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Old 04-15-2018, 07:07 PM   #85
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As a master electrician and contractor for over 40 years reading these posts is maddening.
If you don't understand find someone who does.
Some things are over the DIY ability.
Be safe. Don't kill yourself or anyone else and don't burn your rig down.
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Old 04-15-2018, 07:09 PM   #86
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Originally Posted by followingsea View Post
I was a mechanical with 40 years in the power industry including 10 years as a nuke trained officer. Things do not always work according to theory.



What do you want to do and how do you know it is safe? I did the wiring for a house I built. I used the same 12 gage wire for 15 and 20 amp circuits. The building inspector 'red flagged' my 15 amp breakers. The breaker should protect the limiting component on the expected on the circuit but is conservative to use a heavier gage wire.



So you match individual 15 and 20 amp breakers to the load and the main breaker to the total load.



More often than not shore power is on 20 amp kitchen circuit with a 50' extension cord through the window. Measured voltage with the microwave running 95 volts. Not good!



With generator running power comes from one 20 amp breaker and 30 amp breaker for a total of 50 amps. Voltage is maintained at 120 volts and stays close to that at the loads. Some load management is required by putting loads on propane.



On shore power, power comes from two 50 amp breakers with a possible total of 100 amps on the common wire. Voltage drop depends a lot on the loads that include other RVs in the park. We like to be at the far end and often we are back down to 90 volts.



So yes you may have 100 amps service but I do not recommend burning out your AC unit.



RV power democracy.


If I need any help with nukes, Iíll give you a call. Electricals, I donít think so. Two equal loads on L1 and L2 will give you zero load on the common wire, or neutral as I call it. Remember L1 and L2 are 180 out of phase.
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Old 04-15-2018, 07:15 PM   #87
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Originally Posted by doublechevy View Post
With 49years of electrical experience and the holder of a Master electrical Lisc. I have never seen so much misinformation on electrical as I have seen reading this forum post. some of the responders truly know what they are talking about a very few of them. to the last poster you will never have 100A
on the common (Neutral ) if connected to a properly wired shore power pedestal. On ( 2) 120V lines on separate phases, the neutral will only carry the unbalanced current.

Sample Only

L1 20A L1 20A
L2 10A L2 20A
N 5A 0A

Do yourself a favor If you are not sure what you are doing Hire a qualified Lisc. Electrician
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Old 04-15-2018, 07:38 PM   #88
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With pedestal. On ( 2) 120V lines on separate phases, the neutral will only carry the unbalanced current.

Sample Only

L1 20A L1 20A
L2 10A L2 20A
N 5A 0A

Do yourself a favor If you are not sure what you are doing Hire a qualified Lisc. Electrician
Looks like a typo - should be a 10 Amp load on neutral.
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Old 04-15-2018, 09:01 PM   #89
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Couple of points for what ever its worth...

Typical house hold electric meters measure both volts and amps. Keep in mind Ohms Law Watts = Volts x Amps. So if you measure volts and amps you are indirectly measuring watts. Most meters record and report Kwatt hours. Some report in Joules. This is from Wikipedia:

"The disc is acted upon by two sets of induction coils, which form, in effect, a two phase linear induction motor. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. The field of the voltage coil is delayed by 90 degrees, due to the coil's inductive nature, and calibrated using a lag coil.[16] This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current, voltage and phase angle (power factor) between them. A permanent magnet acts as an eddy current brake, exerting an opposing force proportional to the speed of rotation of the disc. The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power or rate of energy usage. The disc drives a register mechanism which counts revolutions, much like the odometer in a car, in order to render a measurement of the total energy used."

You can find similar descriptions elsewhere if you like to look.

Household or RV park power is generated by a center taped transformer. The center on the secondary coil is the grounded neutral and the two ends produce 120v that are exactly 180 degrees out-of-phase with each other. If measured from either end point to the center it is 120v, if measured between the two ends points it is 240v. This is called single phase or sometimes split phase power. The US power grid is designed on three-phase power on the primary distribution lines and single phase at most customer sites. Larger industrial sites may use three-phase at various voltages other than 120/240V. There was a short time in the early 1900s that true two-phase was produced for use in some motors. Two-phase power is 90 degrees out-of-phase. It is essentially nonexistent today.

What was stated above about possibly having two 120V lines in-phase with a common neutral would be extremely dangerous. Expect a fire. You could wire up two in-phase lines, but only with two neutrals or a common neutral that's double the amp capacity. But why- no one working on a circuit would expect to encounter this.

All those explaining RV parks with 50A service are 240 volts, each leg fused at 50 amps are correct. If in doubt use a multimeter across the two legs to see 240V, and each leg and neutral to see 120V. Assuming the park's power supply is functioning correctly.
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Old 04-16-2018, 01:06 AM   #90
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Originally Posted by rarebear.nm View Post
Couple of points for what ever its worth...


