• Mobile App For Android Now Online!

    Download it here. The app is searchable in the Google Play Store under Sailboat Owners.

    Sorry iPhone/iPad users, we are still waiting on Apple. :(

    Click the X in the upper right corner to make this go away

Sealing wire with butyl and heat shrink

Mar 26, 2011
2,868
Corsair F-24 MK I Deale, MD
I read of this on another forum. I've sealed underground cable junctions up too 100 amps / 480V with butyl kits before; there are huge bulk things and I never associated them with marine application.

Ordinarily, we seal wire junctions in damp locations using either a junction box or adhesive lined fittings. If multiple wires must join, it's a challenge to make this compact. A few days ago I was installing some equipment, and ran into a new (to me) problem. The insulation was so thick it would not fit a normal Ancor crimp of the correct size.

What about using a thin wrap of butly under non-adhisive heat shrink? I tried this on a 3-wire junction (it's not difficult to work the butyl between the wires) on deck as well. It seemed to seal to seal up very well. I didn't have tape thin enough for the job, so I used what I had and sort of rolled it out, which is simple. THe heat shrink holds everything very neatly in place.

My primary concern is heat; the butyl can melt and flow easily. I'm not concerned in this case, since these were low amp cables associate with solar panels and were over sized for low voltage drop. They are located where fire danger is nil. In underground cable usage, of course, heat is dissipated to the soil and fire risk is zero. However, I wouldn't be so comfortable with this splice in a high-load line buried back in a panel somewhere.

Thoughts? Is there some better adhesive to use? I can imagine trying to work with polyurethane under heat shrink and doubt it would do as well.
 
Aug 23, 2009
361
Hunter 30 Middle River MD
silicon chalk works well and most formula's are good to 400 hundred degrees F, so heating wouldn't be a problem except in the most extreme conditions.
 
Dec 28, 2009
397
Macgregor M25 trailer
I'd be careful using silicon caulk or adheasives on electrical connections, most of them use acid based catalysts and tend to be corosive to metals.
 
Mar 26, 2011
2,868
Corsair F-24 MK I Deale, MD
For those that have not worked with utility cables and the like, I should have added that splicing with butyl is common practice.

http://www.rfsworld.com/userfiles/pdf/412690.pdf

The question, is where does this approach fit on boats? Generally there are better and easier ways (sealed crimp fittings and junction boxes), but are there some variations with butyl worth adding to the bag of tricks?

The advantages butyl products bring are:

  • No corrosion
  • Long proven on utility wiring
  • very durable seal--does not lose adhesion
  • Can seal multiple-wire junctions
The down side, as with all butyl sealing applications are:

  • Must be constrained because it can cold flow
  • does not like heat or oil (but properly sealed it is used in refinery operations).
  • More time-consuming than adhesive lined heat shrink fittings
 
Last edited:
Feb 6, 1998
11,417
Canadian Sailcraft 36T Casco Bay, ME
While it certainly can work for this application I would be more inclined to reach into my termination organizer and grab the right diameter of heavy walled adhesive lined heat shrink. 20-30 seconds with the heat gun and your done. The problem I can see with heat shrink over butyl is actually sliding it into place over it and not having it grab the heat shrink when trying to get it into place. They also use butyl on underwater cables for phone lines and power lines to islands etc. so I know the stuff can be waterproof BUT there are many different grades of butyl.

I no longer use anything but adhesive lined heat shrink unless I am using clear to shrink over a label for a wire. Well drillers have known the utility of adhesive lined heat shrink for decades now. They use Sta-Kon's to connect the 3' pump leads to the well pump wire. Sta-Kon's are nothing more than adhesive lined heat shrink butts where you first crimp the tinned copper butt than slide the heat shrink over it and shrink it.

These connections reside up to 250' below water for the life of the well pump which can often exceed 20 years. Our last house had a well 275' deep and when the pump failed, lightning hit, we pulled it up to find the Stakons 100% dry after 14 years.
 
Mar 26, 2011
2,868
Corsair F-24 MK I Deale, MD
How do you seal a side-taps with these fittings? I know of some specialized heat shrinks that do this, but they aren't often seen.

Also, there is the rare problem of high-voltage (thick) insulation that goes beyond the pre-shrinkage diameter of the fitting. I was forced to use a larger size of plain shrink wrap and fill the space with electrical-grade butyl, which I had. A very rare occurrence in this business.
 
Feb 6, 1998
11,417
Canadian Sailcraft 36T Casco Bay, ME
How do you seal a side-taps with these fittings? I know of some specialized heat shrinks that do this, but they aren't often seen.

Also, there is the rare problem of high-voltage (thick) insulation that goes beyond the pre-shrinkage diameter of the fitting. I was forced to use a larger size of plain shrink wrap and fill the space with electrical-grade butyl, which I had. A very rare occurrence in this business.

Side taps are hard and I generally avoid them like the plague. When I do come across them or have to use one I generally use 3M Super 33 followed by self vulcanizing tape. Still don't like it but... If I need to tap into something I always try and do it in a space that is as dry as possible.

I have come across that ultra thick insulation a few times and I still use my standard heavy wall heat shrink. I pick the size that just barely fits over the wire jacket then it shrinks to fit both well.

I will have to try some butyl experiments to see how well I can slide heat shrink over it..
 
Aug 23, 2009
361
Hunter 30 Middle River MD
Just to follow up on the silcon and acid question. Don't think the relatively weak acetic acid present (main acid in vinegar) will cause a problem after all sodering rosin often is an acid and curing breaks down the acid in the silicon. Never have had a problem with corrosion on a coated joint. I think keep air and water out is more critical.