Hi All Experts,

Request to help me to understand reasons for equipment evaluation fail based on the power system worst-case short circuit :

(*N3) Calc Arc Flash Line/Load Side Evaluation Category result is Dangerous!
(*Calc Isc kA) Device did not pass. Device is either marginal (100%) or Failed (100%) of the device library Isc rating.

How to investigate of reasons for "Cabling was found unprotected" under PROTECTIVE DEVICE COORDINATION STUDY.

Thanks in advance.

Best regards,

Riyazahmad,
India.

Hello,
Welcome to the forum!

In regards to your questions:
1. For that scenario, the arc flash hazard result is greater than 40 cal/cm^2, so it is considered Dangerous.
2. The equipment is overdutied. What that means is the available short circuit current at that device is at or exceeds the rating of the device. For example a device (such as a molded case breaker or panel) is rated at a withstand current of 10 kA but the available short circuit current at that device is 12 kA. This device is considered overdutied and needs to be replaced with a device rated above the available short circuit current.
3. I think what the cable unprotected is where a conductor is rated at say 65 A but the breaker protecting the cable is 100 A. In very simple terms (as there are limitations) per the code in the USA, that cable should have a breaker that is 70 A or less protecting it.

Thanks wbd for detail explanation, great help!
1. Clear, no doubt.
2. How to calculate available short circuit current? In our case three transformers (2.5MVA, 33kV/440V, 4.64%Z) feeding three section (parts) of panel, three section (parts) are inter connected with breaker to connect each other to run whole system on one or two transformers if required. No parallel operation of Transformers. As per our calculation one transformer not able to feed short circuit current which shows in our arc flash analysis report. Could you please help to understand this.
3. Yes, breaker protecting the cable is having higher capacity, but in our breaker Schneider Masterpact Mircrologic 2 have current setting. If we set current accordingly (below ampacity of cable) is cable will get protected?


Best regards,
Riyazahmad,
India.

For #2, can you post the one line and possible just the section of the report. Then we can see visually what the situation is. Might be easier to understand.
3. yes, if the breaker has an adjustable pick up, then it can be set equal or less than the cable ampacity.