Sealing set-screw type banana plugs with epoxy

[Ushlambad]

Just made some new 12 gauge speaker wires for my home theater setup. I terminated the wires with Sewell Silverback double set screw type bananas. Cranked on the set screws to get as gas tight a connection as possible. Disassembling an existing connection illustrates that I've made a solid impression in the stranded wire, so I would think this has to be quite tight. I think the plugs are pretty robust already, but...

I was thinking of putting a few drops of epoxy into the back of the plugs for two reasons:
1. This will bolster the mechanical connection so I probably will never have to worry about having to redo the connection.
2. This will effectively make the entire connection air tight, so any exposed copper should take a very long time to oxidize. In fact, if there isn't enough oxygen in the remaining air pocket, it will never oxidize.

Basically, this would result in permanent cables, assuming the gold plating on the bananas never corrodes. My question is whether the epoxy will change the resistivity and/or impedence of the plug in any way? I'm assuming, if I crimped down hard enough, the epoxy will not penetrate the seal between the set screw and the copper wire core...

Any thoughts? No need to tell me this is overkill...I know.

 

[Grador]

I wouldn't do this, If anything should happen to the cables you'll have to throw the whole thing out. Unless your cables are in the way of an area with traffic, the mechanical support of the epoxy will have no net benefit (and really you should get your cables out of harms way ASAP). In terms of oxidation, I'd be more worried about it having oxidized in there with no way of knowing since you've epoxied it shut.

 

[Ushlambad]

To play devil's advocate for a second... Filling the plug with epoxy would eliminate any oxygen to the copper. True, a permanent connection would require new banana plug if I ever had to redo it. But I wouldn't have to scrap the whole thing, just snip of the last 5/8"...and a new plug isn't that expensive. Thanks for the quick response Grador.

 

[gmichael]

I would use Loctite instead.

 

[Ushlambad]

gmichael, what's the advantage of loctite?

 

[Grador]

To play devil's advocate for a second... Filling the plug with epoxy would eliminate any oxygen to the copper. True, a permanent connection would require new banana plug if I ever had to redo it. But I wouldn't have to scrap the whole thing, just snip of the last 5/8"...and a new plug isn't that expensive. Thanks for the quick response Grador.

This is all true, but basically to sum up the way I view it, there are potential downsides with very tenuous potential upsides.

 

[gmichael]

gmichael, what's the advantage of loctite?

Loctite is not forever. You could still reuse that plug if needed.

 

[slipperybidness]

Loctite is not forever. You could still reuse that plug if needed.

I believe loctite only dries once it is squeezed into threads, it won't air-dry while exposed to air. That's the way the old-school stuff was, but I'm not sure if they have other formulations these days.

 

[Ushlambad]

I'm still curious, though, whether the epoxy would change the properties of the connection in any way. Should I worry about it potentially making the contact/connection worse?

 

[Grador]

I would avoid filling the cavity for fear of getting some epoxy under some of the strands, but even if that happened I doubt there'd be a noticeable change in the electrical connection.

 

[j_garcia]

They are connectors. If you want permanent, solder them. There is zero difference signal wise in doing so IMO though even soldered.

Yes, I would expect the epoxy WILL interfere or cause corrosion long term, so I would not do this. I really see no upside to doing it. "Air tight" in this case offers zero benefit since the chance of corrosion from the connection is extremely unlikely. If it DOES happen, this is LEAST of connections you will need to worry about. I've used bananas like this for years with no corrosion.

*edit - also need to mention that once you thread the outer sleeves on, the setscrews can only back out a tiny amount before contacting the sleeve, so unless the wire is far smaller than the connector ID leaving a big gap, they aren't going to back out. If there IS a gap, fold the wire over once and reinsert, but I don't expect this is going to be the case with 12AWG.

 

[avengineer]

Mechanical contact reliability is related to several factors:

1. The type of materials, and their oxidation properties
2. The contact pressure per unit area
3. The voltage present at the connection
4. The exposure to an environment that promotes corrosion or oxidation

On the first point, while copper does oxidize, gold does not, hence the use of gold plating on connectors and contacts. Other contact materials used on connectors oxidize very slowly, like nickel. Some quite quickly, like silver. Copper oxidizes slowly over time, but this factor is almost completely eliminated by others that follow.

The second point, contact pressure per unit area: The higher the contact pressure, the more reliable the connection. Large loose connections can be trouble, but smaller high-force connections are highly stable. The aircraft industry, for example, for years preferred high pressure crimp-on connections over solder-on. A crimp tool applies hundreds of pounds of pressure forming the metal into a shape that continues to apply force pretty much forever. For a given contact force, if the area of contact is small the contact pressure is high. Tightening the screws in a banana plug results in a small area, high pressure contact.

