installing a new ceiling light

Thread Starter

faindelicato

Joined Jul 21, 2018
4
I need to install a new ceiling light. Do not know if the power is on or off as the light is removed. Do not know which circuit breaker will turn off the power. The black wire is the hot wire. When do I disconnect the black wire to remove the bad fixture? For example, do I disconnect the black wire fire, then the red and white? Or, do I disconnect the red and white, and then the black?
 

dl324

Joined Mar 30, 2015
11,003
Welcome to AAC!

If you're not sure if the power is off, you shouldn't mess with the wiring. There are non-contact voltage sensors available at home improvement stores, or you could use a DVM.

You don't mention your location, but in the US, black and red are hot. Order of disconnecting/connecting wires doesn't matter.

If you're not 100% certain that you know what you're doing, you shouldn't work on AC mains. You could electrocute yourself and/or burn your house down.
 

Thread Starter

faindelicato

Joined Jul 21, 2018
4
Thank you, I do understand. I am in the US, I have a 55 year old house. My hallway ceiling light broke. The light is removed. I cannot flip the switch to see if the power is on or off, and the circuit breakers are not marked for this particular light. An electrician recently told me about the black wire and the order of disconnecting and re-connecting so I won't get shocked, but I can't remember.
 

dl324

Joined Mar 30, 2015
11,003
An electrician recently told me about the black wire how the order of disconnecting and re-connecting, but I can't remember.
He must be referring to some old wives' tale. The order for disconnecting and reconnecting is immaterial when the power is off.

As I mentioned earlier, there are non-contact voltage sensors you can buy at a home improvement store. Or you can use a voltmeter. Measure between black to white or red to white to see if line voltage is present.

One caveat is that it's possible for the wiring to not be code compliant. That poses a risk to anyone working it.

If you have black and red wires present, that's 220VAC and you need to be very careful about not getting yourself across them.

There's a device you can buy at home improvement stores that will help you mark your circuit breakers. It's still a pain if you're tracing the whole panel, but not as much as doing it the old fashioned way. Part of the device plugs in an outlet (there's an adapter to plug it into a bulb receptacle). The other part of the device lets you isolate the breaker (audibly or visually).
 

Thread Starter

faindelicato

Joined Jul 21, 2018
4
OK, I appreciate this info. Non contact voltage sensors? Is that something that you can touch to the black wire to see if it's live? And if so, then you can just flip the switch to turn off the power?
 

MaxHeadRoom

Joined Jul 18, 2013
20,927
Also commonly known as Electricians screw drivers/testers, they have a neon in the handle and generally have a metal button on the top or a pocket clip.
Your finger/hand has to be on the top of the handle to indicate.
Max.
upload_2018-7-21_9-16-45.jpeg
 

profbuxton

Joined Feb 21, 2014
419
Firstly, if you are not absolutely sure of what you are doing, get an electrician to do it. Saves your relations the cost of a funeral.
If you insist on doing it yourself. switch off main breaker to whole house. Still need to check for any power at light, just in case of wiring cock-up.
 

olphart

Joined Sep 22, 2012
78
I'll pose a caveat to dl324: 3 wire (black / red / white) is also for 3 way switched lighting.
Two switches controlling same light, like at stairwells.
If you're not Real familiar with ways of 3 way wiring, get help.

There are a few ways that 3 way can be wired.
I only recently learned the code-correct method, and Why.

If you're just replacing the fixture, only 2 wires matter Line & Neutral.
You need to find the breaker for this circuit.
It can be done hot, but I'm not telling since it's stupid / dangerous.
That I'm alive to say this is a story in itself.

Inductance amplifier voltage sensors are Invaluable at this, as mentioned above.
Also called "toners", (IIRC) they use body capacitance as a reference to sense the AC.
Another type includes a transmitter that is attached to 2 wires and is sensed by the receiver.
Note: Toners aren't useful at finding bad neutrals or grounds.
Good Hunting, but Please be prudent... <<<)))
 

profbuxton

Joined Feb 21, 2014
419
In regard to testing for live, as an electrician, I would NEVER use these test pencils or similar. Only reliable thing is suitable meter(calibrated /tested) to check for live circuits. Be aware that many digital meters have very high input impedance and will read "inducted" volts. One way around this is to use a 20Kohm shunt across meter terminals which will dissipate any spurious volts. without harm.
Of course final test is to short the hot wire to neutral wire(if you're that desperate). That should blow the fuse/breaker.
 

sdowney717

Joined Jul 18, 2012
648
If you can not figure it out, turn off the main breaker, and have a portable light to see with.
Doing that cuts all power.
You can drop the old light fixture to see how it was wired and leave the power on.

Connect white to white, black to black, a lamp socket only has 2 wires. Other wires like the red are used for 3 way switches, they are called traveller wires. There are several ways an electrician could have wired things, power to the fixture, or power to the switch.

just connect new light fixture to same wires as old fixture.
 
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