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Getting wiring right
04/03/2017

If you like to work on your own boat---install new equipment or troubleshoot and fix problems that may involve a faulty pump or static on your VHF or a device that sometimes trips an electrical circuit when you flip it on---or so your project doesn't wind up looking like this rats nest---you’ve probably read Ed Sherman’s advice. Ed is the go-to tech guy at the American Boat & Yacht Council (his formal title is vice president/education) who has literally written the book on a lot of this stuff for marine technicians. He’s currently teaching electrical courses for both ABYC and techs at the National Marine Electronics Association. In his spare time, he writes a blog tailored for boaters---it’s called Ed’s Boat Tips---and a column for Marine Electronics Journal. Below is part 1 of a recent MEJ article that’s good reading for anyone about to dive into some boat wiring.

 


By Ed Sherman

 Selecting properly sized and rated wiring is something that both the ABYC and NMEA talk about in all their training programs. But even with that I’m still amazed at how many times we encounter undersized wire or wire with totally inappropriate insulation properties being used onboard.

 

Tinned or untinned?

To get things rolling here let’s clear up one of the biggest misnomers I run into at least annually. That is, does ABYC require the use of tinned wire? The answer is that we do not and never have. Every now and then I’ll run into a survey report that will state that the wiring on boat X does not comply with an ABYC requirement for using tinned wire. This is simply wrong.

Now, is tinned wire a better choice onboard? The answer is probably yes, but unlike others I would argue that it’s not as critical as actually installing wiring in such a way that the tinning is essentially unnecessary. The tinning’s sole purpose is to help mitigate corrosion. My contention is that if wiring is installed so that water—one of the needed ingredients to generate corrosion in the first place—is removed from the equation by building into the wiring job things like proper drip loops, elevation of all wiring in bilge areas to above the bilge high water mark, and in the case of sailboats in both the static floating as well as the dynamic floating position, corrosion should never be an issue.

Anyone with any experience onboard boats has seen the impact on wiring from the occasional hosing down with sea water. As you cut off the terminal and begin stripping back insulation you see the black colored copper strands that are indicative of corrosion that has occurred due to water migrating along the conductor via capillary action and leaving behind a ring that is going to underperform. Tinned copper will help to slow down this process for sure, but it will not stop corrosion from occurring altogether.

The best way is to install the wiring so that it will never get water soaked in the first place. I’ve worked on plenty of 50 to 60-year-old boats built before tinned wire was even available in our market. The wiring was in excellent condition if it had been kept dry. So, tinned wire is nice, but not nearly as necessary as some would have you believe.  

 

What about the insulation?

Everyone will undoubtedly agree that the marine environment can be harsh at times. Installations often require large tight bundles of wire and cabling to get pulled through some pretty cramped areas on the boat where heat can build up. For that reason, ABYC standards exist that talk about derating of wire and cable depending upon how many current-carrying conductors are bundled. The larger the bundle, the more the wires get de-rated for amperage handling.

Whether the cable is routed through engine room spaces where average ambient temperature is going to be higher than outside the engine room is one of the key judgement criteria found within the ABYC E-11 standard. Also, understand that the actual temperature rating of the insulation material is also considered here. The standard clearly states that nothing with a temperature rating less than 75°C or 167°F be used in engine room spaces.  Most of the “boat cable” in use today is rated at 105°C, so this is rarely and issue. The only instance I can recall where I saw this violated was with a battery charger that had a factory-installed flex cord plug assembly with a 60°C rating on the cable. This was a new model charger and the manufacturer replaced it without question.

Insulation properties must go far beyond temperature ratings in marine applications. I can recall some years ago listening to a salesman at one of the boat shows touting the fact that the silicon-based insulation on the South African-built catamaran I was onboard was rated to 125°C. Quite impressive except for one small detail that I didn’t discover until some years later when I found myself doing some wiring work on a similar boat. The silicon insulation, although quite soft and supple feeling, had extremely low chafe resistance compared to any of the PVC insulation I had ever dealt with. In fact, I discovered that I didn’t even need wire stripers to remove the insulation as I could tear it off the wire with a pair of pliers with virtually no effort.

While teaching in South Africa about 10 years ago I mentioned this interesting nuance to the group I was with, one of whom ran the chandlery that provided the wire to the builders at the time. He was shocked, of course, and explained that they wanted to keep business local and the product was made in South Africa. Sorry, this stuff may have had more than ample temperature handling characteristics, but more questions need to be answered to determine suitability. How about chemical resistance properties, resistant to oil and gas? Chafe resistance? UV resistance? Insulation voltage rating? These properties need to be considered. In fact, the ABYC requirement is that the pertinent information be embossed on the insulation jacket. Minimally, the following specifications must be on the insulation jacket:

 

CONDUCTORS – DC & AC

11.14.1.1.1

Minimum surface marking of the individual conductors and their

jackets shall include:

11.14.1.1.1.1-type/style,

11.14.1.1.1.2 voltage,

11.14.1.1.1.3 wire size, and

11.14.1.1.1.4 temperature rating, dry.

So, if you see a bunch of wire with no markings on the insulation jacket, ask questions!

 

Next week: Sizing wire correctly.


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