Incandescent Bulb Dim After Installing Fluorescent

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Old 05-19-13, 12:47 PM
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Question Incandescent Bulb Dim After Installing Fluorescent

Hello,

First, our house was built in 1920 and still has mostly 2 wire, "knob and tube".

A single switch controlled an incandescent bulb at the bottom of our basement stairs. After adding a fixture to the top, that uses a GU24 13W compact fluorescent bulb, by branching off the switch, everything works, but the bottom incandescent bulb is now very weak/dim. The fluorescent works great.

I tested the voltage from the lamp socket at the bottom and it reads 118v. I don't understand. I tried a different bulb and the same thing. I looked online but it seems you can mix fluorescent and incandescent on the same circuit. If that isn't true, could I replace the incandescent with the same type fluorescent and that work?

One last note - there is no ground connection anywhere to these - before or after (no wires there for that or even boxes).

Thanks for any help.
 
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Old 05-19-13, 12:51 PM
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Welcome to the forums! At first glance it appears you may have wired the additional light in "series" with the other lights, rather than in "parallel". Can you describe in detail (or pictures) how you added this fixture's wiring to the old?
 
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Old 05-19-13, 01:00 PM
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Chandler, thanks for the quick reply. If understand this correctly, yes, it is in "series". After I tried to tie both wires to the same switch but I had a problem (I think it was the same). I figured there wasn't a "third wire" / neutral? So I instead took one wire from the switch and tied that to the new fixture. Then from the other side of the fixture to the switch.

What are options if I can't do this another way with present (missing) wiring? Use a incandescent lamp for both?

Thank you.
 
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Old 05-19-13, 01:05 PM
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If there are more than one fixture on this switch, you should come off the fixture with your wiring, hot and neutral and connect them to the hot and neutral of the new fixture.
 
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Old 05-19-13, 01:13 PM
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It is a stairwell and the switch is at the top so its not possible to go off the existing fixture. Is there no way to do this (without running a new wire)? If I return the fluorescent and get a incandescent, would that work in "series"?
 
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Old 05-19-13, 01:34 PM
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Lighting will not work in series, except 1950's Christmas tree lights. Does your switch have a neutral in it? If so, you can come off that neutral and the switched hot to the new fixture, placing it in parallel.
 
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Old 05-19-13, 02:09 PM
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our house was built in 1920 and still has mostly 2 wire, "knob and tube".

A single switch controlled an incandescent bulb at the bottom of our basement stairs. After adding a fixture to the top, that uses a GU24 13W compact fluorescent bulb, by branching off the switch, everything works, but the bottom incandescent bulb is now very weak/dim. The fluorescent works great.

I tested the voltage from the lamp socket at the bottom and it reads 118v... I tried a different bulb and the same thing.

It is a stairwell and the switch is at the top so its not possible to go off the existing fixture. Is there no way to do this (without running a new wire)?

If I return the fluorescent and get a incandescent, would that work in "series"?
All 120V AC electrical loads require a "hot" supply line and a "neutral" drain to work. These days, we run both of those in the same cable or conduit, and usually take both to the switch box.

When wiring was done with individual conductors hung on knobs and fed through tubes, this was never done. One of the two phases was interrupted at the switch and the other went straight to the load. No boxes, as you said. BTW, if you heard in that that it might as easily be the neutral that went to the switch, you're right.

The lampholder for the incandescent light has both hot and neutral connected to it. Only one of those is present at the switch. The puzzle is why your new fluorescent light works great, not why the incandescent one is dim.

An old ungrounded system like this should not be extended. If you want to try, the way to do it is to make a junction box at or near the place where the incandescent light is, and carefully protect each of the two conductors as you bring them into that box through two separate cable clamps. Determine which conductor is hot and which is neutral by using a multimeter and an extension cord plugged into a receptacle with known polarity. From that box, you can run individual conductors in surface conduit to feed the light at the top of the stairs, and mount and connect the incandescent for the bottom. Or a new fluorescent, if you prefer.

The better solution is to have the wiring in your house replaced with modern, safer, materials. Sorry.
 
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Old 05-19-13, 02:34 PM
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Thank you both for the details. I think I'm resolving myself to botching this idea.... for now.

NO MORE QUESTIONS - But if you want details:
The light at the top of the stairs would go out when I removed the bulb from the bottom. Thus, I agree the hot is at the bottom at the top switch is just an extension from that. I also tried switching in parallel (guessing) and series but never got it.

When the bulb is removed from the socket at the bottom, the top 2 wires directly test about 69v (photo: Image 2013.05.19 5:37:52 PM.png). Found this very strange as I expected 0. When the bulb is in, it tests about 118. Weird.

Don't know a lot about this, but found it also strange wires tested near 0 v when on, and 121v when off. (is that norm when current is passing? oops that was a question ) Video of on/off volt reading: IMG_7555.MOV

Later I may try to fish a home run from our electrical box to this for up to date wiring. Problem there is then I'd want just 1 switch for both. Still... one way or the other it seems I'm going to need to get a wire from top of stairs to bottom (which isn't really feasible).

Thanks again!
 
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Old 05-19-13, 02:54 PM
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found it also strange wires tested near 0 v when on, and 121v when off.
Not at all strange for a switch loop. You seem to have only a switch loop at the switch so you can not connect your light there since you have no neutral*. Yoy may need to run srface race (AKA Wiremold) Between the existing light and the new light.

* A white wire isn't always a neutral (grounded conductor). Sometimes it is used as hot (ungrounded conductor) but has not been remarked red or black or any color except gray or green using tape, paint, or felt tip marker.
 
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