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Old 10-23-2015, 10:45 PM   #121
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Originally Posted by OMGIBoughtABus View Post
SJO does not dissipate heat very well, the amperage ratings for 3 prong cords are assuming open air cooling.

For a permanent installation, and if I'm going to enclose the wiring in foam (inside of conduit) I would not use an extension cord.

I also wouldn't use extension cords for appliances with a high draw.
How much draw can you really expect in a bus? I don't foresee anyone using a kiln or welder plugged to the inside of their bus for very long. If you are running cooking stuff they should really be put on their own high amperage circuit anyways (20A+). I would put AC units on 10 gauge. Max run length can't really be longer than 96 feet (that is circumnavigating the bus) which would be dumb on anything larger than a 15a circuit, no on second thought that would just be dumb period.

I will admit I am of the camp that thinks the multi strand will help with the constant earthquake of driving over the heat dissipation of single wire. I feel deep down that there won't be that much difference between either in the long run. Bad idea bear says just fill the conduits with transformer oil.
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Old 10-23-2015, 10:52 PM   #122
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Quote:
Originally Posted by CaptainInsaneo View Post
How much draw can you really expect in a bus? I don't foresee anyone using a kiln or welder plugged to the inside of their bus for very long. If you are running cooking stuff they should really be put on their own high amperage circuit anyways (20A+). I would put AC units on 10 gauge. Max run length can't really be longer than 96 feet (that is circumnavigating the bus) which would be dumb on anything larger than a 15a circuit, no on second thought that would just be dumb period.

I will admit I am of the camp that thinks the multi strand will help with the constant earthquake of driving over the heat dissipation of single wire. I feel deep down that there won't be that much difference between either in the long run. Bad idea bear says just fill the conduits with transformer oil.
Bad Idea Bear he's the lead designer on my project
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Old 10-23-2015, 11:08 PM   #123
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Ampacity/wire gauge is easy enough, though I just learned tonight from the EC&M reference I'll cite later, that flexible cord ampacity should be derated when ambient temperature is above 86 F.. I hadn't realized that! IMHO that's likely inside the walls of a skoolie in the summer.

Wiring with extension cords is a subject of much debate, sometimes rising to religious fervor here on skoolie.net. This conversation is about the insulation over the wires, not their gauge. I'm also not going to call anybody out, say they're absolutely doing it wrong, etc etc because it's just not a war I'm interested in waging. (I haven't been keeping score as to who has used what, either.) My earlier comment and photo with the damaged wire, as well as the following, are the rationale behind my intention to use conventional home/building wiring methods in my skoolie. I found several interesting references through a search that began with the phrase "portable cord permanent wiring."

Through inspection and handling, the insulation and jacket on normal extension cords is seen relatively soft, pliable.. and easily cut. It seems like a good thing to have out in the open, where physical damage can be easily discovered. It's the old conventional wisdom "don't run a cord under a rug."

Mike Holt is a recognized name in electrical wiring circles. He contributed an article to EC&M Magazine Flexible Cords, Cables and Fixture Wire which does a nice job of explaining to industrial maintenance people how NEC permits use of flexible cords, aka extension cords. In his words, summarizing NEC, "flexible cords must not be: used as substitutes for the fixed wiring of a structure, ..." The article is fairly short and an interesting read.

For 120-volt systems, the RVIA standard is NFPA 70, aka National Electrical Code, and it specifically calls on articles 551 and 552.

I think this is a relatively new thing: NFPA allows free access to their standards on their web site. It's a clunky online web viewer designed to making copying the text difficult, but it's not SOOO bad.. This link might work to take you there. One has to register for a free account and agree to terms & conditions to gain access to the docs.

Article 551 is for RVs. Section 551.47(A) "wiring methods" calls out cables and raceways in accordance with (blah blah blah) in articles in the 300's (note from Mike Holt's article that flexible cords are treated in the 400's). Section 551.47(P)(1) is for "direct wired expandable units" -- slide-out rooms, if I understood correctly. It does call for "flexible cord" in this scenario, but with very specific installation requirements to protect the cord and to limit the spread of fire in case the cord does have a problem. Its separate mention for this specific use implies to me that flexible cord doesn't belong in other places in the RV.

