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Proper way to tap into 12VDC wire?

17K views 48 replies 14 participants last post by  L124C 
#1 ·
I haven't seen this answered elsewhere.

What is the proper way to tap into a 12VDC wire on my boat?

My C-25 has one lead for cabin lights that goes to all of them; I'd like to tap into it and wire up 2 more. I can't see a way to do it that isn't an invitation to moisture and corrosion.

The automotive style with the forked blade that cuts into the insulation of both wires is not appropriate. Having a terminal block just for lights and running a separate lead for each light seems like over kill.

That leaves cutting the leads (+ and gnd) and using crimp connectors to make a 'T', but the connectors will not shrink and seal properly because one end will have 2 wires coming out.

Is there an approved way?

What if I twist 'em together really good and wrap that with tape? :eek:
 
#5 ·
Consider using a step down crimp butt splice. Anchor sells them. For example 14awg to 16awg and put the two wires in the 14. As suggested you could put something in the two wire side to seal it. I've used hot glue for that and think it worked pretty well (and it dries quick). Just consider any drip paths (put in drip loops as necessary) and it should be fine.
 
#6 ·
I never liked crimp connections, but in a freshwater environment you can get away with them. In a saltwater environment they're nothing but grief.

If you have relatively good access to the area, strip about 1-inch of the insulation from the main wire. Strip about 1.5 inches of insulation from the other wire.

Next, carefully wrap the second wire around the bared area of the first, then solder the joint. After it cools, apply a couple coats of clear, silicone cement to the connection, making sure to overlap onto the insulation by at least 1/4-inch at each end. The connection will never corrode and the connection is as secure as it can possibly be.

Good Luck,

Gary :cool:
 
#9 ·
Actually, I have. However, because I'm old and in-firmed, I tend not to believe everything I read and rely primarily on my own experiences. Having tried every connection method available for the past half-century, IME, soldering and sealing has never resulted in a single failure, and that's with 19 boats, all of which were used extensively in a saltwater environment. I have yet to have a crimp-connection, even the best, most modern sealed connectors, that did not eventually leak and wick up the wire, thus resulting in either reduced voltage, or eventual connection failure.

Different strokes... ;)

Cheers,

Gary :cool:
 
#11 ·
Thanks, guys!

I guess I'll suck it up and wire the new ones to a terminal strip; then add the others to the strip as I replace them with LED. Should be slightly less current draw with a single unbroken conductor to each light, right?

Ken
 
#12 ·
Your long run to the terminal strip is shared, if that's the same gauge wire as the individual wires going to your LED's then it's going to account most of your losses. Also LED's don't draw much power so I doubt it's a big factor. It's all V=IR with V being the voltage lost and R determined by cable gauge and length.

To answer your question specifically (and with unnecessary detail) it depends. A better connection to the battery will always deliver more watts to your load but whether this matters depends on the load. LEDs lights limit current in 3 main ways: a resistor (simplest), a regulator (constant current/brightness) and a switching regulator (most efficient).

In the first example the LED presents as a resistive load so lower voltage actually means lower current but also lower brightness. In the second example the current is the same no matter what so it doesn't matter (to a point) how much voltage gets to the load. And in the 3rd example, the circuit will draw a more-or-less constant power so then yes, lower voltage means higher current. You might be able to tell by looking at the light as you can sometimes see a resistor, or a chip or a circuit board which would roughly correspond to the 3 scenarios I described.

But again, bottom line, with LEDs there is so little current involved that it's unlikely to matter.
 
#14 ·
Please not that the ABYC code calls for no thinner than 16 gauge wire, no matter how small the load is. Best thing is to go to the marine chandlers, get a long piece of 2 16 gauge core, red and yellow, sheathed "boat cable". (boat cable also has the appropriate temp rating for the insulation). Then whenever you need to do some wiring you'll have the right stuff and won't be tempted to use something else.
 
#18 ·
Most boat builders, and marine electrical installers, will run a port/starboard lighting run and perhaps a third over head run. Each light is then pulled off the main feed in a parallel manner often using a two position bus bar.. Running an individual wire from the panel to the light is nice but not necessary if the lighting circuit is sized appropriately for the allowable voltage drop..

Some even ran one main feed up one side to the v-berth then across the v-berth and back down the other side of the boat. Ericson for example did this on many of their boats. By the time you get to the end with incandescent bulbs the voltage drop gets pretty high if the wire is not sized right....
 
