Electrical continuity - potential daft question

[Ammonite]

As part of some recent continuity testing I thought I would double check my meter by testing something that I thought should definitely be isolated, which happened to be the two jubilee clips holding on the rubber end cap of my MD2040 heat exchanger. There is no metal to metal contact at any point as far as I can ascertain and the cap is clean and dry (the clips are not touching anything other than rubber) Having read that conductive and non conductive rubber hose is a thing is it possible the end cap falls into the conductive category? I've removed the clips and checked that neither have pierced the rubber cap but each time I do up the clips I have conductivity. My assumption was that they both must be touching something metallic but I can't find where they are. The meter is working correctly in other tests.

 

[jamie N]

Just as a thought, your fingers aren't touching the probes during the test are they? I've not seen the "conductive rubber hose" thing, so excuse me if I'm stating something eye rollingly obvious!

 

[[194224]]

Take the jubilee clips out of the equation by placing the probes on the rubber end cap (a short distance apart) and see if you have continuity. Actually what do you mean by continuity? How many Ohms?

 

[Ammonite]

I'm not touching the ends of the probes and I'm using the in-built continuity function which beeps when there's continuity. I can't recall the displayed value but the meter is definitely working. If I touch the probes on the rubber there's no continuity which is what has got me scratching my head and I can't for the life of me see where there's metal on metal contact. The rubber is about 4mm thick and I cant find any sign of a split.

 

[[194224]]

Then I am flummoxed I'm afraid. None of my multimeters has a continuity function like yours. I just used the resistance range and measure Ohms as I like to see a measured value. Does the beep indicating continuity depend on a particular resistance range on the meter? I'm not sure that's even a valid question as I don't know your meter, sorry.

Edit...do you get the same effect on both end caps?

 

[Rich T]

Strange, but one possible explanation is the greater contact area of the clips on the rubber is far greater than the tips of the probes, this helping conductivity and hence the reading you are getting. An actual ohms reading would be more useful than using the continuity setting. Also your continuity setting might also be a diode test setting, this will possibly place a small voltage on the probe, contributing to a false resistance reading.

 

[wingcommander]

Steel wire reinforced rubber y any chance??

 

[Ammonite]

It could easily be operator error. Its one of these and I'm selecting the speaker icon two clicks up from the off position rather than the ohms or diode icon.
Auto-Ranging Multimeter VC99 Amp Ohm Volt Meter Multi Tester with Capacitance Frequency Test and Temperature Measurement - Maximum Reading up to 5999 and 2000uF https://amzn.eu/d/dejZpSq

I imagine there's some form of reinforcement in the cap but it's too flexible to be steel. It feels more like a regular engine hose.

 

[Boater Sam]

There is no speaker symbol, diode test, ohm resistance and buzzer are all at the second position clockwise from off.
Are you on the capacitance setting like -][- at the third position?
In which case you could be measuring a tiny capacitance, then its understandable with an auto ranging meter.

 

[Ammonite]

There is no speaker symbol, diode test, ohm resistance and buzzer are all at the second position clockwise from off.
Are you on the capacitance setting like -][- at the third position?
In which case you could be measuring a tiny capacitance, then its understandable with an auto ranging meter.

Sorry - wrong terminology. I meant the audio symbol that beeps at you when resistance is less than (50±10)Ω having just checked the manual.
I'm not seeing the same with the cap on the other end although that does have steel clips rather than stainless. The end caps themselves were bought as a pair. I shall take another look at the weekend and double check the settings I'm using just in case I'm doing something daft. Thanks for your help.

 

[Boater Sam]

There is the possibility that the two clips and a damp ( slightly acid? ) rubber between them is making a rudimentary battery.
The problem with auto ranging meters that have no fixed range settings is that you have to work out the scaling of the reading yourself, . 001v is very alike 100v to 3 figures!

 

[Alex_Blackwood]

As part of some recent continuity testing I thought I would double check my meter by testing something that I thought should definitely be isolated, which happened to be the two jubilee clips holding on the rubber end cap of my MD2040 heat exchanger. There is no metal to metal contact at any point as far as I can ascertain and the cap is clean and dry (the clips are not touching anything other than rubber) Having read that conductive and non conductive rubber hose is a thing is it possible the end cap falls into the conductive category? I've removed the clips and checked that neither have pierced the rubber cap but each time I do up the clips I have conductivity. My assumption was that they both must be touching something metallic but I can't find where they are. The meter is working correctly in other tests.

Not surprising. Irrespective of whether you have the meter correctly set or not. Many "Rubber" components, ranging from the buttons of your TV remote to the soles of electrically conducting footwear, via fuel hoses and bellows/ couplings for pumps and pipes etc. All have some form of conductance. This can take the form of flexible strips bonded into a hose, copper threads or carbon (Graphite) granules within the structure. This is either to ensure equipotential bonding or prevent the build up of static, or both. The tips of your meter may not be making contact to provide a reading . Whereas the surface area of the clips will.
Just noted your meter link. Setting OK.

 

[gordmac]

Any conducting contaminants such as salt?

 

[[194224]]

Not surprising. Irrespective of whether you have the meter correctly set or not. Many "Rubber" components, ranging from the buttons of your TV remote to the soles of electrically conducting footwear, via fuel hoses and bellows/ couplings for pumps and pipes etc. All have some form of conductance. This can take the form of flexible strips bonded into a hose, copper threads or carbon (Graphite) granules within the structure. This is either to ensure equipotential bonding or prevent the build up of static, or both. The tips of your meter may not be making contact to provide a reading . Whereas the surface area of the clips will.
Just noted your meter link. Setting OK.

All very sound but it doesn't explain why one of the pair of end caps exhibits the phenomenon and the other doesn't. The fact that one has steel and the other stainless steel clips I don't think is relevant. Resistivity of the two materials is not orders of magnitude different, in fact resistivity of stainless is higher that non-stainless .

 

[Ammonite]

All very sound but it doesn't explain why one of the pair of end caps exhibits the phenomenon and the other doesn't. The facts that one has steel and the other stainless steel clips I don't think is relevant. Resistivity of the two materials is not orders of magnitude different, in fact resistivity of stainless is higher that non-stainless .

The one with the continuity is attached to the aluminium heat exhanger body and the stainless exhaust elbow / injection point, which is bolted directly to the engine. The one that doesn't is only attached to the heat exchanger and a 3/4" rubber hose from the raw water pump with a plastic anti siphon sat in the middle of this hose...if that makes any difference. Both are obviously clamped to the HE stack as well. The jubilee clamps don't touch any of the metal components in either case.

MD2040-C Heat Exchanger - Marine Diesel Engines

The left hand cap is the one with continuity between the two large clamps

 

[Scubadoo]

This is something I have experienced too but with Port Trim Tab bellow but not the starboard, never could explain it, so reading with interest. It doesn't happen every time and when it does I double checked the rubber for any splits and never found any.

 

[Alex_Blackwood]

All very sound but it doesn't explain why one of the pair of end caps exhibits the phenomenon and the other doesn't. The fact that one has steel and the other stainless steel clips I don't think is relevant. Resistivity of the two materials is not orders of magnitude different, in fact resistivity of stainless is higher that non-stainless .

Quite, Fully agree. One does not know and without being on site and carrying out some testing , one is unlikely to find out! Could be as simple as a bit of contamination during the manufacturing process or whilst in use. Either way I would suggest that the OP can rest easy as it isn't going to cause any problems.

 

[[194224]]

It would be fascinating to be able to join in the testing!