Community Forums

Forest Grump · 08-26-2015, 10:23 AM

My brain tells me a circuit breaker is to protect the draw side not the input side so I looked it up.

https://en.wikipedia.org/wiki/Circuit_breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow.

So until the circuit breaker figures out what is happening, and until you figure out your neutral now is hot, your ground may be hot and that neither the neutral or ground are protected you will discover why they tell you never to do it. The circuit breaker opening is not going to shut down your neutral or ground which may be hot.

BFlinn181 · 08-26-2015, 02:44 PM

I have a 50 amp RV. I also carry dog bone adapters to plug in to 30 amp or even a 15-20 amp outlet. At home I plug into a 20 amp outlet and have no issues. You just know to not turn on the A/C or plug in a couple of 1500 watt heaters.

The only issue is if you wire your own dog bone converters or try to plug in to a 30 amp outlet that's wired for a dryer or range. Those outlets are wired for 240 v, not 120 v. Many a RVer have learned the hard way that doesn't work.

I also recommend to newbies to install a Progressive Industries EMS.

Progressive Industries RV Surge and Electrical Protection industry lea

It tests the wiring and electricity every time you plug in and won't connect if it's not proper. It also disconnects if voltage drops (common in campgrounds that might have older wiring or a bunch of big RVs using lots of power) or power surges happen. Cheap insurance and they have a lifetime replace/repair warranty, unlike Surge Guard which only covers one year, replacement only, coverage.

Your 30 amp RV can't draw more than 30 amps even plugged into a 50 amp outlet, your circuit breakers are the limiting safety valve. No more power will flow than your RV can handle.

Likewise if I'm plugged into a 30 amp pedestal and try to run both A/C and the microwave while drying my hair, the pedestal 30 amp circuit breaker will trip.

One other 'factoid' to digest: A 30 amp RV is limited to 30 amps of power, 120 v X 30 amps = 3600 watts. A 50 amp RV service is actually 2 legs of 50 ams, so it gives 100 amps of power, 120 X 100 = 12,000 watts, or more than 3 times the power available in 30 amp service.

glarnold · 08-26-2015, 02:57 PM

My suggestion, born from experience:
Get a 50 to 30 dog-bone adapter. Turn the camp ground pedestal breaker off! Plug in the dog-bone to the camp ground pedestal jack, plug your camper cord into the dog-bone, and then turn the pedestal breaker on. Prevention is much cheaper than correction.

Forest Grump · 08-26-2015, 03:15 PM

Quote:

Originally Posted by BFlinn181

I have a 50 amp RV. I also carry dog bone adapters to plug in to 30 amp or even a 15-20 amp outlet. At home I plug into a 20 amp outlet and have no issues. You just know to not turn on the A/C or plug in a couple of 1500 watt heaters.

The only issue is if you wire your own dog bone converters or try to plug in to a 30 amp outlet that's wired for a dryer or range. Those outlets are wired for 240 v, not 120 v. Many a RVer have learned the hard way that doesn't work.

I also recommend to newbies to install a Progressive Industries EMS.

Progressive Industries RV Surge and Electrical Protection industry lea

It tests the wiring and electricity every time you plug in and won't connect if it's not proper. It also disconnects if voltage drops (common in campgrounds that might have older wiring or a bunch of big RVs using lots of power) or power surges happen. Cheap insurance and they have a lifetime replace/repair warranty, unlike Surge Guard which only covers one year, replacement only, coverage.

Your 30 amp RV can't draw more than 30 amps even plugged into a 50 amp outlet, your circuit breakers are the limiting safety valve. No more power will flow than your RV can handle.

Likewise if I'm plugged into a 30 amp pedestal and try to run both A/C and the microwave while drying my hair, the pedestal 30 amp circuit breaker will trip.

One other 'factoid' to digest: A 30 amp RV is limited to 30 amps of power, 120 v X 30 amps = 3600 watts. A 50 amp RV service is actually 2 legs of 50 ams, so it gives 100 amps of power, 120 X 100 = 12,000 watts, or more than 3 times the power available in 30 amp service.

The circuit breakers in an RV are not limiting factors, by definition. They will open on excessive draw and short circuit. You can put higher amps through it like lightning does. But as I said the circuit breaker only protects the hot circuit/circuits not the neutral or ground.

Plugs are bastardized so you can't easily plug the wrong one in. Having the normally non energized neutral and ground would be the issue. How much amperage that gets in is more a factor of your wire size, gauge.

