Frame Ground/Chassis Wire - Fiberglass RV


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Old 03-12-2013, 09:57 PM   #1
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Frame Ground/Chassis Wire

I installed a new converter and have decided to upgrade my ground/chassis wire as my converter requires it to be at least 8g. My existing wire is bare copper and is screwed into the frame under the trailer. There is no shielding on this wire and it's completely exposed to the elements.

Since my new larger wire will be shielded, I'm curious what others have used to seal that ground wire from water where it connects to the frame? Just silicone or something more appropriate for an electrical wire?

Thanks!
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Old 03-12-2013, 10:16 PM   #2
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I installed a new converter and have decided to upgrade my ground/chassis wire as my converter requires it to be at least 8g. My existing wire is bare copper and is screwed into the frame under the trailer. There is no shielding on this wire and it's completely exposed to the elements.

Since my new larger wire will be shielded, I'm curious what others have used to seal that ground wire from water where it connects to the frame? Just silicone or something more appropriate for an electrical wire?

Thanks!
What is the purpose of the "ground" wire to the frame of your Trillium? Are you talking about 12V DC or 110V AC?
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Old 03-12-2013, 10:47 PM   #3
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Actually I'm referring to the case ground, it's a deck style converter. Since that needs to be attached to the frame I don't want the ground wire corroding where it meets the frame.
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Old 03-13-2013, 06:43 AM   #4
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8 ga seems like overkill.

I would use a dab of dielectric grease or whatever is handy. I don't think it matters much as long as you can inspect it periodically.

It doesn't matter is the wire is shielded or not.
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Old 03-13-2013, 07:09 AM   #5
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I'm not sure I even understand the purpose of grounding the inverter. I guess one could otherwise establish an electrical path between the frame and the case of the inverter if it was accidentally live, but in a FG trailer it seems like an awfully long shot.

Time for an electrician's opinion.
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Old 03-13-2013, 07:22 AM   #6
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I'm not sure I even understand the purpose of grounding the inverter.
Drew said "converter", but since we now know this is a case ground, the difference seems irrelevant.

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I guess one could otherwise establish an electrical path between the frame and the case of the inverter if it was accidentally live, but in a FG trailer it seems like an awfully long shot.
I assume that's the intent.

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Time for an electrician's opinion.
I'm not an electrician, and I don't even play one on TV, but I've noticed they don't always have the same opinion - maybe we need three of them and a vote.
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Old 03-13-2013, 09:11 AM   #7
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Well, if you want to follow the National Electrical Code, (US) here is Article 551.20(C) Bonding Voltage Converter Enclosures - "The non current carrying metal enclosure of the voltage converter shall be bonded to the frame of the vehicle with a minimum #8 copper conductor. The voltage converter shall be provided with a separate chassis bonding conductor that shall not be used as a current carrying conductor."
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Old 03-13-2013, 09:14 AM   #8
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Well, if you want to follow the National Electrical Code, (US) here is Article 551.20(C) Bonding Voltage Converter Enclosures - "The non current carrying metal enclosure of the voltage converter shall be bonded to the frame of the vehicle with a minimum #8 copper conductor. The voltage converter shall be provided with a separate chassis bonding conductor that shall not be used as a current carrying conductor."
Jon, what do you think the logic of this code requirement is?
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Old 03-13-2013, 09:21 AM   #9
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Far be it from me to explain the NEC, but I'll guess - Since the trailer frame (chassis) should be bonded to the AC ground, I suspect the reason for the case bond is to provide a low resistance path to trip the main breaker if there is a fault to the case of the converter. Without the bond, it is possible to end up with 120V AC to the earth on the trailer's 12V system when operating on shore power. With it, the breaker should trip.
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Old 03-13-2013, 09:34 AM   #10
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I would hate to have a 120 volt live frame and you be the ground when hooking up your trailer hitch. A bonded frame tripping the breaker would be good.
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Old 03-13-2013, 10:00 AM   #11
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I was just following the instructions from power max My old wfco converter doesn't have a case ground, just a wire running from the negative dc bus bar to the frame.

When the NEC says:

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The voltage converter shall be provided with a separate chassis bonding conductor that shall not be used as a current carrying conductor."
Does that mean the case ground can't simply be connected to the dc negative which also runs to the frame?

But more to my original question....dielectric grease....is that what most have used on these connections to the frame?
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Old 03-13-2013, 10:20 AM   #12
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Current only flows if there is a difference of potential (voltage). By wiring all chassis, metal cases, frame, etc. together you make them all the same potential. Put your voltmeter on the converter case and the frame you will read zero volts. No difference of potential, no shock hazard. Further as Jon suggested, an internal fault in the converter to the case (assumng it's metal) will blow the fuse provided the battery is also connected to the frame. Raz
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Old 03-13-2013, 10:31 AM   #13
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Originally Posted by multi-task View Post
I was just following the instructions from power max My old wfco converter doesn't have a case ground, just a wire running from the negative dc bus bar to the frame.

