Am I only using 50% of my generators output?

[Barn Owl]

I am doing some remodeling in my bus and changing some of the wiring. I have an Onan 6500 NH and my bus is set up for 30 amp service. The PO built a simple plug system that allows me to plug/unplug between shore and the genset. The plug back feeds through a 30 amp breaker. The problem I think I have is this: 120v * 30 amps = 3600 watts. Well I have a 6500 watt generator and so the way I am thinking about this I must be unable to use almost half of my output without tripping the breaker. I have run both a/c units without a problem. Is there an inexpensive and quick workaround for this? I don't have much time or money before my trip.  Am I wrong?

[Sean]

Laryn,

If there is no other connection between the generator and the main panel except your 30-amp shore cord, then, yes, the most you will be able to draw is 3,600 watts, and that is a 3-hour rating.  Long term, you can use at most 80% of that or 2,880 watts.

The easiest way to fix this is to install a 50-amp, 240-volt main panel and shore cord, then equip the generator with a 14-50R receptacle for the cord to plug into.  If you don't want to (or can't) re-strap the genny for 240, you can safely connect the single 120-volt hot output to both hots in the 14-50R simultaneously, as long as you put a 50-amp, single-pole breaker between them.  That would at least get you 6,000 watts from your 6,500-watt genset.

-Sean
http://ourodyssey.blogspot.com

[Nusa]

Also remember that generators are sold by surge ratings. The actual continuous capacity is probably at least 10% lower, maybe more.

[Hi yo silver]

Laryn,
If you need it, I have a Square D 10 load center, sans breakers, you can have.  You have my #'s.  I can meet you with it.
Dennis 

[gus]

Laryn,

My old Onan was rated at 7500KW in three-phase operation but only 5500KW in single-phase.

If that is not the case something is not connected properly.

If it is rated at 6500KW then converting to 240v won't change that, it will just decrease the amp output.

My Honda 6000KW puts out 50amps on two different 120v circuits. One is 30 and the other 20.

The 20 is listed as the "air conditioner" circuit and that is the way I am using it with nothing else connected. The 30 powers the other AC and everything else.

[Sean]

If it is rated at 6500KW then converting to 240v won't change that, it will just decrease the amp output.

But if he is using a cord-and-plug connection scheme, then he can't use more than 6,000 watts unless he converts it to 240.  So he's leaving half a kilowatt on the table.

-Sean
http://ourodyssey.blogspot.com

[Barn Owl]

It looks like a 50 amp upgrade and changing the genny to 240v will be in the future, but unfortunately not in time for this trip. I need to post photos but for now I will try to explain what I have and what I think I might get to work. I have two large receptacles, one labeled shore and the other generator. Out of my circuit breaker box there is a plug that I can switch between the two (poor man's transfer switch). What if I add a 30 amp circuit breaker in-line just before the shore receptacle, and change the 30 amp circuit breaker in the box to a 50 amp? The shore power would travel through the 30 amp cb then the 50 amp cb. The receptacle for the generator would only go into the 50 amp cb when hooked up. There would still be no way to back feed. Will this work? Is there such a thing as an in-line circuit breaker?
               
                                                                                                  
Generator in -------------------------{receptacle}-|                      Circuit breaker box
                                                                       =--{plug}-------/--(50 amp cb)--/-----To bus
Shore power in -----(30 amp cb)------{receptacle}-|

[Barn Owl]

I realize that I need to check the amp rating on the plug and receptacle that the generator uses. They look like three pronged dryer style plugs and receptacles.

[Sean]

Laryn,

It's not that simple.

The cord (most likely) and the plug (for certain) for your shore cord arrangement is only rated to carry 30 amps.  You can't simply increase the size of the genny breaker without a major risk of fire.

This is why I suggested changing to a 50-amp shore cord arrangement, and changing the receptacles out to 50-amp, 120/240-volt models.  No need to restrap the genny, as long as there is a 50-amp, single-pole breaker between the genny and the receptacle.  Wire both hot sides of the receptacle to the single output from that breaker.

At the other end of the cord, where it connects to your panel, you can connect one of the two hots to the existing main, where your 30-amp cord connects now.  Leave the other hot wire unstripped, and insulate it with electrical tape.  Now you have a 50-amp, single-phase system capable of delivering 6,000 watts.

