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Old 05-09-2009, 10:41 PM   #1
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Use of 30 and 20 combo adapter with a GFI

I "thought" that I read a post sometime back that indicated if I used a 30/20 amp combo adapter at a campground wherein the electrical box had a GFI plug, that I would not be able to get 50 "true" amps. Is this a true statement or perhaps I have an electrical problem? I ask because we were out this past weekend and I plugged in my combo adapter and could only run one of 2 A/C units. If I turned both on, one would simply not turn on even though the amps totaled 50 (30 + 20).
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Old 05-09-2009, 11:14 PM   #2
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This is a subject that has caused a lot of confusion. Mainly because a "50 amp" rv hookup is not 50 amps. It's actually 100 amps. On 20 & 30 amp hookups, there is only one leg (one phase) of current going to the outlet. On a 50 amp hookup, there are actually 2 legs, that are 50 amp each. Technically, it doesn't matter if they are the same phase or not, since we don't run 220 v appliances in an rv. But, most of the ones I've seen are opposite phase, which could provide 220 voltage if you were to bridge across them.

Usually you can run two a/c units while using a "cheater", but not if something else is using amps in addition to the a/c unit, if its on the 20 amp circuit. This something is usually a converter or inverter. If it's charging heavily it will use maybe 10 to 15 aps. The a/c will use about the same. 15 amps + 15 amps = 30, which is greater than the 20 amp side can supply.

I've often wondered why they don't call the 50 amp service what it really is (100 amp service). But they don't. Hope this helps.

As an aside, I've never been able to use a cheater when one of the legs is on a GFI outlet. It always trips. This is because the GFI is reading an inbalance in the current flow to the nuetral, since the circuit will use the opposite phase first, instead of the neutral if there is a load on it. This tricks the GFI into thinking that there is a current flow to ground somewhere else (i.e. someone getting shocked) which it is suppose to protect. So, it trips.
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Old 05-10-2009, 07:26 AM   #3
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Quote:
Originally Posted by Darryl View Post
On a 50 amp hookup, there are actually 2 legs, that are 50 amp each. Technically, it doesn't matter if they are the same phase or not, since we don't run 220 v appliances in an rv.
With all respect, it matters a bunch!

In "true" 50 amp service, neutral leg currents are additive. Therefore, if one were drawing 50 amps on both the L1 and L2 legs, the neutral leg current would be (50 + 50 =) 100 amps if L1 and L2 are in phase. Conversely, the neutral leg current would be (50 + (-50) =) 0 amps if L1 and L2 are 180 degrees out of phase as they should be, and N could never be over 50 amps under the worst case (example - L1 @ 50 amps and L2 @ 0 amps).

An overloaded neutral conductor can lead to meltdown and electrical fires since it, like the L1 and L2 conductors, is only sized for 50 amps. Therefore, one should always ensure that L1 and L2 are 180 degrees out of phase and show 240VAC between them.

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Old 05-10-2009, 09:13 AM   #4
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Just as an additional note, some of the the larger and/or highline coaches do indeed have 240v appliances.
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Old 05-10-2009, 09:17 AM   #5
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With all respect, it matters a bunch!
Yep. I've heard of several cases where a motorhome owner will have an "electrician" wire up a 50a service at their house or pad, and the guy hooks the wires up in phase. Usually ends up with most of the electronics and appliances in the coach getting damaged - very expensive mistake.

As for those cheater cords, I wouldn't waste my money on one. You are NOT getting 50 amps on either leg - they give you 30 amps on one and 20 on the other. That's why you couldn't run both air conditioners, Mbl Condo, and the uneven current is what causes the GFI receptacle at the post to blow. If the two feeds are wired in parallel at the post (which I'd assume most are), then those cheaters don't give you any advantage at all.

I'd Rather use a simple 30 amp dog bone. I still cannot run both AC's, and I have to be careful about not running the microwave, a coffee pot, and a hair dryer at the same time, but at least I know I've got equal current throughout the coach, and I don't have to worry about which circuits only have 20 amps.

