Wiring in a new generator in our old rigs?

[ClydesdaleKevin]

Sent: 4/24/2005


Well folks,

Like I said in another thread, the Generac is all bolted in, wired to the battery, and almost hooked up to the gas (I'm short a 6" piece, and didn't realize it until the sun was almost down).

I have a question about the wiring though, and since you all run old coaches like mine, maybe you can help.

My rig is set up with a single circuit coming from the generator.  In other words, in the generator compartment is the relay box where you wire the generator in.  Coming from the box and going into the coach are only two wires, black and white.  These wires make thier way to the electrical panel under the kitchen bench, where the main breaker box is, as well as the converter/inverter and the 50' shore power cord. 

The relay box in the generator compartment has one 30 amp breaker, while there are 3 30 amp breakers under the kitchen bench, isolating the AC, and 2 other circuits.

The new Generac has TWO power wires coming out of it, as well as 2 common wires (white), and a green for ground.  The instructions show pictures of modern relay boxes, with multiple breakers and TWO circuits coming out of them:  The primary, which I have, and a secondary for a second AC unit.

One of the power wires coming from the Generac is red, and its for a 30 amp circuit.  The other is black, for a 20 amp circuit.  Red is the primary according to the directions, and black is for the secondary circuit, which I don't have.

Here is my question:  I do NOT want to rewire my whole rig, so what should I do?  I was thinking that I should tie in both commons to my common white wire, and the RED 30 amp to the Black in my circuit box.  The Green ground gets attached to the relay box, according to the directions, so that's not a problem.  The 20 amp Black wire I'm thinking of just taping off with electrical tape, and leaving it disconnected.

Any suggestions?

In summary, this is how I propose to wire it:

Generac, 2 common whites------->Ark, 1 common white.
Generac, Red 30 amp------------>Ark, 1 "hot" black.
Generac, Green Ground---------->Ark, metal relay box.
Generac, Black 20 amp---------->Ark, disconnected.

Any better ideas?

Should I tie the black and red together into the same circuit, or will this overload my system?  Do generators supply by "demand", or will the combination of 30 and 20 amps create a 50 amp circuit, which might be too much for my system?

I was an electronics technician in the Navy, but this system isn't the same as the battery bank system we use on Submarines.  This is a direct feed from generator to system, and puzzles me. 

Should I wire it the way I'm suggesting, or should I tie black and red together into the same circuit?

Thanks!

Kev and Patti Smith

[HeavyHaulTrucker]

Sent: 4/25/2005

Kevin, you're on the right track, except that your new genset is designed to support 50 amp service.  Use the red 30 amp as your primary, and cap off the 20 amp wire with a wire nut -- you don't need it.  Later, if you do re-wire and put in a 50 amp converter, you can then use both to supply the converter.

John

[denisondc]

Sent: 4/25/2005

Yup, your doing it right. Gensets supply a potential difference of 115 volts, or 230 volts. The amount of current an appliance draws depends only on the appliance. Having more of an electrical load will just involve the governor on the genset opening the throttle a bit wider.
The black wire in your RV 115volt wiring will be the one that is “hot” when the generator is running, or when you are connected to shore power. The white wire is the “return”, aka “common”. Don’t call it a ground. There would be a third connection, via the case of the breaker box and a bare wire (or green insulation) between that and the outlets for instance â€" which is your “ground”. The electric current (in your RV circuits) should all be in the black wire and the white wire, the black going out and the white coming back so to speak. The ground wiring is only for safety, its never to carry current normally; only when there is a fault or short circuit.
Somewhere on your RV there needs to be a “power-source” switching scheme. It would keep you from inadvertently having “shore power” supplied at the same time as the genset is running. Basically you must never have the two power sources connected to each other; your genset would loose the fight with the power company Fast!
On mine there are two pairs of circuit breakers; each pair looks like a ganged circuit breaker that would feed the electric dryer in your house. In a motorhome using only 115volts though, they interrupt both the black wire AND the white wire. The two pairs are back to back and joined by a metal tie-strip. You can switch it so you are connected to the shore power cable â€"OR- connected to the genset. Never both.
On later model RVs that “shore-power” to “genset-power” switching was done with a relay, automatically or semiautomatically.
You can use that 20 amp circuit from the genset for feeding an external duplex outlet â€" to run your power tools when you are boondocking in the wild. I don’t think it would be a good idea to connect it to the 30 amp output from the generator- unless the manufacturer tells you its okay. There might be a phase difference between the 20 amp output and the 30 amp output. It might be 180 degrees out of phase, which would allow the genset to provide 20 amp 220 volt power.

