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Old 04-03-2015, 04:13 PM   #1
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Electrical grounding

Hi Folks,
I am building a tear drop camper. I have wired the trailer for both 110 and 12 volt using a Progressive Dynamics 4060 converter. The wiring is all done, tested with both a meter and load and checks out great while hooked to 30 amps. I saw on another forum that the converter should be grounded to the frame. When I broached this question on the other forum it turned into a contest on who could be more technical. One would say yes the other would say no. Made zero sense. I sent an e-mail to PD and their answer was "call an electrician". No help there. So while I know this has nothing to do with FR I thought I would ask you. The install instructions say nothing of grounding to the frame. The unit is grounded internally with the ground wire coming into the trailer from the CG pedestal. I am using battery ground for the 12 volt. As stated, everything works great. I would think had there been a problem it would show up during testing or the GFI would have activated. The whole trailer is GFI protected. So I ask you. Does the 110 need to be grounded to the trailer frame? While I have a working knowledge of how things work, I don't speak electrician. I do appreciate your help.
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Old 04-03-2015, 11:00 PM   #2
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I usually just read the forums but in this case I will post a little information on this...hope it helps.
First there is a difference in the function of ground in an AC circuit then in a DC circuit especially DC in vehicles and an RV.

In an AC application the ground serves as a safety feature. It normally does not carry any current although it is electrically common to the white or neutral side of the circuit.

In low voltage DC applications and more so vehicles ground is an actual current carrying part of the circuit. Instead of running a - (negative) wire to every component that uses DC we instead run a - line from the battery or converter to frame ground. Now when we wire a load we only need to run a + wire specific to that load and then just run a short wire to ground (frame) to establish the return - (negative) path. Easier and saves wiring. It is also low voltage and is not a safety issue to do this.

Now in the RV obviously our lights and other DC appliances actually have both a + and - wire. I assume this is because there is not that much wiring in an RV and it may just be easier to this verses trying to run a wire to the frame down the wall but you know...I never chased down the DC wiring in my Cedar Creek to see if the - goes just to a frame point or actually all the way to the converter. I would guess there is just a common negative ground block by the inverter but I do not know

SO first off one has to separate the concept of ground from AC and DC...simply ground is a non current carrying safety portion of the AC circuit whereas in DC it is a common connection point for all common - wiring and may not even be common (wired) to earth ground like the AC line.

This gets people twisted sometimes.

Now whether you should ground the converter first would depend on which side. Why ground the DC side unless you use frame ground to carry current. As far as the AC side (since it converts AC to DC) it is already grounded via the wiring. Grounding say the frame of the converter to the RV ground would be redundant personally as it would already be grounded through the AC panel and then the CG panel.

I personally would see no need to ground the converter.
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Old 04-04-2015, 01:13 AM   #3
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Stormrider, Mike Sokol (who is a member here of Forest River Forums, screenname jmsokol) has a great and informative website called the "No Shock Zone".

He may can help you in understanding the RV ground.

Although this article is about generators, it touches on the way RV's are wired vs your homes electrical system.

http://www.noshockzone.org/generator...utral-bonding/
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Old 04-04-2015, 05:58 AM   #4
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I learned more about generators today,and grounding, I;m adding one to the system soon, I'll be running mine in the PU bed, should I have a ground wire from gen frame to earth ground?
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Old 04-04-2015, 07:28 AM   #5
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Originally Posted by shughey00 View Post
I usually just read the forums but in this case I will post a little information on this...hope it helps.
First there is a difference in the function of ground in an AC circuit then in a DC circuit especially DC in vehicles and an RV.

In an AC application the ground serves as a safety feature. It normally does not carry any current although it is electrically common to the white or neutral side of the circuit.

In low voltage DC applications and more so vehicles ground is an actual current carrying part of the circuit. Instead of running a - (negative) wire to every component that uses DC we instead run a - line from the battery or converter to frame ground. Now when we wire a load we only need to run a + wire specific to that load and then just run a short wire to ground (frame) to establish the return - (negative) path. Easier and saves wiring. It is also low voltage and is not a safety issue to do this.

Now in the RV obviously our lights and other DC appliances actually have both a + and - wire. I assume this is because there is not that much wiring in an RV and it may just be easier to this verses trying to run a wire to the frame down the wall but you know...I never chased down the DC wiring in my Cedar Creek to see if the - goes just to a frame point or actually all the way to the converter. I would guess there is just a common negative ground block by the inverter but I do not know

SO first off one has to separate the concept of ground from AC and DC...simply ground is a non current carrying safety portion of the AC circuit whereas in DC it is a common connection point for all common - wiring and may not even be common (wired) to earth ground like the AC line.

