Am I overthinking this? But using a VOM with a RPBG, if I check for voltage from the hot side to ground, I would not see voltage when I should. And conversely, if I checked for voltage from the neutral to ground, I should not see voltage, but with RPBG, I would see voltage. Have I got ‘my’ wiring crossed ? At least this should trigger my noodle, that something is not correct. JAM!
I think clarifying the differences between Earth-Ground, Outlet-Ground and Chassis-Ground will help.
Earth-Ground is the dirt beneath your feet.
Outlet-Ground is the ground contact in a receptacle that should be connected to the shore power EGC. (Equipment Grounding Conductor)
Chassis-Ground is all the metal parts of your RV bonded to the EGC including the chassis, skin, hitch, bumpers, etc…
With an RPBG condition if you measure between the hot leg to Earth-Ground you’ll see close to zero volts. And an RPBG outlet condition between the Neutral and Outlet-Ground to Earth-Ground will measure around 120 volts.
But most testing procedures use the Chassis-Ground or Outlet-Ground as the reference, which is why 3-light outlet testers, advanced outlet analyzers, and metering between H-N-G with a voltmeter will not be able to discover an RPBG. But measuring 120 volts between Earth-Ground and the Neutral/Outlet-Ground is a good indicator of an RPBG.
My house was built in 1956 and had all 2-prong outlets. Fortunately the entire house was wired in armored cable (BX) with the metallic sheath bonded to the main entrance, so I was able to upgrade the outlets to 3-prong with a jumper from the ground lug to the box.
Note that some state and county inspectors will not allow armored (BX) cable to act as the EGC ground conductor, but many do allow it.
I’ve also set up large sound systems in Texas, and they use metallic conduit for the ground conductor. But I’ve never seen this sort of grounding in Maryland.
I’ve also designed large Audio/Video systems for houses of worship in California, and the earthquake codes for the electrical and alarm systems in commercial buildings drove me nuts.
Code was super crazy complicated in downtown Washington DC when I did political gigs such as presidential inaugurations, but in fairgrounds right outside of the beltway they appeared to have zero inspection. Ugh!
So my point is, always check with your local AHJ (Authority Having Jurisdiction) inspector to confirm local code compliance.
Yes, it requires a screwdriver stuck in the dirt to establish earth potential, but is a pretty simple test procedure. I’ve seen this happen at a few old campgrounds that had pre-1970 cabins. They originally ran 2-wire power (hot and neutral) but later changed out to grounded outlets in the cabins. This would have worked and not been a code violation with GFCI receptacles, but their maintenance guy just did a bootleg ground so his 3-light test told him everything was okay when it wasn’t.
My Progressive EMS surge protector has given me an "E-1" before (rev. polarity) and it won't pass power to the rv in that condition. I don't know if the missing ground error will make it do the same thing but as you stated there's no error code for a bootlegged ground.
Hi Mike, As an alternative to running new cable with ground wire in existing installations, code allows the use of a Class A GFCI. If the 1st receptacle in the circuit is replaced with a GFCI and the rest of the circuit is connected to the load side of the GFCI the circuit is protected. This may not be viable with a 30 amp or 50 amp receptacle due to the cost of the GFCI . This is permitted by Canadian Electrical Code C22.1-18 Rule 26-702(2). I’m guessing that the NEC would have a similar provision?
That is true and there is an exception in NEC allowing the use of a Class-A GFCI instead of an EGC ground on a 20-amp branch circuit. But a Class-A GFCI trips at 5mA, and that will often cause nuisance tripping on any feeder circuit powering an RV shore connection.
It can easily occur on a 30-amp outlet, but pretty difficult to happen on a 50-amp outlet. However, a 20-amp to 50-amp dogbone adapter plugged into a RPBG home outlet would create a full-current 120-volt hot-skin voltage on a 50-amp RV.
Remember that a ground rod is not a substitute for a properly bonded ground conductor.
Mike,
Am I overthinking this? But using a VOM with a RPBG, if I check for voltage from the hot side to ground, I would not see voltage when I should. And conversely, if I checked for voltage from the neutral to ground, I should not see voltage, but with RPBG, I would see voltage. Have I got ‘my’ wiring crossed ? At least this should trigger my noodle, that something is not correct. JAM!
