Still confused regarding frame grounding for AC and DC.

Anything electric, AC or DC

Still confused regarding frame grounding for AC and DC.

Postby cracker39 » Mon Sep 19, 2005 4:40 pm

I have read so many posts about the electrical systems and it seems that there are conflicting statements and I have some questions to clear up my consusion.

1. Tail/stop lights: Why bother with frame grounding for my tail lights if I am running a ground wire from my tow vehicle to my trailer lights? All tail lights will return the ground to the tow vehicle's frame. (I have a 5+1 connector with wires for 1) tail lights/clearance markers 2)stop lights 3) left turn 4) right turn 5) ground. That leaves me one for backup lights if I want to use them.)

2. I have seen lots of diagrams where the 120VAC shore power was not frame grounded, and one diagram that did have a frame ground for the 120VAC. Do you ground the 120VAC to the frame or not? In a house, there is no "frame ground". All grounding is done via the ground wire back to the circuit breaker box ground bar. I plan on using a breaker box with 4 120VAC 15 amp breakers in it. One for the Air, one each for front and rear 120VAC outlets, and the last one goes to the AC/DC converter.

3. If you do ground the 120VAC to the frame, do you also ground the 12VDC for the trailer fan/lites/outlets to the frame? If you are running ground wires for all 12VDC usage back to a common ground block, then to the battery, is the frame ground still necessary?
Dale

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Postby cracker39 » Mon Sep 19, 2005 4:56 pm

PS to last post.

Bdsborn stated in a post:

"If there's no circuit breaker, you're right it pretty much doesn't matter what you do. I assume that you will have a circuit breaker from the the shore power circuit because its always required by code to be there. The difference between grounding the trailer frame and not (with a circuit breaker) is how fast the circuit breaker will clear the fault. The circuit breaker will open within a second or two when the hot wire touches the frame if its grounded. The circuit breaker won't open on an ungrounded frame untill something completes the path to ground. This leaves the trailer frame energized untill someone touches it. Also, people are a high resistance path to ground so the circuit breaker may not see enough current to open, leaving the frame energized untill the next person touches it. "

This confuses me because in my trailer, all of the 120VAC wiring runs through my walls and ceiling, never coming in contact with my trailer frame. And, all 120VAC outlets are inside the trailer where one cannot touch the frame. The only contact between the wood and the frame is through 6 carrage bolts that connect the plywood floor to the frame and those bolts are under the vinyl flooring. So, how can someone be in any danger of touching the frame? I also plan on using a GFCI.
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Postby madjack » Mon Sep 19, 2005 5:23 pm

...Dale, I always run seperate grounds for 12v(or a commom wire), I find it best not to rely on frame grounding only, I apply this to both the interior system and the exterior(car/trailer) system
With any 120v system you should ground any METAL you may come in contact with...in other words, ground your trailer frame with the 120vac system...I use an extension cord I made up with a GFI in the plug. The common bus is then grounded to the frame/skin ect....you never know when something might just short to the frame/skin and you cetainly don't want to become the grounding path for that short
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Postby cracker39 » Mon Sep 19, 2005 6:37 pm

Jack, I agree re the 12v grounds all running to a common block, but still see no reason to ground my cabin power battery to the frame as there will be no frame grounding for any of the 12VCD usage in the cabin.

But, regarding the 120VAC grounding tp the chassis, I would think that applies if there is metal in the cabin construction (i.e. skin, matal framing, etc.), that can be shorted. But my cabin is all wood and I unless I am wrong, wood doesn't conduct electricuty. There will be no metal except for screws attaching skin and cabinetry to the wall framing and those would never come in contact with the 120VAC or the 12VDC. In other words, there is no chance of the 120VAC being contacted by the occumant except from an outlet on the wall. I think a lot of the rules of 120VAC grounding are for conventional trailers with skins and/or frames made from metal. I'm no electrician, but here again, I am only trying to use logic and commoin sense (if I have any left that is).
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Postby cracker39 » Mon Sep 19, 2005 6:38 pm

The google seach found the same link, but no luck...still won't find the page.
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Re: Still confused regarding frame grounding for AC and DC.

Postby bdosborn » Mon Sep 19, 2005 11:40 pm

cracker39 wrote:I have read so many posts about the electrical systems and it seems that there are conflicting statements and I have some questions to clear up my consusion.

