Ask Me Help Desk - Adding another bulb

I have a 20amp line that runs into my basement. There are 2 outlets and 2 4 foot fluorescent fixtures on this line. There is a switch at the top of the steps which turns on/off the fluorescent fixtures. I am trying to add another single bulb fixture at the top of the steps. This is "after" the switch and before the fluorescent fixtures. When I put in this fixture and install the single CFL bulb , the fluorescent fixtures barely light up. The CFL barely lights up as well. It's almost as if there is "too much" on this line. Is that possible? I removed the single bulb fixture and joined the positive and negative wires back together and the fluorescent fixtures work fine again. Why does this one fixture "in front' of the fluorescent fixtures prevent them from lighting fully ?

Thanks!

I need to get your installation straight.

The power source cable, does it go into the box in the garage and then a black/white wire go to the switch?

If so, this is a switch loop not a circuit. What you need to do is to run a wire from box with white connected to the other whites.

The white from the switch is not a neutral. It is being used as a hot conductor to feed the switch. The black conductor at the switch is the return.

This black conductor in turn feeds the lights. Yo need to connect the black from the new light into that connection.

Quote:

Originally Posted by donf

I need to get your installation straight.

The power source cable, does it go into the box in the garage and then a black/white wire go to the switch?

If so, this is a switch loop not a circuit. What you need to do is to run a wire from box with white connected to the other whites.

The white from the switch is not a neutral. It is being used as a hot conductor to feed the switch. The black conductor at the switch is the return.

This black conductor in turn feeds the lights. Yo need to connect the black from the new light into that connection.

Thanks for the reply. The power line from the breaker panel is a black/white 18 gauge cable that goes into a large junction box. The black wire from that is in a wire nut with the black line going up to the switch as well as to another line in the basement. At the switch, the black line is on one terminal in and then out to the black wire on the single bulb fixture. The white from the single bulb fixture ties back down to the white wire in the switch box , is wire-nutted back down to the junctiono box. This white wire feeds to the black wire that goes to the fluorescent fixtures thus providing the power to those fixtures. The white wire coming back from the fluorescents is then wire-nutted to the other white wires including the white wire from the power line. So it goes power black->black on switch->black to single bulb fixture.>white to switch box-> white down to junction box in basement->black wire to fluorescent fixtures->fluorescent fixtures->white back to junction box->wire nut to white wire back to power source cable.

Hope that helps.

Before I get into your layout you need to kill the circuit and replace the cable from the breaker to the junction box.

#18 AWG conductors cannot carry 20 amp, they will burn up from the heat. #12 AWG wires are listed for 20 Amp. The entire circuit can only use #12 AWG if it is in fact a 20 amp circuit.

What amperage is embossed onto the circuit breaker?

You design is seriously flawed. Here is what you should do (for a switch loop circuit):

1) Shut off the power to the main panel board. Remove the circuit breaker.from the panel board, install the #12 AWG conductors into the panel board and connect the black to the circuit breaker, the white to the Neutral bus bar and the bare copper to the ground bus bar. Re-install the circuit breaker. MAKE CERTAIN THE BREAKER IS IN THE OFF POSITION. Now turn the Main Breaker back on.

2) Run the new cable (NM-B 12/2 AWG w/ ground) to the junction box and secure it to the box with the correct clamp.

3) Connect the Power Source cable (to the White going to the switch. Place black tape or color with a sharpie to show that this white is being used as a hot conductor, Also, place the tape or coloring at the switch end. This is the wire that will bring power to the switch. Switches normally do not use a Neutral, however, some specialty will require one.

4) connect the black wire (at the switch) to the top screw on the switch. This wire is the return power line to the junction box.

5) At the junction box, connect the black from the switch to all of the other black conductors.

6) Connect all of the white conductors together.

You now have one switch providing the power to all three lights at the same time. The "switched leg" is the power supply black connected to the remarked white to the bottom of the switch through the switch and then to the device's black conductors via the black conductor in the top screw of the switch.

Remember, if this is a true 20 amp circuit you must use #12 AWG conductors, nothing smaller. If this is a 15 amp circuit you must use nothing smaller then #14 AWG conductors. By code, #14 AWG conductors are the smallest you can use in a residence for branch circuit power.