120v / 240v Shore vs Genset Wiring Question

[richard5933]

Looking for a bit of advice before I undertake a revision to the wiring on our coach. The current setup was done in 1990 during the original conversion. Not at all certain who did the conversion, but I'm told he wintered in NM.

Currently the setup is as follows:

There is a 6-breaker Square-D panel to run the 120v inside the coach. It has two legs. Apparently the generator (12.5KW Perkins/Kohler) is currently wired to provide 120v power to both legs. When the generator is running there is power to all appliances and outlets.

When using the manual rotary transfer switch to change from generator to shore power (30amp), only one leg of the panel is powered. Most of the outlets, the CruiseAir, and most importantly the battery charger have no 120v when on shore power only. Really confused why the battery charger would have been set up to only function with the generator and not also on shore power.

In addition, there is another panel. I thought it was the master power breaker for the 120v, but I discovered that in actuality it was the power disconnect for the 240v line running to the JennAir range. Does not apparently have anything to do with the 120v. The 240v line is only powered with the generator (apparently using both of the 120v lines).

My main goal here is to enable use of the other leg in the main 120v panel when on shore power. I realize that if I keep the 30a service I will have limited power available and be limited in what I can run. That said, here are the questions:

1) If I decide to keep the 30-amp service can I just install a jumper at the transfer switch so that when changing to shore power both legs in the 120v panel are energized? Seems like this is what happens when a 50-amp RV is powered by a 30-amp pedestal through the use of an adapter. If I went this option I would have to find another cooktop option when on shore power - not really a big problem.

2) Is converting to 50-amp service as easy as it sounds? Seems like all I need to do is install a new receptacle, run a properly-sized 4-lead cable from the receptacle to the transfer switch, and then connect the 50-amp service for shore power similarly to how the generator is hooked up. Other than the problem of fishing the new power cable from receptacle to transfer switch, this seems pretty simple. The receptacle is currently housed in the OEM service port which was originally used to service the restroom on the bus. It is located just outside of the old restroom location on the passenger side. The transfer switch is located on the wall separating the rear bedroom from the closet, also on the passenger side.

3) Would the 240v JennAir operate by tapping into both of the leads of the 50-amp service to create 240v?

4) Can anyone explain to me why some of these earlier conversions incorporated a 240v JennAir? I know they were the latest and greatest once upon a time, but in a bus? Seems like there had to be more practical options even then which would have permitted cooking on shore power.

Hoping to get some insight before opening things up and getting going next week. Any advice or suggestions would be most welcome.

[scanzel]

I would convert the shore to 50 amp as most rv parks provide 50 and 30. Trying to run multiple items on 30 amp shore especially the cook top would probably trip the 30 amp breaker. Convert over to 50 amp would give you two legs at 120v each for the stove top. Why it was done this way is beyond me.

[TomC]

You CANNOT jump a single 30 amp and run 240vac. A little electrical schooling-20amp, and 30amp are single phase 120vac-or just think of it as more of the same as your standard plug in your house. 50amp service is actually 100amp service-meaning there are two legs of electrical power, but are 180 degrees out of phase-this allows you to only use one common line (plus your green grounding). So a two leg 50amp line will have a combined 100amp available-but only 50 amps per side.
On your 240v stove, is it wired with two wires or three wires? With three wire 240vac, you have two legs of 50amp. If you only wire with the two positive legs, you'll have straight 240vac, but at 50 amps.

I have my bus wired straight 120vac. My 10kw genset has 4 wires plus ground. Two sets of 45 amps (closest to 5,000 watts at 120v) going to my breaker box. Since I'm wired straight 120vac, then when I'm on land line, I only use one side of the 50amp plug. Advantage to this-I never have to worry about balancing the load between the two sides of 120/240vac. Disadvantage-I only have 6,000 watts coming into my bus while on land line. This isn't a problem since A/C loads are far less sitting still than moving down the road. I hope this helps. Good Luck, TomC

[bobofthenorth]

The advice to wire as 50 amp, 240V is the best you have received.  If you do that now you'll be doing what the large RV manufacturers are doing so you'll "fit in" when you are in RV parks.  There's good reasons that is the standard.

You say your existing panel has two legs so wiring it for 240 service should be simple although you may need to pull another conductor from your shore connection.  You are correct that a 50/30 dogbone will simply connect both sides of the panel to a 110 service but you are better to do that outside the bus so as to keep everything compatible with what you are likely to encounter in campgrounds.  I totally agree that a 240V cooktop in an RV is just plain silly.  Get rid of it unless you plan to go pole to pole on 50 amp service.  We had a 110V cooktop in our boat on a 30 amp service and that was a royal PITA.  Cooking with gas is the way to go unless you plan to be plugged in all the time.

Long term I question whether a 6 breaker panel will be adequate but you'll have to answer that question.

[buswarrior]

I am not a fan of splitting the generators in our coaches into 120/240, I prefer it wired straight up full 120.

No need to balance loads, very hard to not have the generator running one legged in the coach.

Often, a larger generator is recommended to combat this, increasing costs.

Unbalanced generators seem to have issues, can't start aging equipment with other loads on, outright failures, blah blah that the combined wire to 120 don't seem to report as much.  

Old school cooking apparatus put a lot of heat into the coach. Good in the cold, not in the heat.

This style rules out 240 appliances, but is that the end of the world in 2017?

Between a good microwave and an induction cooktop, your indoor kitchen doesn't have to be outdoor heat limited.

Induction also uses less power, good for power management?

Lots of choices, lots of philosophies, that's why a busnut rolls their own?!?!?!!!

happy coaching!
buswarrior

[Oonrahnjay]

... Old school cooking apparatus put a lot of heat into the coach. Good in the cold, not in the heat.

