Problem with GFCIs and the ground (both 120V and 12V)

[John From Detroit]

So maybe it would be a good practice to connect the RV to earth (ground rod) for extra safety?

NO in fact that would REDUCE safety..
What most folks do not know.
There are TWO ground points on your 120/240 volt feeds. One is the service panel (In a park that may be the main distro panel or the pedestal) the other is back at the high voltage to 120/240 volt transformer (Pole or big green box on ground)
You see at one time... They only ran one wire from the pole to the house.. SAY WHAT? ONE WIRE, How did that work??? How could it work??? The ground was the other wire you see... Earth ground.
And such systems exist to this day (though now rare)

So here is the reason for the safety ground.
IF something happens (A hot to case short for example) This will not trip the circuit breaker if you only have a 2 wire device but ... Well you now become a current path (not good) and I can pick up the hand grinder from the other side of the room (ER.. It actually happened that way)

BUT with the RV's generator. Since it's not grounded. that return path does not exist (You are thus safe)
Oh.. if you DO have the 3rd wire safety ground.. Breaker trips.
NOTE... The "Safety Ground" running on generator may show 60 volt to either neutral or HOT.
Don't worry about it.

 

[NY_Dutch]

BUT with the RV's generator. Since it's not grounded. that return path does not exist (You are thus safe)
Oh.. if you DO have the 3rd wire safety ground.. Breaker trips.
NOTE... The "Safety Ground" running on generator may show 60 volt to either neutral or HOT.
Don't worry about it.

If you're seeing 60 volts between neutral and ground from an onboard generator, you should worry about it and get it corrected. The neutral and chassis ground should be bonded together at the generator just as they are at the source for shorepower.

 

[Contributor]

NO in fact that would REDUCE safety..

How is connecting the RV chassis to earth ground reducing safety?

I don't follow a lot of what you are saying. Connecting the RV chassis to earth ground is what happens when you connect to pedestal power.

When using the onboard generator, the transfer switch removes this connection and connects at the generator. In this case, the generator chassis and all of it's metal components become the proxy earth ground. Wired correctly with the RV chassis and neutral, circuit breakers will sense shorts and trip. This setup however lets the RV frame float relative to earth ground.

What this set up fails to do is protect in case of lightning strike.

If you go by any private airport, you will notice that all of the parking sites have a ground connection and it is required to connect parked aircraft to it. It's the same principle.

 

[Contributor]

Here is a good article on grounding requirements for generators.




By Michael Johnston

Generators are commonly installed for buildings or structures requiring emergency systems, legally required standby systems or optional standby power systems. Some generators are located within the building or structure they supply; but, frequently, they are located outside. Unless these are small generators supplying branch circuits, the conductors supplied are feeders, and if they are located outside buildings or structures, the requirements in NEC Article 225 apply, specifically 225.31 through 225.39. Section 250.32 also applies to the feeder conductors supplying the building or structure.
Permanently installed generators are separate power sources and are often installed as separately derived systems, which are defined in Article 100. The decision to connect a generator as a separately derived system is determined by the type of transfer equipment specified for the design. There is an important informational note following Section 250.30 that describes the relationship between the transfer switch and how the grounding connections should be made for the generator. First, if a transfer switch for a generator switches the grounded (usually a neutral) conductor, then the generator must be grounded as a separately derived system in accordance with all applicable requirements in 250.30(A). The reason is that, in the normal power mode, the grounded (neutral) conductor for the load is connected to the grounding electrode conductor at the service. In standby mode, the grounded (neutral) conductor for the load is switched over to the generator source, which is grounded as a separately derived system. The result is that, in either position of the transfer switch, the electrical system is grounded. If there is no switching action in the grounded (neutral) conductor through the transfer equipment, then the generator system remains grounded with the transfer switch in either position: normal or standby by the grounding electrode conductor at the service. If the generator is a separately derived system and is located outdoors, a grounding electrode connection is required at the source location to comply with 250.30(C). The equipment grounding and bonding connections, in this case, have to meet the requirements in 250.35(B) for permanently installed generators.
Section 250.35 covers important requirements for providing an effective ground-fault current path, which 250.4 addresses generally. Generators grounded as separately derived systems meet this requirement when installed according to the rules in 250.30(A). If the generator is not installed as a separately derived system, an effective ground-fault current path must be provided in accordance with 250.35(B). This simply means a supply-side bonding jumper has to be installed between the generator and the equipment grounding terminal bar or bus of the enclosure supplied by the system. The supply-side bonding jumper must be installed in accordance with 250.102(C). The minimum size must be based on Table 250.66 or the 12.5 percent rule based on the total circular mil area of the largest ungrounded phase conductors connected to the generator. If the generator has an overcurrent device, the supply feeders from the output side of the overcurrent protective device on the breaker must include an equipment grounding conductor sized in accordance with 250.122, based on the rating of the overcurrent device at the generator.
Auxiliary grounding electrodes

