A question on Voltage

Big Ben · 03-06-2006, 05:43 PM

This question came up at lunch today. When plug in to 50 amps is the voltage 110 volts or 220 volts?
Thanks for any replies.

Big Ben · 03-06-2006, 05:43 PM

This question came up at lunch today. When plug in to 50 amps is the voltage 110 volts or 220 volts?
Thanks for any replies.

Cruzer · 03-06-2006, 05:54 PM

It's both. There are two hot poles on a 50 amp RV circuit. Each pole will have 120 volts from either hot to the neutral terminal but if you check voltage across both hot terminals you'll have 240 volts. This is the same setup as your residential power service.

The difference is that most RVs only use 120 volt devices. But they use either hot leg, depending upon how the breaker panel is arranged. The combined power then goes to a common neutral, which may have ability to pull double amps (100) so it's important to size the neutral wire accordingly. RVs utilize this system so that the generator set (which has two output legs but are "in phase") and a lesser shore power (like 30 amp) can still provide power to both legs of the breaker panel. In the case of 30 amp, the single 120 volt feed of a 30 amp RV receptacle is wyed to both 50 amp legs inside the dogbone cord adaptor.

Big Ben · 03-06-2006, 06:31 PM

Thanks, that was a good explanation.

MrTransistor · 03-06-2006, 07:40 PM

Hi Big Ben & Cruzer,
Actually, with a 50 Amp. service, if both hot legs are drawing 50 Amps. then there would be zero Amps. on the neutral. The neutral should never carry more than 50 Amps. If Line 1 has zero Amps. and Line 2 has 50 Amps. then the neutral will carry 50 Amps. and as the current increases on Line 1, the current will decrease on the neutral. More than 50 Amps. on either line should trip a breaker. Only when the generator is supplying power will the neutral carry more than 50 Amps. and the wiring to the generator accounts for this extra current by having two neutral conductors running to the transfer switch. This setup allows the 50 Amp power cord to have Line 1, Line 2, and neutral conductors of the same gauge wire with a ground of either the same or slightly smaller wire.

The Onan 7.5 will supply 120 VAC at 62.5 Amps. which equals 7,500 Watts. A 50 Amp. service can supply 240 VAC at 50 Amps. which is 12,000 Watts. Of course, a 30 Amp. service will supply 120 VAC at 30 Amps. which equals 3,600 Watts and a 20 Amp. service will supply 120 VAC at 20 Amps. which equals 2,400 Watts. To be nit-picky, the 120 VAC line is not always 120V. But it will normally range between 110 and 125 Volts depending on the power company and the RV parks wiring. Outside of these values won't necessarily cause any damage but it probably should be avoided if practical. Below 100 and above 130 gets into the danger zone.

Bear in mind that to actually realize the full 12,000 Watts from a 50 Amp. service, the current on Line 1 and Line 2 has to be balanced at 50 Amps. In an RV, it is usually a little difficult to get just the right loads on each Line to come up with exactly 50 Amps. The factory tries its best to share loads in the coach between the two lines. But that's okay since all the loads combined in a Winnebago are usually less than what the Onan's 7,500 Watt output can handle. If you are running extra electric space heaters, making a pot of coffee, heating the water with electric, running the AC for heat, and making popcorn in the microwave, then the 50 Amp connection would be a must.

We have been connected to 30 Amps. all winter running two electric heaters inside the coach and a homemade 600 Watt thermostatically controlled heater in the water compartment and have been quite cozy. Our propane consumption running just the hot water heater, fridge, and stove has been less than .6 gallons per day.

I hope this information is helpful.

Big Ben · 03-07-2006, 04:39 AM

Thanks again. I'm not sure my old brain is absorbing the whole thing but I have learn how to check the outlet before plugging in.

Thudman · 03-07-2006, 06:12 AM

So when plugged into 50A shore pwr, do we really have 100 Amps available for use in our 50A coach?
All I know about 'lectrics is On and Off.

Thudman

rebelsbeach · 03-07-2006, 06:40 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">If you are running extra electric space heaters, making a pot of coffee, heating the water with electric, running the AC for heat, and making popcorn in the microwave, then the 50 Amp connection would be a must. </div></BLOCKQUOTE>

You mean....we ALL don't do that??

MrTransistor · 03-07-2006, 05:10 PM

Hi Thudman,
About all you can do is to think of it as 'two' 50 Amp. circuits (a lot more power than 'one' 30 Amp. circuit). That's why RV parks sometimes charge more for a 50 Amp. hookup. Problem is you have no control over which circuit which appliances get powered from. That was determined by the factory. If you would like to know this information, check your wiring schematics to see what is powered on Line 1 and what is on line 2.

rebelsbeach,
Ohhhhh are they going to charge you now! Dony is always happy when we hit the road and hook up to 50 Amps. She doesn't care too much for managing the loads.