kubark42

Modern wiring standards

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I was looking at the marine wiring spec for cabin and nav lights and noticed that it's largely built around spec'ing for incandescent lights. Of course, the modern trend is toward LEDs which consume 10x less and so the required copper is arguably 10x less. Has there been any discussion about updating the specs? How much of them is based on an allowable voltage drop and how much are based on other things, such as corrosion allowance, strength, vibration resistance, etc?

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I can't say for sure, but I'm guessing that ABYC has gone as far as they plan to for now (meaning 18AWG with some stipulations- even that is relatively new)...

and I would guess you are right in that it is likely for strength, ease of making connections, etc.

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Its not just the connections but the strength of light cabling that should be a concern.

 

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2 hours ago, Fleetwood said:

Its not just the connections but the strength of light cabling that should be a concern.

 

Is there any reason to suspect this can't be solved by proper design specs? Cables can be manufactured with reinforcement if it's a pulling strength problem. If the strength problem relates to fatigue from vibration, cars and planes are manufactured with 24AWG wiring and that holds up against far worse vibration than a boat is likely to see. With proper crimps, the insulation can become a crucial part of the stress relief at the connector.

 

EDIT: Interesting conversation at stackoverflow about wire thickness vs. vibration. The accepted answer seems to be that thinner wire having a high number of strands can win out over substantially thicker wire.

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In a perfect world that's all true, but a few years down the track when other wiring and stuff has been put in the way and you're reaching into places you can't see, in less than ideal conditions, the thin wires always seem to be the ones that get yanked and break. At least on my boat.

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Adhesive-lined heat shrink terminals are good for more than just keeping water out, they also act as great strain reliefs on the wire. Between that and proper periodic fixturing of the wire to a support, bundle, or harness and you can mitigate a ton of vibration and abuse.

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11 hours ago, IStream said:

Adhesive-lined heat shrink terminals are good for more than just keeping water out, they also act as great strain reliefs on the wire. Between that and proper periodic fixturing of the wire to a support, bundle, or harness and you can mitigate a ton of vibration and abuse.

+1

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Multi-conductor cables are one solution, but you can only have a short length exposed outside the cable.

 

Also not just ABYC, also USCG.

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43 minutes ago, thinwater said:

Multi-conductor cables are one solution, but you can only have a short length exposed outside the cable.

 

Also not just ABYC, also USCG.

And that exposed length will inevitably be the weak link in the chain so provide generous under-deck service loops. 10 years down the road, you want to be able to pull another few inches out of the stanchion or deck gland and renew the connection. And 10 years after that. 

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Skinny little wires were always the bane of my life with compass lights.  The manufacturers seemed to delight in putting the tiniest wires through holes only just big enough for them then lead them down somehow inside the pedestal.  No idea of the amount of time offshore I spent trying to fix those bloody little things.

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16 hours ago, IStream said:

And that exposed length will inevitably be the weak link in the chain so provide generous under-deck service loops. 10 years down the road, you want to be able to pull another few inches out of the stanchion or deck gland and renew the connection. And 10 years after that. 

If you don't want to have to fuck around with it again, put a bit of heat shrink large enough to join from sheath to sheath if joining 2 multi conductors.  If not, I like a bit of heak shrink shrunk full over the outer sheath, a bit over the start of the multi conductor wire, and less so as it goes along to provide a bit of strain relief.

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18 hours ago, IStream said:

And that exposed length will inevitably be the weak link in the chain so provide generous under-deck service loops. 10 years down the road, you want to be able to pull another few inches out of the stanchion or deck gland and renew the connection. And 10 years after that. 

+1, often a good idea to put a loop of cable in the wiring somewhere out of the way to allow you to pull enough through to re-make the connection. The ones near the bilge or in the cockpit.

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7 hours ago, jgbrown said:

If you don't want to have to fuck around with it again, put a bit of heat shrink large enough to join from sheath to sheath if joining 2 multi conductors.  If not, I like a bit of heak shrink shrunk full over the outer sheath, a bit over the start of the multi conductor wire, and less so as it goes along to provide a bit of strain relief.

Definitely a good idea, particularly if adhesive-lined. 

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4 hours ago, IStream said:

Definitely a good idea, particularly if adhesive-lined. 

Yes, non adhesive heat shrink is not very useful for this.  I don't think I've even had any around in years. 

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You put shorter thin wall, non adhesive on the splice first and then longer thick wall adhesive lined o over that. Makes it possible to get back to the splice.

