Neutral to Frame vs Floating Neutral Question

[BFL13]

Been discussed here a few times, but can't remember the difference if any.

Onan here has neutral bonded to frame and it is for RV use.


https://www.usedvictoria.com/ReportSelectUsedAdPhoto2?used_ad_id=32655856&position=3&hb=1

Typical portable gens have floating neutral and we don't use their chassis grounds. With that Onan are you supposed to link the chassis ground to the RV frame?

In a motorhome set-up, how is that done? (that one in the ad came from the guy's 5er apparently )

[enblethen]

Gensets are normally mounted to the genset pan with rubber motor mounts. The braided cable is to connect around these.
The 120 volt ground buss is connected to the frame normally near the 120 volt power distribution panel.

[77rollalong]

on our motorhome, the onans 12v ground is connected to the frame ground,(for Starting) as well as the green from power output 110v is also connected to the main fuse box, which is also grounded to the frame of the motorhome for both the 110v and for the 12V charging from the converter.

[enblethen]

There should be a braided flexible bonding strap between genset pan and the MH frame.

[BFL13]

Thanks. I missed where the Onan's chassis is grounded to the RV's frame.

I don't dare ask about those big inverter/chargers when "whole house"! 🙂 I only have a regular sort of inverter, did not bother to ground it's chassis to the RV frame, and I do whole house with that.

[DrewE]

The RV generator's ground (and neutral) are connected to the RV frame through the generator's ground connection (which is also used for the 12V return, so it's a good solid connection). Depending on the installation it might also happen to be bonded by the mounting bracket, but the design doesn't rely on that. That is immaterial from the point of view of the 120V electrical system, though, since it has a ground, neutral, and hot coming from the generator, and the neutral and hot are bonded together in the generator. It would work the same if the generator were not electrically bonded to the RV chassis directly.

Since the transfer switch switches both the hot and the neutral wires on an RV, the RV generator's neutral bond is only seen by the EMS (and three light tester and so forth) when it's connected and operating. Otherwise, it sees whatever bond is or is not there at the shore power cord; the only thing left connected to the generator is the safety ground, which is continuous throughout the AC system.

[BFL13]

When you use a portable gen, the shore power cord is plugged into the gen's receptacle and it is floating neutral. OK.

If you plug into a pedestal, the pedestal is from a bonded source, so the RV 120 looks right on a three-light tester in an RV receptacle. OK.

Now this is where I get really confused--- you go on RV installed Onan generator and it is bonded to its own frame, not the RV's ?

So how does the RV EMS get the idea the RV is plugged into a bonded source? I saw that about the shore power/gen transfer switch, but I got lost.

[MEXICOWANDERER]

Wanna choose?

Getting your teeth rattled loose by the positive amplitude

or perhaps the negative amplitude today.


Very hard to pin a moving crossing point in a sine wave.

240 volt (L1 + L2) does have a true neutral.

[BFL13]

Thanks, all clear now.

[enblethen]

Gensets permanently installed in an RV have the neutral and ground bonded together. The one pictures is for permanent RV mounting. Ground should not be switched in transfer case.
Verify which transfer switch you have. Transfer switch should switch phase conductors and neutral.
Many portable gensets do not. It that case you may need to tie the neutral and ground together, This lies to some power systems so they operate correctly. Surge suppressors for one.

[DrewE]

The Onan generator in the ad is a model for installation, not a portable generator. It's a very, very common 4kW model used in a great many class C and smaller class A motorhomes, though the gasoline fueled variant is more popular than the LPG one. I have one of these (a gasoline version) in my motorhome, in fact, though quite possibly a different spec level.

Portable generators don't have earth and neutral bonded because there is little if any safety to be gained by doing so in that application (neither one is typically earthed, and the entire output is floating, so fault current to earth is minimal to non-existent) and because it would lead to difficulties if the generator were ever connected to power an existing system with a ground/neutral bond. Having two bonds is a bad thing, I think at least partly because it leads to the safety ground becoming a current carrying conductor under non-fault conditions.

[BFL13]

I was assuming the LP Onan in the ad is a portable gen, while the ones you see installed in MHs are different. I obviously don't have a clue about Onans, but am curious anyway.

[Chris_Bryant]

Not sure of the question, but for an rev specific Onan, th3 neutral and ground are bonded, as the Onan is the power source. Both hot and neutral are switched in the transfer switch, so they are not bonded while o; shore power.

I *think* that neutral and hot are bonded in RV specific inverters as well.