how do i add shore power?

turf · 12-05-2016, 11:08 AM

hey everyone!
i've decided that i want to add a 50 amp shore line power to my bus and i've been contemplating how to do it.

my bus was previously a bookmobile so i have an awesome 12kw generator for my main source of power, but it would be nice to plug in, when i'm stopped at somewhere that has shore power available.

the generator output is directly wired to my AC distribution panel. i think the right way to add shore power is to disconnect the generator, and wire the distribution panel to a transfer switch. then wire a shore input to one side of the switch and the generator to the other side.

shore........... transfer switch...............gen
............. distribution panel

am i on the right track? where would i put an inverter? any recommendations on a transfer switch? should i hard wire the shore cord to the switch or use a receptacle? are there any issues that i may cause with ground from the generator?

any sparkies have some answers? i'm all ears

Scooternj · 12-05-2016, 11:18 AM

50' extension cord and 50A-rated power strip?

family wagon · 12-05-2016, 02:52 PM

That power strip comment might have come across as slightly sarcastic... but it's really not far off the mark.

First, though, there are a variety of packaged transfer switches. I found a bunch of nice pictures on eBay, but I avoid posting links to there because everything is so temporal. Do a web search for "double throw safety switch" and you'll find lots of options from eBay to Home Depot to online catalog listings from the big names like Eaton, Schneider, GE, Siemens. A single switch could gate between generator and shore. If inverter is to be added to the mix, it'll take a second switch cascaded so that, for example, switch A selects between generator or shore and switch B selects between inverter or whatever's chosen through switch A. A's output feeds into B; B's output feeds into the distribution panel.

Automatic transfer switches are an option too. Look at these only if pricing on the manual switches didn't make you cringe.

If you want to build it yourself you can look for multi-pole contactors. That's the main component inside a packaged automatic transfer switch, and when bought as a single component, costs a lot less than the packaged solution. But you'll have to gather up a few odds and ends, like a housing, on your own.

Ground is a good thing to think about. It is (should be) connected to neutral in your rig now since you have the on-board generator. When shore powered, that connection should be interrupted. The most oops-resistant method is to use a 3-pole transfer/safety switch with the third pole used to make the ground-neutral connection. Set it up so that the two are connected when generator or inverter is the source, but they're separate when shore power is the source.

Now, coming back around to the extension cord/power strip comment.. You could wire an inlet connector to the distribution panel and a cord-end receptacle to the generator, shore power extension cord, and inverter. The "transfer switch" would simply be unplug one source and plug in another. At the moment I'm having a little trouble choosing an appropriate 50 amp connector for that job. If it were 30 amp I'd suggest the L14-30 twist-lock style. Surely something similar exists with a 50 amp rating. Compared to the cost and size of safety/transfer switches, this really isn't such an outlandish suggestion after all.

AlleyCat67 · 12-05-2016, 09:37 PM

Something like this?

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

That's an option I considered for a while.... get a generator with a 50 amp outlet, then my "transfer switch" would be to plug my 50 amp cord into whichever source I wanted to use, shore power outlet or generator output. I've since abandoned that since 50 amp generators are over $1000 and are noisy as hell. Not what you want in a campground. Boondocking with no one else around it would be ok but not if you have neighbors nearby.

family wagon · 12-05-2016, 11:29 PM

Yeah, that connector could feed to the distribution panel. The mate could go on the generator and inverter outputs, and one of each gender on the ends of a length of SOOW cable as a shore power cord.

AlleyCat67 · 12-05-2016, 11:48 PM

If you've got an inverter big enough to supply a full 50 amp service then you'd almost have to have a separate trailer for the battery bank, that's a LOT of amp hours and a LOT of weight.

