Electrical wiring question (outdoor post lamp)

Factual Questions
1

I have a post lamp in my front yard that hasn’t been used for several years, and I’m trying to get it working again. It’s the type that has a lamp on top with a sensor to turn it on at dark and off during the day, and also has an electrical outlet on the post. The wiring is fed from an outside GFCI outlet on my house.

The problem is that whenever I connect all the wires together it trips the GFCI outlet. I have everything wired according to instructions as follows:

[ul]
[li]Black wires for source, post outlet and sensor connected together[/li][li]Red wire from sensor connected to black wire from lamp[/li][li]All white wires (source, post outlet, sensor, lamp) connected together[/li][li]All ground wires connected together[/li][/ul]

If I connect only the post outlet everything is fine. The GFCI does not trip and I can measure 110V at the outlet.

If I connect the outlet and lamp only (bypassing the sensor) the outlet does not trip (unless there is a light bulb in the socket, then it does).

If I add the sensor into the mix, the GFCI trips with or without light bulb.

Using my trusty multi-meter I get the following readings on the ohms setting (this is with everything disconnected).

[ul]
[li]Between the black and white wires on the lamp fixture there is no reading with the bulb out, and complete continuity with the bulb in.[/li][li]Between the black and white wires on the sensor, there is no reading on the X10 scale, but on the XK scale the needle moves about 1/8 of the way across (20K ohms if I’m reading the meter right).[/li][/ul]

I’ve replaced the sensor (twice) and the lamp fixture, but I still can’t get it to work. Any of you electrician dopers have suggestions?

2

It sounds as though the wiring leading to the lampholder from the post receptacle up the inside of the post is damaged. When you’re completing the circuit by either installing a lamp or connecting the Cad Cell eye, sufficient leakage current is present to trip the GFCI. The only other possibility which comes to mind is that the GFCI receptacle at the house is defective. Does the GFCI receptacle trip when you plug something into it? I’d recheck all connections to ensure that they are clean, tight and well-bonded, as well as making sure the wiring within the post is free of abrasion or other damage.

3

Thanks, DWC. I think you’re right, because when I plug anything into the outlet it also trips. The GFCI outlet works OK, but any load downstream causes it to trip. I think I have a pretty good idea where the damage may be, and if so, it will be easy to fix. Otherwise I may have to dig up my front lawn, which I definitely don’t want to do.

Thanks for your help.

4

Before you tear into the lamp post turn off the breaker to the exterior GFI outlet on your house. Check to make certain that the power to the outlet is off. Then pull the receptacle and make sure it is wired correctly. As I understand what you wrote, if you plug any load at all directly into the GFI outlet at the outlet and not out at the lamp post, the GFI trips.

5

No, the GFCI outlet works perfectly with things plugged in at the outlet. It trips when anything is plugged in at the post (or other downstream outlet).

Here is the setup. I’ll try to describe this so it doesn’t get too confusing.

Inside the garage at the front of the house is an electrical junction box near the ceiling. Into the top of this box is a 12/2 wire from the breaker box (after passing thru a couple of other outlets for the freezer and garage door opener). This is on a 20A breaker.

Going off to the right is a 12/2 wire to a motion sensor light mounted on the front of the garage.

To the left is a 12/2 wire to an outlet under the eave of the garage for Christmas lights and from there to the post lamp. BTW all of these wires are in counduit.

Going down from the box is where I think my problem is. There is a 12/3 wire in the conduit, plus a single red wire (making essentially a 12/4 with one wire outside the sheath). This goes down to a box with a switch for the motion lights, and then farther down to the GFCI outlet on the front of the garage.

In the box with the switch, the black from up above goes to the switch, and also to the black of the 12/3 going to the GFCI. The red (inside the sheath) goes to the other side of the switch, and up top is connected to the black wire for the motion lights. The other red wire ties to the red wire going to the GFCI. At the GFCI, the black wire goes to the LINE side of the outlet and the red wire to the LOAD side of the outlet. Up at the top, the lone red wire goes to the black wire for the Christmas lights/post.

With me so far? Here is where the plot thickens. This past month they’ve been redoing the soffit/fascia on my house, so I pretty much had to take all this apart and put it back together again while they undid the electrical boxes on the outide of the garage. Before I started mucking with it, the red wire coming from the GFCI was there, but not in use. The lonesome red wire in the conduit was not connected to anything. The Christmas outlet/post lamp was fed directly from the source wire and had a GFCI outlet of its own.

“Aha!” says I, after verifying that all the wires did indeed go where I thought. “I don’t need two GFCI outlets here, I can hook up these unused red wires and put in a standard outlet here and still have ground fault protection.”

I now suspect that there is a reason these wires were unused in the first place. I was confused because I thought the Christmas light outlet worked. I checked it with my meter and got 110V reading, but until tonight I never actually plugged anything into it. (Want to guess what happened when I did?)

I’m betting that when I disconnect the mysterious red wires and put the GFCI outlet back in that circuit everything will work just fine and I’ll confirm that I really didn’t need to but a new light fixture and 2 new sensors.

6

Also, I forgot to mention that the motion sensor lights work perfectly, as does the aforementioned GFCI outlet.

7

Well, I tried to draw out what you described to help visualize it, and it gets murky with the switching legs. It does sound as though you’ve created a situation wherein any load isn’t balanced between the hot and neutral conductors as seen by the GFCI, which creates the trip condition.

8

Thanks. My gut feelilng is that the lonesome red wire (probably not up to code anyway) had some of the insulation scraped off while being pushed into the conduit and is probably shorting to ground somewhere.