In a switch loop that doesn't have it's own neutral in the box, can I use the neutral from a different loop?

The wiring in my house is partially updated - Half the house is to code as of 2019, a quarter of it is to code as of 2011, and the last quarter is the original cloth wiring (with rubber insulated conductors) from the 1940s. Updating the cloth wiring is on the todo list, but probably not for a year or so.

Anyways, I’ve got two scenarios here I want to understand better:

  1. double gang box, one switch is the original cloth, the other is the load side of a 3 way with neutral in the box. The cloth wiring controls an outdoor sconce. Both of these loops are on the same breaker, which makes me think it might be ok to tap the neutral here since it’s all going to join up at the breaker anyways. Can somebody confirm? I’m currently using a lutron aurora here and would like to upgrade it to a blue series, but it’s not a convenient place for a bypass so likely won’t if I can’t tap a neutral.

  2. double gang box, similar situation to above except the switches are on different circuits, one of which is the same as 1. and the other which is otherwise dedicated to my refrigerator. I think it’s probably a bad idea to tap this, but also don’t need to as a no neutral setup works fine here. Simply asking out of curiosity.

Thanks for reading, and thanks in advance for your input.

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You can use the neutral as long as it’s on the same breaker of the circuits you’re stealing neutral from.

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You can NOT steal neutral from dedicated refrigerator circuit.

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Thank you @harjms! Appreciate you and your prolificness in this community!

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