This gets people twisted sometimes.

Now whether you should ground the converter first would depend on which side. Why ground the DC side unless you use frame ground to carry current. As far as the AC side (since it converts AC to DC) it is already grounded via the wiring. Grounding say the frame of the converter to the RV ground would be redundant personally as it would already be grounded through the AC panel and then the CG panel.

I personally would see no need to ground the converter.
Thank you, thank you, thank you. That makes perfect sense. I really have gone over board wiring this little trailer. All the lighting is LED using 10 ga wire (both + & -). Every 110 volt outlet is GFI protected. For the 12 volt I went ahead and ran all the grounding to the battery. I've tried to do this right and as safe as possible. You have helped me more than you can imagine. Thanks again.
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Old 04-04-2015, 07:39 AM   #6
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Originally Posted by wmtire View Post
Stormrider, Mike Sokol (who is a member here of Forest River Forums, screenname jmsokol) has a great and informative website called the "No Shock Zone".

He may can help you in understanding the RV ground.

Although this article is about generators, it touches on the way RV's are wired vs your homes electrical system.

Generator Ground-Neutral Bonding | No~Shock~Zone
That's a great article. Thank you. I started not to post this on this forum because it had nothing to do with Forest River but I'm glad I did. Since I don't speak electrician it was great to get this info in English. Thanks again.
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Old 04-04-2015, 07:40 AM   #7
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You should ground the chassis. As stated this is a safety thing. If for some reason the hot from the AC should touch the chassis you want that to cause a short and blow the breakers. If you didn't have a ground the chassis could become live and this would be vary dangerous.
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Old 04-04-2015, 08:01 AM   #8
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Originally Posted by Stormrider151 View Post
That's a great article. Thank you. I started not to post this on this forum because it had nothing to do with Forest River but I'm glad I did. Since I don't speak electrician it was great to get this info in English. Thanks again.
I would suggest sending Mike Sokol (jmsokol) a PM. He is extremely knowledgeable in this subject and always is trying to help out. He's a real good guy.
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Old 04-04-2015, 12:58 PM   #9
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I would suggest sending Mike Sokol (jmsokol) a PM. He is extremely knowledgeable in this subject and always is trying to help out. He's a real good guy.
This is Mike Sokol from the No~Shock~Zone. Golly, I'm blushing...

The general idea of AC grounding is that you need a solid connection from the incoming shore power line ground wire (called the EGC - Equipment Grounding Conductor) to the chassis of the RV. The reason for this is indeed to provide a fault current path for any sort of shorted wire or electrically leaky appliance. Note that the green EGC (ground) wires must maintain isolation from the white Neutral wiring inside your RV. There's lots of reasons for this in both the NFPA-70E National Electrical Code and the RVIA build code, but from a practical standpoint an internally bonded Ground-Neutral connection will make your GFCI's trip under ANY load.

Note that without the EGC connection to the RV frame it's possible for the chassis/skin of your RV to be energized at 120-volts with anywhere from a few mA (milliamps) to 20 or more amperes of available current. That's dangerous because standing on the damp ground and touching the skin or door handle of your RV can kill you. I think there was another thread here the other day where some RV technician was testing the RV with an ungrounded shore power connection and stated that the grounding was causing the circuit breakers to trip. That could only occur if the Neutral and Ground were bonded inside the RV itself. As others here have noted, your RV will probably require a Ground-Neutral bond externally when running from a floating neutral generator. And just about all Honda and Yamaha inverter generators are indeed neutral floated. But try as I may, I can't get Honda to even send me a demo EU2000i to video and write about this.

The confusing part of this grounding/bonding stuff is that for the 12-volt DC system the frame/chassis indeed does carry the return current for the DC appliances, and there's no separate EGC ground wire. And to make it even more crazy, in 12-volt DC systems the black wire is chassis/ground, with a red positive wire. While in 120-volt AC systems, the black wire is "hot" while the white wire is the return current, and the green ground wire is the fault current EGC (Equipment Grounding Conductor).

And no, there's no confusion between the 120-volt AC and 12-volt DC electrons. They indeed know where to go in various loops and paths.

