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Thread: arc flash

  1. #1
    Join Date
    Jan 2004

    arc flash

    How can utilities get away with 8 cal no fase shield for all 120/208 energized work? I had an arc flash over 40 cal 120 /208 fed from a 500 kva padmount if that was an inside wireman they would kill or do an arc flash calc I don't get it

  2. #2
    Join Date
    Mar 2013
    Rutland, VT, USA
    Utilities follow two standards for arc flash. One is the NESC and the other the rules in OSHA 1910.269.

    For inside a padmount transformer, the NESC lists 4 cal/cm2 system for 50V to 250V. This is based on actual testing done by two major utilities and a research institute which demonstrated that voltages between 50 to 250V will not sustain an arc for more than 2 cycles. (208-V Arc Flash Testing Network Protectors and Meters, EPRI, Palo Alto, CA).

    For work that is not utility work, the standard used is IEEE 1584-2002 and NFPA 70E. The testing in IEEE 1584 was very limited at 208V and they were only able to sustain an arc at a certain configuration. That is why there is the <125kVA transformer and below 240V exemption. IEEE 1584 also was testing in a certain electrode orientation and gap which was representative of equipment (panels, disconnect switches, etc.) at that voltage. The gap for low voltage equipment used was 1" to 1.25".

    Now, think of the spacing for the secondary spade terminals inside a padmount transformer. They are much larger than the gaps used in the IEEE model and most IEEE software will not allow gaps larger than 6" as that is the limit of the IEEE model for 15kV equipment.

    So until a new version of IEEE 1584 is issued (probably in 1-2 yrs as they have done more testing) we are constrained to use the present version.

    Self contained meters are also at 4 cal/cm in the NESC although most utilities I know use a meter puller and will have a face shield on.

    Per OSHA 1910.269, for three phase work with a hazard of 5-8 cal/cm2, a faceshield rated at 8 cal/cm2 minimum is required. So if the utility is allowing their employees to do 3 phase work that is determined to be an 8 cal/cm2 hazard without a faceshield, they are violating OSHA regulations.

  3. #3
    Join Date
    Jan 2004
    I read in the nesc that if the arc flash is over 8 cal its documented and the effected employee will be notified does that sound familiar ? network meter packs have all the phases behind the meter to help balance load is that considered 3 phase even though meter runs off of 2 phases? Thanks

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