Electric/Wiring Questions - Fiberglass RV


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Old 04-26-2013, 12:45 PM   #1
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Electric/Wiring Questions

Should both my AC and DC be grounded to the frame?

Can I run my battery's negative terminal directly to the negative DC terminal on my new PD4045 converter? Or should I run it to the frame, then the frame to the Converters "-" DC?
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Old 04-26-2013, 12:49 PM   #2
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Just run a ground wire from the converter's ground terminal to the frame. The only reason to ground the frame is to keep it from becoming accidentally electrically live from AC voltage.

If you are using the frame as a DC conductor for lights or brakes, then you would ground the battery negative terminal to the frame as well. Battery to converter should be a straight run. Then you can run a wire to the frame from either battery or converter. In general, is is a bad practice to depend on the frame as a conductor, as it is hard to keep the contacts to the frame from corroding.
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Old 04-26-2013, 01:51 PM   #3
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Typically there two connections to frame. One the green safety ground wire coming from the 120 Connection to external power, the other is the brake wire.

When the converter is connected the to 120 system the safety ground is connected to the negative of the converter, which is also connected to the negative side of the 12 Volt system. This gives the impression when checked with an ohmmeter that the frame is the negative side of the 12 volts system and therefore can be used that way. That was never intended.
The reason the negative side shows up is because UL and other safety organizations want the frame going to safety ground when connected to shore power.

As inside your house safety ground is connected to the Neutral side of the AC line, only in one place and that's at the distribution panel (breaker box).

Thomas is right that to depend on the frame as an electrical conductor is a very poor practice. I don't like for the brakes either.
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Old 04-26-2013, 01:55 PM   #4
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Scamp grounds the trailer brakes through the frame. If you use a breakaway switch then you will need to provide a ground path from the battery directly to the frame. If your trailer looses connection to your tow there is no longer a breakaway power connection so power must be connected through the on board battery.
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Old 04-26-2013, 01:58 PM   #5
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Originally Posted by stevebaz View Post
Scamp grounds the trailer brakes through the frame. If you use a breakaway switch then you will need to provide a ground path from the battery directly to the frame. If your trailer looses connection to your tow there is no longer a breakaway power connection so power must be connected through the on board battery.

Reread my post above. The connection is still there via the converter.
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Old 04-26-2013, 03:42 PM   #6
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Originally Posted by Byron Kinnaman View Post
Typically there two connections to frame. One the green safety ground wire coming from the 120 Connection to external power, the other is the brake wire.

When the converter is connected the to 120 system the safety ground is connected to the negative of the converter, which is also connected to the negative side of the 12 Volt system. This gives the impression when checked with an ohmmeter that the frame is the negative side of the 12 volts system and therefore can be used that way. That was never intended.
The reason the negative side shows up is because UL and other safety organizations want the frame going to safety ground when connected to shore power.

As inside your house safety ground is connected to the Neutral side of the AC line, only in one place and that's at the distribution panel (breaker box).

Thomas is right that to depend on the frame as an electrical conductor is a very poor practice. I don't like for the brakes either.
I'm assuming you are referring to the campground breaker panel, not the trailers.

As to grounding the converter to the frame, NEC code requires at least a #6 wire...
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Old 04-26-2013, 03:51 PM   #7
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I'm assuming you are referring to the campground breaker panel, not the trailers.

As to grounding the converter to the frame, NEC code requires at least a #6 wire...
No! NO! I was referring to your house, anchored home, breaker panel.
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Old 04-26-2013, 04:17 PM   #8
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That is what I thought. The trailer's ground & neutral are separate.
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Old 04-26-2013, 04:29 PM   #9
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That is what I thought. The trailer's ground & neutral are separate.
As they are in your house.
Ground is a misunderstood and misused term. In your house the round pin on the 120 Volt outlet and cord is GROUND.
In your trailer that same GROUND is used where 120 appliances are connected to the 120 system.
The so called ground in the 12 volt system, is simply the negative side of the 12 volt system and has nothing to do with GROUND. GROUND = Earth.
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Old 04-26-2013, 04:51 PM   #10
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But in your house they (the ground & neutral) are bonded at the service entrance. They should not be bonded in a trailer's breaker panel, a mistake that some make, resulting in a shock hazard and preventing the trailer from operating when plugged into a GFCI receptacle.
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Old 04-26-2013, 05:26 PM   #11
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But in your house they (the ground & neutral) are bonded at the service entrance. They should not be bonded in a trailer's breaker panel, a mistake that some make, resulting in a shock hazard and preventing the trailer from operating when plugged into a GFCI receptacle.

The safety ground inside the converter is connected to negative 12 Volt line. PERIOD.
That makes them tied together at the trailer. The safety ground is also connected to frame at that point. PERIOD.

Hard to understand???
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Old 04-26-2013, 05:38 PM   #12
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.........As to grounding the converter to the frame, NEC code requires at least a #6 wire...
Why such a big wire? Doesn't it just need to be large enough to throw the circuit breaker? It would seem like 10 gauge would be plenty.
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Old 04-26-2013, 06:07 PM   #13
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For trailers our size the run is short enough that a #10 would throw a 30 amp breaker - might be a problem with a larger 50 amp with a longer run...
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Old 04-26-2013, 06:09 PM   #14
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For trailers our size the run is short enough that a #10 would throw a 30 amp breaker - might be a problem with a larger 50 amp with a longer run...
Yea, that would explain it. I forget about 50 honking amp RVs.
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