I believe it comes from UL 489. Here is a list I got from somewhere:
Panelboards < 10 kA : pf= 0.5, X/R= 1.732, S2P= 1.645, Std: UL 67
10 kA < Panelboards < 20 kA : pf= 0.3, X/R= 3.18, S2P= 1.941, Std: UL 67
Panelboards > 20kA : pf= 0.2, X/R= 4.899, S2P= 2.159, Std: UL 67
Motor Control Centers < 10 kA : pf= 0.5, X/R= 1.732, S2P= 1.645, Std: UL 845
10 kA < Motor Control Centers < 20 kA : pf= 0.3, X/R= 3.18, S2P= 1.941, Std: UL 845
Motor Control Centers > 20kA : pf= 0.2, X/R= 4.899, S2P= 2.159, Std: UL 845
Switchboards < 10 kA : pf= 0.5, X/R= 1.732, S2P= 1.645, Std: UL 891
10 kA < Switchboards < 20 kA : pf= 0.3, X/R= 3.18, S2P= 1.941, Std: UL 891
Switchboards > 20kA : pf= 0.2, X/R= 4.899, S2P= 2.159, Std: UL 891
Transfer Switches < 10 kA : pf= 0.5, X/R= 1.732, S2P= 1.645, Std: UL 1008
10 kA < Transfer Switches < 20 kA : pf= 0.3, X/R= 3.18, S2P= 1.941, Std: UL 1008
Transfer Switches > 20kA : pf= 0.2, X/R= 4.899, S2P= 2.159, Std: UL 1008
Switchgear : pf= 0.15, X/R= 6.591, S2P= 2.292, Std: ANSI C37.50
Molded Case Circuit Breakers < 10 kA : pf= 0.5, X/R= 1.732, S2P= 1.645, Std: UL 489
10 kA < Molded Case Circuit Breakers < 20 kA : pf= 0.3, X/R= 3.18, S2P= 1.941, Std: UL 489
Molded Case Circuit Breakers > 20kA : pf= 0.2, X/R= 4.899, S2P= 2.159, Std: UL 489
Insulated Case Circuit Breakers < 10 kA : pf= 0.5, X/R= 1.732, S2P= 1.645, Std: UL 489
10 kA < Insulated Case Circuit Breakers < 20 kA : pf= 0.3, X/R= 3.18, S2P= 1.941, Std: UL 489
Insulated Case Circuit Breakers > 20kA : pf= 0.2, X/R= 4.899, S2P= 2.159, Std: UL 489
Power Circuit Breakers : pf= 0.15, X/R= 6.591, S2P= 2.292, Std: UL 1066
Power Circuit Breakers (Fused) : pf= 0.2, X/R= 4.899, S2P= 2.159, Std: UL 1066
Fuses < 10 kA : pf= 0.5, X/R= 1.732, S2P= 1.645, Std: UL 248-1
Fuses > 10 kA : pf= 0.2, X/R= 4.899, S2P= 2.159, Std: UL 248-1
HV/MV Switchgear (kA Rating Basis) : pf= 0.0587, X/R= 17, S2P= 2.59, Std: ANSI C37.09-1999
HV/MV Switchgear (MVA Rating Basis) : pf= 0.0665, X/R= 15, S2P= 2.561, Std: ANSI C37.010-1979
MV E2 Motor Starter : pf= 0.0665, X/R= 15, S2P= 2.561, Std: UL 347
HV/MV Power Fuses : pf= 0.0665, X/R= 15, S2P= 2.561, Std: ANSI C37.41
I'd think a fuse would be almost all resistive. Are these lower limits on PF?I believe it comes from UL 489. Here is a list I got from somewhere:
Fuses < 10 kA : pf= 0.5, X/R= 1.732, S2P= 1.645, Std: UL 248-1
These have nothing to due with the construction of the fuse.I'd think a fuse would be almost all resistive. Are these lower limits on PF?
Symmetric to Peak. BTW, the table came from SKM.S2p?
I'm not sure of the specifics but you will notice the conditions get worse for the higher rated breakers since it is assumed they might be exposed to higher asymmetric conditions. The tested pf ranges are supposed to cover most conditions.I'm just curious why they choose the power factors and X/R ratios listed above for the testing rating.
10.1.4.3 Power Factor Considerations
Normally the short-circuit power factor (X/R) of a system need not be considered in applying circuit breakers. This is based on the fact that the power factors on which the ratings of the circuit breakers in this standard have been established amply cover most applications. For unfused circuit breakers this power factor is 15% (X/R ratio of 6.6). For fused circuit breakers the power factor is 20% (X/R ratio of 4.9), which is consistent with the standards established for fuses. The high short-circuit current rating of fused circuit breakers makes the need to consider power factor even more unlikely. There are, however, some specific applications when the available short-circuit current approaches 80% of the circuit breaker short-circuit current rating, which may require additional consideration because of lower shortcircuit power factors. These considerations are as follows:
? Local generation at circuit-breaker voltage in unit sizes greater than 500 kVA
? Gas-filled and dry-type transformers in sizes 1000 kVA and above; all types 2500 kVA and above
? Network systems
? Transformers with impedances higher than those specified in the ANSI C57 series of standards
? Current-limiting reactors at circuit-breaker voltage in source circuits
? Current-limiting busway at circuit-breaker voltage in source circuits
3.40 Circuit-breaker evaluation for X/R ratio or short-circuit power factor
LVPCBs in general are evaluated for short-circuit interrupting capability on a first-halfcycle basis. As indicated, MCCBs can sometimes operate so quickly that they function in a current-limiting mode, which means they operate to limit short-circuit current before the first current peak is reached. As the peak current is a function of the offset of the rms symmetrical current wave, which is in turn a function of the power factor or the X/R ratio of the circuit, the fact that (1) LVPCBs are tested with an X/R ratio of 6.6 and (2) MCCBs and ICCBs are tested with X/R ratios of 6.6 to 4.89, 3.8 to 3.18, and 1.98 to 1.75, depending on interrupting rating, means they have to be evaluated differently. See Table 3-18 for a listing of the power factor ranges from which the MCCB and ICCB X/R ratio ranges are derived.
BTW, the table came from SKM.
Google "skm breaker x/r ratio" and the first link has a copy as Table 1:Where in SKM did this come from?
The website, or a printout from the software itself?