SERIES RATING

[Toros]

Hi
We are remodeling an commercial space for new upcoming tenant, a medical / dental office.

Existing service -to -remain is 200A 120/240V, 1 ph. with fuse -main.
we have new sub panels , new breakers in different location.

we going to change existing fuses to current limiting, type "J" ones
with 100 k AIC and series rate with down stream new breakers (all from Siemens).

is this acceptable to plan checkers of the city of LA ???

Thank you

 

[petersonra]

Hi
We are remodeling an commercial space for new upcoming tenant, a medical / dental office.

Existing service -to -remain is 200A 120/240V, 1 ph. with fuse -main.
we have new sub panels , new breakers in different location.

we going to change existing fuses to current limiting, type "J" ones
with 100 k AIC and series rate with down stream new breakers (all from Siemens).

is this acceptable to plan checkers of the city of LA ???

Thank you

you have to know what the available short circuit current is at the new panels first. the engineer should have put this on the drawings.

generally class J fuses are by themselves 200 kAIC.

The resultant series rating when you put the fuses in series with the new panels is something that has to be tested by UL and will be found somewhere in the manufacturer's literature. Then all you have to do is make sure the new series rated system rating exceeds the available short circuit current.

 

[wbdvt]

Siemens publishes a table of series connected short circuit ratings for their mccbs. They also list branch breakers with a main being a J type fuse. As long as you are using the breakers in the chart which have been tested with a Type J fuse you should be ok. The lowest rating on the chart is 65kA. Don't forget to label that it is Series Rated.

 

[Carultch]

Siemens publishes a table of series connected short circuit ratings for their mccbs. They also list branch breakers with a main being a J type fuse. As long as you are using the breakers in the chart which have been tested with a Type J fuse you should be ok. The lowest rating on the chart is 65kA. Don't forget to label that it is Series Rated.

Does Siemens have an equivalent list, for series ratings of their breakers with their unfused disconnects? If so, please assist me in finding it.

 

[Smart $]

Does Siemens have an equivalent list, for series ratings of their breakers with their unfused disconnects? If so, please assist me in finding it.

I'm don't believe you'll find a unfused switch with CB series rating listing.

FWIW here's the main-branch and fuse-branch listing:
https://extranet.w3.siemens.com/us/...s/SIE_TA_MoldedCircuitBreakersFullWebsite.pdf

 

[don_resqcapt19]

Does Siemens have an equivalent list, for series ratings of their breakers with their unfused disconnects? If so, please assist me in finding it.

How could you have a series rating with an unfused disconnect? Series ratings are only used with OCPDs connected in series.

 

[GoldDigger]

How could you have a series rating with an unfused disconnect? Series ratings are only used with OCPDs connected in series.

What term would you rather use to describe one SCCR in conjunction with type J fuses instead of two AICs?

 

[Carultch]

How could you have a series rating with an unfused disconnect? Series ratings are only used with OCPDs connected in series.

We had this discussion in another thread:
http://forums.mikeholt.com/showthread.php?t=174824

It is very non-intuitive that OCPDs would affect the SCCR rating of an unfused disconnect in the first place. I would expect that it would have one rating fits all uses, and given any OCPD upstream, it would be safe.

Apparently disconnects require a fuse in the circuit, to get any SCCR rating above a default 10 kA. It doesn't make sense for it to be this low on any device larger than 100A. And suddenly the addition of a fuse, either upstream, downstream or integrated, gives a SCCR rating of 200 kA depending on the class of the fuse.

I see that Square D allows certain breakers to improve the SCCR Rating of their unfused disconnects to match that of the corresponding breaker. And I'm trying to see if Siemens has an equivalent table.

Page 28 of the following catalog:
http://static.schneider-electric.us/docs/Electrical Distribution/Safety Switches/3100CT0901.pdf

 

[petersonra]

What term would you rather use to describe one SCCR in conjunction with type J fuses instead of two AICs?

A tested combination?

The idea is the same but generally such a combination is not referred to as "series rated". In any case no switch has an AIC rating at all. Only an OCPD can have an AIC rating.

As best I can tell unfused switches are all 5kVA SCCR. if you want to use a switch where the available SCC exceeds 5kVA you have to fuse it. All of the manufacturers I have looked at have some kind of information available to tell you what the SCCR of the switch is with certain fuses.