#19 ·
Carbon-
"but the connectors will not shrink and seal properly because one end will have 2 wires coming out." And that can be corrected by using butyl or silicone "self vulcanizing" or "self fusing" tape on the connection. Especially on the 2-wire side, where you start the tape on one of the wires, then come around the pair and back over the crimp fitting. Done neatly and allowed to set up overnight, it will fuse down on itself and make a very nice watertight cover.

Given a little time (for multiple coats to set up and dry) you can use Liquid Lectric (i.e. vinyl dip) instead, it also forms a nice seal. Either way you'd want to secure the connection itself to a bulkhead or something to prevent movement from affecting it, the same way you'd secure a terminal strip down to something solid and not leave it dangling.
 
#22 ·
Maine, all this time later I'm seeing you comment about Ericsson and thinking the same guy did a domestic cable and telephone daisychain I had the displeasure to meet. Saves wire, right. (sigh)

L, are you trying to add all your taps up front at the source? Or along the length of a longer run, at different points? "Additions" are pretty much always a compromise, unless you make home runs to the power distribution panel. Lots of options depending on what you are doing and what you'll accept as a compromise. (Cost, convenience, labor, got to finish today but the store is closed...)
 
#25 ·
L, are you trying to add all your taps up front at the source? Or along the length of a longer run, at different points? "Additions" are pretty much always a compromise, unless you make home runs to the power distribution panel. Lots of options depending on what you are doing and what you'll accept as a compromise. (Cost, convenience, labor, got to finish today but the store is closed...)
I'm not adding anything, just trying to eliminate stuff like this from PO's (see picture). Definitely not doing home runs for each light (does anyone do that?).
Just diagnosed a problem and fixed it with a patch.
http://www.sailnet.com/forums/elect...ghting-circuit-affects-radio.html#post1013657
I'm tired of patching and want to come up with a plan to do it right. Thats how I ended up at this thread.
 

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#26 ·
Well, the "gob it all in a wire nut and tape it over" school of design won't win any awards but it can be perfectly safe and effective for a very long time.

You can replace that with a small bus bar, or place multiple rings over a stud, although IIRC all the standards say no more than two rings on one bolt. I don't know any simple, cheap, elegant standard way to do it except a bus bar or distribution panel, or new wire runs back to one.
 
#27 ·
When I did my wiring I ran lighting to the head where I had a terminal block for lighting and mast wiring. That terminal block distributed lighting to the V-birth and Cabin and to the port side of the boat where I used another very small terminal block in the hanging locker to distribute to V-birth and cabin port side.

The small terminal blocks sort of felt like overkill but they really don't take up much space and didn't take much time to install.

That said in some places I struggled with heat shrink but splices but from now on, when it's convenient for non critical lighting I'll just twist the wires together and shrink tube them or wrap with self fusing tape. For places where but splices aren't needed I think that's fine.
 
#31 · (Edited)
When I did my wiring I ran lighting to the head where I had a terminal block for lighting and mast wiring. That terminal block distributed lighting to the V-birth and Cabin and to the port side of the boat where I used another very small terminal block in the hanging locker to distribute to V-birth and cabin port side.
The small terminal blocks sort of felt like overkill but they really don't take up much space and didn't take much time to install.
That said in some places I struggled with heat shrink but splices but from now on, when it's convenient for non critical lighting I'll just twist the wires together and shrink tube them or wrap with self fusing tape. For places where but splices aren't needed I think that's fine.
Thanks for this, I like the approach.
I ordered 2/10 boat cable which I'll run from the panel to a terminal block midships on Port and Starboard. From the blocks, I'll run lighter guage wire to each light using heat shrink butt connectors. I'll also run the grounds from the bow nav lights through the blocks. Bought a couple of project cases from Radio Shack to house the blocks. If (when!) I have a problem with any of the lights, this system should make diagnosis and repair easy.
Thoughts?
Edit: Using shrink tube butt connectors, NOT twisting the wire. As I indicated, I already have that sytem!
 
#28 ·
If you really want overkill, how about one of these on each side of the boat, powered up by a breaker? Run a length of boat cable from the fuse box to each light. Each light will even have it's own fuse! You can't get safer than that.

