Two Arc flash labels

[natfuelbill]

The arc flash values are nice and low when the power source is the utility but wicked high when powered by the backup generator.

(I believe that there is not enough energy to quickly trip the protective device.)

I am wondering if it is reasonable to have two arc flash labels on one piece of equipment. Perhaps include a energized work permit that specifies a generator lockout while working on system.

A nickel for your thoughts....

 

[zog]

Yep, either 2 labels or 1 label with the higher values on it. Make sure to include the permit as you mentioned and document training of your people on the subject.

5 cents please.

 

[chris kennedy]

A while back I inquired about the AFC fron a 750KW 480V. genny. It came back at around 10K. Why do you think there "wicked high"?

 

[chris kennedy]

I found the paper work. This is from TAW with Kolher TIB's and curves.

"Please pay attention to the short circuit decrement curve and the damage curve in particular.

As you can see, the unit has a pontential of 10KA for one second before damage occurs and our voltage regulator will disengage the excitation well before this can happen."

 

[cowboyjwc]

10k is pretty normal around here from the utility. Seen it as high as 40k, but it drops off pretty fast especially if there is a transformer in line.

 

[jim dungar]

A while back I inquired about the AFC fron a 750KW 480V. genny. It came back at around 10K. Why do you think there "wicked high"?

It sounds like you are confusing arcing fault current (SCA) measured in kA with arcing fault incident energy (AFIE) measured in cal/cm?.

Because many single generators can not produce much fault current for very long, overcurrent protective devices often never reach their instantaneous trip point resulting in fairly long clearing times and high AFIE.

 

[chris kennedy]

Because many single generators can not produce much fault current for very long, overcurrent protective devices often never reach their instantaneous trip point resulting in fairly long clearing times and high AFIE.

That sounds to me like poor design due to the fact that when a 480V 1000A ATS transfers to genny, it transfers through a switch not a breaker since the OCP in this source is at the gen-set.

Where are you guys getting the info on this.

And Jim, we may not quickly reach instantaneous trip level, but Kolher says the voltage regulator will open. Whats up with that?

 

[jim dungar]

And Jim, we may not quickly reach instantaneous trip level, but Kolher says the voltage regulator will open. Whats up with that?

Yes, the voltage regulator will open thereby "stopping" the fault but its response time is probably measured in tenths of seconds. Breakers and fuses normally respond in milli-seconds in their instantaneous region. So all things being equal a generator can produce an extremely high AFIE due to the length of time the arc can exist even though it may be at a relatively low current level.

 

[chris kennedy]

Yes, the voltage regulator will open thereby "stopping" the fault but its response time is probably measured in tenths of seconds. Breakers and fuses normally respond in milli-seconds in their instantaneous region. So all things being equal a generator can produce an extremely high AFIE due to the length of time the arc can exist even though it may be at a relatively low current level.

Thanks Jim,

Would you have any links where I could read more on this? That wasn't my first install of this type nor will it be my last.