Electrical testing

[Rookie]

Funny story....

Years ago, I installed HVAC. Last thing to do for the day was to wire the furnace into the main in the garage, but there was a huge puddle of water. Nervously, I start putting my screwdriver in the panel to attach the ground wire, and I feel this vibration. I screamed (like a girl), threw my screwdriver one way, and dove the other way. When I realized what had happened, I called my wife and told her, "DON'T EVER PAGE ME WHEN I'M STANDING IN A PUDDLE OF WATER WORKING IN A PANEL!"

 

[churchmouse]

Funny story....

Years ago, I installed HVAC. Last thing to do for the day was to wire the furnace into the main in the garage, but there was a huge puddle of water. Nervously, I start putting my screwdriver in the panel to attach the ground wire, and I feel this vibration. I screamed (like a girl), threw my screwdriver one way, and dove the other way. When I realized what had happened, I called my wife and told her, "DON'T EVER PAGE ME WHEN I'M STANDING IN A PUDDLE OF WATER WORKING IN A PANEL!"

I can see this.....literally.

 

[dudley0]

If you get a decent sniffer (non-contact electrical tester) just climb up on the ladder and sweep the fixture. Take the cover off and you will see the wires that feed it. Sweep in there and you should get a light, or tone. Now start flipping breakers and testing as you go. Then you know which breaker it is. The dusk to dawn wiring will not go all the way to your breaker box, it will be housed inside the fixture. This involves more climbing but is the safer method.

Mark the breaker and be sure nobody else is working who might flip it back on. Lock it out if that is a problem. While the breaker is off check other lights and receptacles in the general area that might be on the same circuit. Then you are on your way to solving the mystery of breakers.

Also, if you have two outside lights that you are replacing do NOT trust that all are off just because you killed power to one of them. Sometimes people pull those from the closest circuit available, which isn't always the same as the other fixtures.

 

[Ballistix]

I work on hot circuits frequently, but I don't recommend it. 110 kills more people than 220.

If I understand your question, yes there will be power at the sensor if the breaker is on, and no there will not be power past the sensor during daylight provided the sensor works properly.
You will need to test the circuit at the sensor. Use a volt meter to determine if the circuit is hot.
Most people's landline phone have an intercom feature, so connect the volt meter and have someone trip the breakers until the meter reads zero. The intercom makes it much easier than running up and down a ladder.

Just my