Confused on 50A hookup

[bruceisla]

Originally Posted by njs42

You need to get this right. I'm not an electrician but I just had a box installed. This explanation is correct;

http://www.myrv.us/Imgs/PDF/50-amp%20Service.pdf

Yes .. just do as linked and everyone will be happy.

[Ray,IN]

Originally Posted by FlyingDiver

Just FYI - the pedestal needs to be wired as a true 240V circuit (two hot leads out of phase). If it's not, it's broken and should not be used.

Also, SOME RVs are actually wired with a real 240V subpanel and support 240V appliances (like our dryer). Not all are wired with two independent 120V legs.

You are exactly correct!

[PushedAround]

Originally Posted by TQ60

With the two 120 vac example and ac say 15 amps the neutral is carrying 30.

You were good till you got to this point. Because the A leg is 180 degrees out of phase with the B leg, if you have exactly 15 amps on both legs, you will have 0 volts on the neutral. The neutral leg is necessary here to keep the potential voltage at 120v. Neutrals burn up typically because someone has accidentally tied two A legs (or 2 B legs) on the same neutral.

BTW I did not sleep at a Inn Express but I am a licensed commercial electrical contractor.

[TQ60]

You miss understood...

If there are two 120 vac legs on same source they are not 180 out and an issue.

Correct is to be 180 out but sub panel may not be wired that way.

I used both bad and good examples to direct the point.

[RayJr]

WOW!!! A man has to know his limitations, and electric is mine.

[PushedAround]

Originally Posted by TQ60

You miss understood... If there are two 120 vac legs on same source they are not 180 out and an issue. Correct is to be 180 out but sub panel may not be wired that way. I used both bad and good examples to direct the point.

Yes, you are correct here, but I guess that I did not read your initial post as meaning that. My bad.

[TQ60]

Just checking to see if you were paying attention....you passed...

[wa8yxm]

50 amps is 50 amps at 120/240 volts (50 amps at 240 volts divided).

The three flat blades are

|<-120=>|<-120->|
|<-=-=-240 Volt - -|

All the electrical stuff in your RV is 120 volt.. So why do they do it this way.

Well, let's say you are 1,000 feet from the power source (Transformer) and the voltage drop in the wires is 5 volts per thousand feet at your current power consumption level

If you were sucking 110 volt only.. You'd have 1000 feet (5 volt) from the transformer to your RV and 1000 feet (Another 5 volt) back so 120 volt becomes 110 volt

But by using 240 volt and BALANCING the loads (Example of balance Front AC on Leg 1 Rear on Leg 2 Microwave on 1 Water heater on 2

you now have 1000 feet out (five volt drop) and the neutral is carying nothing, the other thousand feet is the other leg

So the effective voltage drop is five volts instead of 10 in the first example.

Footnote: All figures in this post are examples the odds that I got the voltage drop per thousand feet exact are right next to the odds of a snowball surviving 10 minutes inside an operating blast furnace. (In short zero).

[markroblee]

Originally Posted by wa8yxm

50 amps is 50 amps at 120/240 volts (50 amps at 240 volts divided). The three flat blades are |<-120=>|<-120->| |<-=-=-240 Volt - -| All the electrical stuff in your RV is 120 volt.. So why do they do it this way. Well, let's say you are 1,000 feet from the power source (Transformer) and the voltage drop in the wires is 5 volts per thousand feet at your current power consumption level If you were sucking 110 volt only.. You'd have 1000 feet (5 volt) from the transformer to your RV and 1000 feet (Another 5 volt) back so 120 volt becomes 110 volt But by using 240 volt and BALANCING the loads (Example of balance Front AC on Leg 1 Rear on Leg 2 Microwave on 1 Water heater on 2 you now have 1000 feet out (five volt drop) and the neutral is carying nothing, the other thousand feet is the other leg So the effective voltage drop is five volts instead of 10 in the first example. Footnote: All figures in this post are examples the odds that I got the voltage drop per thousand feet exact are right next to the odds of a snowball surviving 10 minutes inside an operating blast furnace. (In short zero).

The basics here are very very correct. If you want a major math test you can check for exact numbers but IMHO it is not needed. What it comes down to is the big new rigs have more bells and whistles than the older "standard" 30amp does not have the needed capacity to make everything work so manufacturers have had to change to keep everyone happy.

These larger loads is also why at older campgrounds you need to keep an eye on available voltage at your pedestal. Lots of AC, electric water heaters, microwaves, etc. etc. can REALLY stress these systems and cause real problems with the RV equipment.

[wb7auk]

And then install the ground rods required and the voltage drop on the neutral lessens.

[njs42]

[FlyingDiver]

Originally Posted by wa8yxm

All the electrical stuff in your RV is 120 volt.. So why do they do it this way.

Not in my RV it's not. Nor many other high-end rigs.

[FlyingDiver]

Originally Posted by wb7auk

And then install the ground rods required and the voltage drop on the neutral lessens.

Install where? Per NEC, the pedestal and panel combo in the RV are sub-panels and neutral/ground must be isolated. So how is adding a ground rod going to help with the voltage drop caused by resistance in the wires over the distance from the transformer?

[wb7auk]

Originally Posted by FlyingDiver

Install where? Per NEC, the pedestal and panel combo in the RV are sub-panels and neutral/ground must be isolated. So how is adding a ground rod going to help with the voltage drop caused by resistance in the wires over the distance from the transformer?

The neutral and earth ground at the meter as well as at the main panel.