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Old 07-12-2019, 10:11 AM   #1
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For Shore! (power)

It's getting closer to the time I can move out of the ghetto!
Well... to abandon my ghetto setup of heavy-duty extension cords snaked thru the door and strewn in coils about the interior. Finally hooking up a series circuits terminating in kosher outlets, all attached to a b'gawd breaker box.
This project has been left on the back burner, due to other obligations and tasks. And while planned for, the Sun isn't anywhere near the horizon for my anticipated solar system, so here's hoping for a simple solution.
The hiccough that I've encountered is locating the proper wire to run from the breakers to the exterior.
The b-box will be sited in a spare tire storage/closet behind the pilot's seat, facing forward. I'll be routing said jumper thru an open-ended square tube in the pillar between the windscreen & driver's window. Then, mounting an acceptable receptacle between the L steer and battery box.
All I've found so far are ready-go cords with the males & females already mated to the wires. Seems wasteful to whack off the female. Not to mention I'd need to go with a mondo expensive 50-footer to have sufficient slack left over after mangling one of those, to still comfortably connect to Con-Ed.
While I'm not remotely reticent about rigging a home-grown 30A shore power connecting cable, I'm hoping all y'all can steer me towards finding snd securing a nifty, thrifty option for the +/- 15' long wire run needed to safely bring the juice in to the box.
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Old 07-12-2019, 10:26 AM   #2
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8g Romex wire from your local hardware store. Make sure you put rubber bushings around and sharp edges.
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Old 07-12-2019, 10:37 AM   #3
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8g Romex wire from your local hardware store. Make sure you put rubber bushings around and sharp edges.
Thanx! Strand, not solid core, is my understanding.
Seems I recollect reading somewhere that welding cables made for a safe, cost-efficient option...
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Old 07-12-2019, 10:46 AM   #4
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Your choice. If you go stranded you will need a larger gauge. If your ends are terminated properly, the vibrations should not matter. In 40 years If/when the copper becomes brittle, your bus probably wonít even be around.
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Old 07-12-2019, 12:09 PM   #5
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30amp a/c only needs 10 gauge stranded, 4 wire. No harm in heavier though. Buy it by the foot in Lowes, Home depot etc.
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Old 07-12-2019, 12:54 PM   #6
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My shore power feeds in to a 30 amp rv receptacale where it feeds the 120v system via a pigtail. The same pigtail can be plugged into either the genny receptacle or the inverter receptacle. The pig tail itself terminates in the breaker box thus supplying power to the 120v circuits.
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Old 07-12-2019, 01:23 PM   #7
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I'd just buy whatever footage of 10/3 cabtire, type SO and a male end and a female end. You might find 15 ft a bit short at times so maybe buy a longer length. Sometimes a piece shows up off the end of a roll and is under 30 ft. That would work great.


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Old 07-12-2019, 01:37 PM   #8
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I'll second the recommendation for SO (or SOOW) cable. It is oil, water, and abrasion resistant, stranded, and readily available by the foot at big-box home centers and electrical supply houses alike.
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Old 07-12-2019, 02:22 PM   #9
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For reference:

https://www.usawire-cable.com/pdfs/NEC%20AMPACITIES.pdf

It's a 2002 excerpt from the NEC, but I doubt things have changed.

1) Minimum Wire Gauge:

Regardless of what wire you use, your breakers/terminals (what the wire secures to on either end) will determine the temperature rating to be used in the calculations. So assuming the worst-case of 60-degrees (most breakers are 60 or 75), you're looking at a minimum of 10G for 30A (copper). So that's your minimum wire gauge. 10G. You could go larger, 8G for example, but not smaller, no matter what temp-rating of wire you use.

2) Minimum Wire Temp Rating:

In order to dissipate heat from the terminals of the breakers / other terminations, you must meet the minimum gauge above. 10G copper wire is rated at 30A, 35A, & 40A, respectfully, for 60-degree, 75-degree, and 90-degree rated wire. But depending on your anticipated ambient temp (the temp the wire is subjected to), you may need to de-rate the wire. Using the temp correction chart, you'll see that 60-degree rated wire, which has a max ampacity of 30A, would be unsuitable at any temps above 86-degrees. So if you used 60-degree wire, you'd have to go up to 8G minimum. 75 is good to about 104-degrees (.88 x 35A = 30.8A). 90-degree is good to 131 (.76 x 40A = 30.4A). I'd say 90-degree wire would be the only safe choice. If you used anything less then go to 8G.

3) Wire Type:

a) Copper. Don't even consider aluminum.

b) Solid vs Stranded. I personally wouldn't and won't use anything but stranded wire in a mobile / rv application, but this is based mainly on intuition and weighing the opinions of others rather than personal experience.

Disclaimer: I am not an electrician nor do I play one on TV
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Old 07-12-2019, 02:30 PM   #10
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If you go stranded you will need a larger gauge.

