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Old 02-19-2011, 10:43 PM   #16
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Wire Gauge for 30A RV Outlet (long span)


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In this situation we are talking about any adjustments would begin at 90 C insulation for thhn and nmb cable. For #10 copper that would be 40 amps so an attic ambient temp of 132 to 140 F would be required to reduce the ampacity of the wire to less than 30 amps. The 24 inch rule is talking about bundling not distance minimums.
That is correct,the 24 inches which may be 36 inches is refering to nipples which you do not need to adjust apacity for bundling, is the conduit going to only contain 3 wires? That wasnt mentioned. If there are more than 3 current carring conductors there are additional corrections in addition to temp corections. And depending on average abient temp (source would be determined by state code usually) which i am not familiar with summer weather in that state but 140 F is very low for my area in an atic.

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Old 02-20-2011, 10:17 AM   #17
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Wire Gauge for 30A RV Outlet (long span)


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That is correct,the 24 inches which may be 36 inches is refering to nipples which you do not need to adjust apacity for bundling, is the conduit going to only contain 3 wires? That wasnt mentioned. If there are more than 3 current carring conductors there are additional corrections in addition to temp corections. And depending on average abient temp (source would be determined by state code usually) which i am not familiar with summer weather in that state but 140 F is very low for my area in an atic.

I guess your an engineer but you guys always make things 10 times more complicated than it needs to be. Your assuming a 30 amp load and the circuit may or may not be carrying 30 amps. And certainly not continuous load. The op is talking about a 120/240 individual branch circuit to an RV 30 amp outlet. Numbers of wires involved is rather obvious. There is not going to be more than three current carrying wires !!!

Please consider the OP's original question for advice on this RV branch circuit. All this dispute over how to interpret code or trying to give lessons on what the code provides for is not answering the OP's questions. Much of what you have been discussing will not apply to this thread. Ask the right questions and let the op give you the information you need to apply code compliance.
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Old 02-20-2011, 10:48 AM   #18
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Wire Gauge for 30A RV Outlet (long span)


i want to know why the OP is not running a 240v circuit to his RV.
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Old 02-20-2011, 10:53 AM   #19
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Wire Gauge for 30A RV Outlet (long span)


Me thinks we are over-thinking the problem. I installed a 30 amp, 120 volt (not 120/240) circuit for my small RV in my side yard. Prior to that I ran the RV with a 25 foot heavy duty extension cord from a 20 amp receptacle in my garage. My point being that the loads in the RV are relatively small with the exception of the air conditioner (and it is less that 20 amps). Unless the OP were to run the AC, use a microwave and perk coffee all at the same time, the load will be well under 30 amps and voltage drop on less than 100 feet of #10 wire will not be an issue.
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Old 02-20-2011, 10:53 AM   #20
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Wire Gauge for 30A RV Outlet (long span)


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i want to know why the OP is not running a 240v circuit to his RV.
mostly rv's that require a 30 amp are only 120 volt.
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Old 02-20-2011, 12:51 PM   #21
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Wire Gauge for 30A RV Outlet (long span)


NEMA TT–30 (TT stands for Travel Trailer) is a 30 A, 125 V recreational vehicle standard (hot-neutral-ground) which may also be known as RV 30. It is frequently (and sometimes disastrously) confused for a NEMA 10–30. The RV receptacle is common in nearly all RV parks in the United States and Canada, and all but the largest RVs manufactured since the 1970s use this plug. The hot and neutral blades are angled at 45° from vertical and 90 degrees to each other, similar to NEMA 10 devices. The plug is slightly smaller than a NEMA 10 but larger than ordinary 5–15 plugs. The ground pin, however, is round, like those on straight-blade NEMA grounding devices. Referring to the diagram, the orientation is the same as the NEMA 5 plug and socket, with the receptacle neutral on the lower right. Due to the appearance of this plug, many people assume that it is to be wired for 240 V, but this is a 120 V device. Adapters exist with the TT–30 plug on one side and a 5–15 or 5–20 socket on the other side. When the cord is detachable from the RV an L5–30 is usually used on the RV end of the cord.
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Old 02-20-2011, 05:32 PM   #22
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Wire Gauge for 30A RV Outlet (long span)


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Originally Posted by Stubbie View Post
...The op is talking about a 120/240 individual branch circuit to an RV 30 amp outlet.....
Not quite. There is no such thing as a 120/240 30 Amp RV outlet.

Quote:
I'm installing 30A, 120V service for my travel trailer...
RV outlets are either:

30 Amp @ 120 Volts

OR

50 Amp @ 120/240 Volts.
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Old 02-20-2011, 05:35 PM   #23
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Wire Gauge for 30A RV Outlet (long span)


In any case, I would install this with some #10 wire, fed from a single pole 30 Amp breaker. The distance involved should not present much of a problem, even at 120 Volts.
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Old 02-20-2011, 06:42 PM   #24
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Wire Gauge for 30A RV Outlet (long span)


I ran 10 gauge 100 feet from the panel through a large pole building to a 30 amp RV receptacle and connected it to a 30 amp single pole breaker. The RV would run for days at the campground with no problem of any kind, so I knew the RV itself was fine.

When connected to the new outlet 100 wire feet away from the panel; the breakers in the RV would heat up and trip repeatedly when running the AC and the refrigerator at the same time. After upgrading to 8 gauge it worked fine. The 30 amp breaker in the panel never did trip and the wire did not heat up. Apparently there was enough voltage drop with 10 gauge at 100 feet to cause this.

If I were you, at 80 feet I would certainly go with 8 gauge the first time, either in conduit all the way or NM (romex) cable all the way and skip all the extra connections.
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Old 02-20-2011, 08:18 PM   #25
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Wire Gauge for 30A RV Outlet (long span)


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Originally Posted by kbsparky View Post
Not quite. There is no such thing as a 120/240 30 Amp RV outlet.


RV outlets are either:

30 Amp @ 120 Volts

OR

50 Amp @ 120/240 Volts.
Quite correct that was certainly an error of thinking on my part.

Aside from the fact the op stated 120 volts in his 1st post I would at least have a 50/50 chance of being correct.

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