Etap Arc Flash Support
Etap Arc Flash Support
(OP)
I have conducted an arc flash analysis in Etap 14.1.
I'm getting a warning message that states "Exceeds Max. PPE Arc Rating"
I believe this is due to my bolted fault current or Ia (Arc Current) of 2.9KA.
I have a LV (480VAC) Main CB Cutler and Hammer KD Series Breaker, with a Trip Device Part # KT3400T, 4,000 amp trip).
I believe the Fault Current Calculated is too low for the Main CB to trip. My FCT is 136 sec with an Ie = 1277 Cal/CM2.
What is normally done with cases like mine?
The breaker is installed in the MCC and the facility is up and running.
I doubt they would want to change our the breaker. Also another breaker type might break the UL rating of the MCC as well.
Also I have graphed a TCC curve and it shows the fault is before the the trip curve so the main breaker will never trip.
See attached of One Line Diagram.
I'm getting a warning message that states "Exceeds Max. PPE Arc Rating"
I believe this is due to my bolted fault current or Ia (Arc Current) of 2.9KA.
I have a LV (480VAC) Main CB Cutler and Hammer KD Series Breaker, with a Trip Device Part # KT3400T, 4,000 amp trip).
I believe the Fault Current Calculated is too low for the Main CB to trip. My FCT is 136 sec with an Ie = 1277 Cal/CM2.
What is normally done with cases like mine?
The breaker is installed in the MCC and the facility is up and running.
I doubt they would want to change our the breaker. Also another breaker type might break the UL rating of the MCC as well.
Also I have graphed a TCC curve and it shows the fault is before the the trip curve so the main breaker will never trip.
See attached of One Line Diagram.






RE: Etap Arc Flash Support
Obvious remedy is to upgrade the circuit breaker. Many modern types have various 'smart' trip units that can be set to reflect your actual fault current parameters, allow you an instantaneous trip. This reduces fault clearing time. If the low FCT interferes with system operation, you can add a 'maintenance switch' which, when active, reduces instantaneous pickup values to a low and safe level while downstream maintenance is performed.
In your case, you show the issue with your system on generator. do you have similar issues when on utility power?
old field guy
RE: Etap Arc Flash Support
RE: Etap Arc Flash Support
For the mean time I will note and state my findings. If they Client wants to Invest/go another
route I will go with your suggestion.
Thanks again,
R_Roc
RE: Etap Arc Flash Support
RE: Etap Arc Flash Support
Is there a 51V relay protecting the generator that would trip faster for low level faults with low voltage? There will probably be under/over frequency protection that would trip the generator after a short time delay.
RE: Etap Arc Flash Support
I'll state in my report that I clamped the FCT to 2 sec due
to low calculated fault current or should I not mention it
since this sounds pretty typical and the client will see my TCC curves
and data anyways.
RE: Etap Arc Flash Support
RE: Etap Arc Flash Support
I understand what you are saying about limiting the FCT to 2 sec, but what if it was a bolted fault that occurred. The breaker would still not trip.
I plan on making a recommendation anytime the Ie is high turn off genset for trouble-shooting/maintenance.