Open Ground

[CYCLEPATH]

Hello all. Just made the jump from my Lance camper, which I loved, to an Alliance Paradigm 310RL. It's a beautiful rig. The day after bringing it home, I was going over the electrical system. It has what they call the Super Solar Package.

When on inverter power, and onboard Onan generator power, I am showing an open ground on the outlet tester, in all the outlets I tested. On our 30amp home shore power, the outlets test normal. I have read where some say this is normal, others that it is not. Any hard core RV electrical guys out there with an opinion? I have a service call into Alliance, but have not heard back from them yet. Thank you all.

[BB_TX]

Thanks. I think that explains it better than me.

[StirCrazy]

time2roll wrote:

BB_TX wrote:
551.30 Generator Installations

(A) Mounting. Generators shall be mounted in such a manner as to be effectively bonded to the recreational vehicle chassis. The connection of the electrical system produced by the generator shall provide an effective ground-fault return path when operational.

OK and does this mean a N-G bond? Or simply the chassis of the generator needs to be bonded to the RV frame.

N-G bond, a frame bond will do nothing, here is a good article.

https://www.rvtravel.com/rv-electricity-bonded_floating_generators/

[BB_TX]

time2roll wrote:
OK and does this mean a N-G bond? Or simply the chassis of the generator needs to be bonded to the RV frame.

I think it could have been worded more clearly. Sometimes NFPA standards and codes (of which NEC is one of many) has wording assuming the user of that standard or code is well versed in the application of that standard or code. I know, as I served on two committees of one of their other codes and we often had to rewrite some statements for more clarity.

A ground fault is typically, but not exclusively, a short between neutral and ground or chassis frame. Such a short would divert a portion of the NEU return current from the neutral circuit to the ground circuit. That would create the possible imbalance to trip a GFCI. So an N-G bond at the source (generator in this case) would provide the required path for a ground-fault detection.

A short between hot and ground would typically trip the respective circuit breaker. But, if that short was high enough resistance to restrict the errant current flow to a level below the circuit breaker rating, then a portion of the HOT current would be diverted through ground while the rest would continue through neutral. That would also cause the possible imbalance to trip a GFCI. Again an N-G bond would provide the required path for a ground-fault detection.

An additional note on a hot to ground short. When the ground is not bonded to neutral (open ground) the related circuit breaker would not trip on a hot to ground short as there would be no path for current flow from hot to ground and back to the source (the generator). That would mean the ground (including RV chassis) would be hot. If a person somehow touched chassis frame and neutral at the same time then current would flow through that person. If that short was downstream of a GFCI circuit then the GFCI would trip. If the short was on an unprotected circuit then there would be no protection. If there was an N-G bond there would be no danger as neutral and ground would be at the same potential.

[enblethen]

Time2roll: this more to ground the genset to the vehicle.
In addition NEC Article 250.20 and 250.34 para (B) and (C) must be followed along with Article 551.

[time2roll]

BB_TX wrote:
551.30 Generator Installations

(A) Mounting. Generators shall be mounted in such a manner as to be effectively bonded to the recreational vehicle chassis. The connection of the electrical system produced by the generator shall provide an effective ground-fault return path when operational.

OK and does this mean a N-G bond? Or simply the chassis of the generator needs to be bonded to the RV frame.

[sayoung]

BB_TX wrote:
You guys keep telling me I am wrong. So I will ask of all of you again.

A GFCI trips because there is more current flowing from the HOT pin into a load than there is flowing from the load back to the NEU pin. That creates the required imbalance in current required to trip the GFCI. It also means that difference in current has somehow been diverted out of the normal flow path. Now where did that current go? Current can ONLY flow to/from the initial power source, i.e. the required “closed loop”. A most basic principle of electricity. That means the missing current has to have an electrically conductive path back to that power source. If the RV is not grounded to the generator, where is that required path? That current can not simply disappear.

This is a simple question that no one seems to want to address.

You have a frayed extension cord plugged into a RV GFCI & you have your hand in contact with a small tear in the insulation . You are now in contact with the HOT leg & you for some reason grab a metal water pipe. That's a path to gnd with you as the conductor which now is the unbalance the GFCI is there to protect you from . . I know, what are the odds of this happening ?
When GFCI plugs became the requirement , was takeing a class on a product we installed & the instructor made a claim you could hold a hot wire on a GFCI circuit & jump into a swimming pool & not get hurt but we couldn't talk him into doing a demo

[Mike134]

BB_TX wrote:
If you have an open ground, your GFCI outlets are not going to trip on a ground fault.As you explain later a ground fault cannot happen because there is no ground reference They require an electrical path to the power source neutral-ground bond to trip. And if you should have a hot wire shorted to ground or RV frame it will not trip the circuit breaker. It will create a hot frame though. None of which are good conditions. .

My mistake understanding you at this first post.