That connector I posted before was for the shore power cable connection into the rig. If you're looking for the outlet you would connect to a generator or generator head, inverter, etc, to plug the cable into then this is what you would need:

And this cable to plug into it, with the other end in the receptacle connected to the distro panel/load center:

turf · 12-05-2016, 11:58 PM

i'm a bit confused by the ground and electrical nomenclature.

my generator supplies 50a split phase service. thats 4 wires, 2 hots, a neutral and a ground. so do i need a 3 pole? or 4 pole? transfer switch if i want to switch ground from the generator to shore.

the rv transfer switches i see seem to be 3 pole and share ground but switch 2 hots and the neutral. i feel like if i get one of these, that shared ground will fault and trip the shore line. am i missing a way to wire the 3 pole switch?

am i looking for something that i don't need?

dazed and confused

i did find this switch, but dang$$$$$

Blue Sea Systems 8369 AC Rotary Panel 120 + 120/240VAC/6

AlleyCat67 · 12-06-2016, 12:48 AM

If it's the neutral to ground bond you're concerned about, don't be.

The bond for shore power is done at the power pedestal.

For a generator, the manual should tell you how to do the bond if it's not already connected.

Larger inverters usually have it connected, with a means to disconnect it if necessary.

I've seen automatic transfer switches for 50 amp service for less than 100 bucks.

family wagon · 12-06-2016, 10:03 AM

Mike Holt is an industry expert who makes his business helping people understand the National Electric Code. Among the free resources available on his web site is his Generators and Standby Power Systems based on 2011 NEC summary. There's one here for 2014 NEC also, but the 2011 write-up has more/better illustrations for this discussion.

On page 4, Figure 445-5 illustrates what's needed. This figure shows a generator with a built-in ground-neutral connection. The shore power (aka Service) also has a ground-neutral connection. There shouldn't be two such connections in a system, so the transfer switch is shown disconnecting the generator's neutral line from the panelboard. The generator's (or inverter's) ground-neutral connection has no effect when using shore power because its neutral is interrupted by the transfer switch.

Regarding the NEMA 14-50 connector AlleyCat67 suggested: of course it'll work. I prefer to avoid those NEMA connectors because their insertion/removal force is so much higher as compared to the twist-lock variety. That's why I suggest if using plugs and sockets instead of a hard-wired transfer switch to use the other type. They're more expensive but SOOO much easier to plug/un-plug. Campground pedestals are going to have that 14-50 socket though so ultimately you'll have to have a way of getting into that to use their service.

turf · 12-06-2016, 10:14 AM

Quote:

Originally Posted by family wagon

. The generator's (or inverter's) ground-neutral connection has no effect when using shore power because its neutral is interrupted by the transfer switch.

that is the answer i was looking for. thanks for explaining it to me.

PNW_Steve · 12-06-2016, 11:57 AM

Quote:

Originally Posted by family wagon

Mike Holt is an industry expert who makes his business helping people understand the National Electric Code. .

Mike Holt is a VERY sharp guy who does an awesome job of sharing information in a very understandable manner.

His website is a great resource, his license prep classes are fantastic as well.

https://www.mikeholt.com/

PNW_Steve · 12-06-2016, 12:01 PM

Here is an option for an auto transfer switch:
50 Amp Automatic Transfer Switch - TRC 40100 - Generator Accessories - Camping World

I used one like this on a conversion that I did with 50A shore power. It worked out great.

It has a built in delay so that when you start your generator it has time to come up to speed before a load is applied.

Thomas1985 · 12-07-2016, 06:34 PM

Man, you guys are making this complicated. Granted, I don't have a stove or any major power consumption besides my bedside standing air conditioner/dehumidifier. I simply mounted commercial power strips down each side of the bus. I want to say it's about 10 outlets on each side, I snake the cords under the bed and out a small hole in the back corner to my generator sitting on the back. I use the Honda EU 3000 because it's eco silent. If Im camping somewhere that has power I run an extension cord.
I might add solar panels one day just so I can have lights and charge cell phones without running the generator.

-Thomas

New2Skool · 12-07-2016, 06:41 PM

What I did was buy two exterior mounted RV standard 110 male plug in's connected to my two power systems. Solar and Shore, a switch disconnect between the two and redundant systems on redundant power sources. I just ran two extention cords from the garage to the bus side by side. It is easier and cheaper than bigger heavier cords and higher amp outlets and plugs. I divided the shore power into two 25 amp lines, one for appliances and the other for rotating use devices and ports. I haven't had a problem with either unless, I am running a space heater, twin halogen work light and grinder going at once. Then you get the "click" and lights out, turn off one and get back to grinding.