When the NEC says:



Does that mean the case ground can't simply be connected to the dc negative which also runs to the frame?

But more to my original question....dielectric grease....is that what most have used on these connections to the frame?
Yes. As to dielectric grease, I wouldn't bother. If the frame is painted, I'd scrape the paint off under the terminal so there is a good contact, and check it every year when getting the trailer ready...
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Old 03-13-2013, 11:06 AM   #14
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By running a bare wire to the frame you are bonding the system to keep all points at the same potential (SEE RAZ ABOVE) I would use a brass lug not an ALCU lug made from Aluminum . Mount the lug to the frame by scraping paint , drilling a hole and tapping with a fine thread such as 1/4 x 24 ( Sheet metal screws are not approved for attaching an equipment grounding conductor) The brass fittings are approved for damp locations such as swimming pools where the aluminum lugs are not. If you wish you can coat the wire and lug with Pentrox which is a conductive grease normally used on aluminum conductors to stop oxidation.. If you consider the converter as a Service than # 8 "Solid" is the smallest bonding conductor allowed by the code (Stranded wire is not approved because corrosion could eat away the small stands one at a time )
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Old 03-13-2013, 11:25 AM   #15
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Two non-querulous quibbles. 1) Wouldn't spot priming or any common grease retard oxidation around a simple ground strap? 2) Why is paint removal for lug to frame contact necessary given the current path provided by the large area of contact between bolt head and lug and between bolt threads and bare steel of tapped threads in the frame?

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Old 03-13-2013, 11:44 AM   #16
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I would hate to have a 120 volt live frame and you be the ground when hooking up your trailer hitch. A bonded frame tripping the breaker would be good.
But then you guarantee the frame could be energized by connecting the converter to it. In my camper the only thing grounded to the frame are the tail lights.
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Old 03-13-2013, 12:06 PM   #17
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Hi Steve Dunham, I was hoping you would show up. While I know the theory, you know the practice as well. Thanks, Raz
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Old 03-13-2013, 03:02 PM   #18
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Two non-querulous quibbles. 1) Wouldn't spot priming or any common grease retard oxidation around a simple ground strap? 2) Why is paint removal for lug to frame contact necessary given the current path provided by the large area of contact between bolt head and lug and between bolt threads and bare steel of tapped threads in the frame?

jack
I agree about the primer but paint is not UL listed for use on electrical connections and Pentox has conductive grit in the compound and is not injurious to insulation Paint fills the lug and lug threads making it difficult when the paint dries to retougue the lug and insure the connection is tight ,the pentrox does not harden . The flat surface area of the lug is designed to carry a calculated amount of current , if you do not remove the paint you are limiting the conductive area to the area of the screw threads . I always scrape the paint , drill ,tap , put Pentrox on the lug ,wire, bolt , bare frame area plus use a lock washer . If you can find a copy of The NFPA Electrical Handbook it will explain why specific code requirements were enacted
The code is highly influenced by insurance companies who do NOT like paying out for fires ,death and personal injury IE arc fault ,GfCI, and Grounding requirements
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Old 03-13-2013, 03:20 PM   #19
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Grounding

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But then you guarantee the frame could be energized by connecting the converter to it. In my camper the only thing grounded to the frame are the tail lights.
Why then are the frames of Manufactured Homes ( Mobil Homes ) required to be "Grounded" I have repaired several Mobil homes where the wiring passing thru the metal studs or touching the frame of the home has energized the trailer (No equipment ground to frame) . When stepping up on the metal steps of the trailer (One foot on the ground , one on the metal steps ) YOU conduct 120 VAC to ground . When you properly ground the frame of the trailer the shock hazard is eliminated , breakers start tripping and you can now trace the ground fault *Plus Ground Fault Circuit Breakers do not replace or eliminate the code requirements for proper grounding*
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Old 03-13-2013, 03:34 PM   #20
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Why then are the frames of Manufactured Homes ( Mobil Homes ) required to be "Grounded" I have repaired several Mobil homes where the wiring passing thru the metal studs or touching the frame of the home has energized the trailer (No equipment ground to frame) . When stepping up on the metal steps of the trailer (One foot on the ground , one on the metal steps ) YOU conduct 120 VAC to ground . When you properly ground the frame of the trailer the shock hazard is eliminated , breakers start tripping and you can now trace the ground fault *Plus Ground Fault Circuit Breakers do not replace or eliminate the code requirements for proper grounding*
I completely agree. The reason a "hot" chassis is a problem is because the utilities have already established an earth ground. Any leakage to the chassis will be "hot" to the earth. That leakage can come from faults in any AC powered equipment, even plastic water lines (tap water is a conductor).

If your trailer was a completely independent system with no earth ground, you might be able to float the chassis without a shock hazard to the earth, but once you are connected to utility supplied power the bonding & carrying of the ground through to the service pedestal is necessary.
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