Series rating main fuse "poles"

[Tainted]

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?

 

[LarryFine]

Does this mean upstream fuse must only have 2 fuses and that I cannot use 3-phase upstream?

That's my take. Only certain combinations are tested and/or approved.

 

[Tainted]

That's my take. Only certain combinations are tested and/or approved.

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

 

[jim dungar]

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

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.

 

[Tainted]

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.

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.

 

[jim dungar]

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.

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.

 

[petersonra]

The chart also is telling you for some breakers you have to use 300 Volt rated fuses, while some breakers can use any class T fuse.

 

[Tainted]

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.

So based on the chart, I cannot use a 3 pole switch with class T fuses to get series rating with HQS breaker?