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Check out the blue seas app for sizing wiring.  It will give you sizes based on ampacity and voltage drop.  good guide, and really what is the savings to go past 16awg?

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Generally speaking, ampacity is not a consideration for transient loads and all those ABYC tables lead one to choose cables that are massively oversized for those loads that don't see continuous use: macerators, sump pumps, transfer pumps, windlasses, starters, etc.

The savings is considerable in terms of cost, weight, termination complexity and penetration requirements.

 

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Appropriate wire gauge is determined by 2 factors: allowable voltage drop, and allowable resistive heating (of the wire). The first causes the second.

A transient load is one that won't cause the wire to heat significantly. (Significant is determined by insulation type and installation.)

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11 hours ago, longy said:

  Please define 'transient' and how you would pick a wire gauge for such.

This is what I'd like to understand via this discussion. Wiring needs have changed substantially, to the point that in some circumstances 10x less conductor surface area is required for the same end goal. Systems which in the past required a constant DC voltage to perform acceptably can now make up for onset voltage drop with onset current increase.

I think we can consider wire as just another component in a design, and overspeccing anything leads to reduced system performance, higher costs, more disruption, etc... Even if we don't frequently treat boats that way, they are sensitive to weight. Trimming a few dozen pounds of superfluous wiring + insulation is a worthwhile goal.

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Take 6 pennies and arrange them in a circle.  Then place a 7th in the center.  That is the arrangement of most flexable wire sold.  But in marine use, all the wire is made for extreme flexibility so almost regardless of the gauge, are made up of a various number of the same fine strand wire.  The fatter the wire, the more strands unlike house wire that is always 7 strand. Marine wire is also rated for higher temperatures than house wire.  I personally see very little reason to use a smaller gauge wire even if it might not be necessary.  On Papoose, I just bought a spool of 10 gauge wire and used it everywhere.  It was white and I used marking pens to color code it.  Obviously better to use different colors but that is not what I did.  As has been said, wire should be rated for the voltage drop that is acceptable for the application.  I take a bit of issue with ignoring transients as these might be starter currents and might be where delivering the required voltage is most important.

Allen

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On 12/7/2018 at 5:40 PM, Moonduster said:

Generally speaking, ampacity is not a consideration for transient loads and all those ABYC tables lead one to choose cables that are massively oversized for those loads that don't see continuous use: macerators, sump pumps, transfer pumps, windlasses, starters, etc.

The savings is considerable in terms of cost, weight, termination complexity and penetration requirements.

 

I’d agree except the winch or windlass loads and transfer pumps; general usage is tens of seconds, sufficient to reach equilibrium temperature in a wire, and depending on the windlass, if it loads up (e.g. trying to breakout), like any other “winch” the current goes up as the rpm go down. Not many boats have “big pumps (> 1 hp) but that’s still 60-70 Amp. 

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13 hours ago, kubark42 said:

This is what I'd like to understand via this discussion.

.

I think we can consider wire as just another component in a design, and overspeccing anything leads to reduced system performance, higher costs, more disruption, etc... Systems which in the past required a constant DC voltage to perform acceptably can now make up for onset voltage drop with onset current increase.......Even if we don't frequently treat boats that way, they are sensitive to weight. Trimming a few dozen pounds of superfluous wiring + insulation is a worthwhile goal.

Um, when your point of use voltage drops, in part perhaps due to undersized wire, and your load demands more current...through the undersized wire, . how does that work out ?  

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2 hours ago, LionessRacing said:

Um, when your point of use voltage drops, in part perhaps due to undersized wire, and your load demands more current...through the undersized wire, . how does that work out ?  

From experience working with custom brushless motor controllers and other power electronics, if we design the logic correctly it works out fine. What typically happens is that when first energizing a circuit there is an inrush current which can cause voltage to drop outside spec (typically +-10% of nominal voltage). This current is usually associated with either getting things moving-- such as a macerator motor-- or charging up capacitors. The inrush current can be 10-100x the nominal current, so once you make it through this period it's smooth sailing. Modern power electronics are pretty good at this, and are tolerant of inconsistent line voltages.

Regarding the discussion of transients, it feels like there are several different understandings of what that means. This is why when discussing power loads, it's usually important to have a graduated scale of timeframes. For instance, with our 1000V 1A DC/DC converter we gave ratings for peak continuous load, peak 1 minute load and peak 100ms load. Each was different, and since we were using 400' of 28ga wire it was critically important to understand how each affected the system. 

So when designing for the windlass/macerator/transfer pump, the transient we want to watch out for is the inrush current. This is on the order of tens or hundreds of ms, which really isn't long enough to substantially affect the conductor temperature.

