Still confused regarding frame grounding for AC and DC.

[bdosborn]

Don't forget a fuse or circut breaker upstream of your main cutoff.
Bruce

[cracker39]

Powderburn, you said <B>"If the main braker is GFCI,your whole system is GFCI protected. If your camp site offers a 30ampre GFCI protected plug,you are protected without any GFCI's in your trailer."</B>

The box that I looked at HD didn't have a main breaker in it, just slots for two 1" or four 1/2" breakers. I asked a salesperson about GFCI devices other than receptacles and they said they had none. I wanted to put a GFCI before the breakers and didn't know there were main breakers with GFCI at the time. I guess I'd better look again and find someone who knows more about what they sell. Or go to an electrical supply dealer. I would hope that campgrounds have GFCI protected plugs, but there's no guarantee of that, so I want them in my trailer's electrical system.

Thanks for the reply. I'll be back online on Monday to check here.

[Ken A Hood]

My only problem is that the only way I can find the stranded 2+gound is by the foot at either HD or Lowes and it is $.55 per foot for 14 gauge (ouch).

I know a guy who sells [Boat Cable Marine Wire] UL tinned flat 14/3 (AC) awg 100 ft for $24.27. He also has tons of other sizes, and 14/2 (DC) and single stranded wire in dozens of different colors. If you want more info etc let me know.

[cracker39]

I stopped at an RV dealer today, where they work on them. I asked a service tech if he could answer my questions about RV wiring and he sat down for a few minutes and talked to me. He agreed with most of you that both the 12VDC and 120VAC systems should be grounded to the frame, so I am convinced now that I should....and will.

I am still looking at equipment for the 120VAC. I want a circuit breaker box that won't break my budget and still give me what I need. I want a main cutoff switch or breaker (preferably GFCI protected), as well as at least two 15 amp breakers. I want to use cheaper house type and not the expensive Marine type. I am still not planning on a AC/DC converter, but may get one if I can find one not too expensive. The tech I talked to said that my system with the charger would work, and recommended that I install a trickle charger. That would be fine for keeping the batteries topped off when at home, but I'm not sure a trickle charger would provide enough charge to keep them up while camping and running lights, fan, etc.

I used to have a large spool of stranded 3 wire cable that I used for making extension cords, but am not sure if it is packed up somewhere or if I gave it away when I moved back to Florida, and not sure of the wire size. I can always buy it at HD or Lowes, but haven't seen any flat 2-wire cable for the DC there, except for speaker wire which I guess would work. Anyone used this type of wire in their trailers?

[PcHistorian]

I read this forum thread end to end and for the life of me, didn't see anything mentioned about the greatest one reason GFI was invented and required IN HOUSES mentioned here. Ground the AC and the DC because most of you guys with tears have running water. It is CODE everywhere now that any outlet near running water must be GFI'd. Takes power to run the water. Ground the sink while you are at it to the frame. You may say "there is rubber and plastic hose so that even if the pump does short out, no chance for electrical shock." Wrong, the WATER would carry the current through the rubber hose, to electrify the sink, even if the sink is surrounded by rubber, plastic or wood. (you gotta turn it on...) And lastly, even a tiny pin-hole in your walls, from ice cracking open the wood or squirrels or mice, whatever. (you guys using plywood.) If water gets in the walls, even from condensation, you are going to have electrical connections right next to your ear and in the middle of wooden floors.

Ground the "shore line in/green wire", ground the "battery return/-/black wire", and ground the "inverter green wire." Ground the sink, ground the frame, ground the outlets, ground the air conditioner, air heater frames, water heater, water tank (metal frame/shell or just a metal fitting at the tank. this could prevent corrosion of the pump or screens in the tanks.) prevents corrosion at and of the sink.

oh, and if you are electrically connecting from copper wire to aluminum, you should separate the metals, but connect them electrically using stainless steel bolts, screws, nuts and washers, available at most hardware stores. Otherwise the two metals will interact and corrode, and you'll lose your connection and create electrical problems. (or should I say, electrical NIGHTMARES!!!)

I think that is everything on the ground...

I gotta go post on "using the tow vehicle for charging." ;-)

[rossjools]

, Aircraft that use both AC and DC use the airframe as a common earth or ground circuit with no deleteriouos or unusual effects as long as the grounding points are kept clean. I once fitted a 12V alternator to a cousins furniture removal truck (a Hino with a standard 24V system) and there were no ill effects or funny business. It is still running his 12V power tailgate and its battery system and the 12V alternator was fitted about 15 years ago or so. Because of the mileage the truck does I've had to overhaul the alternator a couple of times in that time but it's still doing the job. The old Canberra bombers (B-57s to our Amercian friends) had a number of different voltages and frequency systems that used the airframe as the earth and there were never any issues other than dirty/corroded earth points.