Whenever you are ready, you can change your main panel over to two-pole, and, separately, you can also change the genny over to 240.  That will let you use all 6,500 watts.

-Sean
http://ourodyssey.blogspot.com

[gus]

I think you lost me about a "cord and plug" connection is exactly what I have on mine.

I have two outlets wired directly from the gen, one is 30a and the other is 20a. the gen is already set up with two outlet coils. Two cords plug into these outlets, the cords go to two separate breaker boxes then to the house and the separate AC.

When I go to shore power I unplug the cords and connect them via ext cords to the shore power outlet. Stone simple.

This is all 120v, no 240v anywhere.

It puzzled me at first because it appeared to be unbalanced but I'm pretty sure Honda knows what they are doing.

So, I don't see any reason he has to lose 500 Watts?

[Barn Owl]

Photos of what I am dealing with:

[Sean]

Photos of what I am dealing with:

Aaaaack!

OK, serious issues here, which we can talk about when you have more time.

In the short term:

• Get rid of the 10-gauge "dryer" pigtail.  It's the wrong voltage for the application, and you can't carry more than 30 amps through that cord.
• Replace the two dryer outlets with 14-50R "range" outlets, available at the home center.  They'll have housings just like the ones you have.
• On the "shore" receptacle, wire the single hot from the existing shore cable to both hots in the 14-50R.
• I assume your shore cord has a TT-30P (30-amp "trailer") plug on it.  Make certain you never plug it into anything bigger than a 30-amp circuit until this is all sorted out.
• Replace all wiring from the generator to the receptacle.  What's in there now is waaay too small.  Run four #6's, red, black, white, and green.  For now, just insulate both ends of the red.
• Install a small two-space breaker box at the generator.  Equip it, for now, with a single-pole, 50-amp breaker.
• Wire the genny output through this box onto the black #6 wire.
• At the receptacle end, again, wire the black hot to both hots on the receptacle.  Insulate and store the red end for now.
• Make a 6/4 or 6/3-8/1 pigtail from the existing breaker box to a 14-50P ("range") plug.  You can buy pre-made range pigtails, but they are often 6/2-8/2; don't use this type.  If you can find a 6/3-8/1, it's fine.
• Again, leave the red wire on the pigtail unconnected at the panel end.  Connect the black wire to the existing panel hot lug.

You will now have a system identical to what you have now, except you can get 6,000 watts from the genny.  You will still be limited on the shore to 30-amp (3,600 watts) service until you replace the shore cord, which will require a panel change.

Let me know if any of that is not clear.  When you get back and have more time, give me a shout and we can talk about the rest of what needs doing.

So, I don't see any reason he has to lose 500 Watts?

Because, unlike your setup (with two panels and two cords), he has a single panel and is using a cord-and-plug connection.  A single cord and plug can carry at most 50 amps.  Without rewiring his system to 240-volts, he can only get 50 amps at 120 volts which is 6,000 watts.  His genny is 6,500 watts, so 500 watts is unusable without going to the next step.

-Sean
http://ourodyssey.blogspot.com

[H3Jim]

Being very careful NOT to connect the red and black together on the source side.  Sean is saying to only connect both legs of the coach side, the using side, to one leg of the hot source.  If you connect both legs of the generator or shore side together, you will have some fireworks.

[Sean]

Being very careful NOT to connect the red and black together on the source side.  Sean is saying to only connect both legs of the coach side, the using side, to one leg of the hot source.  If you connect both legs of the generator or shore side together, you will have some fireworks.

Jim, good clarification for anyone else reading, however Laryn's shore cord and generator each have only a single hot, which is the impetus for this whole discussion.

My recommendations above are to allow him to use 50-amps at 120 today, while allowing for expansion to 240 at a later date.  The idea behind wiring the single source to both hot legs of the receptacle is to allow him to split the busses in the panel whenever he's ready; this will facilitate the changeover later.

It's all a little much to follow here in writing; Laryn has contacted me off-board and we are going to speak live about this just as soon as I am back in cell phone range.

-Sean
http://ourodyssey.blogspot.com

[Barn Owl]

To busy working to do much typing but I wanted to post few additional photos so if anyone notices anything seriously wrong it can be fixed as I straighten things out. The shore cord is about 30' long and is a 10/3. The generator feed goes through the wall into the back of the receptacle. I am not sure what size the wire is but it looks factory and you can see it in the photos.