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I spoke of transient loads, not transient currents or voltages. And for clarification, by transient load I meant one with a duty cycle that is small with respect to the heating of it's connecting cables. So, for example, a macerator pump in a toilet that draws 30A but runs for only 30 seconds per flush - this cable should be select only based on IR drop without regard to temperature rise because the transient nature of the load precludes over heating.

There are many reasons why using AWG10 throughout is just dumb. Weight, cost, penetration cross section are the obvious.

Modern high-end performance boats are wired primarily with AWG20 and AWG24. 

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3 hours ago, Moonduster said:

I spoke of transient loads, not transient currents or voltages.

wtf? Here is a nice article with a link to a table that recommends wire size. https://www.westmarine.com/WestAdvisor/Marine-Wire-Terminal-Tech-Specs  They recommend using the 3% table for all wiring but if you have a feather weight boat, perhaps the 10% table can save you several ounces.

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Inrush and the old “lamp load” currents are by nature short term, and typically less than 10ms to achieve back EMF or thermal resistance of a filament. They set your “Fusing” current, which in turn mandates your wire size, or board trace, or metallization width as you go down scale, the electro migration limits for long term reliability are orders of magnitude smaller, and complex in time, cross section dimension and temperatures.  

If you specify and install slow blow fuses or breakers,  to allow the over current startup, then you can install smaller wires to handle the continuous current, that the fuses are rated for. 

Telling someone they can simply put in smaller wire is an invitation to lots of blown fuses or them replacing in field with oversized and fire hazard, 

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Wire is significantly cheaper if you buy 100 feet and connectors are cheaper in bulk.  Standardizing on a single size will save you more money than using a variety of wire sizes to use the smallest for every circuit.  As far as wright savings goes, sizing up will probably cost you less than the weight of one beer.  I know some boats do not allow beer because of its weight and if that is your boat, by all means go for the smaller wire. That said, I would expect a professional to use different colors and different sizes when wiring a boat so I will admit that what I did was not professional.  I also did not actually use #10 wire everywhere as I bought some cables for some of the long runs for example to the blower and the pumps.  They were sized for their load.  Most of the #10 went to wiring the engine, alternator, starter solenoid, ignition coil, and fuse panel.

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Under certain circumstances I'll use 14 or even 18 gauge wire but I use #10 by default because:

1. To allene222's point, it's a lot more convenient and often cheaper to just buy one flavor of wire and connectors in bulk. You can use heavier wire in place of lighter but not the other way around.

2. I like to put high current-capable runs in at strategic places in the boat (breaker panel, stern, bow, etc) using heavy wire and then I have the option to run lighter jumper wires from the junction points to the individual loads that are local to those junctions

3. Even the jumpers are often #10 because over the life of the boat, things change and wire runs can be re-purposed. For example, all the <2' runs from my breaker panel terminal strip to the individual breakers are #10 so I can swap from a 5A breaker to a 25A breaker without worry. 

4. I'm allergic to voltage drop. Voltage drop = heat. Voltage drop also equals battery capacity and solar panel area, which are expensive and constrained on a boat, not to mention heavy. All things being equal, I'd sooner add weight in copper and remove it in lead. 

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Wow, just wow. There's not a single valid point in the last several posts. And when one looks at the amount of time and money you claim to invest in performance, it's remarkable that you cannot see the forest for the trees.

Your dogma regarding wire size won't change the fact that the #1 enemy of performance inside the boat is weight and weight wasted on wire is expensive twice over. You can't replace lead in your keel with copper at the water line - it just doesn't work that way.

Convenience and cheaper are not the hallmarks of performance. Neither is using fat wires because you might need them in five years. 

 

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Last I checked, this was Gear Anarchy and not Racing Anarchy. The priorities for cruising boats are different than for racing boats.

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1 hour ago, Moonduster said:

Wow, just wow. There's not a single valid point in the last several posts. And when one looks at the amount of time and money you claim to invest in performance, it's remarkable that you cannot see the forest for the trees.

Your dogma regarding wire size won't change the fact that the #1 enemy of performance inside the boat is weight and weight wasted on wire is expensive twice over. You can't replace lead in your keel with copper at the water line - it just doesn't work that way.

Convenience and cheaper are not the hallmarks of performance. Neither is using fat wires because you might need them in five years. 

 

Uh, you know I was referring to lead in the batteries mentioned in the prior sentence, not lead in the keel. Give me a little credit.

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