Personally, I have started using molded case switches where I suspect or know that the available SCC exceeds 5kA. Usually more cost effective starting at 100 or 200 A frame sizes.

 

[don_resqcapt19]

We had this discussion in another thread:
http://forums.mikeholt.com/showthread.php?t=174824

It is very non-intuitive that OCPDs would affect the SCCR rating of an unfused disconnect in the first place. I would expect that it would have one rating fits all uses, and given any OCPD upstream, it would be safe.

Apparently disconnects require a fuse in the circuit, to get any SCCR rating above a default 10 kA. It doesn't make sense for it to be this low on any device larger than 100A. And suddenly the addition of a fuse, either upstream, downstream or integrated, gives a SCCR rating of 200 kA depending on the class of the fuse.

I see that Square D allows certain breakers to improve the SCCR Rating of their unfused disconnects to match that of the corresponding breaker. And I'm trying to see if Siemens has an equivalent table.

Page 28 of the following catalog:
http://static.schneider-electric.us/docs/Electrical Distribution/Safety Switches/3100CT0901.pdf

I don't see any of the combinations used with unfused disconnects as being a "series rated" combination. I understand that the SCCR rating of some non-OCPD devices is changed by being in series with a specific OCPD, but I don't see that as being "series rated" as used in 240.86.

In my opinion the term "series rated" as used in the NEC only applies to a downstream circuit breaker used in a circuit that can supply more current than the AIC rating of that breaker, where that lower rated breaker is protected by a specific OCPD installed up stream of the lower rated breaker.

 

[Carultch]

I don't see any of the combinations used with unfused disconnects as being a "series rated" combination. I understand that the SCCR rating of some non-OCPD devices is changed by being in series with a specific OCPD, but I don't see that as being "series rated" as used in 240.86.

In my opinion the term "series rated" as used in the NEC only applies to a downstream circuit breaker used in a circuit that can supply more current than the AIC rating of that breaker, where that lower rated breaker is protected by a specific OCPD installed up stream of the lower rated breaker.

Let me put it this way. Is there any documentation that would say that their unfused switches are safe when a higher than 10 kA fault current is present, provided that it is in series with a specific breaker product line? That's what I mean by "series rated", even though there probably is a better term for this.

 

[don_resqcapt19]

Let me put it this way. Is there any documentation that would say that their unfused switches are safe when a higher than 10 kA fault current is present, provided that it is in series with a specific breaker product line? That's what I mean by "series rated", even though there probably is a better term for this.

Maybe part of the listing process, but I really don't know.

 

[fmtjfw]

A tested combination?

The idea is the same but generally such a combination is not referred to as "series rated". In any case no switch has an AIC rating at all. Only an OCPD can have an AIC rating.

As best I can tell unfused switches are all 5kVA SCCR. if you want to use a switch where the available SCC exceeds 5kVA you have to fuse it. All of the manufacturers I have looked at have some kind of information available to tell you what the SCCR of the switch is with certain fuses.

Personally, I have started using molded case switches where I suspect or know that the available SCC exceeds 5kA. Usually more cost effective starting at 100 or 200 A frame sizes.

This is a problem when unfused disconnects are placed before the meter, especially in applications of 480V self-contained meters. Local POCO requires the switch, but none are rated for available fault current.

 

[electrofelon]

I'm don't believe you'll find a unfused switch with CB series rating listing.

I believe that is correct. As I mentioned in the thread in the PV forum about this topic, I saw a statement in some square D literature that said they have "not been evaluated with circuit breakers". Perhaps different for another manufacturer, but I doubt it.

How could you have a series rating with an unfused disconnect? Series ratings are only used with OCPDs connected in series.

I have been uncertain what to call it. Knowing that "series rating" is technically not the correct term for this situation, I usually put it in quotes to signify abnormal or non-literal usage.

 

[jim dungar]

It just struck me that the question is "can there be a series combination rating between protective devices and unfused disconnects?" - This answer is yes. Ratings with fuse combinations are quite common and easy to achieve, breaker combinations are usually only by manufacturer and even then often with just a few breakers.

Series combination ratings with non-fused disconnects as the higher rated 'protecting' device are unlikely, if not impossible, to exist.