I think clarifying the differences between Earth-Ground, Outlet-Ground and Chassis-Ground will help.
Earth-Ground is the dirt beneath your feet.
Outlet-Ground is the ground contact in a receptacle that should be connected to the shore power EGC. (Equipment Grounding Conductor)
Chassis-Ground is all the metal parts of your RV bonded to the EGC including the chassis, skin, hitch, bumpers, etc…
With an RPBG condition if you measure between the hot leg to Earth-Ground you’ll see close to zero volts. And an RPBG outlet condition between the Neutral and Outlet-Ground to Earth-Ground will measure around 120 volts.
But most testing procedures use the Chassis-Ground or Outlet-Ground as the reference, which is why 3-light outlet testers, advanced outlet analyzers, and metering between H-N-G with a voltmeter will not be able to discover an RPBG. But measuring 120 volts between Earth-Ground and the Neutral/Outlet-Ground is a good indicator of an RPBG.
I will add an NVCT to my TT tools. thank you.
My house was built in 1956 and had all 2-prong outlets. Fortunately the entire house was wired in armored cable (BX) with the metallic sheath bonded to the main entrance, so I was able to upgrade the outlets to 3-prong with a jumper from the ground lug to the box.
Note that some state and county inspectors will not allow armored (BX) cable to act as the EGC ground conductor, but many do allow it.
I’ve also set up large sound systems in Texas, and they use metallic conduit for the ground conductor. But I’ve never seen this sort of grounding in Maryland.
I’ve also designed large Audio/Video systems for houses of worship in California, and the earthquake codes for the electrical and alarm systems in commercial buildings drove me nuts.
Code was super crazy complicated in downtown Washington DC when I did political gigs such as presidential inaugurations, but in fairgrounds right outside of the beltway they appeared to have zero inspection. Ugh!
So my point is, always check with your local AHJ (Authority Having Jurisdiction) inspector to confirm local code compliance.
Can you show us how to test at a pedestal for this with a meter?
Yes, it requires a screwdriver stuck in the dirt to establish earth potential, but is a pretty simple test procedure. I’ve seen this happen at a few old campgrounds that had pre-1970 cabins. They originally ran 2-wire power (hot and neutral) but later changed out to grounded outlets in the cabins. This would have worked and not been a code violation with GFCI receptacles, but their maintenance guy just did a bootleg ground so his 3-light test told him everything was okay when it wasn’t.
Thank you
My Progressive EMS surge protector has given me an "E-1" before (rev. polarity) and it won't pass power to the rv in that condition. I don't know if the missing ground error will make it do the same thing but as you stated there's no error code for a bootlegged ground.
A EMS Surge Protector can’t recognize a bootleg ground. There must be a reversed hot and neutral in the pedestal outlet.
Hi Mike, As an alternative to running new cable with ground wire in existing installations, code allows the use of a Class A GFCI. If the 1st receptacle in the circuit is replaced with a GFCI and the rest of the circuit is connected to the load side of the GFCI the circuit is protected. This may not be viable with a 30 amp or 50 amp receptacle due to the cost of the GFCI . This is permitted by Canadian Electrical Code C22.1-18 Rule 26-702(2). I’m guessing that the NEC would have a similar provision?
That is true and there is an exception in NEC allowing the use of a Class-A GFCI instead of an EGC ground on a 20-amp branch circuit. But a Class-A GFCI trips at 5mA, and that will often cause nuisance tripping on any feeder circuit powering an RV shore connection.
Mike, can RPBG be found on 30 and 50 amp outlets ad well and if so can it be detected with a non-contact device?
And yes, a properly used NCVT will detect any hot-skin potential over 40-volts no matter what caused it.
It can easily occur on a 30-amp outlet, but pretty difficult to happen on a 50-amp outlet. However, a 20-amp to 50-amp dogbone adapter plugged into a RPBG home outlet would create a full-current 120-volt hot-skin voltage on a 50-amp RV.