Switching DC 1

[patm72]

Why is looping serially all the poles of a DC contactor switching a DC load increasing the ampacity it can handle (DC-1 utilization category)?

 

[Skogsgurra]

The problem with DC switching is that there is no natural zero crossing (like you have in AC). So the breaker (or contactor) has to break a non-zero current. That is a tough assignment, especially if there is inductivity involved. Series connecting more contacts reduces the voltage over each contact and increases the breaking capability.

Gunnar Englund

http://www.gke.org

 

[IRstuff]

Additionally, the unipolar voltage may have adverse effects on the contacts.

TTFN

 

[Warpspeed]

Gunnar has nailed it.

The problem with high voltage dc contacts is not current carrying capacity, but current breaking capacity.

All sorts of tricks are used to do this, but at the basic level, contacts in series will definitely allow higher dc currents to be interrupted with less damage from arcing.