Could someone describe 50A shore power systems?

[Goodspike]

Originally Posted by mrschwarz

US residential systems are 240 volts, with a center-tap neutral. Voltage between the center-tap and either leg measures 120V each leg is out of phase with the other. Every 50-amp RV I have seen is wired similarly to residential electrical systems. Each 120 volt hot leg is wired to one side of a 240 volt load center. Breakers in the panel alternate between one leg and the other so any two adjacent full-size breakers go to different legs. 120-volt loads, such as electrical outlets and air conditioners are wired to one side or the other in the load center. Designers try to balance the loads equally between the two sides. If a 240 device is wired in, it is usually connected to two adjacent positions. Many RVs use 1/2 position breakers so they can fit more in a smaller load center. In the case where this is done, adjacent breakers can be on the same 120-volt leg.

Yes they are wired similarly, because the source supply source is often the same. Balancing is actually more important on an RV because of the relatively low supply of power.

The time the supply source could be different is when a generator is in use. Not all 5000+ watt generators (and no portable generators that I'm aware of) provide two "legs" that are out of phase, so there would be no opportunity for 240 volt. And if the RV has no 240 volt devices, there is no need for that.

[mrschwarz]

That's true. Many smaller generators are single pole with one 120-volt breaker. Some of the larger ones are 120 volts, too. If I remember correctly, I had an Itasca Meridian with an Onan 5,500 watt generator. It had two poles but both were in the same phase. I don't recall if the generator could be changed to a 240-volt center tap or not. Unless that was done, 240 volt devices wouldn't work.


My current coach has a 10,000 watt generator. I don't have any 240-volt devices, but one of the options I could have ordered was a Wolf cook top that was 240 volts. Honestly, I have never measured the output voltage across the two breakers.

[Goodspike]

Originally Posted by mrschwarz

My current coach has a 10,000 watt generator. I don't have any 240-volt devices, but one of the options I could have ordered was a Wolf cook top that was 240 volts. Honestly, I have never measured the output voltage across the two breakers.

I suspect you can get 240 unless that cook top also required a generator upgrade. When I referred to portable generators I wasn't including those installed in motorhomes, even though those are not stationary!

Not something I ever researched, but my guess is being able to provide 240 results in a significantly more expensive generator, even though it seems like that really shouldn't be a huge design feat. So if there's no need for 240 and just a need for more watts, that an RV will only have a generator producing 120 volts.

[jerichorick]

Originally Posted by Goodspike

I'm not sure their 240 is the same as our 240, I've never researched that. Somehow I don't think it is or else they would likely have 120 too!

European power is 50HZ. We use 60HZ power. If the 240V is supplied with a Neutral it can be used as 2 120V circuits. The hot legs can be labeled 'X' & 'Y' or L1 & L2. The voltage from the neutral to either of the hot legs is 120V. The actual voltage ranges around this reference number.
All 30A RV's use 120V only. There are several threads that some someone has posted where the electrician installed a 240V 30A dryer outlet at their home for their RV. When they plugged in many things fried in the rig.
Hope this helps.
Rick Y

[mrschwarz]

Originally Posted by jerichorick

European power is 50HZ. We use 60HZ power. If the 240V is supplied with a Neutral it can be used as 2 120V circuits. The hot legs can be labeled 'X' & 'Y' or L1 & L2. The voltage from the neutral to either of the hot legs is 120V. The actual voltage ranges around this reference number.
All 30A RV's use 120V only. There are several threads that some someone has posted where the electrician installed a 240V 30A dryer outlet at their home for their RV. When they plugged in many things fried in the rig.
Hope this helps.
Rick Y

You're right about the frequency, although many electrical devices don't care. Some motors do. European systems have a neutral, but the hot leg is 240 volts. The neutral, like ours, seems to have the same electrical potential as ground. If you stick a voltmeter between ground and neutral, it should read zero. If it doesn't there is probably and electrical problem.


Another way to look at it is in the US, we achieve 240 volts by using two out of phase 120 volt hot legs. In Europe, they use one 240 volt hot leg and a neutral to get the same result. If the neutral were to suddenly measure 120 volts for a European appliance, I am not sure how it would feel about it.



Years ago, when I worked for a recording studio, we were contracted to record a concert tour in Europe with a well-known rock group. To do this, we built a location truck with all equipment set up for 120 volts. It was, in fact, a specially made early 70s Winnebago motor home. It had no interior, other than a bathroom and had two generators and dual 120-volt electrical systems. We installed huge Variacs (variable transformers) and planned to step the 240-volt source down to 120. I don't recall what went wrong with our design, but we were never successful tying into stadiums' and arenas' electrical systems. We did the whole tour using the generators. They performed like champs.


The fact that both standards can support 240 volts doesn't make them compatible.

[jerichorick]

Originally Posted by mrschwarz

You're right about the frequency, although many electrical devices don't care. Some motors do. European systems have a neutral, but the hot leg is 240 volts. The neutral, like ours, seems to have the same electrical potential as ground. If you stick a voltmeter between ground and neutral, it should read zero. If it doesn't there is probably and electrical problem.


Another way to look at it is in the US, we achieve 240 volts by using two out of phase 120 volt hot legs. In Europe, they use one 240 volt hot leg and a neutral to get the same result. If the neutral were to suddenly measure 120 volts for a European appliance, I am not sure how it would feel about it.



Years ago, when I worked for a recording studio, we were contracted to record a concert tour in Europe with a well-known rock group. To do this, we built a location truck with all equipment set up for 120 volts. It was, in fact, a specially made early 70s Winnebago motor home. It had no interior, other than a bathroom and had two generators and dual 120-volt electrical systems. We installed huge Variacs (variable transformers) and planned to step the 240-volt source down to 120. I don't recall what went wrong with our design, but we were never successful tying into stadiums' and arenas' electrical systems. We did the whole tour using the generators. They performed like champs.


The fact that both standards can support 240 volts doesn't make them compatible.

Good story. I can see one problem. The frequency. Our older equipment didn't like the 50Hz and the manufactures made two versions of their products. Then they started putting a switch on the back to select the correct voltage. Today, as you indicated, our equipment is more forgiving and is designed to work over a wide range of voltages and frequencies in many but not all cases. This is a deep topic not practical for here.
I don't recall if the Variac was frequency sensitive or not. You may have been more successful with the power conversion for that tour using 240VAC 50Hz battery chargers, battery banks and 120VAC 60Hz inverters. I have 20/20 hindsight.

When in Mongolia I had to replace some outlets in a house. It's so long ago I don't recall clearly if it had a ground. I am thinking that the European power is 2 wire. One hot lead and one ground with no neutral. We call our 3 wire systems white wire the neutral. When the L1 & L2 are referenced to the neutral, if each leg is pulling the same current level the white (neutral) reads zero current because the L1 & L2 wave forms are 180* out of phase. If they track each other at the same power consumption they cancel out in the neutral. The European system, using this definition, has only a hot and a ground and no neutral.

TMI for this topic?? It's fun in any case.
Happy trails and safe travels.
Rick Y