I don't believe this statement to be correct, but I'm no expert. Could you provide a reference please?
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Old 07-12-2019, 02:46 PM   #11
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I don't believe this statement to be correct, but I'm no expert. Could you provide a reference please?
I too would like to see as well.
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Old 07-12-2019, 02:54 PM   #12
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Electricians must select the appropriate gauge of wire to use based on the amperage load and application of the project. This is determined by the current frequency that passes through the wire. As electrical currents pass through wires, a skin effect occurs. That part of the current closest to the outer layer of the wire, the Ďskiní area, is where electricity travels along the outside surface and is subjected to magnetic fields, tends to dissipate into the air. Power dissipation is an ever-present challenge for electricians & engineers. Because of its thickness, solid wire has a decreased surface area that reduces dissipation. Because of the given thickness of stranded wire, i.e., itís thinner, there are more air gaps and a greater surface area in the individual strands of wire. Therefore, it carries less current than similar solid wires can. With each type of wire, insulation technologies can greatly assist in reducing power dissipation.


https://blog.jemelectronics.com/stranded-vs-solid-wire

There are other references as well, but this one has a clear explanation albeit not a chart. I usually go one grade difference.
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Old 07-12-2019, 04:14 PM   #13
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Quote:
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Electricians must select the appropriate gauge of wire to use based on the amperage load and application of the project. This is determined by the current frequency that passes through the wire. As electrical currents pass through wires, a skin effect occurs. That part of the current closest to the outer layer of the wire, the ‘skin’ area, is where electricity travels along the outside surface and is subjected to magnetic fields, tends to dissipate into the air. Power dissipation is an ever-present challenge for electricians & engineers. Because of its thickness, solid wire has a decreased surface area that reduces dissipation. Because of the given thickness of stranded wire, i.e., it’s thinner, there are more air gaps and a greater surface area in the individual strands of wire. Therefore, it carries less current than similar solid wires can. With each type of wire, insulation technologies can greatly assist in reducing power dissipation.
From my understanding, stranded wire of the same gauge will be slightly larger in diameter than its solid-core counterpart to at least partially make up for the loss of total conductor cross-section (and hence slightly higher resistance) inherent in a stranded design. Not entirely, but somewhat.

As far as I'm aware, it's this slight difference in resistance, not skin effect, that would allow solid core wire to carry more current than stranded. At least at 60hz. But the question is "of what magnitude"? Is the increased ampacity of solid vs stranded of sufficient magnitude to matter? According to the NEC, which real electricians use to inform their wire size decisions, it doesn't. As it is, there's a pretty significant fudge-factor built into the wire sizing guidelines. And from what I've seen the NEC makes no distinction between the two regarding ampacity.

Also, while I'm familiar with skin effect, I never heard it explained in quite this manner, nor do I see where it could possibly make any significant difference at 60hz.

You certainly won't be hurting anything going up in size, but I remain unconvinced there's any good reason to do so.
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Old 07-12-2019, 05:31 PM   #14
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I don't believe this statement to be correct, but I'm no expert. Could you provide a reference please?



I have long forgot this topic in trade school. Just vague flashbacks..but I think Pizotte is right.



Solid conductors have more surface area for current carrying capacity. This application does not seem that critical using copper wire. I would love to see a bus pulling 30 amps at one time, that would be extreme and if high enough might warrant larger guage stranded.


Ambient temp as explained in your post, THB, is everything! Wire designed for really warm locations should be used by those who somehow prefer living in the heat.


Anyway, the of Pizotte's comment does make sense to me, but unverified at this time.


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Old 07-12-2019, 06:18 PM   #15
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The AWG tables are for a single, solid, round conductor. The AWG of a stranded wire is determined by the cross-sectional area of the equivalent solid conductor. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG.
It's been a loooong time since I went to aircraft fundamentals electrician school but, this is what I remember of it.
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Old 07-12-2019, 06:58 PM   #16
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It's been a loooong time since I went to aircraft fundamentals electrician school but, this is what I remember of it.



That spells it out well somewhere. Glad you paid attention in class.




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Old 07-12-2019, 07:26 PM   #17
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Good to hear y'all chiming in.

I agree that Pizote is right. Given the same exact diameter of round wire, the cross-sectional area of solid wire will be more, which should provide less resistance. My question is how much of a difference it makes, and why it's not addressed in the NEC (or if it is, where?).

Either the NEC tables are meant to apply to both solid and stranded wire, which would imply that the difference would not be substantial enough to warrant separate specs, or somewhere there's an equivalence/modifier/something that I'm unaware of.
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Old 07-13-2019, 04:54 PM   #18
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It's not significant at all. It is insignificant to the point that it falls well within the safety margins built into the NEC ampacity derating tables so they are used for both solid and stranded. A 40A range circuit is going to be wired with 8/3 copper, solid OR stranded, even though it can safely carry 60A in regular service.

Your 30A inlet should have 10ga, your 50A inlet should have 6ga. Solid wire should NEVER be used in a mobile environment due to the fact that it is subject to vibration/flexation stress.
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Old 07-14-2019, 04:29 PM   #19
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Quote:
Given the same exact diameter of round wire, the cross-sectional area of solid wire will be more, which should provide less resistance.
For a given GAUGE wire the diameter of a solid wire will measure smaller than that of a stranded wire. If you were to measure the diameter of each strand then add them together the area would be the same or probably slightly larger than that of the solid wire. They will carry basically the same current. Because of that, the diameter on many tiny strands, for a given gauge, will be different than stranded wire that has fewer bigger strands.

Quote:
Solid wire should NEVER be used in a mobile environment
I disagree. Properly secured and supported solid wire is perfectly safe in a mobile environment. I think it is much more likely that , unless proper steps are taken, stranded wire will be more likely to develop a bad connection in standard AC type wire under the screw head of fixtures.
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Old 07-14-2019, 04:35 PM   #20
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I disagree. Properly secured and supported solid wire is perfectly safe in a mobile environment. I think it is much more likely that , unless proper steps are taken, stranded wire will be more likely to develop a bad connection in standard AC type wire under the screw head of fixtures.
Stranded wire should be considered first, as it will "flex" with the vibrations and stresses that could occur in a moving vehicle. Whereas solid wire will flex much less before stress cracking and failing.

Think about this: All automotive and bus wiring from the factory is stranded. It is that way for a reason!

Good luck on whatever route you go with your wiring but the above factors are something you should reconsider before going all solid...
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