Personally, I would use the chassis as the ground but that's just me. everyone has their own ideas on things like this and it's not for me to tell anyone how to do it, I can just make suggestions and share a littel knowledge from experience. I must add here that the chassis needs to be effecively grounded to the ground (earth) for safety reasons. Aspike driven into the ground and connected by a secure connection to the frame will suffice for this purpose.

,
Ross.

[eamarquardt]

Gosh, as is typically the case there is some "misinformation" in this string.

First: The "code" requires that the neutral and ground systems of your trailer be isolated from one another and that they be "connected" at the service point (campground power). This is to prevent a "hot neutral" from making your frame hot and possibly electrocuting you.

Second: The "code" requires that as much metal of your trailer (as practical) be bonded/connected to ground.

The exact references to the "code" and quotes have been published before so if someone is interested they can search the forum, NEC, or the California Electrical code.

A GFI, simply put, keeps track of all the "electricity". If any "electricity" gets lost (as in exactly what goes out doesn't come back in) it opens the hot lead and cuts off the electricity. GFIs are a good thing. GFIs, though, are not fuses or circuit breakers and will not protect the wiring from overloads. All circuits need to be properly fused/breakered with a fuse/breaker matched to the gauge of the wire in the circuit.

12 volt DC exits one terminal of the battery and the only place it can/will go (via a complete circuit) is the other terminal of the battery. There is no potential from either terminal to ground (unless one terminal or the other is grounded). This is different than 120 volts because there IS potential between the hot lead and both neutral and ground. The general consensus/opinion/experience is that there is no reason to ground the negative terminal of the battery. The entire 12 volt system should be fused/breakered as close to the positive terminal of the battery appropriate for the gauge of the wires that go to the positive and negative distribution busses. 12 volts is not enough to electrocute you (and most of the time enough to even give you a "tingle"). Using the frame as a conductor is a notoriously bad practice as the connections corrode, open up, and prevent a complete circuit. Folks have spent a lot of time looking for bad ground connections. Better to run a wire from each load (dc powered doo dad) back to the negative buss or battery. Grounding the negative side of the batter accomplishes little of any value.

Any ground connection to the frame must be "maintained" as in regularly tested, disassembled, cleaned, lubricated to prevent corrosion, etc to maintain it's electrical integrity. Failure to do so will compromise the connection's reliability.

It is not good practice, to determine how to wire your trailer on how aircraft are wired. An aircraft is (at least they should be) meticulously inspected and maintained, the the results of same are recorded for posterity, or the aircraft is "grounded" by the FAA.

Hope this helps.

Cheers,

Gus

[rossjools]

, Yes, I'm aware that the neutral and ground must be separated by law; it's the same here. I was talking purely about the ground circuit, not the neutral. I think there has been a misunderstanding about this. In Australia we assume that the neutral and ground (or earth as we call it here are two different things). I noticed either in this thread or another on grounding it's mentioned that some older houses in the US didn't have to have ground circuits and had only two pin outlets. This was a real surprise to me as houses here have always had to have three pin outlets and be grounded to the ground ever since electricity was introduced here in 1880, Tamworth in northern N.S.W. being the first place in the world to have electric street lights.

When my parents bought the house in now live in in 1955 the GPOs were bakelite and also the switches. Before bakelite both the switches and GPOs were brass insulated with ceramic material. My apologies for any misunderstanding, perhaps I should have made my points clearer. Happy


,
Ross.

[rossjools]

, Just another aside here, do AC outlets in the US have to have the active switched these days or not, as I seem to remember seeing in American movies just the sockets on the wall with no switches. Here in Australia the active has always had to be switched and now I believe the neutral also has to be switched behind the outlet fascia. Also we have uniform wiring laws here under the auspices of the Standards Association of Australia for AC (240V here). This means that a caravan or home built teardrop built in NSW will meet the AC wiring laws anywhere in the country if wired correctly. There are uniform 12V standards as well under the auspices of the Australian Design Rules (Automotive).

,
Ross.

[bobhenry]

In the U.S. The Hot leg is broken at the switch leaving the neutral and ground still fully connected.