Household or RV park power is generated by a center taped transformer. The center on the secondary coil is the grounded neutral and the two ends produce 120v that are exactly 180 degrees out-of-phase with each other. If measured from either end point to the center it is 120v, if measured between the two ends points it is 240v. This is called single phase or sometimes split phase power. The US power grid is designed on three-phase power on the primary distribution lines and single phase at most customer sites. Larger industrial sites may use three-phase at various voltages other than 120/240V. There was a short time in the early 1900s that true two-phase was produced for use in some motors. Two-phase power is 90 degrees out-of-phase. It is essentially nonexistent today.

What was stated above about possibly having two 120V lines in-phase with a common neutral would be extremely dangerous. Expect a fire. You could wire up two in-phase lines, but only with two neutrals or a common neutral that's double the amp capacity. But why- no one working on a circuit would expect to encounter this.

All those explaining RV parks with 50A service are 240 volts, each leg fused at 50 amps are correct. If in doubt use a multimeter across the two legs to see 240V, and each leg and neutral to see 120V. Assuming the park's power supply is functioning correctly.
Fred thanks for pointing out the reason that the current on the common is not the sum of the two hot leads.
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Old 04-16-2018, 07:20 AM   #91
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Let me say again, some of the information in these posts, if not totally wrong, is very confusing for the average RVer. Wiring something wrong can be catastrophic!

ALWAYS have your wiring inspected by a competent Electrician. I always do myself and I have been wiring my homes and shops for a long time. I was schooled in electrical circuits, but I am not an electrician.
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Old 04-16-2018, 10:51 AM   #92
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the 2 cords was just an example to help see what is going on. To use 2 cords to develop 240 you would have to make sure they are out of phase so are supplied by L1 and the other L2 rather than both one side.

the thing is that most folks don't realize that each line L1 and L2 need to have a seperate breaker of 25 amps. If L1 trips then L2 should trip also. If it doesn't then you have a live circuit at the load. Because one line is out off phase, you get double the power at the load(a dryer as example). L1 provides 25 amps, L2 provides 25 amps out of phase, for a total of 50 amps. If the breakers were 50 amps then they wouldn't blow until they hit 100 amps if over loaded. Look at the circuit configuration. parallel or series..... got to think "2 phase" double the amps. I hesitate to use the term"2 phase" because it is not called that.

Each 120v circuit in an rv is 180 degrees out of phase, an rv service entrance should be wired so that they are out of phase. this is really important because rv's with dryers will not operate properly with them in phase. The dryer will not run to speed nor the elements get hot enough to dry the cloths. I've run into this before and corrected it. Fella wired 2 seperate breakers into a box and couldn't figure out why the dryer wouldn't work right. He didn't want to move the other breakers around. The lights on his one leg would dim when the elements turned on.

Ok, but... I did make a mistake, forgot about the "phase difference", so yes 12000 watt at 240 volts, through 2 25 amp breakers in tandem to blow at the same time. The correct math looks like this L1x25 amps = 6000 watts, L2x25 amps = 6000 watts. total across L1 and L2 is 12,000 watts at 240v or 6000 watts between neutral and L1 or L2. a 30 amp service has 3600 watts at 120v.

I stand on the fact that most rv parks had to raise their prices due to the larger power hungry 50 amp service. they use 2400 watts (2.4 kwh) more of power.

My information stands about the meters. They measure how many amperes that a residence uses. voltage at service entrances should be 240v across L1 and L2, it suppose to remain constant. The meter measures the amperage for each leg because it is out of phase then combines and changes it to the familiar kilowatt hours. True, the amperage does go up if the voltage drops, that is the reason they measure the amperage. I've seen a 240v line vary from 210 v to 260v AC.

WANNA GET COMPLICATED?????? Let's talk about 3 phase installs.... if you have a 3 phase 60 amp circuit, wanna make a guess at how much each breaker in the tandem is rated at? Hint, not 60 amps.

That's 14,400 watts because of the phase difference..... The expensive part is that you have to have 3 phase power boxes....
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Old 04-16-2018, 10:59 AM   #93
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Originally Posted by rarebear.nm View Post
Couple of points for what ever its worth...

Typical house hold electric meters measure both volts and amps. Keep in mind Ohms Law Watts = Volts x Amps. So if you measure volts and amps you are indirectly measuring watts. Most meters record and report Kwatt hours. Some report in Joules. This is from Wikipedia:

"The disc is acted upon by two sets of induction coils, which form, in effect, a two phase linear induction motor. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. The field of the voltage coil is delayed by 90 degrees, due to the coil's inductive nature, and calibrated using a lag coil.[16] This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current, voltage and phase angle (power factor) between them. A permanent magnet acts as an eddy current brake, exerting an opposing force proportional to the speed of rotation of the disc. The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power or rate of energy usage. The disc drives a register mechanism which counts revolutions, much like the odometer in a car, in order to render a measurement of the total energy used."

You can find similar descriptions elsewhere if you like to look.

