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Old 12-03-2019, 07:33 AM   #43
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Originally Posted by BruceDeville View Post
It seems like all the reply's and recommendations are dead on. The way I trouble shoot is start with something I know, then go to where it fails. In this case, start at the receptacle on the utility supply end. Read voltage between the two vertical plug elements, usually have black and red wires. You should get approx 240 volts. Then take two readings, one connected to common, middle/centered one with white wire. and the other to each one of the vertical legs. Each one should be approximately 120 volts. These are the two that are black or red. If this test fails, call an electrician.

Next step, plug 50 amp plug (from RV) into receptacle. go to other end of 50 amp cord/plug. This is probably where the transfer switch comes into play. Repeat the steps previously did except now no plug just wires and colors. If this test fails, the RV plug or cord is bad. Most probably the plug. Remove plug from cord and shorten by a few inches. Reinstall plug and repeat previous step. If this does work not go to next step.

If you have 240 volts black to red and 120 volts black to common (white) and red to common, then all previous is OK.

If your transfer switch is like mine, (three different motorhomes) you bring power (from RV plug/cord) to switch. The generator supplies power to the switch, with generator taking priority (that is when generator and shore power are available, it selects generator power). Then lastly the switch supplies power to the coach. If all is OK when running on generator power, ie 50 amp is available, the circuit breakers contained within the coach should be good and untripped.

If you have shore power to transfer switch and generator will supply full 50 amps, then the switch may be the problem.

When you have a poor connection in a plug, it will heat up. this heat will frequently be enough to damage the receptacle. You may need to inspect the receptacle. Bad connections will produce erroneous readings.

Other than that, I don't know.
Bruce Deville
Small point, if you have shore power the transfer switch prioritizes that, not the generator. Most folks with a big genny have an automatic transfer switch, when shore power is lost it AUTOMATICALLY transfers to the generator, hence the term and acronym ATS (Automatic Transfer Switch) it transfers to the generator when the shore power is lost. If it was the other way as you suggest, you would never need to plug into shore power, just always run on the genny.
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Old 12-03-2019, 08:33 AM   #44
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You are incorrect.

Most ATS default to shore power but prioritise generator power.

With no power the ATS is either sitting open or in shore power position.

With shore power plugged in, and nothing else, it is in shore power position.

Once you start the generator, the ATS starts a 30 second timer, to let the generator RPMs stabilise, and then switchs to generator power, regardless of shore power being on or not.

Turn off the generator and it falls back to shore power.Click image for larger version

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Old 12-03-2019, 09:16 AM   #45
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My intent was not to facilitate an argument about "priority" on the aromatic transfer switch. I have not inspected the transfer switch while it transfers nor have I read the manual. My opinion was based on experience on the three motorhomes that I have owned. I could have misinterpreted my observations and come to an incorrect conclusion. My observation were made by monitoring the slight change in voltage when the generator starts while shoe is applied. Generator runs about 119 to 121 volts, shore power is about five volts higher.

Maybe I will figure a fool-proof way to check that out.
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Old 12-03-2019, 02:09 PM   #46
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The adapter brings you only 1 leg of the 50 amps 120 volts to your panel
you panel box. Your main breaker reduces that to 120 volts @ 30 amps.
I'd offer a small clarification: the main breaker doesn't reduce anything - it merely limits the current available downstream from it. It's semantics, I know, but it's more correct...
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Old 12-03-2019, 02:17 PM   #47
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I'd offer a small clarification: the main breaker doesn't reduce anything - it merely limits the current available downstream from it. It's semantics, I know, but it's more correct...
It reduces/limits the available current from 50 to 30.
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Old 12-04-2019, 07:35 AM   #48
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The legs are always split. They are 120 volts each BUT 180 degrees out of phase with each other. L1 to L2 is 240. L1 to Neutral/ground is 120. L2 to Neutral/ground is 120.
Point of order Mr. Chairman...... (have I been watching too many Congressional debates?) The two legs of power that come to your power post are 120 degrees out of phase with each other. Electricity in the US is generated and transmitted in 3 phase. To get nominal 120v we use 1 phase (hot wire) and Neutral. For nominal 240v we pick 2 phases off the feed. For the big boys using lots of power we use all 3 phases and get a nominal 440v.

3 phases split equally (from the 360 degree rotation at generation) is 120 degrees.

And yes, that means absolutely nothing to any of us in practical use of electricity in our RV's, but since we're down in the weeds now about everything else, we may as well empty all the worms out of the can and make all our numbers correct. I turn back my time..........
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Old 12-04-2019, 11:05 AM   #49
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Point of order Mr. Chairman...... (have I been watching too many Congressional debates?) The two legs of power that come to your power post are 120 degrees out of phase with each other. Electricity in the US is generated and transmitted in 3 phase. To get nominal 120v we use 1 phase (hot wire) and Neutral. For nominal 240v we pick 2 phases off the feed. For the big boys using lots of power we use all 3 phases and get a nominal 440v.



3 phases split equally (from the 360 degree rotation at generation) is 120 degrees.



And yes, that means absolutely nothing to any of us in practical use of electricity in our RV's, but since we're down in the weeds now about everything else, we may as well empty all the worms out of the can and make all our numbers correct. I turn back my time..........
You are confusing 3 phase and split phase systems.