Consider that the phone company uses non-gold contacts on bare copper. They are high pressure, low contact area insulation displacement contacts. There are literally billions of these connections, and the picked the most reliable connection method. No gold involved.

Point 3, voltage. Higher voltages literally burn through oxidation. This is because oxidation presents a higher resistance, which when voltage is applied and current flows, the micron-thin oxide layer heats and vaporizes. If the oxidation layer is very thin (new or recently formed) it doesn't take much voltage and current flow to clear it. Speaker level voltages are plenty high enough for this to happen, where as microphone voltages are too low for burn-through.

Number 4, corrosive environment. If the connection is exposed to something like moisture, or worse, sea water, it pretty much needs extremely high pressure or some sort of sealing to be reliable. Crimp on connections are used in marine installations with high reliability. The high pressure of a screw in a banana plug, so long as it does not loosen up, is also adequate. This is a moot point in average homes away from the ocean. The Sewell Silverback connectors are over-kill on the wire side, under-kill on the connector side. One set screw, cranked in tight, is sufficient to create a high pressure contact. The material is 24K gold plated copper, it doesn't get better, and the connector itself won't oxidize at all. Then they added a second screw, which adds nothing, but makes you feel good about buying them. The problem here isn't the screws, or sealing that side of the contact. It's that the banana pin side creates a large, low pressure connection on the banana socket. Each pin contacts the tubular socket with at very least 8 edges of the bands, and probably some of the band body. That spreads the contact force over a very large area, reducing the contact pressure per unit area. However, it's 24K gold plated, so if it goes into another 24K gold plated socket, you have no problems, no oxidation. If you shove it into a nickel plated socket, the nickel will oxidize over a very long time. But none of that matters because of the voltage and current present in a speaker circuit. It's plenty enough to keep micro oxidization burned clean, even without the gold, even without the double screws.

This is all an exercise. One screw alone in a nickel plated connector would do the trick. Sealing, unless you are on a fishing boat in the Atlantic, is pointless. All it accomplishes is making life more difficult.

Ever hear of a speaker connection failing because the contact oxidized? Nope, me neither. In fact, the old cheap spring connections on receivers of decades past, where you shove in a bare piece of wire into a hole always worked because of high contact pressure and high voltage. Spend your money on gold RCA connectors. And don't get me started on the terrible design of HDMI!

A word on the 24K gold plating. It's very, very thin, and 24K is the softest gold there is. It will wear off if you connect and reconnect many times.

 

[Rickster71]

While galvanic corrosion is very common where dissimilar metals are used, there are easier and less drastic solutions than epoxy.

I use something different for high voltage connections.

Below is what I always use on low voltage connections:
DeoxIT® D-Series

 

[j_garcia]

I use Deoxit too. A little dab where they contact and things stay clean for a long time. I have the little nail brush one. It has lasted years because you really don't need much.

 

[avengineer]

While galvanic corrosion is very common where dissimilar metals are used, there are easier and less drastic solutions than epoxy.

I use something different for high voltage connections.

Below is what I always use on low voltage connections:
DeoxIT® D-Series

Galvanic corrosion occurs when two dissimilar metals are immersed in an electrolyte and a DC voltage is applied creating ion migration. In the case of audio connections there should be no DC. Plating with a noble metal (24K gold) retards or prevents galvanic corrosion, and since there's a lack of electrolyte, the citation of galvanic corrosion in the context of this discussion is irrelevant.

There is no point in applying Deoxit unless cleaning is required. Gold on gold connections will not oxidize, and Deoxit in any quantity will have no effect. A high pressure copper to gold contact will also not oxidize.

No treatment to this connection is necessary, or beneficial.

 

[j_garcia]

Gold can get some surface corrosion. The binding posts on the cups on my main speakers have done this, basically losing luster. Not sure if it has any effect on the signal, but I use deoxit to clean that off once in a while. It also serves to clean the contact point when I assemble the connections, but if it looks clean already, I don't bother. I bought the deoxit originally to clean some vintage gear

 

[Rickster71]

Galvanic corrosion occurs when two dissimilar metals are immersed in an electrolyte and a DC voltage is applied creating ion migration. In the case of audio connections there should be no DC. Plating with a noble metal (24K gold) retards or prevents galvanic corrosion, and since there's a lack of electrolyte, the citation of galvanic corrosion in the context of this discussion is irrelevant.

Sorry, you are incorrect on both counts.
I should have also added "Oxidation" to my original post.

