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Old 06-24-2010, 11:41 AM   #1
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Using an adapter to plug 30 amp RV to 50 amp service

My MH uses 30 amp service. I bought a 30 to 50 amp adapter for those times when I'm at a CG where 50 amp is all that is available (it has happened twice).

Got me to thinking, why not just use 50 amp service whenever it's available? I would be assured better quality power, and everything in my MH is protected with breakers, so, why not?

Anyone have any ideas on why I shouldn't do this?
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Old 06-24-2010, 12:04 PM   #2
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In a 50A pedestal there's only one line coming in. They just hook all the plugs to those leads, so even though you're feeding through the 50A plug, you're getting power from the same wires that feed the 30A.

John
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Old 06-24-2010, 08:33 PM   #3
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Angry

Quote:
Originally Posted by Pigman View Post
In a 50A pedestal there's only one line coming in. They just hook all the plugs to those leads, so even though you're feeding through the 50A plug, you're getting power from the same wires that feed the 30A.

John
NO NO NO.
As for the question yes a 50 amp service in your RV would be better but might take quite a bit to retrofit.
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Old 06-24-2010, 09:42 PM   #4
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Quote:
Originally Posted by Dmiles View Post
My MH uses 30 amp service. I bought a 30 to 50 amp adapter for those times when I'm at a CG where 50 amp is all that is available (it has happened twice).

Got me to thinking, why not just use 50 amp service whenever it's available? I would be assured better quality power, and everything in my MH is protected with breakers, so, why not?

Anyone have any ideas on why I shouldn't do this?
You shouldn't do that, because you CAN'T do that. Your coach is wired for 30A service, you stated. The plug on the end of your cable will not fit a 50A socket for good reason. 50A service consists of TWO 120VAC lines, a neutral, and a ground. 30A service consists of a single 120VAC line, a neutral, and a ground.

Additionally, there is absolutely NO difference in "quality". The source for 30A or 50A all comes from the power company.
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Old 06-24-2010, 09:58 PM   #5
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As for the question yes a 50 amp service in your RV would be better but might take quite a bit to retrofit.
Excuse me? OP stated his MH is set up for 30A. He occasionally hits a pedestal where he only has a 50A plug. He bought a 50A (male) to 30A (female) cheater so he could have power when a 50A pedestal plug is the only one available and wants to know if it wouldn't be "better" to use the 50A plug when both are available. I didn't see anywhere in his comments that he was considering rewiring his coach, or trying to force a plug into the wrong receptacle.

The only problem this would cause would be that his coach would lose the 30A protection at the pedestal and would substitute instead the50A protection at the pedestal.

Perhaps we should CLOSELY read the OP's post?

John
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Old 06-24-2010, 10:12 PM   #6
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If OP uses a adapter plug it doesn't matter. There is no way he can bring both phases into a 30Amp unit.

As for the question yes a 50 amp service in your RV would be better but might take quite a bit to retrofit.

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Old 06-24-2010, 10:26 PM   #7
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Pigman Please confirm the following to see if I get this right.
The OP is connecting his 30 amp to a 50 amp protected service. This would be to just one side of the 50 amp service. And, as you stated no 30 amp protection would be provided. This is Not the 30 to 50 amp bone, it is a 50 to 30 amp bone.

This would be okay if only a 50 amp receptical were present but if a 30 amp were there, that one should be used because the pedestal would provide the protection.

The 50 amp would not be able to provide more than 30 amps within the unit because the unit's system would limit itself to 30 amps?
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Old 06-25-2010, 03:56 AM   #8
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Please; everyone take a deep breath and lets keep this discussion on subject of the OP and be polite even if someone provides inaccurate information. Thank you. The above post has answered the OP question.
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Old 06-25-2010, 04:09 AM   #9
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This article does a very good job explaining the difference between 30 and 50 amp RV services.
Click the tab on the left for 50 amp service

RV Electric
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Old 06-25-2010, 06:02 AM   #10
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Because it would make no difference. It doesn't matter if your using an adapter to get 30-amp service from 50-amp, 100-amp or whatever, your rig has a 30-amp main breaker. So even though you're plugged into 50-amp with your adapter you can draw no more then 30-amps without tripping your rigs main breaker.

