Multimeter Help Required

[martybli]

Just bought a new multimeter from B&Q and the instructions assume you are a spark! All I want to do at this stage is check that I am not going to get a shock from the screws on my light switch as the show live with my screw driver.

I have put the black lead into the com and the red into the one with a V on my multi meter. I assume I set my multimeter to 600 (as the other option is 200). To test it works can I place the red lead to a red cable I know to be live and where do I put the black lead? Would it then read 240?

Then how would you test the screws on the light switch? I don't want the kids electrocuting.

 

[Adam_151]

Just bought a new multimeter from B&Q and the instructions assume you are a spark!

Sorry, no disrespect to you, but all they assume is you have a high school grasp of physics

I have put the black lead into the com and the red into the one with a V on my multi meter. I assume I set my multimeter to 600 (as the other option is 200).

Yes, and ensure you are on the AC volts range, as opposed to the DC one, look for a wiggly line

To test it works can I place the red lead to a red cable I know to be live and where do I put the black lead? Would it then read 240?

A voltage is the potential difference between two conductors, when we say we have a supply voltage of 230v, that means there is 230v between live and neutral, neutral is tied down to physical earth so that there is ~0v between neutral and the ground which you stand on, and ~230v between live and it, the earth wire is more a less the same potential as neutral and if anything should actually be closer to the physical ground than neutral.

So black onto an earth or a neutral, you don't know if you have a proper earth, and you are unlikely to have a neutral at your switch, so go and play with your multimeter on a lamp holder

Then how would you test the screws on the light switch? I don't want the kids electrocuting.

You could quickly check the voltage between live and earth at the switch , if the earth is open you would probably see something like half the supply voltage (120v) which quickly drops off if you parralleled a load up with the meter

A better way would be to use continuity/low ohms setting, and check continuity to a fly lead connected to something that is connected to your earth. (wire it to the earth of a pin of a plug for example)

An electrician would most likely connect live to earth at the CU, and test between them where he wanted to check for earth continuity, but CUs are best left un-opened if your are a novice

 

[martybli]

Sorry, no disrespect to you, but all they assume is you have a high school grasp of physics

Its been a long time since I was at school!!!!


Just tried the live wire in the switch with the multimeter and got a reading of 244 whilst it was set to 600. I had the black lead in the earth of a wall socket. When I checked the back box I got a reading of 1 so I changed the setting to 200 and got a reading of 2.44. As you originally thought it must be an earth problem so I will try and trace it.

Am I right in thinking that it is safe to put my lights back on now until I get round to finding the fault with the earth?

Thanks a lot for your help with this, Martin

 

[scousespark]

Given that you seem to be unsure of what you are looking for, may I suggest you call a local spark to check the circuit out. The problem you have described would appear to be a live to earth fault (but you may be worrying about nothing as the original indicator was your neon lighting up - not a reliable piece of equipment).

The test required in this instance is an Insulation Resistance test, to ensure check there is a high resistance between the live (Phase and Neutral) conductors and the Earth Conductor. The multimeter you have purchased will not be suitable to carry out this test. Also, as Adam said, inside a consumer unit is a potentially dangerous place for the uninitiated.

 

[martybli]

Think I know what has been done!

Both the two way light switches are connected directly to each other with a twin and earth cable. Both the live and neg going to L1 and L2 and the earth to the back boxes. I tested this by disconnecting everything and doing a continuity test with my meter. This would explain why my earth is not earthed. Also in one switch (Connected to com) there is a single red permanent live which seems to have come directly from the ceiling rose in my kitchen, the other switch also has a single red wire (Connected to com and not always live) which is acting as the switch wire and goes to a junction box then on to the ceiling rose.

The light fitting is earthed OK as I have done a continuity test with the earth in the Junction box I mentioned.

I have since touched with my hands the earth cable between the switches so I know its not live. Is is important that I run an earth to one of the back boxes? Someone at work said they would just leave it (especially as Im moving house this year) but I do not want to leave it in a dangerous state.

Thanks again for the help.

Martin

 

[scousespark]

Sounds like you've had a lot of fun with this one. The way you describe the connections is normal for 2-way switching. The neon screwdriver is not a releiable piece of kit and most sparks I work with don't carry them.
If the switch face plates are plastic you don't need to earth them.