That is as simple as I could stand to do it myself. I was lost with 240 dc 75 amp twin relays 12v dc to 110 ac converters and 6g jumper cable cords and blah blah. I went cheap and easy within what, I know and understand.

turf · 12-28-2016, 08:15 PM

yea!!!!

i sold some stuff on ebay and got the money to buy some needed bus parts. stay tuned for the transfer switch and cord hookup. i also got a new exhaust manifold on the way!

ol trunt · 12-29-2016, 01:13 PM

N2S, I'd be interested in how you set up your electrical system--particularly the shore power. Do both extension cords start from the same power source (receptacle) and go to the same location in the bus breaker box? What gauge wire is used in the extension cords and how long are they? I don't quite follow the 25 amps on each cord--are you working with a 50 amp service in the bus/garage?
Thanks, Jack

milkmania · 01-03-2017, 08:19 PM

Let me preface this post: I AM FREAKING CLUELESS regarding electrifying my bus!!!

At this moment, I am connected to a campsite pedestal with 20amp, 30amp, and 50amp service. I am using 50' 12/3 extension cord for various things
(one milk house heater and LED lights on the 30amp)

(One milk house heater, refrigerator, laptop, 1 external hard drive, and one CFL lamp on the 20amp with 75' 10/3 extension cord with 4 outlet box.) I "manage & manipulate" my microwave, toaster oven, and coffee maker on this circuit with power strips. If I need microwave, I turn off heater, etc...
Yes, I realize I should have the majority of this on the 30amp pedestal outlet... It just hasn't worked out that way yet, due to length of cords.

I won't always have 50amp service, but I'll try as much as possible.
I have no electrical done, because I don't know what to buy (see a pattern here?)

Ultimately, I'll want a control panel for 110v service with a few wired outlets.
I'll end up adding a 110v clothes dryer, a 110v front load washer, a 110v dishwasher into everything mentioned above, and 2 roof A/C units.

I'm monitoring the temperature of my outlets and cords and they DO NOT ever feel warm to the touch. During sleeping hours, the only things running are the thermostatically controlled milk house heaters, with 3 smoke alarms throughout the bus. So, I'm comfortable with all that. No breaker tripping if I remember to manage my heaters.

Eventually, I'll incorporate the Mitsubishi rear motor with 120/240v 60amp 25k generator, so at some point I'll need to add a transfer switch.

How and where do I start electrifying this thing?!?!

turf · 01-03-2017, 09:06 PM

with 2 AC units, you need to size your system for 50A service.

when i had my little travel trailer, i melted an adapter plugging my 30A system into a 15A service and running the AC. it can happen!

50A service is just like at home. 2 -110v hot wires, a neutral, and ground. you will split the 2 air conditioners and have one on each leg of the hot wires, and then you do your best to balance the rest of the loads, between the 2 - 110 hot wires.

in pumbing terms -
15A is like a little pipe of electricity
30A is like a big pipe of electricity
50A is like 2 big pipes of electricity

my diesel generator puts out the full 50A on both hots, so my bus was already wired for 50A (home like) service. i have an ex bookmobile, so it came with the heavy duty power supply. Now i am just adding the ability to plug in.

milkmania · 01-03-2017, 10:00 PM

Here's something I found unusual when I pulled the generator head from the Generac generator...
80amp?

turf · 01-03-2017, 11:09 PM

that breaker is in the 50A group. DPDT - double pole double throw - both of those would be hots, and the way the breaker box is made, its split the legs for you.
when i say "50 amp" i mean double pole
when i say "30amp" i mean single pole

sorry to confuse

30 amp would be a SPST breaker- single pole single throw

also, i know just enough about electricity to be really dangerous.

ac electricity is in a wave pattern, so each pole takes turns putting out its amp rating. maybe the 80 is the combination of both sides? maybe it accounts for spikes in the generator? idk, but there was probably a pretty good reason for it.

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