In the US, power is indeed generated in 3 phases, each 120 degrees apart, but at hundreds of thousands of volts. High tension power lines (in UK English, tension means voltage) carry the 3 phase power to substations in the local area that step it down into lower voltage, say 40,000 volts. Within about 1000 feet from your house, 1 phase of the 40,000 volts passes through a transformer that puts out 240 volts single phase with a tap in the middle we call nuetral. These 3 wires, 2 hots and the neutral feed your house or a properly wired RV 50A receptacle, known as a (NEMA 14-50) Thus the voltage between neutral and each hot leg is 120V. The two legs are 180 degrees out of phase if you measure relative to the neutral.

In the UK, where outlets are wired for 240V, is not uncommon to have 2 phases of the 3 feeding the home breaker panel. They do not use both legs together however, that would provide 415V.

For more information, see NFPA 79, also known as the National Electrical Code.
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Old 12-04-2019, 10:23 PM   #50
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IIRC (if I remember correctly) everyone knows what IIRC means - LOL (laugh out loud).
I've been reading and learning from these posts for months and someone has finally stated what IIRC means, Thanks!!
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Old 12-05-2019, 07:45 AM   #51
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You are confusing 3 phase and split phase systems.

In the US, power is indeed generated in 3 phases, each 120 degrees apart, but at hundreds of thousands of volts. High tension power lines (in UK English, tension means voltage) carry the 3 phase power to substations in the local area that step it down into lower voltage, say 40,000 volts. Within about 1000 feet from your house, 1 phase of the 40,000 volts passes through a transformer that puts out 240 volts single phase with a tap in the middle we call nuetral. These 3 wires, 2 hots and the neutral feed your house or a properly wired RV 50A receptacle, known as a (NEMA 14-50) Thus the voltage between neutral and each hot leg is 120V. The two legs are 180 degrees out of phase if you measure relative to the neutral.

In the UK, where outlets are wired for 240V, is not uncommon to have 2 phases of the 3 feeding the home breaker panel. They do not use both legs together however, that would provide 415V.

For more information, see NFPA 79, also known as the National Electrical Code.
I stand corrected. However, the transformer near you house does not put out single phase, (see bold and italics above) it puts our 2 phase, hence the 2 hot wires to get 240v or 120v and the 180 degree out of phase.
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Old 12-05-2019, 12:08 PM   #52
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I've been reading and learning from these posts for months and someone has finally stated what IIRC means, Thanks!!
I stand corrected as well. Not to hijack the thread but... Huge List of Texting and Online Chat Abbreviations
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Old 12-05-2019, 12:21 PM   #53
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I stand corrected. However, the transformer near you house does not put out single phase, (see bold and italics above) it puts our 2 phase, hence the 2 hot wires to get 240v or 120v and the 180 degree out of phase.

It may be confusing, but our household electrical systems are, indeed, single phase systems. Industrial buildings may have a 3-phase system being used, where each leg is 120 degrees apart, but residential installations are all single-phase.



Basically, a house is supplied via a transformer. In its simplest form there are 2 wires, each coming from one end of the transformer winding, and the voltage between those 2 wires is 240V. The power company is nice enough to supply a third wire, which is basically a center tap on the output wiinding of that transformer - the result being that you will measure 120V between that center tap and each other wire.


Where the confusion comes in is mostly a matter of semantics: because each hot wire is at opposing ends of the transformer winding, when one wire is at +120V the other one will be at -120V - they are 180 degrees "out of phase". This is why many people think that we are using a 2-phase system - in fact we are using a "split-phase" system.


One can google this if one wants to really learn something...
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Old 12-05-2019, 12:38 PM   #54
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Where the confusion comes in is mostly a matter of semantics: because each hot wire is at opposing ends of the transformer winding, when one wire is at +120V the other one will be at -120V - they are 180 degrees "out of phase". This is why many people think that we are using a 2-phase system - in fact we are using a "split-phase" system.
And you (or the utility) could have just as easily grounded one end of that center-tapped transformer to hold it at 0V (to ground), giving 120V and 240V to ground. Which is not desirable, of course. But you can add as many taps as you like, in as many locations on the secondary winding, and they're all still single-phase. All the voltage peaks occur at the same time, even if they are of opposite polarity to ground.

There actually are 2-phase systems, both 3-wire and 4-wire, and the NEC actually addresses these specifically in a few places, but they're almost extinct at this point. The voltage peaks happen at different times, unlike split-phase systems, which are single-phase with multiple taps.
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Old 12-05-2019, 10:45 PM   #55
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I stand corrected. However, the transformer near you house does not put out single phase, (see bold and italics above) it puts our 2 phase, hence the 2 hot wires to get 240v or 120v and the 180 degree out of phase.

there is no 2 phase power in the US. You transformer is in fact giving you single phase electric. 2 hot legs @ 120 volts 180 degrees out of phase with each other. I don't know how else to explain it. That's why I installed it and not tough it!
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Old 12-06-2019, 05:10 AM   #56
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I've been reading and learning from these posts for months and someone has finally stated what IIRC means, Thanks!!
Just google it or any acronym you don't know.
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