Galvanic action doesn't need to be immersed in an electrolyte.
It takes place in very innocuous situations, i.e. when aluminum siding is installed using steel nails instead of the correct aluminum nails.
No electrolyte solution needed.

There is no point in applying Deoxit unless cleaning is required. Gold on gold connections will not oxidize, and Deoxit in any quantity will have no effect. A high pressure copper to gold contact will also not oxidize.

No treatment to this connection is necessary, or beneficial.

Deoxit prevents oxidation, and prevents galvanic action when dissimilar metals are used.

Copper oxidizes (alone) within minutes of being stripped.

I've made thousands upon thousands of electrical connections. Galvanic action and oxidation are common, and products like Noalox Anti-Oxidant Compound are required by the National Electric Code for copper to aluminum & Al to Al connections and all outdoor connections along with dissimilar metal connections.

 

[avengineer]

Sorry, you are incorrect on both counts.
I should have also added "Oxidation" to my original post.

Galvanic action doesn't need to be immersed in an electrolyte.
It takes place in very innocuous situations, i.e. when aluminum siding is installed using steel nails instead of the correct aluminum nails.
No electrolyte solution needed.







Deoxit prevents oxidation, and prevents galvanic action when dissimilar metals are used.

Copper oxidizes (alone) within minutes of being stripped.

I've made thousands upon thousands of electrical connections. Galvanic action and oxidation are common, and products like Noalox Anti-Oxidant Compound are required by the National Electric Code for copper to aluminum & Al to Al connections and all outdoor connections along with dissimilar metal connections.

I would agree if were were actually talking about connecting a steel contact to an aluminum one, or copper to aluminum outdoors, or using bare copper alone. But, sorry, that's not the case. No steel or aluminum mentioned, and as far as I can tell, we aren't outdoors. We have 24K gold, high point contact pressure screws, and then copper.

You are correct given the situations you cite, they just don't apply here. I would also point out that the electrolyte between the steel nails and aluminum siding (or any other outdoor dissimilar menials) is water.

Your thousands of connections pale by comparison to phone companies making billions, relatively low voltage, bare copper, non-plated, non-treated. The difference is, they are high contact point pressure, and not exposed to moisture, not typically outdoors.

The discussion was about trying to seal gold plated banana plugs against corrosion, I believe indoors, which is simply a non-issue.

 

[Rickster71]

I would agree if you didn't just back peddle.

You originally said, "immersed in an electrolyte and a DC voltage is applied"

Me thinks you're wasting time posting in an audio forum.
Especially when the big bucks would be made when you sue CAIG Laboratories for false advertising.

It also sounds like you're also confusing the phone co. instantaneous punch block connection (where oxidation hasn't time or oxygen) to occur.

With that of some guy stripping copper wire in his living room, exposed to room humidity and his oily fingers.

 

[avengineer]

I would agree if you didn't just back peddle.

You originally said, "immersed in an electrolyte and a DC voltage is applied"

Me thinks you're wasting time posting in an audio forum.
Especially when the big bucks would be made when you sue CAIG Laboratories for false advertising.

It also sounds like you're also confusing the phone co. instantaneous punch block connection (where oxidation hasn't time or oxygen) to occur.

With that of some guy stripping copper wire in his living room, exposed to room humidity and his oily fingers.

With all due respect, I stand by what I said. I'm sorry if you don't see that water is the electrolyte, but outdoors, that's what it is. Yes, if you want to call it back-peddaling, corrosion can occur without a DC voltage, but that's not specifically galvanic then, is it?

Nothing to be gained by suing GAIG, they make a good product that is effective when properly applied.

I'm not confusing anything. I'm fully familiar with good ol' 66 blocks, 110 blocks and I've even installed a huge crosspoint switcher with Krone blocks. The idea is, the blade pierces the insulation during connection creating a seal, which is why you might think there is no oxygen or time, but in reality after a longer period of time the seal isn't perfect. Good, but not perfect. The real saving grace is the high pressure.

I'm pretty sure adequately differentiated between the situations here. I'm sorry if you don't recognize the role pressure plays in reliable contact, I'm sure there's nothing I can say that will change that.

Perhaps you should do your own research. My reference material starts with an article from Electronics, April 4, 1974, by Janes H Whitley, "Low-cost Tin, as a plating for contacts, can sometimes be as good as gold" (yes, the title was that long!), in which he charts contact pressure, voltage and current against contact material and reliability. Then an article from Electronic Design, September 27, 1980 by Stephan Ohr, "Materials (gold, non gold): big issue in connectors", which cites the superiority of gold as a low signal contact material. I'm sure there are more recent articles, but those influenced my own systems design and choice of contacts and continue to do so. Remember, these are all low signal, dry, indoor applications.