Grounding 120v to the frame... - Fiberglass RV


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Old 01-13-2015, 11:42 PM   #1
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Name: Captain Longbelly
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Grounding 120v to the frame...

Hello I am currently upgrading an old Hunter Compact II and have a question about the 120v...I am replacing the original 15 amp breaker box with a new 30 amp...I am using a 30 amp shore power cord and locking inlet...




The original breaker box had a ground wire ran from the ground bar to a frame/body bolt(the large aluminum wire)



I was wondering if I need to reinstall it from the ground bar to the frame again with new breaker box?



Thanks for any information you may share
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Old 01-14-2015, 01:20 AM   #2
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I would certainly ground it to the frame as it was but with copper wire.
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Old 01-14-2015, 06:19 AM   #3
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Given the varieties of electrical standards in campgrounds I wonder if the principle of "double insulation" used in power tools might be a better way. Thoughts?

John
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Old 01-14-2015, 09:02 AM   #4
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I have the same thing on the Trillium I am rebuilding. I question the logic of grounding the frame to the ground from the service. This would be akin to grounding any metal framing in a building, and is not done. Though there is little harm in doing it, I just don't see the need for it.

12V DC is a different thing, where you are really not grounding, but using the frame as a negative bus in many situations. Might there be a conflict 12V negative, and the 120V ground, are both bonded to the frame?

As well, if all the 12V circuits use wires for both the positive and negative, I can't see any reason that the negative to be bonded either. Am I missing something?
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Old 01-14-2015, 09:09 AM   #5
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Originally Posted by Jim Bennett View Post
I question the logic of grounding the frame to the ground from the service. This would be akin to grounding any metal framing in a building, and is not done. Though there is little harm in doing it, I just don't see the need for it. Am I missing something?
Every metal building and metal stud framing job I was ever on was grounded. The building was grounded to the grounding electrode and the metal studs where grounded by the metal electrical boxes screwed to them (the box itself was grounded with a bonding jumper).

On the trailer, I would hook it up like it was, but with better, newer, stronger stuff. We have at least a couple of folks on the board who have self-identified themselves as Electrical Engineers and hopefully they will chime in.
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Old 01-14-2015, 09:57 AM   #6
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Originally Posted by Jim Bennett View Post
I have the same thing on the Trillium I am rebuilding. I question the logic of grounding the frame to the ground from the service. This would be akin to grounding any metal framing in a building, and is not done. Though there is little harm in doing it, I just don't see the need for it.

12V DC is a different thing, where you are really not grounding, but using the frame as a negative bus in many situations. Might there be a conflict 12V negative, and the 120V ground, are both bonded to the frame?

As well, if all the 12V circuits use wires for both the positive and negative, I can't see any reason that the negative to be bonded either. Am I missing something?
The frame / structure of metal frame bldgs are required by the NEC to be part of the electrical grounding system . Agricultural bldgs which house livestock have higher grounding requirements than bldgs housing humans . The electrical advice on this forum is often in contradiction to the code. Refer to Art 250 of the NEC -Grounding, .Refer to Art 100 - The code is not a design standard ,intended to be a manual for the untrained , or best practice The purpose of the code is to insure that an installation is basically safe and is the bare minimum,
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Old 01-14-2015, 10:25 AM   #7
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Definitely ground the frame. Just imagine what would happen if the frame ever became electrically 'hot'.
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Old 01-14-2015, 10:40 AM   #8
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The NEC requires that the frame of a RV is connected to ground. If you never connected to a utility supplied power source, (i.e. only used an ungrounded generator) it would be safe to go without a grounded frame, but the problem is the utilities ground their systems to the earth. If you have a fault in the trailer that connects any appliance to the trailer frame (converter, AC, water heater (even through the water in it)), or a wiring failure, the ground connect will carry the fault current. If it is large enough, it will trip the supplying breaker. If it is a low current fault, most of the current will be carried by the ground connection, lowering the shock hazard to the earth.

If you didn't connect the frame to ground, a fault to it would raise it to the fault's voltage level. Since the earth IS ground (because of the utilities using it), touching the frame while standing on the ground presents a shock hazard. Since it only takes a 1/10th of an amp to kill you, even small fault currents are dangerous.
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Old 01-14-2015, 12:08 PM   #9
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Another reason to ground to the frame is if a short from hot to the frame were to occur the current to the frame to ground (connected to neutral at the incoming boa and at the transformer) would draw enough current to trip the breaker and clear the voltage from the frame. A poor ground might not draw enough current to trip the breaker leaving enough voltage on the metal frame to be dangerous.
Follow the manufacturer's wiring diagrams if available.
GFCI (ground fault circuit interrupters) can be irritating when they might trip for no discernible reason sometimes, but add safety margins for the operator (you).
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Old 01-14-2015, 12:27 PM   #10
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There are limited applications allowed by the NEC for high impedance grounds .Your trailer is not one of those applications . The trailer frame is supposed to be intentionally and effectively grounded ( See the NEC for definitions of the terms intentionally and effectively)
Establishing a ground point on a trailer frame is often done using a lug and a sheet metal screw neither of which is approved or best practice ..Standard ALCU lugs do not hold up well to road chemicals and the threads on sheet metal screws are too coarse to bond properly to the frame . A copper lug attached to the frame with a fine thread machine screw / tapped hole is a better method .A 10x32 screw is the standard grounding screw for grounding boxes and enclosures.
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Old 01-14-2015, 06:47 PM   #11
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Look at harbor freight for:
Electrical Receptacle Tester with GFCI Diagnosis

Always co ect according to the code. A ground connection to the frame provides a level of safety.

And always use one of these when you connect to any receptacle. First: Test the camp ground power B 4 you connect then after you connect, go inside the camper and check again. Should you not have a ground connection correct, this little device will tell you.
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Old 01-15-2015, 02:28 AM   #12
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Thanks everyone for the information...I will ground it back to the frame using one of the bolts that hold the floor to the frame...I also will install CFI outlets first in both runs of outlets...
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