I have one, powered up by the instruments breaker. Each instrument is then run off an individual fuse. Makes wiring tidy and easy.

Blue Sea Systems 12 Circuit with Negative Bus with Cover from Wholesale Marine
 
#30 ·
I've ordered their inline connecters online from their St. Augustine, FL. office. Basically I have three ways to consider installations - convenience, cost, & criticality. Since this is cabin light wiring, convenience and cost carry more weight than criticality. Obviously connections exposed to weather or submerged connections require more protection than interior wiring. If you treat every installation as being critical you will run out of time, energy, and money trying to make them watertight enough for the bottom of Marianna Trench. Thanks. Steve S.
 
#33 ·
Twist and tape, or simply twist, is the kludge to get home. If you're going to twist wires at least put a properly sized WIRE NUT on top of them. Yeah, it gives surveyors heart attacks but it works an awfully long time, even if you haven't put grease in it or taped it over.

If you're too broke-assed to have a full range of proper marine monel alloy pre-greased wire wraps on board, at least buy the dollar bag from the hardware store and pretend.
 
#37 · (Edited)
I disagree, a wire nut is worse because it completely prevents the joint from being properly sealed. Adhesive shrink over twisted wire (with the twist folded parallel to one of the wires) is a decent and compact connection when such a thing is needed for non-critical circuits.

Also I don't think tape should be used for almost anything. I used some gorilla tape for some abrasion protection in a few places and already regret it. And electrical tape is honestly the worst. Self fusing tape or heat shrink should always be used instead of adhesive tape in my opinion.

Further, I don't currently have a single joint like this. I invested in 100% anchor brand adhesive crimp terminals and butt splices. But one connection I had in mind specifically were my alpenglow lights which came with frustratingly short wire leads. Further, I botched that crimp twice because it was such a pain and each time had to cut off the butt splice and lost even more wire. Had I twisted and shrunk it would have gone more smoothly all around and I have complete confidence it would be reliable.

That's just my thought. I agree it's generally a bad idea so I don't fault people for saying that.
 
#36 ·
L, you won't find the monel wire nuts on the civilian market. They're only sold to authorized personnel, along with the thimble-sized thermite fusion welding cups. (Remove lid from thimble, insert both wires, set off thermite. Voila, wires are fusion welded.)

In the Adult Special Tools section, along with the explosive flush bung cutters for those with many teak deck bungs to reset.
 
#38 ·
Both wire nuts and twisted/tape connections are emergency get home solutions. Wire twisting and wire nuts both work best on single strand wire (Romex), which should never be used on a boat anyway.

The neatest solution is a step down butt connector with 2 wires on the large side and the single wire on the small side, covered with adhesive heat shrink. Even then it is hard to seal the 2 wire end with the heat shrink but if it is long enough it works.

Or terminal blocks which I use most often for this.
 
#39 · (Edited)
Thanks to ideas in this thread, I think I came up with a pretty good solution. Mounted boxes midship, Port and Starboard. The boxes came from Radio shack. Plastic with a aluminum plate cover. Not sure why they do the aluminum as it's redundant, but used it anyway. Drilled a 3/4 hole in the boxes and used a 3/4 rubber grommet to the protect wires. Used 2/10 wires for supply/return from the switch at the panel to the terminal strips. Had a lot of 2/18 I purchased before I knew you don't use 2/18 on a boat, so I used it to run from the terminal strip%
 

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#40 ·
Rat Shack probably included two front panels because it takes up less inventory than two types of boxes. If you are installing switches or sockets in the box, aluminum is less likely to break when you tighten them down. Did you have to go to the "adult only" section in the back of the store to buy them? (G)

You might also want to put a couple of large zip ties on the wires just inside the box, next to the grommet. That makes them too wide to be pulled back out, ensures that anything tugging on the wire run can't pull something loose in the box. Cheap insurance.

"Real" wiring hardware has options to actually clamp the wires where they pass through, but finding that at Rat Shack, haha, not these days, except maybe for AC power cords.
 
#41 · (Edited)
You might also want to put a couple of large zip ties on the wires just inside the box, next to the grommet. That makes them too wide to be pulled back out, ensures that anything tugging on the wire run can't pull something loose in the box. Cheap insurance.
"Real" wiring hardware has options to actually clamp the wires where they pass through, but finding that at Rat Shack, haha, not these days, except maybe for AC power cords.
This is one of the few items of use I've been able to buy from Radio Shack. Every time I go in (rarely) , they don't have something they should carry, or are out of it. Usually, I'm the only customer in a store with three clerks, who know less than I do about the products they carry. I don't know how they stay in business!

