how to make a short circuit

I need to make a short circuit (don't ask why, long story). There are two 3mm bare wires some 5mm apart elevated some 5mm over a surface. I have limited access to the conductors -- from the top via 2mm hole and through 2mm hole on the surface (which is under the conductors). I have no control over the conductors, it is probably some copper alloy.

My initial idea was to pour conductive powder, but it will not work out, see http://www.experts-exchange.com/Other/Math_Science/Q_28636514.html for details why. I could find conductive powder (inox or graphite), but the wires are probably oxidised too, so it will not work probably.

Mercury might be a solution -- chances are it will dissolve oxide and make proper short circuit. But it is toxic and also might move away from the conductors from vibration. I was considering warm gallium which might work too, but I am not sure if it will dissolve the oxide layer on conductors. Also it is difficult to clean afterwards.

An ideal solution should be easy to execute and cleanup, cost of materials is less of concern.
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gremwellAsked:
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d-glitchCommented:
Here is some info on wire brushes.  I think you might be able to bend, inset, and twist it to make a good contact.
    http://www.mcmaster.com/#tube-wire-brushes/=wbk0lr

The brush will actually do a good job breaking the oxide for a good connection.
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gremwellAuthor Commented:
Commenting on d-glitch's post from another thread. Mercury is toxic and too fluid -- might move away from the conductors too  easily. There are physical constraints which prevent use of wire brushes. You can think of the task at hand as following -- you have a box with two wires inside somewhere near the bottom of the box and you have couple holes -- one on the side of the box and another on the bottom of the box (nearby the conductors). Holes positioned in such a way you cannot easily insert a rod or something to reach the conductors.
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viki2000Commented:
Could you say what voltages, potentials and currents go through those conductors?
Is it the box around the conductors metallic or plastic?
Do you have access to turn on/off the electricity in the conductors?
Could you upload here a picture with the box and conductors?
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gremwellAuthor Commented:
Low voltage, 5-12V.
Low current, below 1mA.
Box is metalic, but painted inside and outside.
I have no pictures, sorry.
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d-glitchCommented:
What current and voltage you are dealing with in this circuit?  How good does your connection need to be?

Oxidized surfaces are not the end of the world.  Mechanical switches make and break billions of times a day.
Friction and microscopic roughness between the mating surfaces break the oxide and allow contact.

A small conical  wire brush, the sort that would be used to clean out a machined hole, could work.
There are also tin-indium alloys that melt around body temperature.  I believe they are non-toxic.
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viki2000Commented:
Is it any problem if you use the metallic box surface, to touch the both conductors and have the same potential?
Or should be only a short-circuit between conductors and isolated of metallic box?
Should be a permanent short-circuit or removable?
Must be hidden? Or can e seen from outside?

You have no pictures, but could you make any? Eventually with a mobile phone?
If you have access to the box for short-circuit, then you can also make pictures.
Or is it a secret, something fraudulently?
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d-glitchCommented:
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gremwellAuthor Commented:
Connection must be good in a sense it should not go off from vibration and tilting the box (say 10 degrees). It should have resistance of few ohm.

Liquid metal is an option. I have already got Gallium from Amazon. But I think it will be difficult to clean afterwards. and the owner of the test setup insists of me cleaning up after my tests. Also it is quite expensive.

As I said there is no direct line of view between holes and the conductors, that is why I was considering more brute-force solution of pouring in a conductive substance. Conical brush on a bent handle might be an option, but it might create non-robust connection, which is blocking factor.
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viki2000Commented:
Through only 2mm hole, how to insert the alloy above?
Melted, then a syringe. And the melted alloy can pass through the needle?
How about cleaning and removing the alloy after he finished the short-circuit test?
Melt again? How, if there is no access?
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viki2000Commented:
If the sort-circuit device is no concern of being view from outside, then why don't you try with something like "Flexible Claw Pick Up Tool", a grabber:
http://www.amazon.com/Flexible-Claw-Pick-Automotive-Mechanic/dp/B000RB7AGY
http://www.amazon.com/gp/product/B000NPR3WU/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687442&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B000RB7AGY&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=12JYB172K6P5JSHW46D0

It should be one thin 2mm, then when it is pushed it expands through hole and after several trial may it garbs the 2 conductors which are only 5mm distance one of another, then it stay with good contact due to the spring of the tool.
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gremwellAuthor Commented:
> Is it any problem if you use the metallic box surface, to touch the both conductors and have the same potential?
>Or should be only a short-circuit between conductors and isolated of metallic box?