1. Tail/stop lights: Why bother with frame grounding for my tail lights if I am running a ground wire from my tow vehicle to my trailer lights? All tail lights will return the ground to the tow vehicle's frame. (I have a 5+1 connector with wires for 1) tail lights/clearance markers 2)stop lights 3) left turn 4) right turn 5) ground. That leaves me one for backup lights if I want to use them.)

2. I have seen lots of diagrams where the 120VAC shore power was not frame grounded, and one diagram that did have a frame ground for the 120VAC. Do you ground the 120VAC to the frame or not? In a house, there is no "frame ground". All grounding is done via the ground wire back to the circuit breaker box ground bar. I plan on using a breaker box with 4 120VAC 15 amp breakers in it. One for the Air, one each for front and rear 120VAC outlets, and the last one goes to the AC/DC converter.

3. If you do ground the 120VAC to the frame, do you also ground the 12VDC for the trailer fan/lites/outlets to the frame? If you are running ground wires for all 12VDC usage back to a common ground block, then to the battery, is the frame ground still necessary?



1. The reason most trailers use the frame as a ground is that it saves having to run two wires to all the lights. If you're using two wires everywhere, its not essential that you ground the 12V system to the frame. Its good practice from a safety standpoint since that way don't ever have to worry about your frame being at a different electrical potential from the vehicle if your ground wire happens to come loose.


2. All commercial trailers with 120V AC service have the frame bonded to the equipment ground because of NEC requirements. Remember that the green equipment ground is not a current carrying conductor. Its purpose it to conduct shorts to ground. And yes, some old house don't have ground wires but all newer houses do. The idea is to conduct shorts to ground through the green wire instead of through people who happen to touch a metal object that is energized by a loose wire.

3. Its not necessary in the sense that you'll have weird electrical problems or your 12v devices won't work. Its to make sure that the 12V ground is at the same potential as the AC equipment ground. That way, you can't get shocked by touching the negative post of the battery and the frame at the same time.

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Postby bdosborn » Mon Sep 19, 2005 11:56 pm

cracker39 wrote:But, regarding the 120VAC grounding tp the chassis, I would think that applies if there is metal in the cabin construction (i.e. skin, matal framing, etc.), that can be shorted. But my cabin is all wood and I unless I am wrong, wood doesn't conduct electricuty. There will be no metal except for screws attaching skin and cabinetry to the wall framing and those would never come in contact with the 120VAC or the 12VDC. In other words, there is no chance of the 120VAC being contacted by the occumant except from an outlet on the wall. I think a lot of the rules of 120VAC grounding are for conventional trailers with skins and/or frames made from metal. I'm no electrician, but here again, I am only trying to use logic and commoin sense (if I have any left that is).


You're probably right; if you don't have any conductive material in your trailer at all, it might be okay to leave the ac equipment ground off the frame. But, are you that sure that the a wire will *never* accidently come off and make some weird conductive path to the frame? 10 minutes worth of work and a dollar worth of materials takes care of Mr. Murphy.
Bruce

P.S. I was leaning up against my door opening and discovered I had nicked a 12V wire with a screw. I got shocked by the exterior trim holding the roof skin on. I had a cut on my hand and wouldn't you know that's right where I touched the trim. Otherwise I never would have felt it.
P.P.S. Don't tell anyone. I'm kind of embarrassed that I hit a wire with a screw. :lol:
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On AC frame grounding

Postby Steve_Cox » Tue Sep 20, 2005 5:53 am

Hypothetically writing. On your AC power the neutral and the ground are bonded together and the ground is bolted to the frame. You go to "Poppy's by the Tree" campground and it turns out Poppy is an amateur electrician. You get the campsite with reverse polarity (all Poppy's campsites have reverse polarity). You set up and plug in your power cord. You go to take your bicycle off the tongue mounted bike rack and suddenly you find that you can't let go of the handlebars because you're getting about 112 of the 117 volts available right into your continuously constricting muscles in your hands. Don't you wish for a split second you hadn't tied the ground to the frame as you feebly jump into the air to get your wet bare feet off the damp ground and break the circuit?

