k)Series & Parallel combination

Series & Parallel combination

QUESTION:

How do load ratings change when contacts are connected in parallel or in series? Which option should be chosen?

ANSWER:

Series connection of contacts:

A series connection of contacts allows a certain current even at increased voltage values (as stated in technical data of contactors). This is because the switching arc is divided into a certain amount of smaller arcs, depending on the actual amount of contacts in series. A series connection of contacts also strongly reduces contact erosion which means increased contact endurance. Series connection of contacts is used for DC-loads.


Parallel connection of contacts:

Since -due to mechanical tolerances- all contacts within one contactor never close or open simultaneously, a parallel connection of contacts neither increases the making capacity nor the breaking capacity of a contactor. The making- and breaking capacity of each contact is the upper limit also in this instance.
Parallel connection of contacts can be used to increase the continuous (thermal) current of a contactor.

The AC-1 ratings of contactors can be increased as follows:
- parallel connection of 2 contacts: Ie AC-1 x 1,8
- parallel connection of 3 contacts: Ie AC-1 x 2,5


Fig:parallel connected contactors
In order to avoid current unbalance we recommend to connect only neighboring current paths in parallel.

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