Can you measure live voltage (240v) to earth?

Question

I know you can to neutral. I want to measure the voltage at the back of a light switch, to see which is the common live.

I want to measure the voltage at the back of a light switch, using a multimeter can i go across the each wire (3 of them) to find the common live, and measure it down to earth (UK hall and landing light circuit).

Answer 1

I don't think you can use earth as a reference in the UK (not 100% sure though). My understanding is you do not solidly ground the neutral like in the US, in which case it would not be a reliable reference. Also, even if you could measure it, one of the travelers will always have voltage, so you have to understand that when measuring. The other traveler could read an induced voltage also. Aren't the terminals labeled in some way? In the US, the common usually has the word common on it, or uses a different color screw from the other two (the brand I use does both).

Answer 2

A light switch doesn't have a common, It has a hot and a switch leg. Common is such a misused term. Common is a term used in control circuits since a hot wire can be a common. The return is called the neutral. The neutral wire is grounded in the panel to the ground. The neutral is not a common. Looks like you should have a professional look at your situation.

Answer 3

Hello, Sounds to me that you working with a three-way switch one with three wires. Which is probably 110 volts. What you call common live, is known as the hot wire. Yes you can measure it to ground if you can find a true ground. A ground wire or maybe a metal water pipe. Hope this helps.

Answer 4

If it is a 3 way switch the bottom wire should be the hot. The top wires are the travelers to the other switch as it sounds to me that this is what you have (ie Hall and Landing light), you can operate it from two places. This answer is for the U.S. I believe your U K standards are very similar.

Answer 5

You lost me...
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