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Old 03-29-2016, 06:04 PM   #1
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Need help with 50 amp generator wiring

Hello all, it's been awhile but I could use some help from the electricians on here. I will post some pictures at the end that will hopefully help.

My new tow vehicle is a freightliner toter home, it has an onboard Kubota diesel generator. After finding the specs on the generator to insure I could use it, I found it has a 240 volt, 50 amp output. Only problem was it had a strange end on the cord so I just replaced it with a female 50amp end.

Now, when testing my plug (using the diagram in picture) across my pins Y,X I have 240 Volts, across pins Y,W and X,W I have 120 Volts. W,G is 0. The problem I am having is that it states I should have 120v between Y,G and X,G but I am getting random numbers like 39v and 18v.

Can anybody explain why this might be? My first guess was a grounding issue so I bought a new strap and cleaned the area good but no change.
Could it still be a ground issues just because the genny sits on rubber pads and obviously the truck sits on rubber? Just throwing things out there. I don't want to plug my 5th wheel in until I'm 100% positive I'm good.

Thanks in advance for any help!

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Old 03-29-2016, 08:23 PM   #2
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As usual, digging to answer questions for this forum brings up all sorts of interesting things. It turns out that many generators do not have their neutral connected to ground. RVs never have the neutral connected to ground since they assume that the connection will be in the power pedestal and since there is no neutral to ground connection, if the RV is mistakenly connected to reverse polarity, the outer skin will not become hot and cause a dangerous shock hazard.

However, it seems that most generator transfer switches automatically bond the neutral to ground when the generator is running. In your case, your measurements appear to indicate that the generator has a floating ground and as such, you cannot get the 120V to ground measurements.

Some people indicate that the way to solve this problem with a generator that has multiple outlets is to plug in a male plug that only connects the neutral leg to the ground leg. You could do that.

Right now I do not see any reason not to permanently connect the neutral to ground in the generator itself. If you were plugging the generator into your house, the neutral is connected to the ground in the meter panel. Apparently there are some people who cannot even power their RVs without bonding the neutral to ground since their surge protectors refuse to operate without a hot to ground voltage and they assume that the lack of that voltage represents an "open" ground.
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Old 03-29-2016, 09:19 PM   #3
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Thanks for the reply. This genny does not have multiple outlets, it's just the one cord coming out.

With that being said, your last suggestion of doing it permanently, does that just require a jumper wire or is there more too it then that?


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Old 03-29-2016, 09:36 PM   #4
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You could wire it inside the genny, simple jumper between the ground and the neutral. Most transfer switches will do it for you so...in this case...you are the transfer switch. If you ever power anything else you might have a ground loop, but that isn't dangerous, it just can generate some "hum" on audio circuits.

the important thing is not to connect the neutral and the ground on the TT side, since that will certainly be a double connection when you plug into a pedestal. I would open up the junction box on the generator and put in a neutral to ground jumper and then put a label on the generator to say that it has "ground to neutral bonding."
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Old 03-29-2016, 10:01 PM   #5
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Sounds good!
Thank you very much!


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Old 03-30-2016, 01:43 PM   #6
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I think another thing to consider is that the genny needs to be bonded to the chasis of the truck. If the genny is connected to the neutral and the TT is handled at the same time as the truck, there would be a shock hazard between the truck & the trailer. If the genny is bonded to the truck chasis, the TT & TV are forced to be at the same potential, no voltage should exist between the metal of either vehicle.

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Old 03-30-2016, 01:59 PM   #7
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I think another thing to consider is that the genny needs to be bonded to the chassis of the truck. If the genny is connected to the neutral and the TT is handled at the same time as the truck, there would be a shock hazard between the truck & the trailer. If the genny is bonded to the truck chasis, the TT & TV are forced to be at the same potential, no voltage should exist between the metal of either vehicle.

Swampy
I would assume that the genny is already bonded to the truck chassis, since without that the starter probably wouldn't work. The real issue is the floating neutral. Lots of generators have floating neutrals, but both the truck and the TT are not grounded through a ground stake anyway and the neutral in the TT is isolated from the chassis ground.
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Old 03-30-2016, 02:31 PM   #8
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I would assume that the genny is already bonded to the truck chassis, since without that the starter probably wouldn't work. The real issue is the floating neutral. Lots of generators have floating neutrals, but both the truck and the TT are not grounded through a ground stake anyway and the neutral in the TT is isolated from the chassis ground.
I agree if the generator is using the truck battery to start, maybe not if it has it's own battery. Regardless, I think the genny should have a neutral to ground bond at the genny and verify a connection to the truck chasis. Since the loads in a RV are mostly one sided on the 240V system, there will be appreciable neutral current back to the genny vis a vis the voltage drop on the neutral makes a voltage difference between the ground circuit and the neutral. So with the TT having no ground bonding to the neutral and the truck having a floating neutral and perhaps no grounding, the potential risk of shock hazard between the chasis of both vehicles is high if there is no neutral to ground bonding at the source end.

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Old 03-30-2016, 03:46 PM   #9
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The genny does use the truck batteries for starting and it does also have a ground strap from the genny to chassis.


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Old 03-30-2016, 05:28 PM   #10
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x2 on neutral to ground at the gen. Make it like a pedestal.
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