in a series combination (three-tier), the series combination would have to be marked on the panelboard housing OCPD (C). NOTE:Schneider Electric has three-tier ratings for multi-metering equipment. Multi-metering three-tier series ratings are not addressed in this bulletin. Applicable ratings appear on the appropriate equipment.