If generators are installed outdoors, the design often specifies an auxiliary grounding electrode. The NEC does not require auxiliary electrodes; however, if installed, 250.54 provides specific requirements that must be met. The auxiliary electrode provides a direct connection to the earth at the generator location. This grounding connection is in addition to the grounding and bonding required by either 250.30(A) or 250.35(B), as covered above. The auxiliary grounding electrode must be connected to the equipment grounding conductor in addition to the frame of the generator. The earth is not permitted as an effective ground-fault current path. When auxiliary grounding electrodes are installed for equipment, they are not required to meet the 25-ohm requirements specified in 250.53(A)(2) Exception.
Summary

Section 250.30 Informational Note No. 1 provides essential information that assists users in determining system grounding requirements for generators. The transfer equipment applied in the design is a key factor for determining if a generator must be grounded as a separately derived system. An effective ground-fault current path is required between the generator and the equipment supplied by the system. The effective ground-fault current path is required to be either a supply-side bonding jumper in accordance with 250.102(C) or a load-side 
equipment bonding jumper in accordance with 250.102(D). Installing an auxiliary grounding electrode for a generator is not an NEC requirement; however, if installed, the installation must meet the requirements of 250.54.

 

[NY_Dutch]

Here is a good article on grounding requirements for generators.




By Michael Johnston

Generators are commonly installed for buildings or structures requiring emergency systems, legally required standby systems or optional standby power systems. Some generators are located within the building or structure they supply; but, frequently, they are located outside. Unless these are small generators supplying branch circuits, the conductors supplied are feeders, and if they are located outside buildings or structures, the requirements in NEC Article 225 apply, specifically 225.31 through 225.39. Section 250.32 also applies to the feeder conductors supplying the building or structure.
Permanently installed generators are separate power sources and are often installed as separately derived systems, which are defined in Article 100. The decision to connect a generator as a separately derived system is determined by the type of transfer equipment specified for the design. There is an important informational note following Section 250.30 that describes the relationship between the transfer switch and how the grounding connections should be made for the generator. First, if a transfer switch for a generator switches the grounded (usually a neutral) conductor, then the generator must be grounded as a separately derived system in accordance with all applicable requirements in 250.30(A). The reason is that, in the normal power mode, the grounded (neutral) conductor for the load is connected to the grounding electrode conductor at the service. In standby mode, the grounded (neutral) conductor for the load is switched over to the generator source, which is grounded as a separately derived system. The result is that, in either position of the transfer switch, the electrical system is grounded. If there is no switching action in the grounded (neutral) conductor through the transfer equipment, then the generator system remains grounded with the transfer switch in either position: normal or standby by the grounding electrode conductor at the service. If the generator is a separately derived system and is located outdoors, a grounding electrode connection is required at the source location to comply with 250.30(C). The equipment grounding and bonding connections, in this case, have to meet the requirements in 250.35(B) for permanently installed generators.
Section 250.35 covers important requirements for providing an effective ground-fault current path, which 250.4 addresses generally. Generators grounded as separately derived systems meet this requirement when installed according to the rules in 250.30(A). If the generator is not installed as a separately derived system, an effective ground-fault current path must be provided in accordance with 250.35(B). This simply means a supply-side bonding jumper has to be installed between the generator and the equipment grounding terminal bar or bus of the enclosure supplied by the system. The supply-side bonding jumper must be installed in accordance with 250.102(C). The minimum size must be based on Table 250.66 or the 12.5 percent rule based on the total circular mil area of the largest ungrounded phase conductors connected to the generator. If the generator has an overcurrent device, the supply feeders from the output side of the overcurrent protective device on the breaker must include an equipment grounding conductor sized in accordance with 250.122, based on the rating of the overcurrent device at the generator.
Auxiliary grounding electrodes

If generators are installed outdoors, the design often specifies an auxiliary grounding electrode. The NEC does not require auxiliary electrodes; however, if installed, 250.54 provides specific requirements that must be met. The auxiliary electrode provides a direct connection to the earth at the generator location. This grounding connection is in addition to the grounding and bonding required by either 250.30(A) or 250.35(B), as covered above. The auxiliary grounding electrode must be connected to the equipment grounding conductor in addition to the frame of the generator. The earth is not permitted as an effective ground-fault current path. When auxiliary grounding electrodes are installed for equipment, they are not required to meet the 25-ohm requirements specified in 250.53(A)(2) Exception.
Summary

Section 250.30 Informational Note No. 1 provides essential information that assists users in determining system grounding requirements for generators. The transfer equipment applied in the design is a key factor for determining if a generator must be grounded as a separately derived system. An effective ground-fault current path is required between the generator and the equipment supplied by the system. The effective ground-fault current path is required to be either a supply-side bonding jumper in accordance with 250.102(C) or a load-side 
equipment bonding jumper in accordance with 250.102(D). Installing an auxiliary grounding electrode for a generator is not an NEC requirement; however, if installed, the installation must meet the requirements of 250.54.

