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Lars(wi) 
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Joined: 14 Sep 2009
Location: Permian Basin
Points: 7849
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 Topic: Outdoor 240v………..
Posted: 30 May 2025 at 6:23pm |
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outlet for 50 amp RV. Sub panel in garage is 50 amp, but ‘3-wire’, 2 hots and 1 ground. Inside the sub panel the neutral and ground wires all are together on the only bus bar. The RV has the modern 4 prong plug on the cord. What changes to the sub panel is needed? TIA.
Edited by Lars(wi) - 30 May 2025 at 6:24pm
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I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.
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Lars(wi)
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Joined: 14 Sep 2009
Location: Permian Basin
Points: 7849
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Posted: 30 May 2025 at 6:35pm |
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Also the garage is detached.
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I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.
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steve(ill)
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Location: illinois
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Posted: 30 May 2025 at 6:38pm |
put a ground rod next to the RV plug and connect the 4th wire (ground) to the rod... Use the 3rd wire on the plug as the NEUTRAL ( even tho they are connected to ground in the breaker box).......
There are SOME Campers that are SMART and look for a millivolt drop between the neutral and ground.. If you connect BOTH together in the RV box, the Camper might not cooperate.. GROUND the wire to a ground rod and it will work..
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Lars(wi)
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Posted: 30 May 2025 at 6:52pm |
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Ok, should the wire from sub panel to the outlet be 2 hots, 1 neutral ?
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I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.
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steve(ill)
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Location: illinois
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Posted: 30 May 2025 at 7:44pm |
yes.. the normal 3 wire is 2 hots and 1 neutral... If your BUYING wire, you could get 4 wire cable ...( that is probably code).... but you still have to connect the GROUND the GROUND ROD and not the box to get the milivolt differential between N and Grd.... So i have used 3 wire and put the ground rod at the RV box..... Found this out when a NEW CAMPER would not take the power with the G and N together in the breaker box..
Your GARAGE panel probably only has 3 wires feeding it ?? And all the Ground and Neutral are connected together... and you dont have a ground rod at the garage ?
Edited by steve(ill) - 30 May 2025 at 7:55pm
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Like them all, but love the "B"s.
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Lars(wi)
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Posted: 30 May 2025 at 9:28pm |
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Yep, 3 wires going into the panel, no ground rod that I can see. It is a steel shed bolted in on a concrete pad.
Shed is 36x36, with 12x12 double door, gable roof. Early 1980’s construction.
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I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.
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steve(ill)
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Location: illinois
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Posted: 30 May 2025 at 9:51pm |
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yep... that would have been standard procedure to run 3 wires and tie the Neutral and Ground together in the box... I think code would be 4 wires to the RV box .... but like i said, if you connect the NEUT and GROUND together at the garage, the RV plug might not work on SOME campers..... Ground rod is the better option to guarantee it works.
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Like them all, but love the "B"s.
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DaveKamp
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Joined: 12 Apr 2010
Location: LeClaire, Ia
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Posted: 31 May 2025 at 2:04am |
What Steve said...
And keep in mind, your main service entry point (where the meter is) will have a ground rod. The NEC rule forbids multiple grounding points, however, in a distributed service of a farm, having one ground point several hundred feet (or even yards) from the electrical service ground pin tends to make the ground circumstance ineffective for any purpose, and in the instance of a ground potential rise (like a lightning strike in the neighboring field) can cause serious damage.
The only other option, would be to have an isolation transformer at your RV power pedestal, where the feeding mains through a breaker to to the ungrounded transformer primary, and your receptacle is grounded, along with the center (n) tap. Not a common thing, but that's what I did with service feeds to floating boat docks... local isolation is a MUST when you have sailboat masts everywhere.
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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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Coke-in-MN
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Posted: 31 May 2025 at 2:15am |
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that separate ground rod serves as path for GFI trip / detection of that stray voltage .
when one gets into NEC on grounds , bonding , and such it gets a little confusing .
There is also a OHM reading for ground rods - also in buildings now the rebar in footings is part of grounding system
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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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DMiller
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Posted: 31 May 2025 at 5:00am |
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For code Four Wire IS Required, as to ground there had better be a Ground Rod around that garage somewhere. If not ADD One and a hard Ground Connection to the Service Panel.
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