Steve in St Augustine 8)

PS - I'm building a woody teardrop and have a ground wire to my frame. I also have a "reverse polarity " warning light on my AC electrical panel. There are lots of Poppys out there in the world.
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Re: On AC frame grounding

Postby cracker39 » Tue Sep 20, 2005 6:50 am

Steve_Cox wrote:Hypothetically writing. On your AC power the neutral and the ground are bonded together and the ground is bolted to the frame. You go to "Poppy's by the Tree" campground and it turns out Poppy is an amateur electrician. You get the campsite with reverse polarity (all Poppy's campsites have reverse polarity). You set up and plug in your power cord. <B>You go to take your bicycle off the tongue mounted bike rack and suddenly you find that you can't let go of the handlebars because you're getting about 112 of the 117 volts available right into your continuously constricting muscles in your hands. Don't you wish for a split second you hadn't tied the ground to the frame</B> as you feebly jump into the air to get your wet bare feet off the damp ground and break the circuit?

Steve in St Augustine 8)


Steve, you put into words my doubts of frame grounding the 120VAC coming into the trailer. I didn't think about the possibility of reverse polarity making the frame carry a positive charge. Since my trailer cabin is made of wood, and I plan to carefully avoid putting any screws or brads where I have run a wire with 120VAC current, I could only see making a problem with the frame being grounded that woudn't exist if it were not grounded. I think I'd rather carry a metal rod in the trailer to pound into the ground to connect my ground wire to. And if the ground were wet around it, you might still get a shock if the polarity were reversed.

As for the 12V systems. I removed my tail/stop lights from my boat trailer, because all that I've tried over the years eventually get water inside and corroded. I made a light bar that I strap onto the rear of the boat deck to travel and remove and put in the back of the truck when the boat goes into the water. There is no ground connection between the lights and the boat or trailer frame. The ground wire and light grounds all connect to the aluminum bar, and one wire runs to the connector with the positive wires and connects to the tow vehicle's ground via the connector. There is no reason for having frame grounding on the trailer for tail/stop lights either since I'll run the ground wire to the connector. BTW, I have experienced the weird way lights react with a bad ground to the tow vehicle. Unless you have done it, it's hard to believe what happens to your lights. It drove me crazy until I checked and fixed the ground.

Same as above with the internal lights and other 12V systems. With a ground wire run back to the battery/converter for each light/fan/outlet, I see no need for frame grounding except as a "backup" ground, and to have that you'd have to individually frame ground each light, fan, outlet, etc. in order to use the frame as a "backup" ground. OK, I can frame ground this system if everyone thinks it's necessary, but I really don't see the need. I'm not just being stubborn (I don't think so anyway), I am just not convinced that all of the grounding to the frame is necessary, and in the case of the 120VAC could create a problem that could prove to be unsafe.

Am I really wrong on any part of this? Althought it may appear that "my mind is made up, don't confuse me with facts", that's not the case. I'm still listening to opinions. Alright, maybe I am saying that I still need convincing of the need.
Dale

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Re: On AC frame grounding

Postby cracker39 » Tue Sep 20, 2005 7:07 am

Steve_Cox wrote:PS - I'm building a woody teardrop and have a ground wire to my frame. <B> I also have a "reverse polarity " warning light on my AC electrical panel. </B>There are lots of Poppys out there in the world.


Stave, did you buy the polarity warning device or make it? I found one in a catalog for $29.49 that plugs into an AC outlet and monitors voltage as well as testing the polariry. They also have plug-in DC voltage monitors for $15.79 which is about as cheap as building one with parts from AllElctrics.com. I haven't gotten as far as designing my panel (or deciding if I even need a panel with these plug-in devices) or just where I'll mount it yet. Being to the point where I install electrics is several months away. I haven't even started to construct my chassis yet.
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Re: On AC frame grounding

Postby Steve_Cox » Tue Sep 20, 2005 9:17 am

cracker39 wrote:
Steve_Cox wrote:PS - I'm building a woody teardrop and have a ground wire to my frame. <B> I also have a "reverse polarity " warning light on my AC electrical panel. </B>There are lots of Poppys out there in the world.


Stave, did you buy the polarity warning device or make it? I found one in a catalog for $29.49 that plugs into an AC outlet and monitors voltage as well as testing the polariry. They also have plug-in DC voltage monitors for $15.79 which is about as cheap as building one with parts from AllElctrics.com. I haven't gotten as far as designing my panel (or deciding if I even need a panel with these plug-in devices) or just where I'll mount it yet. Being to the point where I install electrics is several months away. I haven't even started to construct my chassis yet.


