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Old 03-08-2009, 09:25 PM   #1
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Default Electrical Joint Compounds

Gentlemen:

Hopefully this is the right place for this as I have been striking out-------I have been struggling with coming up with a plausible explanation (in layman terms) as to defining a particular trait that dielectrics or "near" dielectrics" seem to possess when applied in-between, or on to electrically conductive materials (in this case, I am referring to electrical terminals or metal threaded connections)


QUESTION: Why do most any common petroleum ("Vaseline" for example, or a synthetic based dielectric (or "near" dielectric) compounds (from common lithium grease, many pipe dopes, silicone based dielectric greases and even #2 diesel) seem to exhibit the quality of a perfect dielectric compound when tested with a typical DVM, or at lower AC or DC voltages (maybe up to 300V ?) , and yet when put in-between two electrical terminals / connections, or other mechanical connections ( treaded, bolted, etc) , the insulating properties of the compound disappear completely and in general use, seems to make for a better electrical connection??


Is this a phenomenon that that has been discussed in the past in a semi-technical fashion, but I cannot find a reference to? I believe there are many misconceptions about this subject as to how could a dielectric do anything but weaken the connection or insulate two surfaces. A very common example of this property is one you may have under the hood of your car is a WIF (water if fuel) sensor circuit that is part of the fuel filter system on your Dodge, BMW, etc., diesel engine. The probe is immersed in #2 (a "near" dielectric) , but as soon as water is present, the probes complete the circuit although #2 is still in the mix and still coating the probes.. The reason I mention this particular example is because we are current developing a "universal" WIF circuit instrument that can be easily adapted to aftermarket uses.

A few years ago I wrote a small piece for a marine forum on the subject, but I am still not happy with my thoughts and explanations on the subject– a small excerpt:


Dielectric compounds (greases and the like) are used in most connections to help maintain a good electrical contact which is established by the mechanical connection of two or more pieces, whether it be a fixed connection or a switched/sliding contact connection.

To put it another way, always use non-reactive, non-conducting, moisture displacing dielectric greases or lubricants when making electrical connections. These "moisture displacers" prevent moisture and oxygen present in the environment from contacting the metal surfaces of electrical contacts, thereby limiting corrosion and preventing the buildup of resistance within the connection. The basic principle used here is the "exclusion principle" and simply put, it is using a material (a dielectric grease or lubricant in this case) to occupy all of the spaces near and around an electrical connector that could otherwise be occupied by contaminants (possibly conductive) or moisture.

Is there anyone out there that would care to share some thoughts on this subject or steer me to some reference material that would cater to the less formally educated on the subject? I know you guys use assembly type greases of both the non-filled, and the filled type ( aluminum connector stuff), so what is the actual principle makes it work ?


Tony Athens
http://www.sbmar.com


Last edited by MDShunk; 03-08-2009 at 09:37 PM. Reason: edited out your stupid large ass font.
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Old 03-08-2009, 09:33 PM   #2
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Anti-oxidant joint compounds used in electrical wiring are doped with zinc particles. The grease keep out oxygen to prevent corrosion, and the zinc particles enhance conductivity. The connection does not rely on the conductivity of the paste anyhow. There is metal to metal contact between the terminal and the conductor. The zinc doping just enhances any other incidental contact that is not at the precise terminal-to-conductor interface and I suppose reduces any other potential difference that might cause heating of the paste.

Dielectric grease is not really used in electric wiring on terminals (except maybe in your marine industry). Dielectric grease is used to lubricate moving internal parts of disconnects and circuit breakers where the reduction of arcing between internal parts is desirable, (where incidental amounts of grease between metallic parts with potential difference would cause trouble if the grease had less than dielectric properties). A bit of it is also used on plug-on circuit breaker stabs to make it easier to get the breaker plugged on. It's essentially wiped off when metal to metal contact is made at the point of electrical interconnection.

