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Question DetailsAsked on 2/9/2016

A red, white, and black 110V wire was cut during a demolition. It connected to a red, white, black and yellow wire

What is the color pattern to connect everything back up? Or in other words, where does the yellow wire connect to???

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2 Answers


I presume there is also a ground in the works here - just not mentioned. Yellow is usually only used for instrucmenttion wiring (smaller gages) and for 277/480V multi-phase wiring, so sounds like someone grabbed what was handy to use in your house.

With two (presumably) hot wires coming in (black and red) are you sure this is 110/120V and not 208/220/240V ? Or maybe instrumentation wiring for an alarm/security system or such ?

You need an electrician for this to be sure and on the safe side - sounds to me, especially since you have both black and red in the one wire run, unless a really unusual situation for single-phase residential wiring, likely with the odd wires out (red and yellow - would normally be red only for 3-way switch wiring) is that you are into a 4-way switch situation - where multiple switches (probably 4) control one light fixture (or set of fixtures). Google 3-way and 4-way switch wiring to see how it is done - if at a switch and it has more than two wire mounting screws on the side that is probably what you are into. An electrician would have to figure out the wiring, because do it wrong (or contrary to how the other switches are wired regardless of right or wrong) and at the best they will not all work the lights right - at worst you get fireworks in the switchbox.

Another possibility - you are into a situation at a fan with light where the control is in the switch rather than at the light, where you may have hot leads for light (or even two for different light combinations) and one or two leads for the fan motor - which can be just about any color, though neutral should still be white or gray and ground green or bare uninsulated wire. In that case you would have to download the manual on the unit to determine proper wiring unless it is labelled on the device itself.

Another possibility - that you are into an interconnected alarm circuit - typical with fire alarms but can also connect to flooding and appliance power loss and ovearheat and freeze alarms. In that application, the black and white are the usual live and neutral, and the red would be the interconnect feed between alarms so all sound when one goes off. This does not explain the yellow wire however - unless that is a feed continuing on past the alarms to a central alarm box to indicate when an alarm is going off.

The other possibility is that it was a DIY or handyman job and the homeowner or handyman just used whatever scrap wire he had available, and the yellow was never used.

I certainly would not mess with it without tracing them out - I would put my RF (radio frequency) tracer on it and map all the wires out and see what is going where - will probably become clear once a wiring diagram is in hand. Likely about an hours work or less to trace it out depending on how many devices it goes to.

Other way to handle it - if this was a demo for a major remodel - figure out if, under the new plans, if anything other than normal 2-wire wiring is needed anywhere hear that cut - if not, just terminate the unused leads with wire nuts and abandon the red and/or yellow leads in place, as applicable.

Answered 4 years ago by LCD


You need to call an electrician. Hopefully one that has worked in similar houses in your neighborhood.

Answered 4 years ago by Kestrel Electric

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