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Kevin
Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 3528
Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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I am replacing a dining room light in a 1925 home. I have

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I am replacing a dining room light in a 1925 home. I have two wires- one black and the other I have no idea- coming from the ceiling. I have a black, green, and a white/black wire coming from the light fixture. I can get the light to come one, however, I am not able to get the lightswitch to turn the light off or to dim it.

Hello.....my name is XXXXX XXXXX I will be happy to assist you with your electrical question. My goal is to exceed your expectations on Just Answer!

 

1) How many wires in the ceiling box? Are they both black in color? Are you not able to differentiate between the switched loop wire and the neutral wire?

 

1A) Since the house is 1925 era, I assume that the house is wired with Knob & Tube wiring and you do not have any bare copper grounding conductor in the ceiling box and there is no metal conduit, correct?

 

2) How many wires in the wall switch box? Same thing, are they all black in color?

 

3) How many switch locations do you have for the dining room light? One or more?

 

4) What type of light bulbs are you trying to dim? Incandescent, Compact CFL or LED?

 

4A) How many wires on the dimmer switch? What colors are they?

 

5) Do you have a 2-prong AC voltage tester (contact type) or an AC voltmeter handy or can you borrow one from a neighbor or a friend?

 

6) Do you have any existing 3-prong receptacles in the house that are grounded?

 

7) If you have a 3-prong receptacle, do you have a long 3-prong extension cord (50 or 100 footer)?

 

Let me know what you have and we can take it from there............Thanks.............Kevin!

Customer: replied 3 years ago.

Hi Kevin,


 


Here are the best answers I can come up with for you:


 


1) How many wires in the ceiling box? Are they both black in color? Are you not able to differentiate between the switched loop wire and the neutral wire?


 


Two and both are black in color. One is thin and I believe is my hot wire; the other is black but is thicker and has like a cloth like clothing on it. Not sure which you mean by switch loop and all.


 


1A) Since the house is 1925 era, I assume that the house is wired with Knob & Tube wiring and you do not have any bare copper grounding conductor in the ceiling box and there is no metal conduit, correct?


 


I do not have any bare copper grounding.


 


2) How many wires in the wall switch box? Same thing, are they all black in color?


 


3) How many switch locations do you have for the dining room light? One or more?


 


One.


 


4) What type of light bulbs are you trying to dim? Incandescent, Compact CFL or LED?


 


Incandescent


 


4A) How many wires on the dimmer switch? What colors are they?


 


 


5) Do you have a 2-prong AC voltage tester (contact type) or an AC voltmeter handy or can you borrow one from a neighbor or a friend?


 


6) Do you have any existing 3-prong receptacles in the house that are grounded?


 


7) If you have a 3-prong receptacle, do you have a long 3-prong extension cord (50 or 100 footer)?


 

1) Jamie.........thanks for the replies

 

2) In order to figure out which is the switched loop hot wire and the neutral wire in the ceiling box, you will need a 2-prong AC voltage tester or an AC voltmeter as well as a 3-prong extension cord.

 

3) The use of these items will allow us to differentiate which wire in the ceiling box is the neutral and which wire in the ceiling box is the switched loop wire leaving the wall dimmer switch. We also need to confirm the hot wire in the existing wall dimmer switch box.

 

4) Without the use of these items, we will only be wasting both of our time and a lot of guessing going back and forth to determine which wire is which. Once we can confirm the true identify of the hot and switched loop wires, the rest is easy.

 

5) Do you have a 2-prong AC voltage tester or an AC voltmeter and a long 3-prong extension cord that can plug into an existing 3-prong grounded receptacle. Hopefully, somewhere in the house you have a 3-prong grounded receptacle. Let me know.

 

If you do not have these items, can you borrow them? Or we can leave the question open until you can obtain them?

Customer: replied 3 years ago.

Kevin,


I went to the store and got a three prong extension cord; and a 2-prong AC voltage tester. I tested the two wires coming out of the ceiling and they both together registered 120v. When I put both of the prongs on each individually I got nothing.