Think about the pedestals themselves, even though they may have either a 30-amp and/or a 50-amp breaker these pedestals are fed from transformers and main panels at the campground. These transformers and associated main panels will provide a lot of amps in order to feed every pedestal in the campground. But even so, this won't give more current then you can draw. It just means you'll pop your circuit breaker if you exceed the current draw but you won't pop the 50-amp breaker on the pedestal.
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Old 06-25-2010, 07:36 AM   #11
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As stated above you have a 30 amp main. The only thing subject to the higher amperage would be the cord .
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Old 06-25-2010, 07:57 AM   #12
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I've seen pedestals where the 30A outlet suffered from low voltage. Use of the 50A outlet on the same pedestal might alleviate that. I say "might", because it depends on how the pedestal is wired.
In any case, there is no harm in using the 50A outlet and an adapter. The worst "risk" is that the shore power cord does not have the protection of a 30A breaker. Hardly worth mentioning, in my book.
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Old 06-25-2010, 11:55 AM   #13
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I'm not an electrician but have worked a bit on electrical wiring. A 50 amp circuit has four wires with two hot, 1 neutral and one ground and a 30 amp has three wires with one hot, 1 neutral and one ground . When you use the 30 amp receptacle I think you are simply using three of the four wires that run to the 50 receptacle - you have excluded one of the two hot wires. So a 50 amp system could be 60 amps - just like your plugs are really 120 volts not 110 and 240 is not 220 volts. Does this make sense?
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Old 06-25-2010, 01:29 PM   #14
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If the original poster has a 30 amp cable that's wired for a 30 amp receptacle but has access only to a 50 amp pedastal. A cheater cord made expressly for that application can be used. A little background is needed here though for a through understanding of what's happening when you use a 30 to 50 amp adapter.

Firstly, a 30 amp receptacle has a single phase of 110 power, a neutral , and a ground supplying the 110 volts through a single phase with a breaker set not to exceed 30 amps. In a 50 amp receptacle the pedastal is wired with 2 phases of 110 (Directly opposite each other) a neutral, and a ground. Each leg of the 2 phases is set with a breaker not to exceed 50 amps each. So in direct comparison, a 30 amp receptacle can deliver only 30 amps of a single phase. A 50 amp receptacle can deliver 50 amps on each leg of 110 delivering a total of 100amps on two phases.

When you use an adapter thats designed to use a 30 amp plug to a 50 amp plug it completely ignores one leg of the 2 110 phases and delivers one 50 amp leg to the hot side of the 30 amp cord. It also connects the grounds and neutrals together normally. So, now you are getting one 50 amp leg of power to your 30 amp cord, a neutral, and a ground. Your coach 30 amp main breaker becomes the safety valve for not pulling too much amperage through the cord. I suppose if the original 30 amp cord develops a short before the main breaker in the coach, you could overheat the 30 amp cord but that is unlikely.

The 2 phases of 110 can be connected to each other to produce 220 also but that is never done in any coach wiring I have ever seen. The 110 loads are split up among the 2 110 phases so you only have 110 at any given time. All the draws return to the pedastal through the neutral. The huge difference between 50 amp 110 and 30 amp 110 comes directly from the 50 amp recptacles offering 50 amps of 110 power on each leg giving a total power of 100 amps instead of 30amps total on one leg of a 30 amp system. That's more then 3 times worth of power available. The breakers on a coach wired for 50 amp have 2 mains one for each leg supplying power. On a 30 amp system the coach has a single breaker rated at 30 amps because it only uses one leg to get power through. The cable supplying power to the coaches are also different.

In a 50 amp system the cable will have 4 conductors of either #8 or # 6 wire to supply both phases of 110 , the neutral and ground. Sometimes the ground wire is a # 10 because it's used only as a safety and no current should be flowing under normal conditions through ground. A 30 amp system uses a 3 wire cable of #10 wire. One conductor for 1 leg of 110, a neutral, and a ground. The 50 amp sysem uses larger wire because you can draw more current through it.

Is the 50 amp system better power? As stated above, the power all comes from the same system so, no, it's not better, it's the same. There is more power available but it's limited by the coaches 30 amp breaker. My assessment is that it probably makes little difference when a brown out occurs which amp system, plug, or pedestal is used. Brown outs occur from too much draw on a system at any given time dropping voltage on any phase below 110 volts. When this happens motors and compressors found in coaches draw more power to start and keep running anything because voltage is low. Remember Ohms law that states simply that lower voltage = more current draw.

In conclusion, it 's OK to use a cheater cord to access the 50 amp receptacle when your coach is wired with a 30 amp drop cable and it's probably safe. Is it better? Not really.
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