Series rating

[binwork91]

I want to confirm something relate to series rating.
For example, in 480/277 3P system, There is upstream fuse A (200kaic), it feeds panelboard P (65Kaic fully rate), it has main breaker B and branch breaker C. The calculate fault current at panelboard P is 80kA. After I check manufacture series rate table, I found out B and C can series with fuse A up to 100kaic in the series rate table.

Question: in this case, can I say Panelboard P is 100Kaic series rate? Can branch breaker C skip main breaker B to series rate with fuse A? Is the panelboard P good at this case?

 

[jim dungar]

Question: in this case, can I say Panelboard P is 100Kaic series rate? Can branch breaker C skip main breaker B to series rate with fuse A? Is the panelboard P good at this case?

You can not cascade series ratings. Because of the main breaker B, you cannot use the fuse A and branch breaker C combination.

 

[binwork91]

You can not cascade series ratings. Because of the main breaker B, you cannot use the fuse A and branch breaker C combination.

see below picture or attached PDF. They are Square D and Eaton's document.

Original, my opinion is breaker C can not series with fuse A. Only main breaker B can series rate with fuse A. Therefore, my suggestion is change main breaker B to 100Kaic, and branch breaker C have to series with main breaker B up to 100Kaic. as picture 1 (square D)
Or Panelboard P to be 100Kaic fully rate.

However, after I read the second picture (eaton). I feel confuse. Did I misunderstand it? it said "Breakers A, B, and C are in series respectively from
main to branch." therefore, B and C is not parallel. So it apply to my example.


Square D page 2

Eaton Page 4

 

[jim dungar]

Series rating are generally for two devices in series. It is possible to have multiple devices in series but they must have been specifically tested that way, for example a meter center main in series with an individual apartment main in series with a branch breaker.

 

[binwork91]

Series rating are generally for two devices in series. It is possible to have multiple devices in series but they must have been specifically tested that way, for example a meter center main in series with an individual apartment main in series with a branch breaker.

See picture below. The second highlight paragraph is same as what you explain.

But if you compare both highlight paragraph, you will find out they are two different scenarios.

 

[jim dungar]

Have your specific combination of 3 devices been tested?

 

[electrofelon]

I am not clear on what you have. Can you provide more specifically the actual fault current at each point and the series ratings?

If you have A,B, and C, it is acceptable if B rates with A and also C rates with A. What you CANNOT do is rate B with A, and then rate C to B USING THE INTERRUPTING RATING OF B. (Unless they have a triple rating).

That's just restating the yellow sections you highlighted, not sure if it's any clearer.

 

[binwork91]

Have your specific combination of 3 devices been tested?

I think only tripe rating need to be test. tripe rating is B series rate with A, C series rate with B.
But in my example, it is B series rate with A, C also series rate with A.

 

[binwork91]

I am not clear on what you have. Can you provide more specifically the actual fault current at each point and the series ratings?

If you have A,B, and C, it is acceptable if B rates with A and also C rates with A. What you CANNOT do is rate B with A, and then rate C to B USING THE INTERRUPTING RATING OF B. (Unless they have a triple rating).

That's just restating the yellow sections you highlighted, not sure if it's any clearer.

The calculate fault current at panelboard P is 80kA. it mean B and C have 80kA fault current. A is fuse, it will 200Kaic rate. Let's assume A has 90kA fault current.

Thank you for the explain.

What you CANNOT do is rate B with A, and then rate C to B USING THE INTERRUPTING RATING OF B. (Unless they have a triple rating).

C to B USING THE INTERRUPTING RATING OF B

Do you mean series rating of B?

 

[electrofelon]

The calculate fault current at panelboard P is 80kA. it mean B and C have 80kA fault current. A is fuse, it will 200Kaic rate. Let's assume A has 90kA fault current.

Thank you for the explain.


Do you mean series rating of B?

Yes, both actually.

Let's say I have three devices A,B,C. Let's just say for simplicity actual fault current is 65k at every one. Let's also say AIC of A is 65k, B is 22k, C is 10k. Say B series rates with A, and also C series rates with B. What you CANT DO is "build your own" triple rating. It seems tempting at first because one might think "ok B is fine, and the chart says C with B is fine....." Now if C also rates with A, it is ok.

 

[binwork91]

Yes, both actually.

Let's say I have three devices A,B,C. Let's just say for simplicity actual fault current is 65k at every one. Let's also say AIC of A is 65k, B is 22k, C is 10k. Say B series rates with A, and also C series rates with B. What you CANT DO is "build your own" triple rating. It seems tempting at first because one might think "ok B is fine, and the chart says C with B is fine....." Now if C also rates with A, it is ok.

Thank you for the explanation. it solves my concern.