A carpenter recently added (2) can-lights to an outdoor porch with an on-at-dust-off-at-dawn sensor attached to them. The problem is the single porch light on the house and can-lights under the porch won't work together. That is, either the can-lights are ON or the porch light is ON, not both (cans + porch light) (All 3 lights are hooked up to the same light-switch). The lights can be both wired, however, if I put in a light bulb in the house light, the can lights go off in about a minute. How can I test the particular circuit to see what type of load it is taking? I was using a heat gun on the same circuit for about 30 minutes and it blew the heat gun. That is, the heat gun over-charged and fried. The heat gun was new. I used a second same-model for days doing the same thing on the same circuit before the lighting was installed with no problem. How do I test the line load? How do I know the limits of the line besides the obvious 15-or-20 amp outlet?

Sounds as if when the porch light comes on it fools the light sensor controlling the cans into thinking that's it's day time, and so the cans turn off - is that right? If so, can you add some sort of shade around the light sensor so that it's not fooled by the porch light?

I don't understand what you're talking about regarding using a heat gun that "overcharged and fried." Sounds like a faulty heat gun to me - if the use of the heat gun tripped the circuit breaker that would be a different issue, but here you say that the heat gun broke - that's not the fault of the electric line but rather the design of the heat gun not being able to run too long without overheating.

Thanks for the reply. If this were a "shade" issue, then the lights would go off immediately when the hit with light. This is not the case. The can-lights delay about a minute and a half before they turn off. I tested this several times with different types of light bulbs. And I've shined different light straight into the sensor without the can-lights going out. I think the light-sensor is a UV-light sensor rather than a light-dark sensor. And I vaguely remember reading about a UV sensor taking on some type of circuit modulation.

I would start by checking the voltage at the outlet that fried the heat gun if you have a volt meter. I am wondering if the carpenter messed up the neutral on a shared neutral circuit. If you check the voltage and post it, it will help tkrussell when he checks in.

If I was going to pay somebody for a job, I think I would try to find one licensed in the field.

I agree with Labman, the wiring may have disturbed a shared neutral, which will cause abnormally high voltages to occur. This sounds what is causing the light problems. Inside the cans is a thermal sensor that shuts off power to the lamp in the event the lamp gets too hot.

If you have a volt meter and know how to use it, let us know, we can help you. Really need to know how the circuit is run.

If not, you may be best to hire an electrician to trouble shoot this problem and repair as necessary.

Does the carpenter have the proper license, training, and insurances to be performing electrical work? May be a blessing in disguise this problem surfaced quickly, rather than at night sometime with smoke billowing out of the roof and fire apparatus parked on your lawn.

I used a Radio Shack Digital multimeter set to "V" and measured .017 to .022 Volts or 3.7 to 4.5 mV. That's without the outside can-lights on. So I'll test it when the sun goes down and see if the reading changes substantially. I swapped out regular bulbs with compact fluorescent and also tried LED light bulbs on the single-light/can-light combination. The LEDs have the greatest delay, that is, the can-lights will stay on longer when an LED light bulb is secured to the single-light. Thanks for your input. I didn't think to ask the guy if he was licensed to do the work since he suggested putting the lights in while replacing some pillars on a porch.

How about putting a bucket/tape over the sensor to see what the delay is?

How about putting a bucket/tape over the sensor to see what the delay is?
I think the can lights are connected to a UV-sensor because the can-lights don't turn on if the sensor is covered. That is, if I cover the sensor completely with tape or my hand or material of some kind, the lights don't automatically turn on. This is unlike indoor lights with light-sensors or outdoor solar lights that both respond immediately when something covers the light-sensor.

I would do testing with the sensor bypassed, maybe wire a switch in place of photocell to see correct actions. When good neutral and other connections determined correct, reinstall sensor, any problems, replace sensor. Intermatic makes a photocell that switches instantly
(It is gray and about 2" diameter, they handle a higher load. You won't have to wait for the delay.