I'm attempting to power a 50kW DC Fast Charger with 3 phase 277/480V. It needs ~55kW which is 66A per phase. I'm trying to find a contactor. This one is CDC65-24. It is a 3 pole, 100A continuous. However, when you look at the technical information, it says at 3 phase 400-480V it is rated at 50HP (horsepower). This is much less than 100A per phase.

50HP = 37kW 37kW/277V/3poles = 44.5A

What rating should I go off? Does the HP rating only apply to motors?

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    \$\begingroup\$ Inductive loads like motors are more likely to arc when switching. I don't know if that's definitely the reason, but it could be. \$\endgroup\$
    – Hearth
    Jul 3, 2019 at 21:36
  • \$\begingroup\$ Inductors arc on opening thus derated while batteries arc on closure, same problem \$\endgroup\$ Jul 3, 2019 at 21:53
  • \$\begingroup\$ @SunnyskyguyEE75 - for DC fast chargers the typical approach is to have a separate medium current contactor with current limiting (resistor) arranged to precharge the bus before the main contactor engages. Also the DC supply will be arranged to supply zero current until the main contactor has engaged - there should not be any arcing of the main contactor on close or opening under normal conditions. All switching occurs while it is closed or open. \$\endgroup\$ Jul 3, 2019 at 21:58
  • \$\begingroup\$ If so then this should be stated in user’s question for surge current limit \$\endgroup\$ Jul 3, 2019 at 22:00
  • \$\begingroup\$ But for any dry contact switching it applies to any reactive current not just motors. +/- reactance is always derated relative to R only. \$\endgroup\$ Jul 3, 2019 at 22:01


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