[DanD2Soon]

Sent: 4/27/2005

The problems mostly arise from the fact that there have almost always been Previous Owners and unless & until you KNOW how your rig is wired, you need to be really careful.  The human element is what makes it dangerous - I've seen a rig that did have the two tied together, completely dependent on the owner's remembering to KILL  the Genset disconnect BEFORE he PLUGGED in the Shoreline and not even realizing the the loose end of the Shoreline had a LETHAL dose of 110 volts on the open lugs!  All that saved him or his Genset was the fact that he TOTALLY FRIED the breaker at his State Park hook up!

As Dave Denison described above, Power transfer between Shore and Genset is accomplished one of three ways.  Both sources of power must NEVER be connected at the same time so the key to all three is "BREAK-BEFORE-MAKE."  All three techniques BREAK the connection to one source BEFORE they MAKE a connection to the other one.

Manual Transfer - This is what you apparently have and Kevin is planning to install on the Ark.  It is completely manual and absolutely Foolproof.  Since the Shoreline Plug can only be in the Genset receptacle or another Shore Power receptacle at any one time, You are "forced" to BREAK one connection BEFORE you can MAKE the other.

Mechanical  Transfer Switch - This is what Denison has -  Essentially, his breaker panel is fed with two MAIN Breakers - One connected to the Genset and the other connected to the Shoreline.  Those two Breakers/Switches are mechanically "Linked" together in a way that "forces" one of them to BREAK its connection BEFORE the other can MAKE its connection.  The advantages to this type of Transfer Switch are mostly convenience & speed - You can actually have the Genset running and the Shoreline plugged into Shore power and "Transfer" between them fast enough to not lose the picture on the TV or reset the digital clocks on the coffemaker and microwave.  Pretty handy when you're making or breaking camp...  And Most important - the rigs' breaker panel is NEVER connected to both sources at the same time.

Automatic Transfer Switch - Basically this is a BREAK-BEFORE-MAKE  RELAY usually wired so that the Genset is connected to the NC (Normally Closed) contacts and the Shoreline is connected to the NO (Normally Open) contacts with the COM (Common) contacts feeding the rigs' Breaker Panel.  The coil that energizes the relay is usually connected to the Shoreline cord so that if there is power available on that line, the relay provides that power to the rig.   If not,  the de-energized  relay  (default) provides a connection to the Genset.  The advantages of this setup are pretty much the same as for Mechanical Transfer Switching - You pull into your campsite with the Genset running, plug your Shoreline into the site receptacle, it automatically Transfers to that power, you shut down the Genset,  Finish hooking up the sewer and water, maybe a little leveling, come back inside the rig hot & sweaty and mother and the kids who've been uninterrupted watching a video wonder why you're reaching for a cold one? 

Ain't life Grand?!

You're right on both counts, Rick - Your manual system is "Un-fry-able" and no Designer/Engineer has ever produced an RV where you could even accidentally connect both at the same time regardless of  which of the three methods was used when it was manufactured.

The problems happen when a well meaning but electrically ignorant/challenged person decides to modify/alter/improve or FIX something himself - AND does Something Stupid. 

That Ignorant & Challenged person is ME about most every other system on my coach - Fuel, Brakes, Steering, Engine, Plumbing, LP gas, Ignition, & tons of other stuff.  That's CWM's greatest value to me - Helping me to not do Something Stupid.

I'm guilty of Overthinking things, check every thread here everyday for the opportunity to learn something that will help me later, and never start an RV project without doing a message search with every word I think might "Hit" on the subject.

Preaching to the choir again;  Aren't I?  O.K. Enough...

Later,
DanD