Non-conductor ruins a lot (9)

I believe the answer is:

insulator

I'm a little stuck... Click here to teach me more about this clue!

'non-conductor' is the definition.
(I've seen this before)

'ruins a lot' is the wordplay.
'ruins a lot' can be anagrammed to 'INSULATOR'.
But, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for insulator that I've seen before include "Non-conducting material" , "Non-conducting solid" , "Non-conductor" , "safety device" .)

I've seen this clue in The Irish Independent.

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