Arcing - What affects size of arc when switch is opened?

  1. When an electrical circuit is opened or closed there is an arc between the terminals/buss that the switch or breaker is connecting or disconnecting and the arc is greater depending on the amount of voltage. My question is, is the arc greater when there is a resistance/load on the circuit? I'm guessing yes, but what is the effect and how could you calculate it?
  2. jcsd
  3. mfb

    Staff: Mentor

    You have to consider the whole circuit to determine that.
    In general, inductances (especially coils), large switching voltages and large currents will increase the amount of arcing you get.
  4. OmCheeto

    OmCheeto 1,945
    Gold Member
    2014 Award

    Without a resistance/load, you wouldn't have a circuit in the first place, and therefore wouldn't have an arc at all.
  5. So then if a main breaker was closed outside of a building feeding equipment inside the building but their individual circuits were open then there would be no arc as that breaker closed? There would be voltage but no current and my understanding is that it will arc
  6. OmCheeto

    OmCheeto 1,945
    Gold Member
    2014 Award

    That is correct.
    No, it will not arc.
  7. To emphasize this point - for medium voltage switches - there are two general classes "no load disconnect" and "load disconnect" - The no load types are ideally interlocked ( often literally with locks and keys - ref Kirk Key) - with the load side circuit breaker. The Load side circuit breaker must be open - to get the key that allows the line side "no load" switch to be operated ( opened or closed).
    TO feed a transformer a MV switch used on the primary is technically a load break switch (it will have an arc chute & arcing contacts- separate form the main contacts) , but only rated to interrupt the magnetizing current of the transformer it feeds - so you still see the interlocking scheme.
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