A good conductor is on the beat (6)

I believe the answer is:

copper

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'a good conductor' is the definition.
(I've seen this in another clue)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for copper that I've seen before include "Metallic element and British bobby" , "Police officer (slang)" , "A little cash" , "Red-brown metal" , "English policeman" .)

I've seen this clue in The Globe and Mail.

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