Anyway....can you show an example of "real" (ouch!:laugher) hardware for this purpose? I've looked all over and this was the best solution I could find. Bought the wire and terminal strips from Genuine Dealz, and they didn't have anything. I was even considering AC boxes, but these boxes seemed less clumsy.
 
#42 ·
L-
Not really, but if you look at pictures for any "DB9" type clamshell, you'll see there's a small metal clamp that screws over the wires, just inside the shell. That's to prevent them from being pulled out. Similarly, go to any hardware store, look at the boxes and fittings for BX (armored) cable. There's always a wire clamp inside the junction box, and little red plastic chafe liners to go inside the cable ends as well. There are fittings that bolt into the holes in the junction boxes, again with clamps, even though some folks just run a wire through the hole.
Is the clamp overkill? Most of the time, sure. A knot, a ziptie, some type of strain relief is always cheap insurance though. You never know, when the boat gets tossed by a waqke, who's going to grab whatever is nearby. Like a wire bundle.

Digikey and Newark Electronics are good places to get parts, once you wade through the catalogs and ignore any shipping charges. There are a batch 'surplus' suppliers on line as well. Rat Shack? Well, it beats nothing. Sometimes.
 
#43 ·
L-
Not really, but if you look at pictures for any "DB9" type clamshell, you'll see there's a small metal clamp that screws over the wires, just inside the shell. That's to prevent them from being pulled out. Similarly, go to any hardware store, look at the boxes and fittings for BX (armored) cable. There's always a wire clamp inside the junction box, and little red plastic chafe liners to go inside the cable ends as well. There are fittings that bolt into the holes in the junction boxes, again with clamps, even though some folks just run a wire through the hole..
Is the clamp overkill? Most of the time, sure. A knot, a ziptie, some type of strain relief is always cheap insurance though. You never know, when the boat gets tossed by a waqke, who's going to grab whatever is nearby. Like a wire bundle.
No...As I indicated, even the box was probably overkill in this case. Nobody is going to be grabbing these wires. Besides, if I had to add another wire I'd have to drill another hole. They are snuggly contained within the grommet.

Digikey and Newark Electronics are good places to get parts, once you wade through the catalogs and ignore any shipping charges. There are a batch 'surplus' suppliers on line as well. Rat Shack? Well, it beats nothing. Sometimes.
Boy! You aren't kidding about "wading". Thanks for the sources. Though my initial search didn't disclose any boxes much better than the ones from "Rat Shack". I'll search further for my next project.
 
#45 ·
L-
There's a reason some hobbyists use Altoid tins and hardshell sunglass glasses, even small Otterboxes and the like on clearance sales, instead of looking for cases in the shops. Sometimes a trip in the supermarket or the dollar store finds tins or plastic containers that are cheaper--with contents--than "real" boxes.
 
#47 ·
Wow. This thread lives on. :)

I've purchased the 14g boat cable and 2 small terminal strips; I'll scope out the head side of the cabin/head bulkhead for a good place to mount them.

I'm going to go full on professional with the heat shrink crimp connectors.

I need a good 8g crimper for non-insulated battery fittings; I'm getting poor results with yellow slot of my red/blue/yellow Xcelite crimper.

Ken
 
#49 · (Edited)
Wow. This thread lives on. :)
I've purchased the 14g boat cable and 2 small terminal strips; I'll scope out the head side of the cabin/head bulkhead for a good place to mount them.
I'm going to go full on professional with the heat shrink crimp connectors.
I need a good 8g crimper for non-insulated battery fittings; I'm getting poor results with yellow slot of my red/blue/yellow Xcelite crimper.
Ken
It not only "lives on", but inspired me! I searched for it before starting a new thread with the same question. Thats why I laugh when people talk about stale threads. Few topics get stale when you are dealing with Sailboats!
I went "full on professional" on my project as well (apparently, with the exception of the boxes from "Rat Shack"). Genuinedealz.com makes it easy. Check them out for your crimper and wiring supplies. They will even crimp the battery cables for you. I'm not related to them in any way, just a very satisfied customer.
 
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