What were they testing and how?

[Ingwe]

During our habitation service, one technician (there were two) went to the side of the van near to the locker where the hook up point is. He took a multimeter and tested what I believe was an earth wire (green and yellow) bolted to the chassis. He said that I should replace the bolt at some point or at least clean the existing bolt.

I intend to do this soon but am guessing that it was the earth for the mains hook-up socket. If I’m right, then was he testing voltage, resistance or continuity? I’d like to test with a multimeter both before and after replacing the bolt.
Thanks.

 

[Odd-no-more]

During our habitation service, one technician (there were two) went to the side of the van near to the locker where the hook up point is. He took a multimeter and tested what I believe was an earth wire (green and yellow) bolted to the chassis. He said that I should replace the bolt at some point or at least clean the existing bolt.

I intend to do this soon but am guessing that it was the earth for the mains hook-up socket. If I’m right, then was he testing voltage, resistance or continuity? I’d like to test with a multimeter both before and after replacing the bolt.
Thanks.

It would have been continuity earth pin in the socket and an earth point on the chassis. Are you sure it was a multimeter and not a low ohms tester?

 

[Ingwe]

It would have been continuity earth pin in the socket and an earth point on the chassis. Are you sure it was a multimeter and not a low ohms tester?

Thank you for this. I’m not sure what the device was; I’d just assumed it was a multimeter because they used one when checking the leisure batteries. So if I tested the continuity of the earth wire using a multimeter, it would show continuity but that’s all?

 

[berni109]

You could test resistance if u have the gear but just clean up the bolt as advised and test continuity to a metal part of the van somewhere othe than the bolt.

 

[Odd-no-more]

Thank you for this. I’m not sure what the device was; I’d just assumed it was a multimeter because they used one when checking the leisure batteries. So if I tested the continuity of the earth wire using a multimeter, it would show continuity but that’s all?

A multimeter is only capable of measuring resistance to about 1 ohm a low ohms tester can get to much lower. The only true test is an earth loop impedance test, which in a MOHO is not a proper test as it would be different at every EHU point. As long as the bolt is clean and the multimeter shows continuity I would be happy with that.

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[autorouter]

So if I tested the continuity of the earth wire using a multimeter, it would show continuity but that’s all?

A continuity test is only for checking metallic continuity along metal like a wire or busbar. It will pass the test even if the resistance is several ohms. An earth connection needs to be a small fraction of an ohm. So it could pass a continuity test and still not be good enough. Most multimeters can't measure resistances of much below 1 ohm, as The Ex-Gasman says.

To get the best indication, touch the probes together and read the display, it will probably be about 0.3 ohms. That's the resistance of the probe leads. Then test the earth connection, and see how much it changes. It should be so low that the reading will hardly change. It's not an accurate test, but it's a good indication.

 

[Ingwe]

A continuity test is only for checking metallic continuity along metal like a wire or busbar. It will pass the test even if the resistance is several ohms. An earth connection needs to be a small fraction of an ohm. So it could pass a continuity test and still not be good enough. Most multimeters can't measure resistances of much below 1 ohm, as The Ex-Gasman says.

To get the best indication, touch the probes together and read the display, it will probably be about 0.3 ohms. That's the resistance of the probe leads. Then test the earth connection, and see how much it changes. It should be so low that the reading will hardly change. It's not an accurate test, but it's a good indication.

Thank you all. I report that I went out the van this morning and had a partially successful morning. After all the advice and following the explanation given by autorouter this morning I tested the earth wire. The probes on the mm read 001. This didn’t change when I tested the earth wire.
However, the bolt attaching the earth wire to the chassis was so corroded, that I was unable to release it and clean properly. I sprayed the bolt and nut liberally with WD40 to try and release it. The bolt-head is buried somewhere inside the chassis amd I was unable to see it. The bottom of the corroded bolt stuck out of the bottom of its corroded nut and both turned when I tried to loosen the nut. I couldn’t get a sufficient grip of the bolt end with a mole grip and manage the 17mm spanner on the nut. Access was pretty tight in any event.
Not wanting to stress the earth spade connector too much by further trying to release the nut (even after waiting 30 minutes after the WD40) I decided to abandon the job and instead simply did as suggested and measured firstly the probes and then the earth point getting 001 on both.
So, for the moment (and definitely until it warms up a bit) I will leave it.
Thank you all for your help, advice and suggestions (especially The Ex-Gasman, autorouter and berni109).

