0

I have installed a ceiling light myself (there is no ground wire in the light unit).

I want to confirm that electricity is not flowing through the unit and it is safe to touch the unit. Can I use a multimeter to test this or do I need a no-contact voltage detector (like this one)?

If a multimeter can be used then how?

I have this multimeter:

enter image description here

4 Answers 4

4

If the light fitting requires an earth / ground connection then it would be foolish to use it without the earth / ground connection. The earth connection is designed to prevent the metallic parts going live in the event of an internal fault. It also causes the fuse / circuit breaker to trip when a fault does occur.

Even if you do prove that the fitting is isolated today it doesn't guarantee that a fault won't occur in the future.

Can a multimeter be used to detect if current is flowing through an appliance's body?

Current will only flow when there is a path from the live supply to neutral or ground. The danger is when voltage is present on any of the exposed conducting surfaces.

4

Set "AC 600 V" range. Connect the one (black) voltmeter's probe to the nearest earth wire (green and yellow); you may need to use an extension wire. Where to find it depends on the AC system in your country. For example, where I live, we use the so-called Shuko. It has "two flat contact areas on the top and bottom side of the plug and socket" that are connected to the earth (or neutral) wire. So, connect the black voltmeter probe to one of the two metal plates on the socket. Also, if your plumbing has iron pipes, you can use the faucet as "earth". Finally, you can use the housing of a grounded electrical appliance as "earth".

Then touch the metal parts of the ceiling light by the other (red) probe to see if there is a voltage.

A basic safety rule in such experiments is to work with one hand.

4
  • thanks. I didn't understand what you meant by "nearest neutral wire. I don't have neutral wires hang around. Dec 28, 2021 at 12:47
  • I actually meant the earth wire (green and yellow). For your purpose, they are the same but it is easier to find the earth wire. It depends on the AC system in your country. For example, where I live, we use the so-called Shuko. It has "two flat contact areas on the top and bottom side of the plug and socket" that are connected to the earth (or neutral) wire. So, connect the black voltmeter probe to one of the two metal plates on the socket. Dec 28, 2021 at 13:28
  • Also, if your plumbing has iron pipes, you can use the faucet as "earth". Finally, you can use the housing of a grounded electrical appliance as "earth". A basic safety rule in such experiments is to work with one hand. Dec 28, 2021 at 13:37
  • 1
    You can edit your answer to correct it. Dec 28, 2021 at 23:14
3

I want to confirm that electricity is not flowing through the unit and it is safe to touch the unit.

I would check for voltage, not current. Even if no current is flowing, a dangerous voltage could be present that would kill you.

Set your Cat III meter to the 600 V AC range marked "V~". Put your black lead into the "COM" socket on the multimeter and the red lead into the right hand "V" socket.

Don't do anything if there is water on the floor or elsewhere. If possible wear gloves - even typical thin synthetic woven work gloves will give a small amount of protection.

First check your meter by carefully probing a known live outlet and ensure it shows the appropriate value (230 or 120 etc depending on where you live)

Second, at the main panel (consumer unit) turn off the circuit for the ceiling light and carefully probe the two ceiling light connections. The meter should read zero.

Third re-probe the known live outlet - this is to make sure your meter didn't fail between the above two steps giving you a false reading of zero.


Related:

1
  • Be sure to remove the protective caps from the probes.
    – fred_dot_u
    Dec 28, 2021 at 16:03
1

The only time a meter like that is useful is if the fixture you replaced is on a box installed prior to an equipment ground being required. It could measure if voltage is present on the frame of the fixture that has potential for current to flow to ground if a path was made. Connect the leads to the COM and mAVΩ ports, set to 600v remove lead protectors, touch one to a known earth/ground point and the other to the fixture chassis. Some cheap meters may error and display a volt or two, but the display should show zero if safe. The hardest part about that is identifying an actual ground connection which would likely be a plumbing or heating pipe.

No ground wire either means either you have a metallic raceway system and metal box that provides the earth/ground path, or the wire is missing due to age or damage and there is no ground.

If you have a metallic raceway system then you need to connect the fixture ground to the box, in the US the box would have a hole for a 10-32 screw to make this connection. This ground connection would direct any current leaked to frame to ground and cause the breaker or fuse to blow. No test with that meter is really necessary.

If no ground is present because of damage then really you are obligated to repair it and bring it up to code. No test with that meter is really necessary.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.