Note that nothing there applies to grounding mobile mounted generators like the ones RV's are equipped with. Obviously an earth ground is not possible or practical for generators that can be operated while moving down the highway.

 

[Contributor]

NO in fact that would REDUCE safety..

I'm still trying to understand why grounding an RV chassis to earth reduces safety

 

[John From Detroit]

I'm still trying to understand why grounding an RV chassis to earth reduces safety

Let's say you are workign outside, using a hand power tool and there is a hot-case short
If the electrical system is not "Earth Grounded" there is no path via ground.
You are "Double Insulated" (The other way to protect the tool user is double insulation).

If it IS earth grounded. then there is a return path.

 

[NY_Dutch]

Let's say you are workign outside, using a hand power tool and there is a hot-case short
If the electrical system is not "Earth Grounded" there is no path via ground.
You are "Double Insulated" (The other way to protect the tool user is double insulation).

If it IS earth grounded. then there is a return path.

If it's earth grounded in that situation, a breaker would trip. No earth ground, the breaker will still trip.

 

[Gary RV_Wizard]

When using the onboard generator, the transfer switch removes this connection and connects at the generator.

The ATS does NOT remove the ground connection - just the hots & neutral. If you start the generator while still plugged to shore power, the load switches to the generator but the RV still has a ground connection to the park system via the shore cord. I do not believe this is any less safe than if the shore cord was physically unplugged. Note also that flipping the breaker at the pedestal doesn't disconnect either neutral or ground - just the hot(s).

 

[Contributor]

EDITED after posting

I don't have an RV with a ATS but am curious by nature, especially with electrical things. I found this schematic for an ATS and have a couple of questions.

Q1 - is the line labeled AUX from either shore power and generator the ground line?
A1 - no t ground, it's a spare for any other use

Q2 - how does the RV still have a ground connection to the park via the system cord when running on the generator? Is there some additional connections not shown here?
A2 - shore power cord brings ground to bound bar to RV, the ATS 5070 schematic does not show the ground connections

Comment - if the AUX is the ground line, then it would indicate that the ATS does indeed switch the ground away from the pedestal and moves it to the generator chassis.

 

[Contributor]

EDIT after posting

So I'm beginning to think I understand the wiring, somewhat. The AUX is not the ground wire, but a secondary neutral wire?

The grounds are all tied to the GROUND BAR which is not switched. They sure make it confusing on the schematic above by not showing how the ground is handled.

 

[John From Detroit]

If it's earth grounded in that situation, a breaker would trip. No earth ground, the breaker will still trip.

I keep hearing "The breaker will trip"
The breaker is normally 15 amps. . Less than 1 amp can kill you.. Less than 0.1 amp can kill you.
That means by the time the breaker trips. You may be dead 150 times (Or more) Over.

Do not count on the breaker to protect you.
Remember I told o a hand grinder that gave me a nasty shock.. (Thankfully I threw it).
The breaker did not trip.. Only once has the breaker ever tripped.. You don't want to know how bad that shock was.. (Thankfully it was a "Safe" shock. did not pass through my body. only my hand)
The restence of the body is about 1,000 ohms This means 120 MA I think i takes 30 to kill you (or less depending on the path. Takes ma is amps/1000 so to trip the breaker takes over 100 times what your body will pass. DO NOT TRUST THE BREAKER TO PROTECT YOU FROM SHOCK.. that's not it's job.

 

[Contributor]

The ground wire is for safety. It is the conductor for the electrons in case of a short. If a 120VAC line shorts the the frame of the RV and the frame is connected to earth ground and you also happen to be touching the frame, then two things will happen. One, electrons will choose the path of least resistance to ground and the wire will be selected, two, the CB will protect the wires from overheating and starting a fire and remove the hazardous condition, THIS DOES PROTECT YOU FROM SHOCK.

I'm guessing that the incident with the grinder was that 120VAC shorted to something you were touching (power switch, case) and the grounding path from where the short occurred was either loose or had lot's of resistance and the electrons chose you. That the CB did not trip points to bad grounding or badly designed grinder.

Had the grinder shorted while you were not using it, it should have tripped the CB and when you picked it up for use it would have protected you from shock.

 

[NY_Dutch]

I keep hearing "The breaker will trip"
The breaker is normally 15 amps. . Less than 1 amp can kill you.. Less than 0.1 amp can kill you.
That means by the time the breaker trips. You may be dead 150 times (Or more) Over.

