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Old 01-22-2004, 04:56 PM   #15
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Dear John

Always wanted to have a subject line just like that.

I'm going to look into the sizeing of factory AC power cables to the trailer. I think it might have something to do with it being a feeder cable. I just don't know the thinking was on their chooseing that size cable.

I know that a lot of manufacturers of extension cords have down sized their ratings 12awg = 15amp cord 10awg = 20amp cord....

I'm confused on this one, Are there any factory people out there who can shed some light on why the AC feed lines don't match what the NEC says on ampacity.
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Old 01-22-2004, 05:54 PM   #16
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gary

my guess without digging out my lineman books would be that the mfrs figure 60% to 80% use max.

we certainly size transformers that way at the power company.

meaning that with the univolt on and the ac running and the odd lightbulb or two would add up to 20 amps.

that would leave you with 10 amps for corrosion, loose or otherwise crappy connections. or too long extension cords.

there are short term overloads to factor in such as compressor starting or some one hosting a party and runnin 3 nesco roasters in the kitchen.

go figure!

john
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Old 01-22-2004, 08:28 PM   #17
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So, Maurice,John, Gary, et al...

Where exactly are we on this? I have already purchased a 10/3 extension with a 30 amp plug. However I certainly have no reservations about exchanging it. I am only an hour from the Myrtle Beach Campers' World.

My primary concern is also safety, but what about the existing 10/3 cable that came with this 1979 Sovereign? The over heating plug was on my '72 International 31'. I haven't used this '79 very much.

In the limited time I have spent in camp grounds, I don't recall seeing cables heavier than 10/3. Is this an acceptable standard?
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Old 01-22-2004, 08:52 PM   #18
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lets do some math...

skip

lets do some math, o.k. lets not!

lets use the handy dandy wire size calculator instead...

http://www.pljohnson.com/electrical/...voltdrop.shtml

now lets look at the varibles:

120 volts, copper wire, single phase, 30 amps 50 foot run (assuming 25 foot cord on the trailer and 25 extension cord)

lets see what we get...

thats right, 8 gauge!

of course that is calculated for 3% voltage drop, insuring no damage to your ac compressor.

now, without the extension you would be o.k., with it, are you going to overload? probably not.

as suggested elsewhere, actually checking the circuit with a clamp on ammeter would tell you for sure how much load is on that cable with everything running.

also it all depends on what your voltage at the outlet is to begin with, the lower you start with the less you will have in the end. the load in the trailer is essentially fixed, the lower voltage, the higher the current draw will be. ohms law!

if it was my setup i would try to find ways to avoid use of the extension if at all possible.

-but- if you find yourself with no other way to get power to the trailer i would not hesitate to use it sparingly.

you are right on the edge of capacity.

just keep that in mind!

john
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Old 01-22-2004, 09:04 PM   #19
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Re: lets do some math...

Quote:
Originally posted by john hd
... actually checking the circuit with a clamp on ammeter would tell you for sure how much load is on that cable with everything running...

john
john,
I quit doing that the answer scared me too much After measuring voltage at the campgrounds on a couple of weekends. One holiday we were getting around 106v at the freakin box, didn't even try to run the AC that weekend. Just used a bunch of cheap fans. I have wondered if one of the "soft start" kits for my AC might not be a bad idea, the ones that help smooth out the voltage. BTW I use the 10 ga cables for extensions, just grab ahold of one every now and again to make sure the connections aren't hot. Watch the cords being sold at Wally World they had a bunch of 30 amp cords the other day that were 12 ga..."I don't think so Tim!"

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Old 01-22-2004, 09:20 PM   #20
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Thanks John,

I think I'll take the 10/3 back & go with 8 ga.

The only question I have is the availability of 8/3 with 30M plug on one end & 30F on the other. It also seems that every time you use an adapter plug you increase the potential for problems. (debris,wear, disconnect, etc.)

Am I just overlooking ready made cords or should I just fabricate one ? I haven't checked CW catalogue, but I didn't see any in stock this past wk. end. Lowe's didn't have anything like that either.
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Old 01-22-2004, 09:57 PM   #21
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Skip, you've got my advice. Read the imprinting on your Airstream cable and you've got their advice. If you want a much larger sampling of opinions, join RV.net and post the question in the Tech forum. Ask if anyone's ever seen an 8AWG 30A RV cable. I haven't.
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Old 01-23-2004, 12:31 AM   #22
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it ain't all that bad...

skip

go ahead and keep that cable you have!

like moe sez, you will have a hard time finding one. you could make one, home depot and or menards have all the stuff you need to make one.

but to what end?

if you find yourself in a situation like aaron mentioned, a cable as big as your wrist isn't gonna help anyway!

like i said, be aware of the limitations.

john
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