Wall plug-in outlets can be either unswitched or switch controlled. As an example a hard to reach outlet that might control accent lighting ( Lamps) can be switched for the convenience.

[eamarquardt]

:), Yes, I'm aware that the neutral and ground must be separated by law; it's the same here.
,
Ross.

Here in the US to get 220 volts you go across two hot leads that are 110 volts to neutral/ground and 180 degrees out of phase so that there is 220 volts across them. If you want 110 volts you use one hot lead and the neutral. How does it work where you are? You talk about a neutral but if you were here there would be no neutral with 220 volts, just two hot leads. Also, as only one lead here is hot, it is the only one that needs to be switched. If youse guys have two hot leads are both of the switched?

Always fun to learn how other folks do things.

Cheers,

Gus

[Engineer Guy]

I'll chime in on this one...

U.S. power is 3 Phases, 120 degrees 'out' from each other. When you measure across our 2 'Hots', it reads 208 VAC; not 240. I had to dig into this detail when installing a 240 VAC Demand 'Flash' WH at a House. The following WH performance down-rating quoted below from Wikipedia was also noted about this Demand WH in Manufacturer's Documentation imported from the 240 VAC U.K. by 'Grainger':

'In North America, a typical three-phase system will have 208 volts between the phases and 120 volts between phase and neutral. If heating equipment designed for the 240-volt three-wire single phase system is connected to two phases of a 208 volt supply, it will only produce 75% of its rated heating effect.'

Wikipedia: Single-phase Electric Power

In my Int'l Travels to there, and in dealing with Instrumentation there, Oz Voltage is a single 240 VAC Hot; Neutral return; and Earth[ed] Ground. Thus, their Hot is simply 2x our Wall Voltage here. I'd forgotten all about the std. protocol of switched Outlets there; an initial mystery at Hotels when you check in Jet Lagged and need power.

I've seen and handled 2 Pin Oz Plugs, but they're on Double Insulated Tools, as is the case with our Drill Motors here:

'A commonly used version has only two pins, without the Earthing pin. These are for devices where it is assumed that other safety standards are in use (e.g. earth-leakage, double insulation, etc.).'

Wikipedia: Oz Electricity

After I wired my own House glitch-free, the Colorado State Inspector expressed his disfavor for GFIs connected in series. Though legal by Code, they 'false trip' inordinately.

One of our Houses has Main Power Box GFI Breakers, but I've never seen 1/2 width ones. For my TTT, I have a 'pigtail' 20 Amp Duplex Outlet GFI in a single metal Box with short Cord so that I can have at least 20 Amp protection when I feel the need, and when there's no visible GFI where I [rarely] plug in.

Switch-controlled Wall Outlet protocol [for a Floor Lamp] is to break loose the 'Hot' Brass piece between our 2 Receptacles in a single Duplex Outlet. This allows Wall Switch Control of 1, and constant power to the other. Such a Receptacle is mounted upside down as a visual indicator it's Wall Switch-controlled. The same White Wire Neutral Conductor is shared.

I firmly believe in safety-grounding the Trailer Chassis, and not using it as a Power return for DC. Full stop. Mainly because intermittent connections develop over time... Chassis' deal with weight load and mechanicals. Electricity is a whole other issue. I choose to not combine the 2 issues.

I also drop my Safety Chains on the Ground 'just because'.

[rossjools]

, Here in Oz our normal AC supply is 240V 50Hz per phase 3 phase with the phases 120 degrees apart and star wound and most houses are connected to one phase of the 3 phase supply. Our power outlets (we call them power points) have 3 pin sockets; active, neutral and earth/ground with the ground wire going back to a terminal in the meter box and then to ground around the pipes of a convenient water tap. If you need 3 phase for some reason it can be done but it costs you somewhat to have it connected. GFIs (called ground fault switches here) are now mandatory in all new houses and other new buildings. Mine doesn't yet have one but I intend to get one fitted shortly.

As for 12V tail light earth/ground connections corroding; well, yes they do, even if there is a separate ground wire running back to the battery or tow vehicle. That's why I remove the lense covers once a year on my caravan to check all the connections, power and earth. Same with my trailer. Being an ex RAAF aircraft electrician I'm well aware how important such things are.

,
Ross.

[rossjools]

[quote="Engineer Guy"]
Switch-controlled Wall Outlet protocol [for a Floor Lamp] is to break loose the 'Hot' Brass piece between our 2 Receptacles in a single Duplex Outlet. This allows Wall Switch Control of 1, and constant power to the other. Such a Receptacle is mounted upside down as a visual indicator it's Wall Switch-controlled. The same White Wire Neutral Conductor is shared.