It is not a problem to short metallic box to conductors.

> Should it be a permanent short-circuit or removable?

Removable. I must be able to clean up after the test.

> Must be hidden? Or can be seen from outside?

Not important.

> You have no pictures, but could you make any? Eventually with a mobile phone?
> If you have access to the box for short-circuit, then you can also make pictures.
> Or is it a secret, something fraudulently?

I know how my questions look like, but I am not committing any fraud. However, technically, the border between committing fraud and what I do for living (penetration testing) is rather blurred ;). I am under NDA so cannot give any specific details, sorry.
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gremwellAuthor Commented:
I think melted alloy will easily pass through a fine straw. The plan was to attach a straw to a syringe and push it in. It remains an option, but I will probably not do it in practice to avoid ruining the test system. Also I am not sure if how effectively molten metal short-circuit oxidised conductors. But this is something I can test I guess.

For cleanup I can take the box apart, no restrictions there. Cleanup is needed to keep the owner of the system happy, it is not part of the test.

And option with the brush remains on the table. I will try to get some to experiment.
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gremwellAuthor Commented:
> ... why don't you try with something like "Flexible Claw Pick Up Tool" ...

Yes, it is an option too, but more complicated if you have to do it in blind. I would also need a fibrescope (there are some used one on eBay of 2K USD) to steer the process.
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viki2000Commented:
If the cleaning up is no concern, then you may try also a conductive paint, conductive gel, eventually mixed up with the  conductive powder
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☠ MASQ ☠Commented:
Thinking laterally - can you not have an electrical switch which closes to create the short rather than the requirement for something that will flow?  Then you can look at options for things that can close the switch.
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d-glitchCommented:
Maybe go back to larger conductive particles, specifically 1.9 mms ball bearings.
They usually have a chrome surface that resists oxidation.  If you can plug the bottom hole, fill the volume, and keep pressure on the stack (rubber band or stopper on the top) you should be able to get a solid connection.
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gremwellAuthor Commented:
Thanks to all for valuable input.
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JohnBusiness Consultant (Owner)Commented:
I participated in your first question and am a bit late here. I subscribe to the wire brush or rolled up wire to insert through the hole. It might work and remain connected and would be easy to clean up.
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gremwellAuthor Commented:
Thanks for your input, John.
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JohnBusiness Consultant (Owner)Commented:
@gremwell - You are very welcome. I muck around with this stuff in my basement and you posed a couple of very interesting questions.
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viki2000Commented:
For such small current you need a good contact made with pressure in case is not soldered.
The pressure comes from a spring-like contact.
If the number of trials are not important, so you can make contact, then try again until you are sure, then I would try a simple solution.
The 2mm hole is good for a thin conductor, under 1mm, maybe 0.5mm diameter. Then I would make a loop, like half of 8 and the bottom side I will bent them as an L. The conductor must be as a string for violin, guitar, something of stainless steel, a spring-like material. When you bent the conductor in the loop, then you need a small ring to keep the L parts together. I would try that. Maybe tomorrow I can make a picture for you.
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gremwellAuthor Commented:
Number of trials is very important ).
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gremwellAuthor Commented:
@d-glitch, ball bearings is nice alternative to filing a table spoon to harvest inox particles :). They are quite expensive in large quantities though (http://www.ebay.com/itm/10-000-1mm-Chrome-steel-bearing-balls-/380442493456?pt=LH_DefaultDomain_0&hash=item589423c210).
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jmcgOwnerCommented:
Rather than ball bearings, how about birdshot? #12 should fit. Steel or copper-plated lead.
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viki2000Commented:
If it is only temporary short-circuit, as a reset or for some seconds. then I try first an omega wire/conductor made of an elastic material as a spring materials. It is easy to be made and tested.
Something like in the picture below. You insert point1 in the hole, then point 2 and because is elastic, when both points are inside, they should come back to their initial omega shape. Then you just push down and touch the 2 wires.
Omega
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gremwellAuthor Commented:
> Rather than ball bearings, how about birdshot? #12 should fit. Steel or copper-plated lead

Steel will probably oxidise like iron, creating non-conductive film.
Not sure about copper oxides, can't find conclusive data on it, seems to be a semiconductor.
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gremwellAuthor Commented:
@viki, interesting idea. Not sure it is practical for my case, might be difficult to steer the loop inside the box.
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