SC Rating of Panel

[Charz]

Attached is the panel board GA drawing . All the breakers have a interrupting capacity of 65kA @ 480V AC, then how come short circuit rating of the panel board is mentioned as 42kA

 

[jim dungar]

Attached is the panel board GA drawing . All the breakers have a interrupting capacity of 65kA @ 480V AC, then how come short circuit rating of the panel board is mentioned as 42kA

The panelboard SCCR rating is also based on the short circuit bracing of the bus bars.

 

[wbdvt]

as noted above, the panel rating is independent of the breaker ratings. It is based on the panel being able to hold together during a fault due to the magnetic forces of a fault.

 

[electrofelon]

But why would the PB mfg sell a panelboard with a 42 SCCR and 65k breakers (assuming the FC is over 42k)?

 

[Jraef]

But why would the PB mfg sell a panelboard with a 42 SCCR and 65k breakers (assuming the FC is over 42k)?

Probably because in their breaker line, the next lower breaker rating is 22kAIC or 25kAIC and the AFC was over that amount, but under 42kA.

Still, I get your point, it seems kind of silly, especially if you have ever compared a panel built for 42kA bracing vs one with 65kA bracing. In one case I saw, it was one more mounting screw on the insulation.

 

[electrofelon]

Probably because in their breaker line, the next lower breaker rating is 22kAIC or 25kAIC and the AFC was over that amount, but under 42kA.

Still, I get your point, it seems kind of silly, especially if you have ever compared a panel built for 42kA bracing vs one with 65kA bracing. In one case I saw, it was one more mounting screw on the insulation.

So If I have a mid to large sized panelboard, say an I-line or a siemens P4, it will not necessarily have a SCCR of 65k? I always kinda assumed that they would all be designed around that "common max" 65k number.

I looked at some past Siemens gear proposals, and the drawings dont give a SCCR. They give an "IR" rating which isnt even correct on some of them. The place I have gotten Square D stuff from doesnt provide me with nice formal quote drawings so I cant see what square D says on theirs.

 

[wbdvt]

Typically the purchaser will specify what SCCR panel rating is needed based on the short circuit at the location of the panel. The breakers that come with the panel are then sized for an AIC rating to meet that specified short circuit current.

For example: I recently completed a study where a couple panels are overdutied. They are rated at 18kA but the fault current at that location is 33.4kA. They are replacing these panels with SQD I-Line panels rated at 42kA. The breakers are SQD BJ which are rated at 65kA. The other choice of breakers in this frame is BG which are rated at 35kA. The 35kA is too close to the fault current so the next highest, 65kA, was used. Therefore, the panel is 42kA while the breakers are 65kA. This is at 480V.

 

[paulengr]

At least with Square D you give them the SCCR and they size accordingly. It's part of the options when the part number is generated.

Sent from my SM-T350 using Tapatalk

 

[electrofelon]

Here is what it says on a Siemens panel, a P1. I read it like 5 times, still trying to figure out exactly what that means.... Seems like the SCCR "follows" the series ratings.