Protecting low voltage connections from corrosion in marine environment

[Lomax]

I'm about to start making up the battery cabling for my boat, which will be done using hexagonal crimp ring terminals covered by heat shrink tubing. For long term corrosion protection I would like to put some kind of "gunk" in the seam between the terminals and the (PVC) cable sheath, but what kind of gunk exactly? Similarly, I would like to coat the terminal posts and ring terminals with something to stop these from corroding. I see people mentioning silicone grease as suitable for this but would like to confirm before I make any (costly) mistakes - I am concerned that silicone, being an excellent insulator, might actually degrade the connections? I am also concerned about the long-term effects of silicone on the PVC cable insulation, and the heat shrink tubing.

[SeanB]

Use heat shrink with a conformal inner low melting point glue, which melts before the outer fully shrinks and then provides a good seal. Make sure the cable sheath and the connector are clean before shrinking, cleaning with a scotchbrite pad and wiping down with some IPA as well to ensure the best clean surface for the glue to bond to. then over the outside by the connector side some dielectric grease, available at your boating supplier, to keep the connection corrosion free. the grease is non conductive, but as the tightening of the connector to the lugs displaces the grease and provides metal to metal contact, it will not have an effect on the connection, but will keep it free from corrosion for a long time.

[Lomax]

Thank you, now I know what to do. After posting I also found this, detailed, discussion of the pros & cons of "dielectric grease" use on high/low voltage high/low frequency connectors - from which I quote:

In single low-voltage terminals or connections, such as metal-to-metal joints, grounds, or battery posts, almost any pure grease of light viscosity will be acceptable. Caution should be used with greases containing metallic powders to be sure any metal is compatible with the embedded grease metal. Connection enhancement from embedded metal powder is very minor, if it exists at all, and there is increased risk of bad connections if the metal powder has any interaction with the base metals.

In single high voltage connections, such as spark plug boots or other high voltage connectors (x-ray, neon sign, or HV power lines), only pure dielectric silicone greases should be used. Generally a light coating or wipe is all that is required. Dielectric grease will actually increase voltage breakdown across insulators, especially in the presence of moisture. Never use or allow a metalized grease around HV connections.   

The important physical characteristic is that any grease must have low enough viscosity to push out of the way at contact points, be water or liquid resistant, and be stable enough to remain in place as a protectant against moisture and air for a long time. It will not do any good to apply a grease that does not do required functions of excluding air and moisture, and lubricating the interface to prevent galling or fretting, for extended periods of time.

Contrary to silly Internet rumors and articles, silicone dielectric grease will NOT insulate pressure connections. Silicone dielectric grease will prolong connection life as well as, and have just as good conduction performance, as a properly selected metallic powder grease (conductive grease). On the other hand, and [sic] improperly selected "conductive" grease can actually cause connection problems.

[GerryBags]

You could use resorcinol which is an excellent dielectric, but not very common. I had some that I got to repair the cascover on my old Grand Banks woody I used to live on. Much less hazardous would be to melt some ABS or styrene (evergreen rod, for example) in either DCM - dichloromethane, or MEK - methyl-ethyl-ketone. Apply the resultant goo to your exposed metal area and wait a couple of minutes for it to cure and then apply more. Build it up like this and it will be better than the PVC insulation on the rest of the cables and you'll get no corrosion. The solvent has no effect on the PVC by the way.

[rhb]

I reworked the mast  connections for a friend using silicone grease and a couple of layers of heatshrink.  I also slathered silicone grease on all the power panel connections which had corroded from salt air..  I chose the silicone grease because it had a 400 F melting point.  Not much help if the grease oozes out over time.

Unfortunately my friend is deceased and I don't know where the boat is.  It's a documented vessel and I've been meaning to get in touch with his son to see if he knows the vessel number.

Glue has the problem that it is stiff and a gap can develop between the glue and the connectors.

[gildasd]

I work offshore, so this is my daily Lot!

For short term, low exposure, or simply something that needs to be regularly checked: clean with WD40 and cover with Vaseline.

For moderate exposure, storage and medium exposure, clean with WD40, two coats of Tectyl. Note, if you need to tighten a bolt or scratch the Tectyl, apply a new coat. If outside, add aluminium backed grease tape over sensitive stuff like connectors.

For stuff that can get exposed to sea water (not just spray) but not immersed. Take apart, clean with WD40 then with a heavy duty degreaser, paint with conductive Zinc paint, assemble, Tectyl, fill voids with thick high temp grease (that does not go soft or liquid in direct sunlight) and aluminium backed grease tape.

Wavy lines...

But, if at all possible, we use watertight connections boxes (on the cabling and closure) because it’s less of a long term hassle.

[tautech]

Historically here, the power co's used self amalgamating tape and/or Denso tape.

On copper overheads (now mostly obsolete here), the joints when uncovered some decades later looked as the day they were made and although we're not right at the coast, we do get significantly more corrosion than those further inland.

[BravoV]

Another interesting long term (years) characteristic of this hot snot glue exposed for "years" in salt water and sun, from another forum fellow (Rufus), read carefully this particular -> POST and subsequently the -> Proofs, quite interesting imo. 

[BradC]

Historically here, the power co's used self amalgamating tape and/or Denso tape.

On copper overheads (now mostly obsolete here), the joints when uncovered some decades later looked as the day they were made and although we're not right at the coast, we do get significantly more corrosion than those further inland.

+1 for denso tape on anything thicker than your little finger. Pretty much anything subject to corrosion. Amazing stuff.

Silicone grease and self amalgamating tape are my favourite marine treatments for anything passing electrons, but just keeping them dry and away from salt wins. Good quality boxes with quality glands make life easy if you need serviceability.

[Electro Detective]

Brush on regular WD40 sprayed into a container, and keep a check every few weeks and re- apply if necessary

Sealing stuff up also seals up any chance of spotting corrosion problems and creep-age, YMMV