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I want to install a light fixture on a box that's in the ceiling. I opened it up and I saw WAY MORE wires than I expected. I expected just a green, black and yellow wire.

Here are two photos of the wires. enter image description here

Here's a close up. enter image description here

Can someone explain what each of these wires do? I see a single green wire, a single blue, 4 green wires twisted together, 4 white wires twisted together, 4 yellow wires twisted together, and a single red wire that I can't pull out of the box. Which one do i use as my ground, live and neutral wire?

Just to give some context, I live in a condo in Toronto, Canada. The condo was completed in 2014. Thanks.

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    Interesting question, the wiring guides I found online for Canadian color codes don't list Yellow for 120V wiring, only for 277 and 480V 3 phase wiring (which seems unlikely for a ceiling lamp). Based on those guides, I would have expected a bundle of black, red, or blue plus white plus green. Hopefully someone can answer your question, I'm curious too.
    – Johnny
    Jul 31, 2015 at 1:20
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    Is there any chance you've stumbled on signal cables for smoke/CO, as well as regular power cables? If so, you might need to talk to your condo people to see if there's something missing that's required.
    – Aloysius Defenestrate
    Jul 31, 2015 at 1:50
  • Was there a light installed here previously, or something else?
    – Tester101
    Jul 31, 2015 at 2:17
  • My money's on the yellow one being the switch leg. What happens when you turn off the light switch? Also, this is a dead end if you don't have the proper test equipment. – no pun intended.
    – Mazura
    Jul 31, 2015 at 3:13
  • How many switches control this light? how many other lights are controlled by the switch(es)?
    – Tester101
    Jul 31, 2015 at 11:14

3 Answers 3

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Some condos are multi-use, i.e., both residential/commercial mix, so maybe it's possible the yellow is a high leg, 277V for the common area lighting that is just there for "future development". Ask the building superintendents. They are usually filled with many great stories of advice.

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It might be possible that more than once the electrical work has been carried out after the house has been constructed. These multiple wires has to be checked whether which one is the live wire, neutral and the earth wire. You must check the voltages with a multimeter to verify the existing voltages.

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    True, but probably unlikely that this is anything other than the original wiring considering the unit was completed in 2014.
    – mjohns
    Jul 31, 2015 at 10:15
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Can someone explain what each of these wires do? I see a single green wire,

This is a grounding pigtail that was supposed to ground the junction box itself. It should be joined to the other greens most likely.

a single blue

hot leg of a 120/208 system?

4 green wires twisted together

almost certainly earth ground

4 white wires twisted together

Neutral, most likely. Are you sure those aren't 'grey' instead of white?

4 yellow wires twisted together

only real guess would be a hot of a 277/480

and a single red wire that I can't pull out of the box.

another 120/208 hot that is traveling to another junction box.

Which one do i use as my ground, live and neutral wire?

I think this is the time you call building management and make them explain what the hell they were thinking.

With no other information, I don't think you have what you need there to wire a 120v light. You MIGHT be able to install a 277v light using green for ground, the grey bundle for neutral and yellow for live. But you should probably make mgmt do this.

277 has become quite common in large buildings for lighting. Carefully measure the voltage between yellow and grey, and between yellow and ground.

In 277/480, neutral is Grey, not white, and yellow is a hot.

Is this a large building with significant electrical utility rooms and the like?

I'm also going to guess concrete slab ceiling? That would be a common reason to run 120 and 277 in the same conduit, but then where's the 120/208 neutral? Something is off here.... I'm guessing that red wire doesn't have a junction in this box, but runs down conduit to another.

Pictures from another angle would help. (To know what is coming from what direction.) But you might just want to put the lid back on and back away slowly!

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  • Are you even allowed to have 277/480V in a residential condo in Canada? If yes, WHY would you????.... This is obviously a conduit job, if you've ever seen residential conduit jobs like from the Chicago area, it's obvious that not everyone cares about "conventional" wiring colors. Brow, orange and yellow are not always used only for 277/480V, and grey is quite regularly used for 120V neutrals.
    – Speedy Petey
    Jan 8, 2016 at 11:33

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