2 fuses and branch breakers series rating

[Tainted]

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

So does this mean what electrofelon said above your comment is false?

He said "Like Jim said, I think it's just two single series ratings across three devices."

Meaning 3 overcurrent protections can be used together as long as

B series rate with A
and C series rate with A

You said that you cannot cascade series rating, but isn't the example I gave above cascading?

 

[jim dungar]

So does this mean what electrofelon said above your comment is false?

He said "Like Jim said, I think it's just two single series ratings across three devices."

Meaning 3 overcurrent protections can be used together as long as

B series rate with A
and C series rate with A

You said that you cannot cascade series rating, but isn't the example I gave above cascading?

In this case A is being used to protect B. Two breakers with a series rating. End of story.
In this case A is being used to protect C. Two breakers with a series rating. End of story.

What is not allowed is A protecting B and then B protecting C.

 

[Tainted]

In this case A is being used to protect B. Two breakers with a series rating. End of story.
In this case A is being used to protect C. Two breakers with a series rating. End of story.

What is not allowed is A protecting B and then B protecting C.

Ok

Why doesn't Siemen's literature say you can do this with 3 overcurrent protections? They only show examples for 2-tier combo overcurrent protections

But suppose the fault occurs downstream of C

Why is it not A and B protecting C?

Why does it have to just be A protecting C in this case?
and also why is it not B protecting C when A is protecting C?

 

[electrofelon]

But suppose the fault occurs downstream of C

Why is it not A and B protecting C?
Why does it have to just be A protecting C in this case?

A-C have a series rating, end of story that's all you need. For a B-C rating, B would need to be fully rated which it is not in our example.

and also why is it not B protecting C when A is protecting C?

See above

 

[electrofelon]

Tey keeping this in mind:

1. The first device in a series rating must be fully rated

2. You can insert a device in between a series rating, but just like any other device, It must either be fully rated, or be series rated.

 

[jim dungar]

Why does it have to just be A protecting C in this case?
and also why is it not B protecting C when A is protecting C?

Because these are the combinations the published literature says has been tested.

 

[jim dungar]

Tey keeping this in mind:

1. The first device in a series rating must be fully rated

2. You can insert a device in between a series rating, but just like any other device, It must either be fully rated, or be series rated.

Actually you may be able to have a device in the middle, per the above Option 4.
It does not appear to be addressed in the Schneider Electric bulletin.

 

[Tainted]

I think I get it now.

But let's say we have this scenerio:

B series rate with A
C series rate with A
C does not series rate with B

A opens before B and C

Is this going to be a concern since B and C are not series rated? Or the fact that A opened first already protects B and C during the fault already? Meaning since A opened first, no fault current passes through B and C at an instance.

 

[Tainted]

I found comments from @GoldDigger and @LarryFine say otherwise. From this post: https://forums.mikeholt.com/threads/3-tier-series-rating.2555731/

They are saying it's not acceptable to have B series rate with A and C series rate with A.

Unless A, B, and C series rate altogether.

 

[jim dungar]

I think I get it now.

But let's say we have this scenerio:

B series rate with A
C series rate with A
C does not series rate with B

A opens before B and C

Is this going to be a concern since B and C are not series rated? Or the fact that A opened first already protects B and C during the fault already? Meaning since A opened first, no fault current passes through B and C at an instance.

Series ratings does not mean the upstream device will 'open' first. Series rating simply says the combination of the devices is adequate for the available fault current.

 

[jim dungar]

They are saying it's not acceptable to have B series rate with A and C series rate with A.

Unless A, B, and C series rate altogether.

It all depends on the particular device manufacturer.
In my experience, most manufacturers do not address a breaker in between the two series rated devices, therefore it is not allowed.

In this thread we have specifically been discussing 'Option 4' in the document you referenced. The Options in that document may not be applicable to other manufacturers.

 

[electrofelon]

It all depends on the particular device manufacturer.
In my experience, most manufacturers do not address a breaker in between the two series rated devices, therefore it is not allowed.

In this thread we have specifically been discussing 'Option 4' in the document you referenced. The Options in that document may not be applicable to other manufacturers.

It seems like, logically they would have to specifically say no ocpds allowed between series rated devices, and barring such a statement there would be no restriction?

 

[jim dungar]

It seems like, logically they would have to specifically say no ocpds allowed between series rated devices, and barring such a statement there would be no restriction?

Not necessarily.

Did you read the information from Schneider Electric in post 40? Every table is shown with only two devices immediately in series.

But the Eaton document, in post 6, says:
Any FULLY RATED breaker can be applied upstream, downstream, or in the middle of any of the series ratings stated in the tables.

What does your manufacturer's literature say?

 

[Tainted]

Eaton says:

"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"

What's the point of saying "at the same interrupting level (or higher)."?

Should it be written like this?:

"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 together. It is allowable to use A, B, and C together at the A-B series rating"

The extra wording is making me over think and I just don't know what is meant by interrupting level. Does interrupting level mean interrupting rating?

 

[electrofelon]

Eaton says:

"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"

What's the point of saying "at the same interrupting level (or higher)."?

