Pig tail wiring question - Fiberglass RV


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Old 11-21-2010, 09:25 PM   #1
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Pig tail wiring question

Thanks for all the help so far. I have the converter and 12v/120 hooked up and working and just have the wire hanging out in the front of the trailer waiting to install to the battery.

My question. I'm hooking up the car to trailer pig tail, for the trailer. Looking at the scamp diagram I'm trying to figure out the correct way to hook up the black and white cables to the converter and battery. I have a positive and negative already coming from the converter to the battery. Can I tie into this line at the battery for the Pos & Neg pigtail, then continue a white ground onto the inside useing it for completing the circutes on the lights, brakes, ect? Should I connect the converter +- and Pigtail +- inside and run one line to the battery. I'm a little confused which will correctly charge my battery. I see I'll need a fuse to the battery. Can I use the current trailer frame ground from my 120, tied into my converter, as the ground for the pig tail.

Thanks to all those electrical know how people.
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Old 11-23-2010, 04:55 PM   #2
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Here's a simplified response. (Some of this you may know and may seem redundant, but just to be clear...):

1 NEVER connect the 120VAC ground wire to the frame in any way!

Each wire of your hook-up/house power (black/power, white/neutral and green/ground) gets connected to discrete and separated points inside your converter (or circuit breaker box) ONLY. Any 120V trailer needs should be wired back directly to the converter's circuit breakers. Should there be a short anywhere, the 120VAC ground needs to return to the hook-up source (and consequently, the "earth") via your hook-up cable/power cord. NOT the trailer...

2 The 12VDC side of your converter features fused circuits to power your "in trailer" needs. Typically, to help you identify its application, COLORED WIRES are used to provide POWER to your cabin lights, refrig, etc., WHITE wires are used for GROUND.

Each 12VDC app could be ground in a variety of ways. For example: a) each wired directly to the frame; b) each wired straight back ("home run") to the converter; c) or, daisy-chained together, then to the frame, or, back to the converter.

3 The 12VDC side of your converter itself gets grounded to the frame.

4 A HD (10ga or bigger) black power wire with in-line fuse runs from the converter to the on-board battery. Though rendundant, I run another HD white ground wire parallel with the black wire to the battery. These two wires can then be connected directly to the appropriate poles of the battery.

5 The black and white wires within a 7-pin wiring harness provide power and ground to your trailer battery from your tow vehicle. These, too, are connected directly to your battery.
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Old 11-23-2010, 05:07 PM   #3
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I may have put my foot into it by saying NEVER attach a 120VAC ground wire to the trailer frame. Obviously, this is my preference, but seems to me to be the safest way to divert a short circuit back to the "earth" and away from conducting metal anywhere on the trailer.
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Old 11-24-2010, 12:39 AM   #4
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Quote:
Originally Posted by DannyH View Post
I'm hooking up the car to trailer pig tail, for the trailer. Looking at the scamp diagram I'm trying to figure out the correct way to hook up the black and white cables to the ... battery. I have a positive and negative already coming from the converter to the battery.
Just connect the pig-tail's black wire directly to the battery's positive terminal, and the pigtail's white wire directly to the battery's negative terminal.
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Old 11-24-2010, 06:25 AM   #5
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Quote:
Originally Posted by Robert Johans View Post
Here's a simplified response. (Some of this you may know and may seem redundant, but just to be clear...):

1 NEVER connect the 120VAC ground wire to the frame in any way!

Each wire of your hook-up/house power (black/power, white/neutral and green/ground) gets connected to discrete and separated points inside your converter (or circuit breaker box) ONLY. Any 120V trailer needs should be wired back directly to the converter's circuit breakers. Should there be a short anywhere, the 120VAC ground needs to return to the hook-up source (and consequently, the "earth") via your hook-up cable/power cord. NOT the trailer...

2 The 12VDC side of your converter features fused circuits to power your "in trailer" needs. Typically, to help you identify its application, COLORED WIRES are used to provide POWER to your cabin lights, refrig, etc., WHITE wires are used for GROUND.

Each 12VDC app could be ground in a variety of ways. For example: a) each wired directly to the frame; b) each wired straight back ("home run") to the converter; c) or, daisy-chained together, then to the frame, or, back to the converter.

3 The 12VDC side of your converter itself gets grounded to the frame.

4 A HD (10ga or bigger) black power wire with in-line fuse runs from the converter to the on-board battery. Though rendundant, I run another HD white ground wire parallel with the black wire to the battery. These two wires can then be connected directly to the appropriate poles of the battery.

