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Determine available arc fault value

Question asked by tdotts on Jan 24, 2020
Latest reply on Feb 6, 2020 by tdotts

I am currently supporting development of a contractor electrical safety program w/ implementation of NFPA 70e. My question is regard determination of  Fault Current (Available) in order to satisfy the use of table 130.7(C)(15)(a). After much review and debacle, it appears that dialing into such data is only possible after performing an arc flash  / coordination study - or damn close to it. 

 

My example is as follows:

Case Study:

Task:

Install new 2-pole 50A 10ka IC circuit breaker. Panel type accepts bolt-in breakers only.

  • Removal of cover required
  • Removal of dead front required
  • Installation of new CB at main bus

 

Hazard Assessment_1:

  • Equipment is “Energized” Panelboard, 15yrs of age / conditions unknown:
  • Task places individual w/in restricted approach boundary & arc flash boundary (min distance per 70e is 18”)
    • Shock hazard determined via voltage class
    • Arc Flash / Blast Haz Undetermined – Assumed present, but level not calculated

 

Mitigation_1:

De-energize / shutdown Panel board w/ coordination of client.

 

Job Planning:

  • Shutdown request authorized, signed by client
  • Determine source of Panel board
    • Reference single line drawings, panel schedules, visual walk down.
      • Source was located and determined to be 125A breaker located within Main switchboard fed from Utility Transformer. No hazard label existing on electrical equipment.

**Determined that isolation (switching) of CB at MSWB could result in possible hazard and release of arc flash energy in the event of mechanical failure and short circuit or bolted fault.

 

Isolation Task

De-energize existing circuit breaker / Re-energize; post installation of downstream panel board CB (main task)

Hazard Assessment_2:

 

Review Conditions / Probability per 130.5(C)

Panel board is approximately 15yrs old w/ no electrical label indicating incident energy or PPE level requirements. There is no data relative to installation (providing information w/ regards to proper or suitable installation practices). There is also no "maintenance" data which would reveal any type of predictive, preventative or routine upkeep or inspection of the said switchboard. 

 

Likelihood of Arc Flash Hazard (per Table 130.5(C)):  YES

Risk / Hazard                                                              Arc Flash / Blast

 

Mitigation_2:

De-energize Panel: Shutdown request:                       Denied by client.

 

Reasoning:                                                                       

Infeasible due to overall impact of process equipment and resulting de-energization of cooling equipment. Said equipment is noted by client to provide process material stabilization. If material reaches temperatures greater than 40Deg. F, auto ignition possible and detonation. Probable injury or death resulting to plant personnel.

 

(Resulting) Mitigation_3

Determine available Arc Flash Hazard Level in order to determine proper PPE per table 130.7(C)(15)(a)

 

Need: Equipment Type& Volt: ☒  Clearing Time: ☒  Working Distance: ☒ Available Fault Current ☐

 

Assuming accurate calculation of appropriate PPE to execute Isolation task cannot be determined w/out coordination study…

 

 

 

Outcomes