It's full of useful bits of wire (4,3)

I believe the answer is:

fuse box

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'wire' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?

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

Can you help me to learn more?

(Another definition for fuse box that I've seen is " Container for electrical safety devices".)

I've seen this clue in the Evening Standard.

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