Household or RV park power is generated by a center taped transformer. The center on the secondary coil is the grounded neutral and the two ends produce 120v that are exactly 180 degrees out-of-phase with each other. If measured from either end point to the center it is 120v, if measured between the two ends points it is 240v. This is called single phase or sometimes split phase power. The US power grid is designed on three-phase power on the primary distribution lines and single phase at most customer sites. Larger industrial sites may use three-phase at various voltages other than 120/240V. There was a short time in the early 1900s that true two-phase was produced for use in some motors. Two-phase power is 90 degrees out-of-phase. It is essentially nonexistent today.

What was stated above about possibly having two 120V lines in-phase with a common neutral would be extremely dangerous. Expect a fire. You could wire up two in-phase lines, but only with two neutrals or a common neutral that's double the amp capacity. But why- no one working on a circuit would expect to encounter this.

All those explaining RV parks with 50A service are 240 volts, each leg fused at 50 amps are correct. If in doubt use a multimeter across the two legs to see 240V, and each leg and neutral to see 120V. Assuming the park's power supply is functioning correctly.
Actually, Watts = V x I x (PF)

PF = Power Factor which makes the difference between real and reactive loads in an AC circuit. Basically, if the Voltage and Current are out of phase some of your load is reactive instead of real.



Now back to your normally scheduled AC Theory confusion.
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Old 04-16-2018, 11:11 AM   #94
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the 2 cords was just an example to help see what is going on. To use 2 cords to develop 240 you would have to make sure they are out of phase so are supplied by L1 and the other L2 rather than both one side.

the thing is that most folks don't realize that each line L1 and L2 need to have a seperate breaker of 25 amps. If L1 trips then L2 should trip also. If it doesn't then you have a live circuit at the load. Because one line is out off phase, you get double the power at the load(a dryer as example). L1 provides 25 amps, L2 provides 25 amps out of phase, for a total of 50 amps. If the breakers were 50 amps then they wouldn't blow until they hit 100 amps if over loaded. Look at the circuit configuration. parallel or series..... got to think "2 phase" double the amps. I hesitate to use the term"2 phase" because it is not called that.

Each 120v circuit in an rv is 180 degrees out of phase, an rv service entrance should be wired so that they are out of phase. this is really important because rv's with dryers will not operate properly with them in phase. The dryer will not run to speed nor the elements get hot enough to dry the cloths. I've run into this before and corrected it. Fella wired 2 seperate breakers into a box and couldn't figure out why the dryer wouldn't work right. He didn't want to move the other breakers around. The lights on his one leg would dim when the elements turned on.

Ok, but... I did make a mistake, forgot about the "phase difference", so yes 12000 watt at 240 volts, through 2 25 amp breakers in tandem to blow at the same time. The correct math looks like this L1x25 amps = 6000 watts, L2x25 amps = 6000 watts. total across L1 and L2 is 12,000 watts at 240v or 6000 watts between neutral and L1 or L2. a 30 amp service has 3600 watts at 120v.

I stand on the fact that most rv parks had to raise their prices due to the larger power hungry 50 amp service. they use 2400 watts (2.4 kwh) more of power.

My information stands about the meters. They measure how many amperes that a residence uses. voltage at service entrances should be 240v across L1 and L2, it suppose to remain constant. The meter measures the amperage for each leg because it is out of phase then combines and changes it to the familiar kilowatt hours. True, the amperage does go up if the voltage drops, that is the reason they measure the amperage. I've seen a 240v line vary from 210 v to 260v AC.

WANNA GET COMPLICATED?????? Let's talk about 3 phase installs.... if you have a 3 phase 60 amp circuit, wanna make a guess at how much each breaker in the tandem is rated at? Hint, not 60 amps.

That's 14,400 watts because of the phase difference..... The expensive part is that you have to have 3 phase power boxes....
This is wrong! Each half of the breaker is capable of 50 amps of current. It is NOT measuring 50 amps total for the circuit. If that was the case the NEC wouldn't allow 2 - 50 amp single pole breakers, with an approved handle tie, to serve a 50 amp 240 volt circuit.
Each half of the breaker is rated at the current stamped on the breaker. This is how a multi-wire branch circuit works. One half can draw up to the breaker rating and the other half nothing or also up to the rating. Three phase / 3 pole breakers are also the same rating per pole. Watt to amp calculations on 3 phase involve dividing the watts by the voltage x square root of 3 since you added the third leg. But that's not relevant here.
Too much bad information in this thread.
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Old 04-16-2018, 11:12 AM   #95
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Not if the pedestal is wired according to code. A properly wired 50 amp shore power connection will have a max of 50 amps on the neutral, and it would be damn hard to get anywhere near that with any conventionally wired RV.
My 240 volt dryer takes 30 amps when on. Add in the washer, electric floor heat, three 15Kw heat pumps, both electric elements on the AquaHot, the household refer, the induction cooktop, the Advantium micro/convection oven and I can easily attempt to draw over 100 amps.
I'm retired, I don't do phase angles or power factors anymore!
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Old 04-16-2018, 11:32 AM   #96
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I almost cannot believe this thread has run this long with the same people repeating the same erroneous comments. Some just don't get it.
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Old 04-16-2018, 11:33 AM   #97
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Old 04-16-2018, 01:14 PM   #98
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I think I have a headache!
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