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We specialize in arc flash evaluations so any advice we can provide for a designer would be for arc flash reduction type ideas.   Below are a few ideas.

The main theme you’ll see in this post is to use an appropriate OCPD  (overcurrent protective device i.e. breaker or fuse) to reduce arc flash for downstream equipment.  If possible, isolate this OCPD so that there is no need to interact with it (this of course can add to cost).  Areas of typical concern are the secondary side of larger transformers.

Some design wins from an arc flash perspective include the following

    • Main Switchgear
      • Install the main breaker in a separate enclosure (preferably outdoor, i.e. near the transformer)
        • This will isolate arc flash hazards to a separate enclosure
      • Add a second main breaker indoor near the main gear
        • This creates an isolation point for the rest of the gear which eliminates the need to interact with the upstream main (where a higher hazard would be)
        • Drawbacks include additional cost
    • Floor Level Equipment
      • Place the local disconnect in a separate enclosure, i.e. fused disconnect or main breaker in small enclosure on the side of the main equipment’s enclosure
        • This allows for potential isolation of arc flash hazards.
      • Allows better and more effective LOTO.
    • Secondary sides of transformers and equipment connected to the secondary side (even if 100ft away)
      • Most transformers bigger than 30kVA will have a decent size arc flash hazard (4 cal/cm^2 or bigger)
      • Install an OCPD for arc flash reduction upstream of any equipment that will be touched
      • This OCPD will then only act as arc flash mitigation and won’t be interacted with unless LOTO is performed on the primary side of the transformer
    • Utilize breakers with electronic trips
      • These can be very valuable for arc flash reduction
      • Sometimes fuses or thermal breakers accomplish arc flash reduction but if they don't then electronic trip is the next thing to consider.
      • An engineering model will need to be created to understand when necessary, see below.
  • Calculate arc flash prior to purchasing equipment
    • We can model and verify if reduction is necessary
    • You never know an arc flash hazard until it's calculated, more information about what causes different sizes of arc flash can be found here:  https://www.70econsultants.com/arc-flash-size/ 
    • Many of our customers run part numbers by us prior to purchasing anything
    • We can also calculate available fault current at each point in the system to ensure you aren’t paying extra for higher duty sizes.
  • There are other arc flash reduction techniques such as flash sensors which can then trip protective devices, arc rated gear, etc.  But if you can remove the flash through design then there is no need to sense and trip in the event of a fault.