This style rules out 240 appliances, but is that the end of the world in 2017?...
happy coaching!
buswarrior 

    Yes, exactly, and I think you're edging close to an answer to the question "why a JennAir in a bus".  ISTM that most buses need a good cooking/kitchen vent fan or extractor setup and the JennAir does that -- but at a big cost in power use, need for 240, etc.  Much better to go induction and a plain fan and hood, all wired for 120V.

[richard5933]

I've also given serious consideration to trying to salvage and reuse the 'Air' part of the JennAir. Looks like the exhaust fan runs on 120v, and the ducting and all are in great shape. The ducting goes out the bottom of the bay below the kitchen. If I could retrofit a 120 cooktop to fit the space normally occupied by the 2-burner insert I'd be in business. Haven't yet found a 120v JennAir insert though, so I may have to create my own.

[Oonrahnjay]

I've also given serious consideration to trying to salvage and reuse the 'Air' part of the JennAir. Looks like the exhaust fan runs on 120v, and the ducting and all are in great shape. The ducting goes out the bottom of the bay below the kitchen. If I could retrofit a 120 cooktop to fit the space normally occupied by the 2-burner insert I'd be in business. Haven't yet found a 120v JennAir insert though, so I may have to create my own. 

     Sounds like a good plan - the "air handling" part of JennAir is really good.   If you're going to create your own, you may want to look at induction -- they're really super for what we need.  But either 120V cooktops or gas will simplify things a lot, if you'd rather pick one of those.  It's good to have plenty of good choices.

[Zephod]

My bus could be run on a 50A but I've wired for 30A as it's the most common (and cheapest) connection. I'm not a great big electricity hog. My cooling is provided by solar powered extraction and induction fans. Cooking is gas or electric if plugged in. Refrigeration is either a cooler or a mini fridge depending on whether I put the mini fridge in the mini fridge space.


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[dtcerrato]

We recently upgraded our 30 amp 110 volts to 50 amps at 220 volts but kept both configurations so when we are plugged into a 30 amp outlet - there is power on all circuits (both panel legs). The 6.5 kW gen set is wired for 220 volts so we can back feed the foundated home main panel in power outages. The conveneance of having the option for either plug configuration when plugging into shore power (110 @ 30 amp or 220 volt @ 50 amp ) is really nice & of coarse if need be we can adapt down to 110 volt @ 15 amp if need be with all circuits energized but used wisely...

[daddysgirl]

You might think of this as overly simplistic, but it's nearly foolproof.

Why not set it up...
one bay plug dedicated to the generator next to...
one bay plug dedicated to inverter/house batteries with...
The shore cord powered by your electrical "system" that either...

Plugs into the generator OR
Plugs into the Inverter OR
Plugs into a pole
?

[Oonrahnjay]

You might think of this as overly simplistic, but it's nearly foolproof.

Why not set it up...
one bay plug dedicated to the generator next to...
one bay plug dedicated to inverter/house batteries with...
The shore cord powered by your electrical "system" that either...

Plugs into the generator OR
Plugs into the Inverter OR
Plugs into a pole   ? 

     A lot of people have done it that way and it works fine.  The one thing that can be said is that if you have a power failure at 3 AM you have to go outside in the rain (it's always raining when things need to be done, right???) to make the switch over; also, it doesn't allow for an auto-start for the generator when batteries get to a certain level.  So, this system works for what it is -- and has the great benefit of being inexpensive -- but a more sophisticated system may or may not offer some features that are helpful.

[richard5933]

I thought about doing separate plugs to simplify things, but I kind of like the ease of just rotating the transfer switch.

I'll have to dig in deeper to see what's going on.

If I'm lucky I'll find that there is an unused lug on the shore power side of the transfer switch, and then all that will be needed is to install and 50amp receptacle and a new 4-conducter cable to the transfer switch. Not usually so lucky, but hope runs eternal.

Then, I'll only need to verify where the 240v circuit for the JennAir is coming from/going to to be sure that I didn't mess it up.

If I understand correctly, the 240v JennAir should be able to run off of 50-amp shore power IF the JennAir is using a 2-wire (double hot) feed currently. I can just do the same from the new 50-amp shore power if I'm able to add it, correct? I do understand that none of the 240v appliances will function properly when I'm plugged into shore power using a 50-amp to 30-amp adapter plug, and that I'll have limited amperage available on both legs of the 120v panel with the adapter.

Am I missing something?

Once I get into the walls/panels I'll post some photos of what I've found and how I work it out.
Richard

[daddysgirl]

     A lot of people have done it that way and it works fine.  The one thing that can be said is that if you have a power failure at 3 AM you have to go outside in the rain (it's always raining when things need to be done, right???) to make the switch over; also, it doesn't allow for an auto-start for the generator when batteries get to a certain level.  So, this system works for what it is -- and has the great benefit of being inexpensive -- but a more sophisticated system may or may not offer some features that are helpful.

I've been lucky enough to never have a power failure, but agree there are many ways to connect a system. My generator and inverter both have switches in the cockpit. The only change I have to make is where the cord is plugged.

But I noticed I didn't emphasize (in that post) the importance I place on keeping the house batteries totally separate from the engine batteries. As you said, there are other ways to connect power systems, but if I ever do have a power failure while camping, I don't want it to be the engine batteries.

[buswarrior]

Put the @#%^$ plugs UPSTAIRS?

As noted, it always rains when you need to change configuration...

Watch busnuts set up/tear down camp. How many different doors have to be opened to get it all working or packed up?

We really are nuts...

happy coaching!
buswarrior