Generator Prep Wiring Question

My new 5th wheel came generator prep with no generator.  We do not want to buy and install a generator and plan to remove the generator shroud to make room for additional batteries, solar and inverter installs and may remove the generator start/stop switch inside of the coach in favor of the inverter remote. I would like to make use of the transfer switch to install my inverter.  The transfer switch has the generator wiring leading the opposite direction of where the generator would be installed and there is bundle of wires with a connector next to where the generator would go.  I am wondering, is the wiring from the generator side of the transfer switch going to the generator start/off switch inside on the electrical panel, and then to where the generator would go?  Trying to get an understanding of how generator prep is wired as i have no wiring diagram. 

When I get ready to install my inverter, can I cut the wire from the generator side and wire that to the inverter or is it best to disconnect those wires at the transfer switch and wire in new wires from the inverter?

Not sure I understand what your trying to do but the transfer switch is really nothing but an A/B switch design to automatically switch AC power from either AC shore to Gen or opposite depending on how it's wired. When the switch is energized it switches a set of contacts inside to transfer the AC power source from one to the other. In my MH I have it set to switch from shore AC power to gen AC power since the shore power outlet may not be rated for the AMPs my MH needs in which case I would start the generator.

In your case you are always running on 12v so I don't know why you would use it. I guess you could have set sets of batteries that are separate so when one set dies you can switch to the others but in this case the switch needs 120v to operate as far as I know.

Hope that helps

Thanks, I understand what a transfer switch does.  What I want to do is wire my inverter to it where the generator would normally be wired since I am not going to install a generator.  Since my coach came gen prepped I am trying to understand where the wire from the generator is going since there is no generator and if to make things simpler, simply cut the wire going to the generator connection and wire it to my inverter.  It seems to me since I have no generator the wire theoretically from the generator is otherwise useless and begging to be routed to my inverter.
I will

So your 5th wheel came with a 120V system wired for a gen but no gen and also no inverter installed. So you want to install an inverter and connect the 120v out to the 5th wheels 120v wiring that would normally be connected to the gen to provide 120v power. I don't see why you can't do this but make sure everything is over current protected correctly. Not sure what size inverter your looking for but the larger ones have remote on/off switches which you would need based on where your putting the inverter. The only other thing I can think of is ventilation/cooling to the inverter along with weather protection. The gen compartment is likely exposed to the outside but I doubt the inverter would tolerate that. I would say you need to seal the gen compartment for the inverter install and check the requirements for cooling of the inverter. With this install the transfer switch will work correctly to ensure you don't feed the AC panel with two AC sources!

Yes you have it right, no generator but generator prep. Thank you.

The inside generator switch wiring goes directly to the generator compartment, to connect to the generator's stop-start circuits.  Find out what kind of generator the factory would have installed, then look online for it's Installation Manual to see which pins are which on the multiplug.

There's no connection between the inside generator start and the transfer switch, it just senses voltage from each source and switches as is appropriate.  Normally when the transfer switch is relaxed it passes shore power, then when it sees voltage from the generator it switches to that source, maybe after waiting a few seconds for the generator to stabilize.

When the generator voltage goes away, it returns to the shore power position.

You can connect the inverter output to the generator side of the transfer switch and it will work properly.  Whether you use the existing wires or run new ones is your choice.

Thanks Lou.  It is set up for an Onan generator and the wires coming from the inside switch are irrelevant to me, I am still trying to figure out to satisfy my curiosity, where the wires that feed the transfer switch from the generator are coming from since I do not have a generator.  I would have thought they would go to the vicinity of the generator, but appear to go in the opposite direction.

Gizmo, I have a few questions. First, are you planning to be able to run your entire trailer from the inverter? Including the air conditioners? What size inverter? What size battery bank? And how will you charge them?

ChaseA I am planning to install a substantial battery bank (adding 4-100AH lithium batteries to my current 3-100AH for a total of 700AH and 1200-1500 watts of solar.  This will be my third solar installation.  We have a portable 2000 watt Genenerac generator to charge the batteries if needed.  I am not panning to run the entire trailer with the inverter and definitely not the air conditioner.  Initially I am planning to install my Samlex 2000 watt inverter I removed from my previous rig, then down the road, if use dictates, move up to a 2800 or 3000 watt inverter. 