So anyway, with all that said: I might use NM "Romex" cable, but probably I'll be using THHN/THWN, likely of the stranded variety, when I finally get to that point. Probably in hard PVC conduit. I just wish I knew of some decent conduit-friendly plastic junction boxes. The outdoor boxes are $$$, the boxes for the ENT "smurf tube" conduit are too hard to find with any sort of variety.. and using steel boxes with plastic conduit seems like a lousy idea.
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Old 10-24-2015, 10:11 AM   #124
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Looks like Im dying in an electrical fire. At least I tried to do it all right!

Even if my 12/3 was derated by over 20%, id still be well in the clear.

I do have the piece of mind of knowing that the kind of wire my bus came with from the factory is closest to the stuff i used and not romex-type stuff. I wouldn't put solid wire in a bus, either. I guess I'm still happy with my choice.

So much of this is code based and anecdotal. I wish someone with some money and time would hurry up and do a study already
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Old 10-24-2015, 11:06 AM   #125
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One basic consideration in wiring a bus, RV, truck, anything that will be bounding & bouncing over the roads is...the use stranded wire vs solid. Solid copper wire will work harden fairly quickly when exposed to constant vibration and can give it up pretty quickly. Virtually every vehicle made in the last hundred years uses only stranded wire for just that reason.
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Old 10-24-2015, 01:20 PM   #126
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keep up the debate boys, I want some damn answers.
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Old 10-24-2015, 05:26 PM   #127
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It is the choice of 2 evils. One if a strand breaks nbd the other if one breaks it is done. my suggestion is to over size the gauge of the in wall wire by at least one whole gauge if you are going to use multi strand wire. I say this for 2 reasons, 1 a larger diameter wire will have more copper and act as a bigger heat sink. 2 larger diameter will have lower resistance meaning less heat build up. I plan on going to home depot or wallyworld and getting the longest biggest extension cord that they have that will probably cost in the $1-1.4 per foot range. I plan on laying out the electrics putting the electric control panel in a place that is central to the distribution and not effecting other systems. I can't really see needing more than 150 feet of wire.
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Old 10-25-2015, 02:18 PM   #128
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I wanted to use this, but couldn't find it locally: Ancor - Triplex Boat Cable


I'm ok with the solid 12/3 I used since it's encased in the spray foam (except for the device boxes, of course), but the boat cable would have been nicer all around.
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Old 10-25-2015, 06:34 PM   #129
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If boats use multi strand wire then that settles it for me. Fire on a boat = death, pure and simple.

Often you hear people talk how over built things are for boats, it is because failure of even a hatch on the open sea can lead to death. Therefore you can't have failures, If given the chance build it like a boat. I don't know if we need tinned wires in skoolies but that is cool. I have bookmarked that page for future reference.

I also want to point out I don't think it is wrong or abhorrent to use romex. Your rig won't explode from using it and it more than likely won't fail, your screws might loosen on the terminals over the course of 10000 miles though. I will also say I have never heard a compelling reason other than money not to use oversized wires.

As a side note the more I hear about the RVIA and industry standards, the less I care what their accepted practices are. Mainly RVs are designed to be used probably no more than one weekend a month 8 months out of a year for 10 years or a total usage of about 200 days spread over a decade. I don't care if that is all you plan on using your skoolie for, I want people to build like you are going to live in it everyday for the next 2 decades. It won't cost that much more to do and it will never fail you or the next owners.

Also this place sells it too, their price make me rethink using simple extension cords.
Marine Cable - Tinned
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Old 10-26-2015, 12:16 AM   #130
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Yes, I should have mentioned that there are many suppliers of the triplex boat cable. Any marine store worth its salt () will have some in their suppliers catalogue. I've seen it come untinned as well
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