BFlinn181 · 08-26-2015, 03:20 PM

Quote:

Originally Posted by Forest Grump

The circuit breakers in an RV are not limiting factors, by definition. They will open on excessive draw and short circuit. You can put higher amps through it like lightning does. But as I said the circuit breaker only protects the hot circuit/circuits not the neutral or ground.

Plugs are bastardized so you can't easily plug the wrong one in. Having the normally non energized neutral and ground would be the issue. How much amperage that gets in is more a factor of your wire size, gauge.

A lightning surge happens faster than a CB can react. An EMS protects against lightning, bad neutral or ground connections or mis-wired pedestals. If you're not using an EMS, you of course are leaving it to the Gods to protect your RV.

Forest Grump · 08-26-2015, 03:22 PM

I took this from the RV Dreams web page:

<<So why can we run so many appliances at the same time with 50 amp service when we were more limited at 30 amp service?

Well, using our equation above - Watts = Volts X Amps - at 120 volts, 50 amps produces 6,000 watts as opposed to 30 amps which produces 3,600 watts. Quite a difference. Ah, but there is more to the story.

Remember at the beginning when we talked about a 30-amp power cord having 3 prongs? Well, those three prongs correspond to a hot 120-volt wire, a ground wire, and a neutral wire.

But the 50-amp power cord has 4 prongs. Those four prongs correspond to a ground wire, a neutral wire, and 2 120-volt hot wires!

So, going back to our equation - Watts = Volts X Amps - we have 2 50-amp lines at 120 volts each. We have two lines capable of 6,000 watts each, not just one. Our total is now 12,000 watts of potential power for 50-amp service as opposed to only 3,600 watts for 30-amp service. Now you can see why 50-amp service gives us so much more capability than 30-amp service.

Another note on 50-amp service. Almost all RVs are wired such that the two 50-amp, 120-volt lines are used separately. In other words, some of the appliances are wired to one hot leg of the 50-amp service and the remaining appliances are wired to the other hot leg of the 50-amp service.

And now we also know why there are two 50-amp breaker switches shown on our pedestals - one for each hot line. But even though there are two switches marked "50", they do not operate independently. The whole circuit will trip if one line is overloaded.

Finally, this is another good reason to have a 50-amp surge protector with voltage protection on your 50-amp rig. Those devices test both lines of the 50-amp service and protect all your appliances no matter which leg they may be on. If you do not have one of these devices, one bad leg could be the reason some appliances work and others don't. However, one bad leg will probably lead to much worse problems than that.

The neutral in a 50-amp circuit is there to help balance the total 240 volts between the two hot lines so they each carry only 120 volts and no more.>>

BFlinn181 · 08-26-2015, 05:13 PM

Quote:

Originally Posted by Forest Grump

The neutral in a 50-amp circuit is there to help balance the total 240 volts between the two hot lines so they each carry only 120 volts and no more.>>

All of your copied explanation was O.K. until the above. Electricity, whether DC or AC require two conductors. In alternating current, it 'switches' directions or polarity 60 times a second. Think of the hot lead providing one side, the neutral provides the other. The neutral doesn't 'balance' anything, it's there to allow the current to flow. The two hot legs of RV 50 amp service is also 180º out of phase with each other. At no time does the neutral wire 'see' more than 120 volts. That's why the 3 wires can be the same gauge, None of them ever has more than 120 v at any one instant.

If the pedestal isn't wired properly and both hots are in phase, then the neutral would have 240 v running through it and could overheat or melt the plug, outlet, or cord. Without a meter or EMS you'd never know of this wiring mistake until the smoke forms.

Forest Grump · 08-26-2015, 09:08 PM

I was wondering what that meant too.

Hooligan · 08-27-2015, 04:21 PM

The 30 amp adapter only connects one side of the 50 amp plug. You have a hot (120) a ground and a neutral. I have used this any number of times on a 30 amp MH with no problems... AND in my previous 50 amp motorhome, all appliances worked when connected to 30 amp input, just not all at the same time.

BFlinn181 · 08-27-2015, 04:36 PM

Hooligan, Your picture shows a 50 amp to 30 amp dog leg. In my 30 amp to 50 amp dog leg there is also a connection across the two hot leads in the 50 amp plug. This allows 30 amp service to supply power to both legs of the 50 amp service in my RV. All dog legs I've seen do the same, without that cross connection you'd only provide power to half of your 50 amp RV on a 30 amp pedestal. In the case of a 50 amp to 30 amp dog leg, like yours it provides as much as 50 amps to the RV, but the circuit breakers in the 30 amp breaker box would only allow 30 amps, anything more and it would trip.