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Old 03-09-2009, 12:28 PM   #3
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"Last edited by MDShunk; Yesterday at 09:37 PM. Reason: edited out your stupid large ass font. "


hard to believe a moderater on a professional site such as this would treat a newcomer this way.
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Old 03-09-2009, 12:39 PM   #4
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I agree with MDShunk and I think it is important to resolve some of the misconceptions that exist, even among professionals. The clarification was right on the money, leaving out only one argumentive aspect: Whether or not common measuring devices and methods can accurately measure the conductivity of dielectrics or corrosion inhibitors. I doubt they can.
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Old 03-09-2009, 06:00 PM   #5
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Quote:
Originally Posted by Joefixit2 View Post
"Last edited by MDShunk; Yesterday at 09:37 PM. Reason: edited out your stupid large ass font. "


hard to believe a moderater on a professional site such as this would treat a newcomer this way.
You didn't see the font.
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Old 03-21-2009, 08:16 PM   #6
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MDShrunk,



Sir, first I must apologize for the "font" ( I picked 3 this time--hope that is OK).. I guess the default font size was very large and I did not look.. I'm a total newbie to your forum and did not know about selecting font size.

As to my question and the answers I received.. I do appreciate the responses, but I'm not sure I got what I was looking for, or even if an answer is actually available.

I am quite familiar with filled (zinc particles, etc) dielectrics and their uses.. These certainly do not apply here nor to my question as they are engineered to operate differently.. Think about a multi-pinned connector, like the many that are used in the wiring harnesses in automotive or marine electronic engine wiring-- For sure, a "filled” dielectric would not be applicable and would only create havoc overall, but a product-type like a Dow Corning silicone dielectric grease, a petroleum based liquid like "Corrosion-X" or a white lithium grease may (ut a product or would) be applicable for assuring a long term high-quality electrical connection in a nasty high-moisture laden environment.

So, can I surmise that the dielectric compound that is applied to these connections does not improve, worsen or degrade the electrical contact, but only helps to maintain the initial contact that is made by the mechanical connection that always "wipes off" when assembled?

Seems too simple an answer to explain to someone that has the misconception that you should never use any type of dielectric compound when trying to make an electrical contact between two connections and that they should always be assembled or left dry.. BTW, all of this is based on my field experience of dealing with electrical connections at all levels of electrical power and signal distribution over the last 27+ yrs in a marine environment and the failures that have occurred and why they have occurred, and why some, or many, have never occurred.

Here is a summary argument of a “typical someone” on the opposite side of the fence:

The term "dielectric" refers to the insulating property of a material. The higher the dielectric strength, the better a material is at "preventing" the flow of electricity. For example on the Corrosion X website they claim... "With a dielectric strength of nearly 30KV, it is exceptional in its ability to stop electrolysis between dissimilar metals." On the Corrosion Block website they say in part... "Corrosion Block actively penetrates the corrosion on the surface of the metal, electrically isolating it from the base metal... with a 40KV dielectric barrier."

Ask yourself the following question... On a diesel engine harness where the nominal voltage is 12 to 24 volts, why do I want to spray my electrical contacts with a material having a dielectric [insulating] film strength of 30,000 or 40,000 volts? I think the answer is... "Don't Do This!"

Not to leave out WD-40 and LPS-1, one of their major claims to fame is they "protect tools from rust." If you go to Radio Shack and purchase a can of Electrical Contact Cleaner you will not be satisfied with its anti-rust properties when sprayed on tools. But tools are made of steel, a material that would NEVER be considered suitable for electrical contacts! Electrical Contact Cleaner is a virtual opposite to petroleum based dielectric sprays! The former is engineered to provide excellent conductivity for silver and gold plated electrical contacts, while the later is a corrosion inhibitor with an insulating film!

