Multimeter question

[Eric1066]

Hi all,
I'm replacing a light fitting. It was a cheap plastic thing to a new light fitting that seems to be aluminium.

The light fitting was attached to a metal frame that is grounded, as all metal should be, such as pipes etc....

As the new light fitting is aluminium, I screwed a wooden sheet between the new light fitting and the metal frame.

The screws used to screw the wooden sheet to the metal frame are out of the way and isolated and do not connect or touch the light fitting.

The screws used to screw the light fitting to the wooden block do not pass through the block. Therefore haven't pierced through and touching the metal frame above.

What does all this have to do with a multimeter?? Well...

I want to make sure I haven't electrified the frame.

I first do a continuity test, using the audible sound setting on the multimeter. I get no sound. Great, I think.

I flick on the power.

Just to be sure though. I won't touch anything and proceed to do a power test.

Using the multimeter, red probe on live (hot) wire inside the light fitting and black probe on neutral wire inside the light fitting... 240V. Great!

Now, my key worry, have I electrified the metal frame? I keep the red probe on live (hot) but I now touch the black probe on to the metal frame... it reads..... 240V... huh?? What?!?!?

Then I think I'm just being stupid, the metal frame goes in to the ground, no different to a ground rod and it has a ground wire going back to the breaker box... so I think that the multimeter has become the pathway...

If I want to know if I have electrified the frame i need to see if the frame is 'hot'. So I touch the frame with the red probe and now use the black probe on the neutral wire inside the light fitting... this reads ZERO.

HOWEVER, all this has shook me a little.

IS the multimeter completing this circuit AND was the pathway for a hot wire to ground via the frame? Or am I getting this wrong and I have, somehow, electrified the frame???

I guess what I am asking. If i touch, with a probe, ANY live/hot wire and touch another probe to ANYTHING neutral or grounded, that isn't in the specific circuit, such as this metal frame, would I see 240v displayed???

I have a feeling I am freaking out about nothing, but, how am I supposed to test for this scenario???

Any help greatly appreciated!!

 

[binky]

Yes, is the short answer, you are displaying the potential difference between two items, one at 240V one at zero volts.

 

[Eric1066]

Yes, is the short answer, you are displaying the potential difference between two items, one at 240V one at zero volts.

I'm sorry. Thank you for the reply, much appreciated...

But, Yes is the answer to which of my questions... that I have electrified the metal frame?

Or the 240v reading that freaked me out?

 

[Eric1066]

Yes, is the short answer, you are displaying the potential difference between two items, one at 240V one at zero volts.

I'm so sorry, reading that again I'm assuming you're explaining why I see 240v displayed on the meter... potential difference... ok....

That doesn't mean anything to me. Is there 240v electric running across my frame and if i touch it I will get shocked... or, is the 240v displayed because this is not how to test if I have electrified the frame and touching ANY hot wire to ANY neutral/ground would display this despite no actual live power is running along the metal frame?

For example: an independent free standing metal ladder that has been earthed, which I know I can touch and is not electrified in any way. If i touch it with a probe and the other probe is on a live wire out of a nearby socket... would my display read 240v???

And if this is so, then this is not how to test the electrification of something. So, if I wanted to know isomething was electrified, using as an example again, an independent metal ladder? how would I do that?

i know that there are these screwdriver looking things with a little light, but I dont have one of those, i thought the multimeter would be better.

Please, with no liability to anyone and with the information and the installation description I have given, lets call this a perfectly 100% described hypothetical situation, is the metal frame going to electrocute someone?

 

[Marvo]

...............Using the multimeter, red probe on live (hot) wire inside the light fitting and black probe on neutral wire inside the light fitting... 240V. Great!

........I keep the red probe on live (hot) but I now touch the black probe on to the metal frame... it reads..... 240V... huh?? What?!?!?

.........So I touch the frame with the red probe and now use the black probe on the neutral wire inside the light fitting... this reads ZERO.

All these test results would be as expected.

As Binky said, the tester will show you the difference in voltage between the two probes. The first test is between live and neutral so you would expect the voltage difference to be 240v. The second test is between live and the metal frame which will be grounded/earthed so again you would expect to see 240v. The third test is between the ground/earth which is zero volts and the neeutral which is also at zero volts so the voltage difference between them is 0v which is what the tester showed you.

 

[Eric1066]

Thanks for the replies.

I think I get what you are saying. So when I tested the frame and the neutral wire, I got 0v, this means there's no electric running through the frame.

So when I tested the live wire and the earthed metal frame all I did was prove that my live wire is live.

I appreciate all your help. I was hoping for an answer that was more like touchy wirey thing you go bang bang. but I think I'm just gonna touch the frame and see if I get shocked, as I'm still not sure what the correct way to see IF something has power running through it, is.

Seems to be something that needs answering. In a basic laymans way!

EVERY video on Youtube I looked at always goes back to 'wires'. Even I know that. Touch any wire with a probe and one probe on the earth cable and I'll soon now which is live and which is neutral. But when dealing with objects there doesn't seem to be anything.

I just want to know if I'm staring at a ladder, or anything metallic, out in the world, there are no wires around. Just me, a multimeter and an object... what would I do to see if this thing has electric running through it?

Or another way to put it...

Im in a field. I come across a metal fence... it goes for miles in both directions. There's no boxes near it, just a fence... and I happen to have a multimeter on me... what would I do to see if it's an electric fence??

 

[binky]

Im in a field. I come across a metal fence... it goes for miles in both directions. There's no boxes near it, just a fence... and I happen to have a multimeter on me... what would I do to see if it's an electric fence??