Gizmo said:

Thanks Lou.  It is set up for an Onan generator and the wires coming from the inside switch are irrelevant to me, I am still trying to figure out to satisfy my curiosity, where the wires that feed the transfer switch from the generator are coming from since I do not have a generator.  I would have thought they would go to the vicinity of the generator, but appear to go in the opposite direction.

Click to expand...

It is a bit confusing when you use a vague statement of "the wires" and not specifying exactly which wires you are speaking of.

I am guessing you are looking for 120V AC wires going from the generator prep to the transfer switch.  If that is correct, there should be a standard 120V set of household wires (should be 10 gauge wire for 20amp) in the generator area which goes to the transfer switch.  If the trailer is 50amp then there should be 2 sets of 10 gauge wire.

Are you saying you can't find the 120V wire in the generator prep area?

Is your inverter a charger as well?  If so you will need two sets of 120V wires going to the inverter.  One to supply 120V to the inverter and one to go back to the AC CB panel.

Attempting to answer some of your specific questions:

I am wondering, is the wiring from the generator side of the transfer switch going to the generator start/off switch inside on the electrical panel, and then to where the generator would go?  Trying to get an understanding of how generator prep is wired as i have no wiring diagram.

Click to expand...

The 120V wires from the generator should be going directly to the transfer switch.  The gen on/off would be low current wiring to just pick the start solenoid and monitor the run condition of the gen.

When I get ready to install my inverter, can I cut the wire from the generator side and wire that to the inverter or is it best to disconnect those wires at the transfer switch and wire in new wires from the inverter?

Click to expand...

Use a multi meter to verify the 120V wires do go to the transfer switch.  Use the ohm function to be sure where the wires go.  Disconnect the gen wires from the transfer switch, meter them to verify they have no continuity to each other or to frame ground, then, at the transfer sw end tie the hot & neutral together and then insure you have continuity at the generator area.  If you find that the wires go directly to the transfer sw then yes, you can use those wires for the inverter.  Remember as I stated above,  if you have a charger with the inverter you will need a second set of 120V wires.

Thanks, I understand what a transfer switch does.  What I want to do is wire my inverter to it where the generator would normally be wired since I am not going to install a generator.  Since my coach came gen prepped I am trying to understand where the wire from the generator is going since there is no generator and if to make things simpler, simply cut the wire going to the generator connection and wire it to my inverter.  It seems to me since I have no generator the wire theoretically from the generator is otherwise useless and begging to be routed to my inverter.

Click to expand...

I'm confused about why you are concerned about the direction the wire goes from the transfer sw.  As long as the wires go directly to the gen area it doesn't matter which direction the wires leave the transfer sw.

NOTE:  If you don't have an inverter with a built in charger, you will need to add a very heavy wire gauge cable from the converter to the battery area to charge your batteries from the external generator or shore power.

I see no inherent problem with wiring the 120V output from the inverter to the transfer sw.  Yes it will go through the transfer sw to the main 120V panel and be available to all the high power 120V devices, but as long as you leave them off when using the inverter they should not be a problem.  I would prefer a sub panel so that the inverter 120V only powers the 120V outlets and the microwave, but that gets into a lot of work and additional wiring.

Additionally, if the inverter has a charger, be sure to disconnect the converter or be sure the converter DC output doesn't go to your new batteries.  Otherwise the inverter will take 12V from battery to supply 120V to converter which will try to charge the batteries.  This loop will drain your batteries.

Pretty much what AStravelers says.  The transfer switch is a Y, with one leg coming from shore power, another from the genset, and the third output side goes to the load center (breaker box) in the RV.  There is no "direction" with 120vac power - it is a point-to-point connection.

Since you don't have an actual genset, that leg of the Y is either dangling wire or simply not there (just the terminals on the transfer switch).  Two of those legs are already in place, so not much to guess about with the 3rd one.  Since you say you have an auto-transfer switch, the switch inside that you mentioned is probably just a generator starter switch. An auto transfer operates on its own, switching to the genset if it is on and supplying power but otherwise engaging shore power.