Maybe, what I was looking for in explaining the properties and attributes of applying a dielectric compound to electric connections does not exist at any higher level that I have already tried to explain. What I was hoping for was a better way, or an alternate way, to explain how the mechanical connection of pins, plugs, screw contacts, etc. work and how the use and application of the correct dielectric compound will only help to assure and maintain that initial contact made by the connection due to its own mechanical design… I thought there may be something more at the “molecular level” of two components touching each other and that when the film of a dielectric gets thin enough by the mechanical interaction between the two connected pieces, the dielectric property of that compound goes to zero resistance, and hence, the connection is now 100% complete. I guess what is really happening is the components just touch each other through the normal mechanical interaction of their design, and the dielectric just surrounds and fills any spaces that do not touch and keep and degradation on this connection to a minimum by mitigating any oxidation or moisture from reaching the contact area..

Additionally, a perception that I have developed over the years tells me that the other property (lubrication) that a dielectric can add to any type mechanical connection is that the added lubrication between the two connection points in the contact area is actually increased because of less friction between them, and hence, allows a higher contact pressure at the exact connection or touching point(s) .. Yes, that would be a very hard one to quantify………

Thanks again for allowing me to post my thoughts and questions.. Should anyone else care to add more, I will continue to monitor this thread….

Tony
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Old 03-21-2009, 09:28 PM   #7
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I have had no experience with dielectric greases and I am only a second year apprentice so you can shoot this down in flames without offending me.

Dialectrics are not only defined by their insulating properties. The most important property is the ability to deform their electron orbits in an electrostatic field. This is why they are used in capacitors.

Assume you have a contact where the actual surface area in contact is 1 square mm and there is a 10 square mm area where the surfaces are .01 mm apart. Without the dialectric you have a total area of 1 square mm to pass the current through.

If you use a dialectric grease and it has filled those small gaps, that area acts as a capacitor and the effective area of contact is 11 square mm. Larger gaps will not have as much capacitance and not carry as much current.

I don't have the time to do the math but I am sure that it is doable if you want to go to the trouble.
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Old 03-21-2009, 11:16 PM   #8
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Tony, you might be better served by posting on a different type of electrical forum. Most of the people here wire buildings, not boats. You'll have the best luck here: http://www.eng-tips.com/
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Old 03-22-2009, 08:32 AM   #9
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May I ask if you are looking for an antioxidant or a dielectric? The two are entirely different items. The antioxidant is to stop oxidation of metal and the dielectric is to stop electron flow.

One thing for sure is that no type of substance that is flammable should be used for any application of electrical circuits such as Vaseline or any other petroleum based product.
A cotton ball saturated with Vaseline is one of the best items for starting a camp fire known to mankind.

It is my guess that you are looking to stop oxidation of electrical connections on some sort of water craft due to the exposure to salt water. If this is the case, in my opinion, your best approach would be an air tight connection instead of applying something to the connection to stop oxidation. If salt air or moisture cannot get to the connection then there will be little oxidation of the connection.

Another approach would be the type of metal used in the terminations. Metals such as copper, aluminum and silver will oxidize in the best of conditions even with an antioxidant applied. Metals such as stainless steel and surgical steel do not oxidize as easily.
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Old 03-22-2009, 10:05 AM   #10
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Quote:
Originally Posted by jwelectric View Post
One thing for sure is that no type of substance that is flammable should be used for any application of electrical circuits such as Vaseline or any other petroleum based product.
.

Actually many of the lubricants utilized in switchgear for movable parts, breaker fingers, contact surfaces up to the late 70's were petroleum based (I was told this by Pringle and GE). The number one issue was the lubricant would dry out causing seizing or ******ing the action of the movable part.
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Old 03-22-2009, 10:47 AM   #11
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The dielectric grease that I use on open switches is actually non-curing silicone gel. I just looked up what the propellant is, and they use nitrogen in that particular product instead of butane or some of the other flammable propellants. Granted, I know for a fact that some of the other dielectric greases are petroleum based. The orange-yellow stuff from Square D sure is.


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