 


What do I need the three prong extension cord for?

1) Hi Jamie...thanks for the replies

 

2) Since the circuit does not have an equipment grounding conductor and you are not able to identify the switched hot loop and the neutral wire in the ceiling box, we will use the ground portion of the extension cord to assist in identifying the wires.

 

3) 1st off, you need to plug the extension cord into a nearby 3-prong grounded receptacle. The receptacle must be grounded in order for this to work.

 

Next, bring the female end of the extension cord up to the ceiling box. Using your 2-prong AC voltage tester, you will touch 1 probe to either of the 2 ceiling box wires and the other probe will be inserted into the round hole (ground portion) of the extension cord. We need to be able to get 120 volts from the ceiling switched hot loop wire leaving the wall dimmer switch to an equipment ground, thus the reason for the extension cord.

 

The circuit breaker for the lighting circuit needs to be in ON position. Be careful and DO NOT touch any two wires together, otherwise you will have a short and the breaker will trip and sparks will fly.

 

Make sure the dimmer switch is turned up to maximum level. Once you get a 120 volt reading from a ceiling box wire to the extension cord ground (round hole), that's your switched hot loop wire. The other wire in the ceiling box will then be the neutral. This is how to confirm the proper polarity of the wires since you don't have a bare copper equipment ground. Get some black electricians tape and label the ceiling hot wire with it. If you have some white tape, you can label the 2nd wire as this will be your neutral wire.

 

Let me know if this makes sense and then we will do the same at the wall dimmer switch.

Kevin and 2 other Electrical Specialists are ready to help you
Customer: replied 3 years ago.

Kevin,


So I am able to get the light on, but with the dimmer switch there is a little light that is normally on even when I have the light off. Now, it is not on. I feel like there is no "power" to the light switch now. Do I need to do something different at the ceiling to get power to the outlet to be able to turn the light on, off, or dimmed?

1) Did you perform the steps using the extension cord? What were the results?

 

Forget about if the light illuminates for now. You need to identify your hot's, switched loop and neutral since all of your wires are black. You do not know what wire is the hot or the switched loop or the neutral. Thus, that's the purpose of this exercise. Remember, in 1925 when they wired homes using Knob & Tube wiring, they did not have a color code... all wires were black. Thus, we need to find the hot and the neutral so you can match up the new dining room colored wires to the proper ceiling box wires.

 

2) Next, turn the breaker to OFF. Carefully remove the 2 dimmer switch wire nuts that connect to the other wires in the wall switch box, but do not untwist any of the remaining wires that were connected to the dimmer switch.

 

Use the extension cord and perform the same. Spread the 2 bundles of wires apart so they don't short out. Turn the breaker back to ON. Using your 2-prong tester, touch one bundle of the twisted wires inside the wall box. Simultaneously, insert the your 2nd probe into the extension cord round ground hole. Measure for 120 volts. If you don't get 120 volts, move the probe to the other bundle of wires and re-measure. Only 1 bundle of wires measured to ground will give you the 120 volts we are looking for. Once you identify the hot wire to ground, place a piece of black tape on that wire. Confirm that this is the hot feed wire from your main electrical panel by turning the breaker to OFF. If you don't get 120 volts with the breaker OFF, but 120 volts with the breaker ON, then that's your hot wire feeding into the wall switch.

 

3) Refer to the diagram below. The black wire that leaves the switch and goes to the light is your switched hot loop wire. The other wire into the switch is your hot circuit feed from your electrical panel. You need to identify both of these wires in your wall box. Disregard that the diagram is a single pole ON/OFF switch and yours is a dimmer switch. The principle is identical for either type of switch.

 

 

graphic

 

Hello Jamie...........thank you for the excellent service rating as well as the bonus.... much appreciated!

 

If you have any other questions, just let me know.

 

Take care and have a great Sunday................Thanks................Kevin!

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