You have to solve two problems if you install batteries and an inverter where the genset would go.  The batteries need a charger when shore power is active, so you need to either (a) run heavy duty battery cables from the existing converter/charger, or (b) have a second charger along with the inverter (part of it or separate).  Second, you need to disable the onboard converter/charger when the inverter is supplying power. Using inverter power to run a battery charger creates a power loop that wastes battery amps and quickly runs them down.

You also need to accommodate the weight of the batteries and its effect on pin weight.  Whether the batteries weigh more or less than a generator depends on what you choose to install, but the weight effect needs to be factored in regardless. It may not be a problem at all, but needs to be considered.

Thank you Gary for addressing the generator leg wiring and your most helpful response, kind of what I was suspecting but it seemed odd to me that the wire from the transfer switch to the generator would not have been coiled up next to the transfer switch or generator since the two are very close together.  Instead the wire is routed forward and what appears pretty far, though I have not tried pulling on it or seeing if it terminates for some reason elsewhere.  In any case it sounds like I have the option, option to cut that wire and wire to my inverter  I have the charging aspect solved as I have a stand alone Progressive Dynamics 65 Amp charger specifically programmed for the lithium batteries I have.  I have the option of plugging into the 20 amp plug on the pedestal, or plugged to my portable 2000 watt generator.  In my previous rig I kept my converter shut off and relied on solar and when needed the standalone charger, so I believe I am good there.  Also if my 2000 watt inverter proves not adequate enough for our needs, plan B is to get a 2800 watt or 3000 watt inverter/charger.  As for weight, while I will be adding 4-additional lithium batteries, I suspect the total weight since they are considerably lighter than AGM or LA is likely less than the 5K Onan generator that would have been installed, but erring on the side of caution, I will verify the weight capacity just the same. 

Yeah, lithium batteries should help solve any weight concerns.  However, do not assume that the RV was designed to handle the genset weight either.  RV builders have a terrible track record of messing up on weight distribution, even shipping with an actual overweight condition at times. The weight of a component they didn't actually install probably never showed up on their radar. If they even have any radar...

Where is this transfer switch located?  You mention "going forward', but I'm not getting a mental picture to envision that.  If the transfer switch is near where the shore cord comes in and the genset area is much further away, obviously the wires need to run in that direction.  Is there any actual wire provided for the genset?  Often that is left as an exercise for whoever installs it.  Since the factory did not install a genset, who nows?

Thanks again Gary and once again you may be spot on.  While poking around to free up space in the generator cabinet up front, I had a look at the floor and it does not inspire confidence.  So once I get the rest of the batteries I am going to build some extra support under the floor to make sure it will support the batteries.  To your question, I incorrectly said going forward, actually the wire goes towards the back.  The generator in a 5th wheel as you know is located up front behind the king pin, behind the generator cabinet is the large basement storage area, the transfer switch is located just behind the back wall of the basement storage.  The wire coming from the secondary (generator) side of the transfer switch continues on back then, seems to make a u-turn but does not go anywhere near the generator .  I tried to follow it and tug on it some, it gave a little then did not budge and I did not want to force the issue.  I have a little time before I get to the inverter install and perhaps during my other installs, it will reveal itself, In the mean time just trying to get an idea of the lay of the land and how things are put together in our new rig.

Today while installing my Progressive Industries 50-Amp EMS (Hard Wire), I went on a little fishing trip and found where the wire coming from the generator side of the transfer switch terminates.  It takes a circuitous route back, then takes a U-turn and terminates in a junction box within the generator/battery front storage.  So my curiosity is finally satisfied and this will make a much easier inverter install since my plan is to install the inverter in that forward compartment close to the batteries. 

> In the mean time just trying to get an idea of the lay of the land and how things are put together in our new rig.<

Indeed! There is SO much variation in the way things can be put together in an RV that I well understand!  The first couple of years with any 'new to us' RV I have spent doing exactly the same thing. THEN I have understood better how I might modify things to our benefit.