Do not count on the breaker to protect you.
Remember I told o a hand grinder that gave me a nasty shock.. (Thankfully I threw it).
The breaker did not trip.. Only once has the breaker ever tripped.. You don't want to know how bad that shock was.. (Thankfully it was a "Safe" shock. did not pass through my body. only my hand)
The restence of the body is about 1,000 ohms This means 120 MA I think i takes 30 to kill you (or less depending on the path. Takes ma is amps/1000 so to trip the breaker takes over 100 times what your body will pass. DO NOT TRUST THE BREAKER TO PROTECT YOU FROM SHOCK.. that's not it's job.

Are you assuming that people routinely operate power tools while barefoot standing in a puddle of water? Even ordinary shoe soles can provide enough insulation to prevent a shock. I was doing rough-in wiring when I was 12, and wired or rewired many houses and businesses in my younger years. I know what a shock from a 120 VAC source can feel like, and yes, it is possible to get a nasty jolt before the breaker trips. Whether an RV is earth grounded or not though, is irrelevant in your "hot case" scenario. As long as some part of your body is touching a ground reference, you could suffer a shock. Standing on the ground next to an ungrounded generator powered RV with your arm touching a chassis grounded metal housing when you plug in or pull the trigger on that faulty tool is going to bite you either way. An earth ground would not make that either safer or less safe.

 

[Contributor]

Maybe you are doing something wrong if getting shocked is a normal thing for you.

 

[John From Detroit]

The ground wire is for safety. It is the conductor for the electrons in case of a short. If a 120VAC line shorts the the frame of the RV and the frame is connected to earth ground and you also happen to be touching the frame, then two things will happen. One, electrons will choose the path of least resistance to ground and the wire will be selected, two, the CB will protect the wires from overheating and starting a fire and remove the hazardous condition, THIS DOES PROTECT YOU FROM SHOCK.

I'm guessing that the incident with the grinder was that 120VAC shorted to something you were touching (power switch, case) and the grounding path from where the short occurred was either loose or had lot's of resistance and the electrons chose you. That the CB did not trip points to bad grounding or badly designed grinder.

Had the grinder shorted while you were not using it, it should have tripped the CB and when you picked it up for use it would have protected you from shock.

You are correct that the grinder did not have a 3-rd wire ground. (By design) and that something shorted internally.
You are wrong about it tripping the breaker BEFORE I picked it up. plus the short only happened occasionally.
But I told you what happened. You keep arguing it could not because it would have tripped the breaker. But I told you what happened.. Why do you keep saying it could not?

 

[Contributor]

That explains it, no ground path from the grinder. Then you are correct, you were the only choice for the electrons.

What you are saying doesn't conflict with what I'm saying. What I've said all along is that if the grinder had a 3 prong plug with a ground and was plugged in to a grounded outlet, you probably would not have gotten shocked.

 

[Gary RV_Wizard]

A breaker reacts much too slowly to protect a person from shock and probably too slow to prevent electrocution as well. The latter mostly depends on the path the electrons take through your body.

People talk about electricity taking the path of least resistance and it's true, but it's not an all or nothing thing. A really low resistance path will accommodate most of the flowing electrons, but not every single one of them. Some will still move through the higher resistance path. It doesn't make many milliamps flowing thru your heart or brain to kill you, so make sure that safety ground path is a good one! No corroded connections and adequate wire size.

 

[Contributor]

from OSHA

The most frequently cited OSHA electrical regulation is improper grounding of
equipment or electrical circuitry. If the frame of a piece of electrical equipment or machinery does
not have a grounding conductor attaching the frame to ground, as required to divert dangerous fault
current to ground, and an electrical fault occurs, anyone touching that frame and any other object at
ground potential would receive an electrical shock. Should a fault occur with a grounding conductor
present, the circuit would open or trip as an alert that a problem existed, except in high-resistance
grounding applications. Damaged guards can expose workers to energized conductors in proximity
to their work areas. Additionally, damaged extension cords or extension cords with their ground
prong removed can expose workers to the danger of electrocution.
Failure to maintain a continuous path to ground can expose entire electrical systems to damage and
can expose the structures within which they are housed and workers within these structures to electri-
cal and fire hazards.

 

[John From Detroit]

That explains it, no ground path from the grinder. Then you are correct, you were the only choice for the electrons.

What you are saying doesn't conflict with what I'm saying. What I've said all along is that if the grinder had a 3 prong plug with a ground and was plugged in to a grounded outlet, you probably would not have gotten shocked.

That is true. But it did not have a 3 prong plug.. .... The Grinder I bought to use instead of it did. also was double insulated (All plastic housing) and lasted many years before it died of old age.
The one I have now is a 2 prong but again double insulated (All plastic case) So I'm not worried.