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  1. LFAVianna

    Time-graded Overcurrent Protection

    The maily reason to dont use an overcurrent time-graded without any directional control (ANSI 50/51 functions) is the dificulty to obtain selectivity and coordination since, as above mentioned, you will have different currents flowing by the ring with a large range of current values. Overcurrent...
  2. LFAVianna

    sizing of breakers in an electrical distribution panel

    Usually, it is necessary to take into account the coordination e selectivity of the panel. As mentioned above, the conductor must be specified to the nominal current of the load and the circuit-breaker will need to protect the condutor, according to its overload/damage curve. Whatever, the...
  3. LFAVianna

    PPE and Safety checklist for switching

    Here in Brazil, we do not have an expecific standard to deal with arc flash evaluation. In our standard, we are oriented to seek international references, like the IEEE 1584, that refers to the NFPA 70E. The scope of the NFPA 70E (2018) excludes "Installations under the exclusive control of an...
  4. LFAVianna

    PPE and Safety checklist for switching

    The studies assume several points of analysis. In the mathematical model there are classifications of the point in analysis, like "Open air","Switchgear" "MCC, Panels", "Cables". It is important to define that the method proposed by NFPA 70E refers to the IEEE 1584, where only are valid to the...
  5. LFAVianna

    PPE and Safety checklist for switching

    The arc flash study should define the ATPV of each electrical power system location. These studies follow the standard NFPA 70E. Please see the attached table where the NFPA describes the PPE list for each ATPV level determined. The NFPA also describes a list of PPE to some activities in systems...

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