The reverse polarity warning light came in the 120 volt boat panel I got at a surplus place here in St Augustine. It has a 2 pole main, the reverse polarity light, and 4 ea 15 amp breakers, I like it too because its connector bars are behind an enclosure on the back, no accidental jolts if I am groping around behind the panel. I paid $35 for it and it had been sent to the factory for inspection just a couple of months ago.
I've got one of the plug-in outlet testers you mentioned, but it is the cheapy with the 3 lights on it, when I get into a questionable work situation I always test.
Steve in St Augustine
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Postby IraRat » Tue Sep 20, 2005 11:17 am

One of two things is going to happen to me:

My head is either going to explode from all of this electrical talk that I'm totally ignorant about. Or I'm going to be the first one on this site to die in my sleep from a TD electrical fire. (And man, wouldn't THAT be embarrassing!?)

Steve, please look at this, which I plan to order Friday:

http://www.boatersworld.com/webapp/wcs/ ... escription

I plan on doing just 120, so if I run grounds to all devices, and this is grounded to the shore station via the connector, do I have to ground anything to the frame?

PLEASE give me the easy answer or else that head is going to explode.
--Ira

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Postby cracker39 » Tue Sep 20, 2005 11:43 am

That's a nice looking panel Ira. They also have an 18/20 amp converter for $119.99. That's plenty of DC power for me and less money than the 30 amp units I've seen (cheapest was $184 at Flagship RV. I've seen the same unit for up to $212 frpm different sources).
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Postby cracker39 » Tue Sep 20, 2005 12:34 pm

Waffle, waffle, waffle...that's me. Can't seem to make up my mind. I know I am becoming a pain in the ying-yang.

The more I read, the more I think about simplifying to the nth degree. I've seen wiring diagrams where some of you use a charger and no converter. Mike Nemeth's article on 12 volts mentions doing that, but with a 3-stage charger. I can't get his site up, and the cached version doesn't show any of his diagrams or photos.

I checked out my Exide charger that I use at home. I can't find where it states that is is 3-stabe, but it does have full protection against overload. It shuts down when voltage is sufficient in the battery, and starts charging again when it drops. Just using my existing charger to keep my 12V system up and running when on shore power makes $$$ sense to me. And, no converter to ground to the frame. My battery and charger will be in the box on the tongue, along with my 30AMP shore power cord and I may put my AC breaker box there as well.

I can use a 200 or 400watt inverter that plugs into a 12V outlet for the TV when no shore power is available. Xpower has one that they claims works with TVs, computers, and all other electronics, so I guess it is at least a modified sine type. To prevent excessive battery drain when no shore power is available, I may just install two group 24 or group 27 deep cycle batteries, which together will have about 50% and 80% more juice than a single group 31 (what I use for my boat trolling motor). Even with occasional TV use, two batteries should easily last through a 3-day weekend without dropping below 40%. As previously mentioned, plug-in AC and DC voltage meters can be used to check power at the outlets, so no panel is needed either.

This will be a bare-bones system, but I think it'll work for my needs.
Dale

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Postby Steve_Cox » Tue Sep 20, 2005 1:21 pm

IraRat wrote:One of two things is going to happen to me:

My head is either going to explode from all of this electrical talk that I'm totally ignorant about. Or I'm going to be the first one on this site to die in my sleep from a TD electrical fire. (And man, wouldn't THAT be embarrassing!?)

Steve, please look at this, which I plan to order Friday:

http://www.boatersworld.com/webapp/wcs/ ... escription

I plan on doing just 120, so if I run grounds to all devices, and this is grounded to the shore station via the connector, do I have to ground anything to the frame?

PLEASE give me the easy answer or else that head is going to explode.


Ira,
If your head explodes, don't forget "we love da pictures" (Madjack quote). That panel looks great, same mfg as the panel I have, to ground to the frame or not is your choice, as all the things you do with your teardrop. I will ground to the frame knowing that if I have a reverse polarity situation I'll know from the panel indicator when I power up after plugging in the power cord. I'm just not going to lose too much sleep over any of it, it's not that big of a deal to me.....but it wasn't my TV that went up in smoke before my eyes....

Steve in St Augustine :D
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