Should it be written like this?:

"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 together. It is allowable to use A, B, and C together at the A-B series rating"

The extra wording is making me over think and I just don't know what is meant by interrupting level. Does interrupting level mean interrupting rating?

I am still not entirely clear on that wording also. Wayne's theory in post #26 and 28 seems plausible. it accounts for a situation where the max allowable fault current to achieve the series rating is lower than the interrupting rating of the first device. To reiterate, For example devices A and B, A is 65KAIC and B is 22KAIC, the test fails at 65K but passes at say 50K. However I am unable to find an example of this actually being a thing, and the series rating always seems to be the AIC of the first device. If someone can find a counterexample I am all ears. So if that is indeed what is meant by interrupting level, and there are no counter examples, then it appears that part of the wording could be eliminated and be stated as you propose.

 

[Tainted]

Eaton says "Breakers A and C series rate at the same interrupting level (or higher)"

Could it be that Eaton is saying A and C must be fully rated?

 

[electrofelon]

Eaton says "Breakers A and C series rate at the same interrupting level (or higher)"

Could it be that Eaton is saying A and C must be fully rated?

I doubt it, because they say just a few words before "A and C series rate". Then also in that Eaton document the first bullet under "other applications of series ratings" they already state that a fully rated breaker can be added downstream of a series combination.

 

[wwhitney]

Eaton says "Breakers A and C series rate at the same interrupting level (or higher)"

Could it be that Eaton is saying A and C must be fully rated?

This raises a basic question for me. Say you have breakers A, B, C, D, E, F, etc in series. For each breaker location you calculate the AFC and compare it to the breaker's AIC. If the AIC >= AFC for all them (they are all fully rated), great.

But now say D is not fully rated, while the rest are. And say D has a series rating with C that is sufficient for the AFC at D. Does that mean everything is OK? Or can either (a) the presence of breakers A and B upstream of C create additional dynamic impedance that would interfere with the proper operation of the C/D pair, or (b) the presence of D upstream of E, F, G, etc create additional additional dynamic impedance would interfere with the proper operation of E, F, G etc?

If the answer to the last question is no in both cases, then Eaton won't be talking about the case that C is fully rated. Because in that case there's no need to consider C at all, you just have to worry about B and whether it is series rated with A.

Cheers, Wayne

 

[electrofelon]

This raises a basic question for me. Say you have breakers A, B, C, D, E, F, etc in series. For each breaker location you calculate the AFC and compare it to the breaker's AIC. If the AIC >= AFC for all them (they are all fully rated), great.

But now say D is not fully rated, while the rest are. And say D has a series rating with C that is sufficient for the AFC at D.

Going to just stop you there because I have an issue with "is sufficient for the AFC at D". I don't really know what that means. It seems that those words should just be deleted. D is not fully rated so the available fault current at D will exceed its AIC. Ok continue......

Does that mean everything is OK? Or can either (a) the presence of breakers A and B upstream of C create additional dynamic impedance that would interfere with the proper operation of the C/D pair, or (b) the presence of D upstream of E, F, G, etc create additional additional dynamic impedance would interfere with the proper operation of E, F, G etc?

If the answer to the last question is no in both cases, then Eaton won't be talking about the case that C is fully rated. Because in that case there's no need to consider C at all, you just have to worry about B and whether it is series rated with A.

Cheers, Wayne

Joseph Eaton Was very clear that you can insert fully rated devices ahead, in between, or after. Now that said, I have heard it stated that you cannot do this because dynamic impedance can mess up the series rating.... But I think that just must be playing false because why is it okay for eating but not for other brands? It seems like allowing fully rated devices inserted anywhere would be a universally allowed (or not allowed) thing, and that it would be established that you can (or can't) do it. I haven't read over this Schneider document Jim posted (I've been out in the field all day, I'll look at it now) , but he implied that they implied that you cannot do other device insertion.

 

[Tainted]

This raises a basic question for me. Say you have breakers A, B, C, D, E, F, etc in series. For each breaker location you calculate the AFC and compare it to the breaker's AIC. If the AIC >= AFC for all them (they are all fully rated), great.

But now say D is not fully rated, while the rest are. And say D has a series rating with C that is sufficient for the AFC at D. Does that mean everything is OK? Or can either (a) the presence of breakers A and B upstream of C create additional dynamic impedance that would interfere with the proper operation of the C/D pair, or (b) the presence of D upstream of E, F, G, etc create additional additional dynamic impedance would interfere with the proper operation of E, F, G etc?

If the answer to the last question is no in both cases, then Eaton won't be talking about the case that C is fully rated. Because in that case there's no need to consider C at all, you just have to worry about B and whether it is series rated with A.

Cheers, Wayne

If D is the only thing that is not fully rated, then either A, B or C must be series rated with D for this to be ok.

E and F don't matter since they are fully rated downstream of D.

But that brings up more questions... from previous conversations and Eaton's option 4

Is it acceptable to use A, B, C, D, E, F in series in this scenario?:
B rate with A, C rate with A, D rate with A, E rate with A, and F rate with A

B, C, D, E, F don't rate with each other