Arc Flash to IEEE1584 - Equipment Type

[EddyWirbelstrom]

I need to do an Arc Flash study using SKM-PTW softare to IEEE 1584.
The software "Equipment Type" options are "Switchgear", "Panel", "Cable", and "Air".
The option determines how the arc energy is focused towards operating personnel. "Cable" and "Air" are self-evident, however "Switchgear" and "Panel" I am unsure.

Does "switchgear" mean normallly enclosed but with open panel door. Arc energy would be focused through the open door.
Does "panel" mean the switchgear is not enclosed. Arc energy would be dissipated in more directions than at personnel in front of the "panel".

 

[davidbeach]

I've always found the folks at SKM to be very helpful, drop them an email or give them a call.

 

[Eleceng01]

mnewman,

The software "equipment type" is the same as that stated in IEEE-1584's Table 2 & 3. One use of the setting is to define the bus gap for the equipment. I am not sure if it has anything to do with open panel doors at all.

Also, davidbeach's recommendation is a great one, SKM has been very helpful to me as well.

 

[mls1]

The difference in the analysis is in the arc gap and distance X factor. For LV systems (<1000V) the switchgear arc gap is 32 mm and for MCC/Panels it's 25 mm.

The IEEE 1584 calculation first calculates a normalized energy at 610 mm from the arc. It then adjusts the energy for the actual specified distance by multiplying by (610^x/D^x) where x is the distance x factor, 1.473 for switchgear and 1.641 for MCC/Panels.

As for what constitutes switchgear vs. a panel, an easy way to look at it is if it has power circuit breakers (open frame) then its switchgear, if it has contactors and molded case breakers its probably an MCC or panel. There are, of course, exceptions.

 

[dpc]

The only real difference between switchgear and panel will be the assumed arc gap. Both use the "in box" equations. Doors open or closed is not considered - but the inherent assumption is that the front door is open in all "in box" cases in IEEE-1584.

If you play around with the gap, you'll find it doesn't change the arc energy too much - not nearly as significant a variable as bolted fault current or arc time. But there will be a major difference between "in air" and "in box" results.

 

[EddyWirbelstrom]

Thanks for your help with "Equipment Type" for Arcflash studies.
I am a novice with arc flash studies and have another question :
IEEE 1584 equations for arc flash are based on bolted 3 phase fault current. Arc duration time is based on the phase overcurrent protection device operating time.
In an earthed system, the initial arc may be phase to earth and tripped by fast acting earthfault protection. In this case the incident energy would be much less than that caused by operation of the phase overcurrent device.
My understanding is that IEEE 1584 ingnores the operate time of earthfault protection and only uses the phase overcurrent protection time. Is this correct ?

 

[mls1]

You are correct, it is based on the three phase fault only. However, system grounding is taken into account in the empirically derived formulas. It was found that for grounded systems the observed energy was less, most likely for the reasons you described. So while you can not take ground trip settings into account directly, you will find that for two systems, one solidly grounded and the other high impedance or non-grounded, the solidly grounded calculation will be lower.