If it was electrified it would have insulators of some sort, or any charge would just dissipate into the ground.

You could bang an earth spike in and test with your multimeter between spike and fence, or go old school and get a long blade of grass and touch it to the fence. Fencing is usually 12v so it's not dangerous as such.

 

[Eric1066]

If it was electrified it would have insulators of some sort, or any charge would just dissipate into the ground.

You could bang an earth spike in and test with your multimeter between spike and fence, or go old school and get a long blade of grass and touch it to the fence. Fencing is usually 12v so it's not dangerous as such.

Got you! Ok thanks.

I just touched the frame... i figured as its above me, if I got shocked I'd just fall to the ground and away from it. No probs. Anyways, no shocks so I'm guessing I did it right. Light works too.

Thanks.

 

[Eric1066]

And this wasn't to avoid paying for a sparky, i'm in Cyprus and can never seem to get one to come out, well, unless I want something done 3 weeks on Sunday... not including the cancellations so nearer 6 weeks. and then, even when I do get one out turns out the last one did a crappy job.

I've had solar panels installed, and they told me I had leakages, a reading of 0.001... cant remember how many 0's. Which is the worst possible result apparently. It needs to be 1 to be perfect, but no where is perfect, just get as close to 1 they told me... anyway, I need to get the leakages sorted before the electric company comes to check everything and turn the solar on. Ok, i call an electrician. He comes out eventually, does what he does and tells me its all done €200 later.

Because everything takes so long here I didnt want to risk it not having been done right and for the electric company to not approve the installation and send me another 3 months down the line... so I called another electrician. He checks everything, says its all good, that the last guy missed a couple of things... €60.

So yesterday the solar installers came to check everything a couple of days before the electric company come to do their checks (which is tomorrow) and to make sure I've sorted the leakages... he does his tests and asks me... why haven't you dealt with the leakages? Huh???? What??? I've had 2 electricians here! Apparently there's been a minor improvement.

I dont know anyone here and have no idea what I should be looking for. Actually if anyone knows of a good electrician in Cyprus, please let me know!!

 

[ProDave]

What do the instructions with the light fitting say? Is it class 1 (needs an earth and will have an earth terminal) or class 2 (square inside square symbol and no earth terminal)?

Why have you gone to great lengths to insulate the frame of the light from the earther metal plate you are attaching to. Even if class 2, there is no harm in connecting the frame of the light to earth. That would be the safer option.

 

[Eric1066]

There wasn't any instructions as its a light fitting I removed from elsewhere and had in my garage. It does have an earth terminal... i didnt even think of that, i think you're right

I suppose my cousin frightened me... the fitting is metal and the frame is metal... put a wooden board between them...

So I don't need a wooden board between them?

 

[ProDave]

Remove the wooden board and connect the earth.

Reading your later posts you have other problems in the house I don't even understand what you are measuring when you talk about leakage, if you want help with that we need to know what you are measuring from where to where and what units you are talking about. A simple multimeter is not the tool to use for leakage measurements.

 

[Eric1066]

For the leakages I don't know. It wasn't me and yes, the solar panel installers used another tool with a display. I do not know what they do. However we had to go around the house turning everything off.

They just said that the reading is 0.001 or something like that, could be 0.01. Either way they said that was the worst possible result. Leakages everywhere. They said get to near 1. Whether that means 0.9 or 0.8 i have no idea, nor can I measure it. I also do not know what this metric even is. 0.01 of what?? No idea. They said get an electrician and they would have the tool.

The 2 electricians that came claimed all the leakages were with the outdoor lights and sockets. They dealt with those. Mostly using silicone around everything.

Apparently that was it.

Then yesterday the solar installers came back, just to see what had been done. And they say their tool still shows abnormally high leakages. Its improved from 0.01, but i didn't ask what the new number was as its meaningless to me, but it was over the limit allowed. He said that the improvements were negligible.

What I do know, there are parts of the house where there is a steady 8v running through the earth wire. I asked about this and was told... 'not to worry about it.' I have no idea what this is or whether its a leak. Could be a separate issue.

 

[ProDave]

Leakage is normally measured in Mega Ohms, so 1 Mega Ohm might be the target in the regs where you are . If the electrician found high leakage in the outside sockets and lights he should have disconnected them and tried again. The high leakage might be due to damp getting in, but silicone on it's own won't immediately solve that. It might stop water getting in again if the fittings have been properly dried out and good readings restored.

It sounds like you need a better electrician, if only to disconnect the things causing high leakage to get your solar connected and working and you can worry about fixing those high leakage things later.

 

[Eric1066]

Great idea! Thank you so much!

 

[binky]

Great idea! Thank you so much!

Those dirty of test numbers are showing almost a dead short, but could also just be something connected to the circuit. It's a bit hard to give advice on foreign electrics as the standards aren't the same as the UK.

 

[johnb2713]

If it was electrified it would have insulators of some sort, or any charge would just dissipate into the ground.

You could bang an earth spike in and test with your multimeter between spike and fence, or go old school and get a long blade of grass and touch it to the fence. Fencing is usually 12v so it's not dangerous as such.

It most definitely is not 12v, it's usually between 2000v and 9600v, the higher voltages used in winter time to penetrate the winter coats.

 

[binky]

It most definitely is not 12v, it's usually between 2000v and 9600v, the higher voltages used in winter time to penetrate the winter coats.View attachment 15439

Don't think there's many 30km fences in the UK. Anyway it's not the volts that kill, it's the amps. Volts jolts, to coin an old phrase

 

[kerching]

Never straddle an electric fence, no matter how much your mates bet you

 

[MikeJhn]