In short, the chassis of your RV needs to be "bonded" to the incoming EGC "ground" wire from your shore power line. The Neutral and Ground wires inside of your RV must maintain electrical separation. Those same Neutral and Ground wires will be bonded externally when plugged into pedestal or home power. When running form a generator, you may need to "bond" the Neutral and Ground wires together at the generator itself, which can be my simple G-N bonding plug. You'll be forced to create a generator G-N bond if you're using a Progressive Industries EMS surge protector since if it detects an open "ground" it will shut down the power. Progressive Industries is aware of this and will be offering a pre-wired G-N bonding plug on their website soon, along with selling my No~Shock~Zone book there. There's really no need to earth-ground a portable or built-in generator for an RV unless you're distributing AC power to multiple receptacle drops.

Let me know if this makes sense to you.

BTW: I've been pitching the idea of teaching some on-site seminars about RV wiring and safety at FROG conventions this summer, but I'm not getting any traction with the idea. However, I'm a firm believer that education makes RV owners safer, so I'm doing my best to teach consumers and technicians about RV wiring and electrical safety even though I have zero budget for this. It's just a shame that the RV industry won't support electrical safety education.

Mike Sokol
www.NoShockZone.org
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Old 04-04-2015, 08:30 PM   #10
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Quote:
Originally Posted by jmsokol View Post
This is Mike Sokol from the No~Shock~Zone. Golly, I'm blushing...

The general idea of AC grounding is that you need a solid connection from the incoming shore power line ground wire (called the EGC - Equipment Grounding Conductor) to the chassis of the RV. The reason for this is indeed to provide a fault current path for any sort of shorted wire or electrically leaky appliance. Note that the green EGC (ground) wires must maintain isolation from the white Neutral wiring inside your RV. There's lots of reasons for this in both the NFPA-70E National Electrical Code and the RVIA build code, but from a practical standpoint an internally bonded Ground-Neutral connection will make your GFCI's trip under ANY load.

Note that without the EGC connection to the RV frame it's possible for the chassis/skin of your RV to be energized at 120-volts with anywhere from a few mA (milliamps) to 20 or more amperes of available current. That's dangerous because standing on the damp ground and touching the skin or door handle of your RV can kill you. I think there was another thread here the other day where some RV technician was testing the RV with an ungrounded shore power connection and stated that the grounding was causing the circuit breakers to trip. That could only occur if the Neutral and Ground were bonded inside the RV itself. As others here have noted, your RV will probably require a Ground-Neutral bond externally when running from a floating neutral generator. And just about all Honda and Yamaha inverter generators are indeed neutral floated. But try as I may, I can't get Honda to even send me a demo EU2000i to video and write about this.

The confusing part of this grounding/bonding stuff is that for the 12-volt DC system the frame/chassis indeed does carry the return current for the DC appliances, and there's no separate EGC ground wire. And to make it even more crazy, in 12-volt DC systems the black wire is chassis/ground, with a red positive wire. While in 120-volt AC systems, the black wire is "hot" while the white wire is the return current, and the green ground wire is the fault current EGC (Equipment Grounding Conductor).

And no, there's no confusion between the 120-volt AC and 12-volt DC electrons. They indeed know where to go in various loops and paths.

In short, the chassis of your RV needs to be "bonded" to the incoming EGC "ground" wire from your shore power line. The Neutral and Ground wires inside of your RV must maintain electrical separation. Those same Neutral and Ground wires will be bonded externally when plugged into pedestal or home power. When running form a generator, you may need to "bond" the Neutral and Ground wires together at the generator itself, which can be my simple G-N bonding plug. You'll be forced to create a generator G-N bond if you're using a Progressive Industries EMS surge protector since if it detects an open "ground" it will shut down the power. Progressive Industries is aware of this and will be offering a pre-wired G-N bonding plug on their website soon, along with selling my No~Shock~Zone book there. There's really no need to earth-ground a portable or built-in generator for an RV unless you're distributing AC power to multiple receptacle drops.

Let me know if this makes sense to you.

BTW: I've been pitching the idea of teaching some on-site seminars about RV wiring and safety at FROG conventions this summer, but I'm not getting any traction with the idea. However, I'm a firm believer that education makes RV owners safer, so I'm doing my best to teach consumers and technicians about RV wiring and electrical safety even though I have zero budget for this. It's just a shame that the RV industry won't support electrical safety education.

Mike Sokol
www.NoShockZone.org
Well it's obvious you know what your talking about for sure. Thank you very much. I took a pretty bad shock fighting a fire once and I don't want a repeat performance. That's why I want to make absolutely sure I get this right. The idea of education is a good one and I agree it's a shame to let talent go to waist especially as important as the subject is. Thanks again for your help.
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