Series rating main fuse "poles"

Tainted

Tainted

Senior Member
Location
New York
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Engineer (PE)
I am looking at the series rating chart. I am confused by the "poles" column I drew in red:

Why does some fuse say 2,3 poles while others just have 3?

HQS and QRH2 are both 2 pole breakers yet it says 2 and 2,3 respectfully

Let's say I wanna series rate HQS breaker below with class T fuses. It only says "2" for poles as shown in chart below. Does this mean upstream fuse must only have 2 fuses and that I cannot use 3-phase upstream?



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LarryFine said:
That's my take. Only certain combinations are tested and/or approved.
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It's weird because look at the 2-pole QRH2 breakers. It says 2,3 poles for fuse. Why would the 3 fuses play any role in this combination? if a short happens downstream of a 2-pole QRH2 fuse, it will only affect 2 fuses, not 3
 
Tainted said:
It's weird because look at the 2-pole QRH2 breakers. It says 2,3 poles for fuse. Why would the 3 fuses play any role in this combination? if a short happens downstream of a 2-pole QRH2 fuse, it will only affect 2 fuses, not 3
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The 2, 3 refer to the number of fuses in the system feeding the breaker.
There are differences in how breakers operate (i. e internal gas exhaust paths) based on if the fault is single phase or three phase.

Do not try to figure out the rational behind these series ratings. There is a reason they are determined by actual testing.
 
jim dungar said:
The 2, 3 refer to the number of fuses in the system feeding the breaker.
There are differences in how breakers operate (i. e internal gas exhaust paths) based on if the fault is single phase or three phase.

Do not try to figure out the rational behind these series ratings. There is a reason they are determined by actual testing.
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I get that, but how can a 3 phase fault occur downstream of a 2-pole breaker it makes no sense. That is what the chart is implying. 2-pole QRH2 breaker tested with 2 and 3 pole fuse? Makes no sense.
 
Tainted said:
I get that, but how can a 3 phase fault occur downstream of a 2-pole breaker it makes no sense. That is what the chart is implying. 2-pole QRH2 breaker tested with 2 and 3 pole fuse? Makes no sense.
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The chart is telling you it is possible to use 1 or 2-pole breakers on single phase or three phase systems. You must also consider the L-G voltages shown in the third column. Your QRH2 breaker rating is limited to a 240V single phase circuit even if the system is fed by a 3-pole main switch.
 
jim dungar said:
The chart is telling you it is possible to use 1 or 2-pole breakers on single phase or three phase systems. You must also consider the L-G voltages shown in the third column. Your QRH2 breaker rating is limited to a 240V single phase circuit even if the system is fed by a 3-pole main switch.
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So based on the chart, I cannot use a 3 pole switch with class T fuses to get series rating with HQS breaker?
 
Why does it bother you there? Series rating charts are manufacturers' public posting of the configurations that were tested by them and proved that series-rating protection were successful on those specific configurations, nothing more/ nothing less. If you would insist on using your own arrangement, the manufacturers cannot guarantee that the upstream protection can protect the downstream OCPD / fuse or vice versa.
 
topgone said:
If you would insist on using your own arrangement, the manufacturers cannot guarantee that the upstream protection can protect the downstream OCPD / fuse or vice versa.
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This is exactly why it bothers me. I cannot use a chart if I have no idea what the intent was with information on the sheets that are never explained. One can misuse the chart because the user may have interpreted the wrong way. There are manufacturer's such as Eaton who make their series rating charts more simple than Siemens
 
Tainted said:
This is exactly why it bothers me. I cannot use a chart if I have no idea what the intent was with information on the sheets that are never explained. One can misuse the chart because the user may have interpreted the wrong way. There are manufacturer's such as Eaton who make their series rating charts more simple than Siemens
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Yeah I agree, they need to provide better instructions of using these charts. Eaton seems to be the only one that has a decent document explaining how to use the chart and applications. Everyone else seems to dump you the info and say good luck, figure it out
 
electrofelon said:
Yeah I agree, they need to provide better instructions of using these charts. Eaton seems to be the only one that has a decent document explaining how to use the chart and applications. Everyone else seems to dump you the info and say good luck, figure it out
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It maybe because there are lawyers in the corporate ladder who have the power to tweak company bulletin wordings and cover their company asses! By being vague in their publications the company has provided (or not provided) definite verbiage so users can't sue them when things get damaged! What good is large sales if you'll be hit with lots of claims? The workaround for the users is just a phone call away I guess.
 
Tainted said:
How come no other series rating chart from other manufacturer's tell you whether the main fuses must be 1,2, or 3 pole?

Also this other Siemens series rating chart that does not tell you whether the fuses must be 1,2 or 3 pole.

https://support.industry.siemens.com/cs/attachments/109810907/SIE_TA_CircuitBreakerSeriesRatings.pdf
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Fuses do not have multiple poles; what I assumed from looking at the chart is that it is saying that some fuses are only to be used with 2 pole switches while others can be used in 1, 2, or 3 pole switches, etc. Is that not correct?
 
ggunn said:
Fuses do not have multiple poles; what I assumed from looking at the chart is that it is saying that some fuses are only to be used with 2 pole switches while others can be used in 1, 2, or 3 pole switches, etc. Is that not correct?
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You just proved my point. These manufacturers need to give us instructions on how to interpret these sheets, otherwise design will be a dangerous and expensive mistake.
 
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