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Old 01-31-2016, 01:18 PM   #71
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My understanding is that the 50 amp service is 50 amp per leg.
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Old 01-31-2016, 01:21 PM   #72
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Originally Posted by Springerdad View Post
Interesting reading. Not to hijack this thread, but I was reading a thread the other day about the 30 to 50 and 50 to 30 amp adapters, and surge protectors, and it was brought up that the loss of the neutral in a 50 amp setup could cause an over voltage on either leg. Someone there was advocating using the 30 amp supply and adapting up to your 50 amp cord (if that is your setup) to protect against that. Can an expert here clarify this for me?
With a true 50A RV service, you have 2 - 120V, 50A services. If you measure Hot to hot , you have 240Volts, if you measure either hot to neutral, you have 120 Volts. Since all TT loads are 120Volt loads, you have the amperage on hot on one leg flowing back to the source on the neutral. If you were to have an equal current on both hot legs, the neutral current would drop to zero due to the amperage being 180 degrees out of phase. In reality, the neutral is also the reference point for measuring the voltage, so if you lose that reference point Neutral, the voltage from the reference point could be as high as the full 240 volts or as low as zero volts all depending on what is connected to the other hot leg and how poor(high the resistance) the physical connection of the neutral. You always have this risk with 120V loads working from different phases when the neutral return path is compromised. The loose neutral connection can happen in the pedestal or even from the power company providing the service.
With regaqrds to converting a 50A service to a pair of 30A, I would ask how often do you really lose the Neutral connection in the TT? Even with parallel 30 Amp cables, if the neutral is open anywhere from the
CG pedestal, all the way back to the serving transformer, you still have the risk of a lost neutral. Is the second cable worth the expense?

Jim Knoch
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Old 01-31-2016, 02:06 PM   #73
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With a true 50A RV service, you have 2 - 120V, 50A services. If you measure Hot to hot , you have 240Volts, if you measure either hot to neutral, you have 120 Volts. Since all TT loads are 120Volt loads, you have the amperage on hot on one leg flowing back to the source on the neutral. If you were to have an equal current on both hot legs, the neutral current would drop to zero due to the amperage being 180 degrees out of phase. In reality, the neutral is also the reference point for measuring the voltage, so if you lose that reference point Neutral, the voltage from the reference point could be as high as the full 240 volts or as low as zero volts all depending on what is connected to the other hot leg and how poor(high the resistance) the physical connection of the neutral. You always have this risk with 120V loads working from different phases when the neutral return path is compromised. The loose neutral connection can happen in the pedestal or even from the power company providing the service.
With regaqrds to converting a 50A service to a pair of 30A, I would ask how often do you really lose the Neutral connection in the TT? Even with parallel 30 Amp cables, if the neutral is open anywhere from the
CG pedestal, all the way back to the serving transformer, you still have the risk of a lost neutral. Is the second cable worth the expense?

Jim Knoch
Thanks for your input Jim. My TT is set up for 50A service as an option for a second A/C if wanted, which we don't have, but it uses a 50A power cable. I'd set up a power supply at the house for my prior unit, which was 30A. Rather than rewire for 50A I simply bought an adapter dog bone, which works for me. So at this point, I have the option of plugging into the tower on either amp supply. I've been using the cable on the 50A side, simply because it's easier. My question was in part as to whether I have 'protection' against an over voltage caused by an open neutral by using the 30A adapter. And, like others have said, the 30A supply often looks questionable compared to the 50A supply.
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Old 01-31-2016, 08:04 PM   #74
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Originally Posted by Springerdad View Post
Interesting reading. Not to hijack this thread, but I was reading a thread the other day about the 30 to 50 and 50 to 30 amp adapters, and surge protectors, and it was brought up that the loss of the neutral in a 50 amp setup could cause an over voltage on either leg. Someone there was advocating using the 30 amp supply and adapting up to your 50 amp cord (if that is your setup) to protect against that. Can an expert here clarify this for me?


????? How is the Neutral being "lost"??????



A 50A service has four prongs; one ground, one neutral and two legs of 50A each. The only thing that might be considered "lost" is one of the 50A legs. The ground, neutral and ONE of the 50A legs are carried over from the 50A four prong service to the 30A three prong service via the adapter / dogbone. Even though 50A are available, a rig wired for 30A is still limited and protected by the 30A master breaker.
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Old 01-31-2016, 08:59 PM   #75
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You still have a 30A cord & plug ends being protected by a 50A breaker.

I plug my 28 gauge iPhone charger cord into a 20 amp circuit as do millions of others. You can plug a smaller rated cord into a larger rated circuit. It's whatever is at the end of it can draw that is the concern. If there is a breaker at the end of the cord (the RV's main) restricting the load that can hit the cord, then there is no issue no matter how big the breaker is feeding the outlet and the attached cord.
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Old 01-31-2016, 09:04 PM   #76
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Your I phone charger reduces the voltage going down the cord.

OK, I have an 18 gauge cord feeding my lamp plugged into a 20 amp circuit. The example doesn't matter. Smaller gauge cords are plugged into larger circuits all over your house.
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Old 01-31-2016, 09:08 PM   #77
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Install a new water heater in your house that is rated for 30A wired with #10 wire & connect it to 50A breaker. Then call for inspection & see what happens.


Plug in any lamp you buy at Walmart with smaller gauge cord than your outlet is wired with, don't call an inspector because who cares, and see what happens. Inspectors have nothing to do with what's plugged into an outlet. Only with how an outlet is wired.

Cords of a smaller gauge than the feed cable and breaker ratings of the outlets they are plugged into are all over your house. End of story.
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Old 01-31-2016, 09:15 PM   #78
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Guys, I could be wrong but from what I'm reading, you're both right.

The risk with plugging your 30A cord into a 50A protected plug with a dogbone is the potential for a short along the cord and inside the RV along the main line up to the 30A breaker in your converter. Past the 30A breaker in the RV that same risk of a short still exists with smaller gauge wiring potentially being exposed to whatever amperage the individual circuit breaker will allow, usually 15A.

Maybe one of the resident electricians can confirm this?
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Old 01-31-2016, 09:18 PM   #79
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There is always potential of a short in a cord. Cords are very frequently not the same gauge and rating as the outlet and breaker they are plugged into. A short in a 30 amp cord will pop a 50 amp breaker. A short in a lamp cord will pop a 20 amp breaker. Shorts draw much more that the cords rating.
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Old 01-31-2016, 09:19 PM   #80
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You are correct Karl4Cat. I only worked in the electrical industry for about 40 years, so I probably don't know what I'm talking about. Just trying to keep someone from damaging their plug ends or cable, that's all. Do as you will, as will I, & good luck.

I know I'm correct but thanks for confirming.

I hope you upgraded the cord sizes of all the electronics and lighting in your house because 90% of it will be below the breaker rating and cable of the outlet feeding it. Or is your concern only to the singular issue of an RV umbilical?
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