Arc Flash Energy in Medium vs Low Voltage Systems 2

[HenryOhm]

I've noticed in some fault current and arc flash studies I've seen lately, that the low voltage systems produced higher incident energies (cal/cm2) than those for medium voltages of similar power levels. My sample size is probably just too low and I know that it is probably quite complex. I am talking about different systems, not the same system with upstream and downstream medium and low voltage interconnected systems.

I've tried to research this a bit, but for example the IEEE-1584 equations are a bit too complex for me to see any clear cut differences. But, does the fault current have a greater effect than system voltage? Will a low voltage system with nine times lower voltage but 9 times higher fault current typically have higher arc flash numbers?

Thanks in advance for any help.

 

[davidbeach]

Voltage plays almost no part; current and time are essentially the only factors.

 

[deltawhy]

Arcing current is a function of voltage, conductor gap, enclosure type, and most importantly, the bolted fault current.

Clearing time is a function of the arcing fault current and the protective device time-current characteristics.

Arc flash energy is a function of clearing time and arcing current.

It is very common to see higher arc flash energies on LV systems, most notably directly downstream of a transformer where the protective device is the transformer primary protection.