5 The black and white wires within a 7-pin wiring harness provide power and ground to your trailer battery from your tow vehicle. These, too, are connected directly to your battery.
To prevent possibility of electrical shock when the trailer is connected to 120 Volt AC the green safety ground has to connected to the trailer frame. That's the only connection to the trailer frame that should be made. My guess is that it's also law to have the safety ground connected to the frame.
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Old 11-24-2010, 12:14 PM   #6
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Originally Posted by Robert Johans View Post
I may have put my foot into it by saying NEVER attach a 120VAC ground wire to the trailer frame. Obviously, this is my preference, but seems to me to be the safest way to divert a short circuit back to the "earth" and away from conducting metal anywhere on the trailer.
If the power source was completely independent of the earth (such as a small generator) not connecting the frame to ground might be safer.

Unfortunately, the problem is the shorepower 120v neutral & ground are connected to the earth at the campground's service entrance. If a fault occurs in your trailer that connects the hot to the frame & you have not connected it to the AC ground wire, there will still be a connection through the earth between the campground service entrance & your feet. Since it only takes a few hundred milliamps to kill you, even though the connection probably has a fairly high resistance, there will likely be enough current available to cause problems.

If the frame was connected to the campground ground wire (the green or bare wire) through your bonding or connecting a wire between the ground buss in the RV's breaker panel, enough current would flow due to the fault to trip your RVs or the campground's breaker, shutting off the power.

By the way, it is also critical that the ground & neutral be kept independent of each other in the RV. The neutral (white wire) should never be connected to ground or bonded in an RV. If it is, it increases the chance of a shock between the frame & the earth, and will cause a shorepower GFCI to trip when connected to the RV.

Obviously, for this to work the ground must be carried throughout the entire RV & campground system. In a properly system wired to code it is.
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Old 11-25-2010, 10:51 AM   #7
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Sorry, I shoulda thought this through a bit more carefully. The humble pie is bittersweet, but not altogether unfamiliar...

So, though 120VAC ground wires CAN be run back to the on-board circuit breaker box as "home runs," they can be connected directly to the trailer frame. However, a ground wire SHOULD be connected between the circuit breaker box (or converter) and the frame.
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Old 11-25-2010, 11:54 AM   #8
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As posted earlier: If the power source was completely independent of the earth (such as a small generator) not connecting the frame to ground might be safer.

In the military, they drive a ground rod next to the generator and next to the communications van and both units are grounded. They attach the hot, return and ground cable to the generator and communications van.

Your portable generator should have a Ground Lug so you can attach a wire to it and to a ground rod. It seams that no one does this however that does not make it right.

Byron Said: To prevent possibility of electrical shock when the trailer is connected to 120 Volt AC the green safety ground has to connected to the trailer frame. That's the only connection to the trailer frame that should be made. My guess is that it's also law to have the safety ground connected to the frame.

To do things any other way could have a serious consequence on the user.

To be absolutely sure things are done correct, one should take the time to look up the National and State codes on the subject.

Does anyone have the National Electrical Code number for campers?
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Old 11-25-2010, 12:56 PM   #9
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NEC Code, Grounding & Bonding

The NEC section dealing with RVs & Campgrounds is Article 551. If you don't want to purchase a copy or go to your local library to read it, check the Minnesota Electrical page - they adopt the NEC 2008 version & make copies available on line in a number of formats, including PDF & Kindle. You can also read the current version (as well as a couple of older versions at the NFPA Site (the publishers of the NEC). You must sign up (it is free) and it is a difficult to use reader, so I usually refer people to the MN page.

As to grounding a portable generator - this may be more information than necessary but there are good reasons not to ground a small, 120v portable generator. For some reasons, check This PDF by John "Grizzy" Grzyacz from the OSHA Training Institute. Before deciding on grounding a portable generator, please read the second page of this article.

As to bonding the neutral (white wire) to the generator frame, this is again controversial. It is not required for 120v generators under 5000 watts, but is required for dual (120/240v) generators. Most small inverter generators such as the Hondas & Yamahas do not bond the neutral to the generator frame (ground). In fact, if the generator only produces 120v, there is no neutral according to the NEC's definition of a neutral. Again, there are advantages & disadvantages of bonding of small generators - although not usually a problem for small fiberglass trailers, many trailers with energy management systems will shut down if they don't see a bond. The device assumes that there is an open ground. Some Autoformers used to bump up low campground voltages also will not work with unbonded sources. In that case you may need to add the bond through an adapter when using an inverter generator. John "Grizzy" Grzyacz's PDF also has some discussion on bonding.

A letter from OSHA that explains their view of bonding is Here.
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Old 11-25-2010, 05:06 PM   #10
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This is from our 3000W Inverter Generator Manual

To ground the generator to the earth, connect the grounding lug of the generator to the grounding spike driven into the earth or the conductor which has been already grounded to the earth.

If such grounding conductor or grounding electrode is unavailable, connect the grounding lug of the generator to the grounding terminal of the using electric tool or appliance.

My Note: The appliance in our case would be the camper.

Note: I do not use a ground stake or additional wire from the lug to the camper as I rely on the ground wire inside the power cord. According to the book, that ain't right but I along with many just do it this way.
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