What you should have perhaps said as you explained in further posts no need for a GFI because there is no reference to ground. No different than the bird sitting on the transmission wire.

[enblethen]

From Mike Holt

[BB_TX]

You guys keep telling me I am wrong. So I will ask of all of you again.

A GFCI trips because there is more current flowing from the HOT pin into a load than there is flowing from the load back to the NEU pin. That creates the required imbalance in current required to trip the GFCI. It also means that difference in current has somehow been diverted out of the normal flow path. Now where did that current go? Current can ONLY flow to/from the initial power source, i.e. the required “closed loop”. A most basic principle of electricity. That means the missing current has to have an electrically conductive path back to that power source. If the RV is not grounded to the generator, where is that required path? That current can not simply disappear.

This is a simple question that no one seems to want to address.

[BB_TX]

For those who did not fully read page 1 of this discussion here is relevant info.
The National Electric Code has a long section, Article 551, dedicated to Recreational Vehicles and Recreational Vehicle Parks. Here is the specific requirement for RV generators.

Article 551
Recreational vehicles and recreational vehicle parks.

Part III. Other Power Sources

551.30 Generator Installations

(A) Mounting. Generators shall be mounted in such a manner as to be effectively bonded to the recreational vehicle chassis. The connection of the electrical system produced by the generator shall provide an effective ground-fault return path when operational.

[opnspaces]

I lived in an old house built in the 40's with 2 wire outlets. There is no path to ground. Sure the panel might have a wire that goes to a water pipe. But the outlets themselves with their 2 wire green fabric coated insulation do not have a third bare wire to get to a ground (copper pipe or otherwise).

The GFCI will protect and trip on a 2 wire system with no ground connection.

The Imbalance you are looking for is the person holding the plug as they are plugging in a lamp with a bare wire poking out of the insulation. Yep happened to me but no GFCI to test it against. I just got the tingle and let go. But the bottom line is the GFCI is there for current getting where it doesn't belong. Whether the unintended path is a persons hand, a dog's nose, or whatever.

[BB_TX]

I never said Mike was wrong. GFCIs are permitted in older homes with no ground. And they work because of home plumbing being earth grounded by being buried underground. RVs do not have that same grounding and is a totally different story. That is why NEC specifies an RV using a generator must have a ground-fault path provided. Different requirement than that for an older home.

And I will ask you the same question. If there is no path back to the source power for current "leakage", how can an imbalance occur between the hot and neutral? That missing current can not simply disappear. And the same statement. Current can not flow without an electrical path back to its source.

I really want to know.

[ScottG]

Mike134 wrote:

BB_TX wrote:
If you have an open ground, your GFCI outlets are not going to trip on a ground fault. They require an electrical path to the power source neutral-ground bond to trip. And if you should have a hot wire shorted to ground or RV frame it will not trip the circuit breaker. It will create a hot frame though. None of which are good conditions. .

This is incorrect. GFI outlets work just fine without a ground wire present.
In fact, the NEC allows you to replace old 2 wire outlets in old homes not having ground wires with 3 wire outlets provided you use a GFI outlet.
https://www.ecmweb.com/content/article/20896746/replacing-2wire-ungrounded-receptacles

Mike is correct and indeed it is even allowed by NEC to replace an ungrounded bathroom receptacle (as found in old homes) with a GFCI that has no ground connection at all. A GFCI's function has nothing to do with its ground connection.

[BB_TX]

enblethen wrote:
Get away from the GFI talk and get to basics of the electrical system. Bonding of the neutral and ground needs to be accomplished in accordance with NEC Article 250-92.

And NEC 551.30(A) which is specific to generators in RVs and requires “an effective ground-fault return path”.

[BB_TX]

Mike134 wrote:


Be happy to explain why your wrong about GFIs needing a "ground reference" to work and trip.
They operate to save your life from an electric shock by constantly comparing the current flowing in the hot and neutral wires. If there is more than a 5-milliamp difference between the 2 wires it trip. They don't need any type of "refence to ground" they just monitor amperage in the hot and neutral wire to be sure they are within .005amps of each other.

I'm not your typical armchair expert (retired master electrician) What is your training in the electrical field if I may ask?

Note the last sentence in the first paragraph of "how do they work"
.
https://www.cpsc.gov/s3fs-public/099_0.pdf

I am well aware how they work. But if you have 5 amps flowing in the HOT pin and 5 amps minus 5 milliamps flowing back into NEU pin (5 ma imbalance), where did that lost 5 milliamps go? It can’t flow out into thin air. It can only flow back to the power source through some conductive path. Again, a very basic principle of electricity. Tell me where that conductive path is in an RV where there is no ground path back to the generator when the neutral and ground are not connected.

And I am a BSEE, registered professional engineer state of Texas (retired), and worked 35 years as a safety system design engineer. Thank you for asking.