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I went to replace an old mechanical timer for a bathroom extraction fan with a more up to date timer. The new single pole timer has a ground of course (no more mention of that), a black hot, a white neutral and a red load. All good, but when I took out the old timer, the wiring in the box simply had a black and a white wire terminating at the old timer.

Can I connect neutral, white from timer to white house wire and then both black hot and red load from the timer to black house wire?

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  • Can you post photos of the inside of the box please? Is rewiring this circuit an option? – ThreePhaseEel Jun 19 '20 at 11:49
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No. The white wire to the old timer is actually the load, not neutral (and technically should have some black tape over the white insulation to mark it as such).

Unfortunately, your switch box does not have a neutral wire (they were not required in switch boxes until relatively recently, 10-15 years ago).

You need to return the new timer and find one that does not require a neutral connection.

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  • Thank you. I’m on it. – Pronto Jun 20 '20 at 0:57
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This is the classic dilemma when substituting any simple switch for a powered/sophisticated switch. Many light switches in legacy (pre-NEC 2011) homes are wired with switch loops, which bring only "always-hot" and "switched-hot" to the switch - no neutral since plain switches don't need them.

You have what is very common - that switch loop with always-hot and switched-hot. The installers did what is now a Code violation by failing to mark the white wire as a hot on both ends. Code also requires the white be used for always-hot if it's not being used for neutral (so it's easier to detect).

The upshot is that you cannot use a "smart switch" unless that smart-switch is designed to not require a neutral wire. And this is something you better get used to, as it's probably true for half the light circuits in your house. As it happens, I just yesterday saw a listing for a GE pushbutton timer of the type you seem to want, which did not require a neutral wire but did require a ground wire. That might suit your needs.

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  • Thanks for that I will look for that GE product or go back to a better rheostat type timer. – Pronto Jun 20 '20 at 0:57
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Without a neutral wire you will have to stay with a mechanical timer which are still available today, or you could rewire the box with a 3 conductor wire from another source.

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