Both AC and DC contactors work on the principle of electromagnetic attraction. However, there are minor constructional differences between them. AC contactors have a shading coil which is a metallic ring with high remanence which provides magnetism during the zero crossing of the AC voltage.
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AC contactors can be used with DC voltage, in theory. However, the presence of the shading coil in AC contactors can result in a higher drop-off voltage which can cause delay in contact operation.