 

[berni109]

Ok u have made some progress but now you have been moving that bolt about u may have reduced the contact area. I would disconnect the wire from the bolt and find another point to attach it to that is a good fix to the metal of the chassis/ bodywork. Or run a new wire from the back of the inlet to a good earth point.
Couple of weeks should be warmer.

 

[Ingwe]

Thank you berni109. I agree. In fact, when I was struggling due to the limited access, I thought it a good idea to drill a hole in the steel bracket obscuring the bolt and connecting the earth wire to a new bolt pushed through the newly drilled hole. Much more accessible.

 

[ctc]

Always worth cleaning earth connections on any 12v vehicle, can make a big difference to the performance of any equipment especially if you are running an older Discovery. For some vehicles there are lists of earth connections available usually on American sites or forums but well worth doing.

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[autorouter]

Not wanting to stress the earth spade connector too much by further trying to release the nut (even after waiting 30 minutes after the WD40) I decided to abandon the job

Plus-Gas is a proper dismantling fluid, WD40 is a Water Dispersant and lubricant, quite good, but not as good as the real thing.

 

[Ian Bosman]

During our habitation service, one technician (there were two) went to the side of the van near to the locker where the hook up point is. He took a multimeter and tested what I believe was an earth wire (green and yellow) bolted to the chassis. He said that I should replace the bolt at some point or at least clean the existing bolt.

I intend to do this soon but am guessing that it was the earth for the mains hook-up socket. If I’m right, then was he testing voltage, resistance or continuity? I’d like to test with a multimeter both before and after replacing the bolt.
Thanks.

Should be testing for a high resistance joint therefore set it to a low a resistance setting (start high then work down to resistance scale to get a good reading, (expect some resistance) on a multimeter, preferably one with a digital readout.

 

[Ingwe]

Plus-Gas is a proper dismantling fluid, WD40 is a Water Dispersant and lubricant, quite good, but not as good as the real thing.

WD40 was all that I had in the van when I did the testing. But yes, I'll get a proper release agent.

 

[pappajohn]

WD40 was all that I had in the van when I did the testing. But yes, I'll get a proper release agent.

If you've relocated the earth wire why bother freeing the old bolt ?

 

[Ingwe]

If you've relocated the earth wire why bother freeing the old bolt ?

I haven't yet relocated the bolt but it is useful to have a release agent in any event. Whilst lying under the van, saw lots of bolts/brackets/stays etc that all looked pretty seized. So future works will probably require use of such an agent.

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[Richard n Ann]

The new bolt should be brass, I was told years ago by a sparkie when I used a steel one in a control panel

 

[Ingwe]

Just by way of an update, a function of the weather, going to France in the car and both of us suffering Covid at the moment, I haven’t do e anything further on this. But today, being the first day I’m allowed (and feeling up to it) I went to check on the van. It’s been left for 7 weeks with connection to hook up being controlled by a timer coming on for two hours every Monday.
The van is in a hangar and so the solar gives no power. The 2 lithium batteries were showing a state of charge of 93%. So I’m quite relieved as there is a Battery Master fitted and the cab battery was reading 12.6volts.
Os on Monday, if I feel up to it, I’ll trek out with the cordless drill, a new brass nut and bolt, a new spade terminal and will fix the earth wire to the new brass bolt in a freshly drilled hole. Leave the old seized nut and bolt where it is.