About the only situation where these cheater cords may prove useful, is someplace (like at home) where you are sure you can get a full 30a feed and a 20a on two seperate breakers. Then you would have more total power available than you would with a dog bone pigtail, but not nearly as much as you would with a true 50 amp cirucit, which gives you 50 amps on BOTH legs.
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Old 05-10-2009, 09:50 AM   #6
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Hi Mbl Cndo,
To get back to your OP questions, I've been using this http://www.campingworld.com/shopping...-adapter/25774 for years, with complete success. Why your coach would run only one A/C unit depends on how your coach is wired, is there an EMS involved, the size of the A/C units, how the CG pedestal is wired, etc. Not knowing the details of your coach it is not possible to provide potential solutions. All I can say, it that the device works as advertised and allows two A/Cs to be run at the same time (not much else).
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Old 05-10-2009, 10:07 AM   #7
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I use the same cheater as GaryKD because we use to summer camp in the heat of Sacramento and the campground only had 30 amp service. The cheater allowed me to run both A/C's, but as Darryl stated, I had to be careful as to what else was running. The women would usually get me with a blow dryer after we came back from boating!

I think the cheater is worth the money and one of those things that is nice to have if you need it.
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Old 05-10-2009, 10:22 AM   #8
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Don,

Just wondering... Does your 05 Diplomat have the Intellitec EMS on the house control panel?
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Old 05-10-2009, 10:46 AM   #9
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Quote:
Originally Posted by RustyJC View Post
With all respect, it matters a bunch!

In "true" 50 amp service, neutral leg currents are additive. Therefore, if one were drawing 50 amps on both the L1 and L2 legs, the neutral leg current would be (50 + 50 =) 100 amps if L1 and L2 are in phase. Conversely, the neutral leg current would be (50 + (-50) =) 0 amps if L1 and L2 are 180 degrees out of phase as they should be, and N could never be over 50 amps under the worst case (example - L1 @ 50 amps and L2 @ 0 amps).

An overloaded neutral conductor can lead to meltdown and electrical fires since it, like the L1 and L2 conductors, is only sized for 50 amps. Therefore, one should always ensure that L1 and L2 are 180 degrees out of phase and show 240VAC between them.

Rusty
Yes, you're absolutely right. It was late when I posted this and I was only thinking about it from the voltage perspective. I hope I didn't mislead anyone into thinking it doesn't matter at all. Thanks for pointing this out to everyone.

Route 66, I wasn't aware anyone had started using 240 volt appliances. Thanks for the info. Out of curosity, what is the appliance?
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Old 05-10-2009, 01:13 PM   #10
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Hi Mbl Cndo,
To get back to your OP questions, I've been using this http://www.campingworld.com/shopping...-adapter/25774 for years, with complete success. Why your coach would run only one A/C unit depends on how your coach is wired, is there an EMS involved, the size of the A/C units, how the CG pedestal is wired, etc. Not knowing the details of your coach it is not possible to provide potential solutions. All I can say, it that the device works as advertised and allows two A/Cs to be run at the same time (not much else).
Yuppers, that's the unit I have and was using. The only different is on one end, right or wrong, I had an adapter on it to plug it into a standard 110v outlet that was next to the 30 ampr' outlet. The last time I used the adapter was plugged into twin 30's at a place in Sandy Eggo. No problems there.
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Old 05-10-2009, 01:27 PM   #11
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The answer your original question, it is TRUE that you cannot use your combo adapter if either of the outlets is a GFCI outlet or is on a circuit with a GFCI breaker. The GFCI will trip immediately and you will lose the power on that "leg". That means whatever things in the coach are powered on that leg (roughly half the coach circuit breakers) will not operate at all.

I have one and use it from time to time, mostly when staying in friends driveways or ards where there is no real RV hook-up to be had.
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Old 05-10-2009, 08:57 PM   #12
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Old 05-10-2009, 09:15 PM   #13
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220/240v appliances like separate clothes dryers and the elec secondary heating elements of hydronic furnaces (like often the Oasis brand when on HI vs LO elec setting) are pretty much the norm in higher line rigs today... Makes it a little tougher when on 30amp for those folks - hence why many of those owners will claim 30amp (or the infrequent but code legal 120v 50amp) is boondocking!!!.
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Old 05-11-2009, 05:29 AM   #14
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Route 66, I wasn't aware anyone had started using 240 volt appliances. Thanks for the info. Out of curosity, what is the appliance?
In addition to Jeff's post above, I believe some cooktops are 240v.
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