Q: found 12 gauge and 14 gauge wire on same 20 amp circuit.. problem?

Old 07-09-19, 08:09 PM
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Q: found 12 gauge and 14 gauge wire on same 20 amp circuit.. problem?

Recently bought our first house and am very new to home ownership.

I wanted to upgrade the light switches in the bathrooms with countdown timer switches. There was modern 14 gauge wiring inside the electrical box, so everything was compatible and seemed pretty straightforward.

When attempting the same upgrade in the master bathroom, the set up was different. The wiring is very old. There are three 3-wire electrical lines and one 4-wire electrical line. One of the 3-wire electrical lines had a neutral wire and hot wire cut, and the ground wire is pigtailed to the three other ground wires (none connected to the old rocker switches). I sent a photo to my dad who pointed out that the older wiring was original 12 gauge wiring (from the 60s) and that I had exceeded my experience level for the day. This is when we started putting together the following:

-20 amp circuit (per newly upgraded electrical box from previous owner).
-14 gauge wiring (newish) in guest bathroom (with 1 single light fixture, 1 light/fan combo, and 1 GFCI outlet).
-12 gauge wiring (original/from 60s) in master bathroom (with 2 single light fixtures, 1 light/fan combo, and 2 GFCI outlets.
-All GFCI outlets are 15 amp outlets.

My dad proposed the following: hire electrician to change the circuit to a 15 amp circuit, get rid of the old 12 gauge wiring and upgrade it with 14. He also had me put a wire nut on each cut wire until further notice. After discussing with a close friend and avid DIYer, they said this set up is not ideal, but ok, and there are times when 12 and 14 gauge wiring can be on the same circuit. I'm curious what the best route is at this point.
Old 07-09-19, 08:44 PM
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Welcome to the forums.

#12 and #14 are not supposed to be on the same circuit. If they are...... the circuit needs to be protected at the amperage of the smallest wire size. That means that circuit needs to be protected at 15A.

Getting rid of the #12 and installing #14 is not an upgrade. A modern bathroom, by code, needs to be on a 20A circuit with #12 wiring. The bathroom circuit cannot be shared outside of the bathroom unless it's another bathroom.

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