So, am I understanding this correctly? Your normal GPOs aren't switched even on the active lead? To someone who has grown up with switched actives and they were for 70 odd years before I was born this seems pretty strange. I know that your supply voltage is only half what yours is but 110V is still enough to kill an adult let alone a child. I'm learning here as well. Here our wire colours are Active:- Brown, Neutral:- Blue and Earth/Ground:- Green with Yellow trace. Older houses may have Active:- Red, Neutral:- Black and Earth/Ground:- Green.

,
Ross.

[Engineer Guy]

Q: 'So, am I understanding this correctly? Your normal GPOs aren't switched even on the active lead?'

A: Yes, you are correct. No, they are not switched on any of the Leads.

Right or wrong, our right-most Receptacle Slot carrying the 'Hot' 120 VAC is the smaller of the two Slots. Items like a Woman's Hairpin or a Jeweler's Screwdriver would fit into that Slot, but it's skinny and hard to get to.

As is the case in all the Countries I've done Tech Biz in, our round Earthing 'prong' is longer, and connects first.

Oz Wire Color Coding finally 'grew' on me and became 2nd nature. But, it took a while.

We had an Organization called 'REA' back about the 1920s and 1930s that worked to electrify - ta da - Rural Farm areas. Chicken Coop Voltage was something like 32 Volts: our Line Voltage divided 'about' by 4. In one case well-known to many of us 'Sparkies', a fellow standing in damp Earth/Mud in a Chicken Coop was electrocuted when he touched a live Lamp Wire/Socket, and the Electricity went through his Heart. Of course, current matters a lot.

No argument from me re: your sound thinking on Voltage Lethality thresholds. The flip side of this thinking re: what one is familiar with [and what makes 'sense'] is that it took me some time to get 'comfortable' around 240 VAC about everywhere I traveled [save ~100 VAC Japan].

Last time I checked on Code with a Pro Electrician Pal, Code allows us to serially-connect up to 9 Receptacles on 1 Circuit Breaker. I over-wired my new House by about 2x, and put 4 or 5 Outlets on each 20 Amp Breaker [vs. 15 Amp Circuit Breakers used more for Lighting Circuits]. Wire is cheap, as are 'ordinary' Circuit Breakers.

Our newest Code demand is for Arc-sensing Circuit Breakers in all Bedrooms. Pricy buggers. They are supposed to sense arcs and shorts, and then trip. When I went to a Big Box Store here to get them @ USD $50-/each, they were out of Stock. Why? There had been a Manf. Recall because they were unreliable! *Guffaw*. The thinking on Arc Suppressing Circuit Breakers is that they functionally work in tandem with now-mandatory Smoke Detectors that must be installed just outside a Bedroom Door.

Circuit Breaker Discussion

THEE funkiest wiring I've run into is in Mainland China, and the former E. Germany just after The Wall came down. Anything and everything prevailed in Code-free environments. Also, the 240 VAC Demand Water Heaters IN THE METAL SHOWER STALL WITH YOU in Scotland Caravan Parks that take 'Dime' Coins fed in to keep operating totally weirded me out 1st Trip to there. There have been ~5 deaths of U.S. Soldiers in the Middle East, reportedly, from similar, incorrectly-grounded [by Sub Contractors] Demand Water Heaters. So, 'risk' - like U.S. un-switched Receptacles - is in the Eye of the proverbial Beholder, I guess.

My hunch is that other Household Accidents, like Falls, take more lives than Receptacle-related Electricity Accidents. Now, we burn down our Houses while using ill-advised Extension Cords on Space Heaters, or those Heaters near Draperies. But, that's random stupidity having nothing to do with un-switched Receptacles [GPOs].

I used to build large Sound Systems. Grounding/Earthing out at the House Sound Mixing Board runs back through the Mic 'Snake' Cabling to ground ONLY at the Amp Racks on Stage, even if Mixing Board AC Mains Power is taken from a different, remote AC Receptacle. This ensures safe, no-hum Sound Engineering via 'Single Point Grounding'.

In the old 2 Prong AC Plug days, a Stage Mic and a classic Fender Guitar Amplifier with a built-in 'Hot' - 'Neutral' reversing Switch on the rear Panel could be on different AC Mains Phases. I don't know if the Urban Myth is true that touching Guitar Strings simultaneous with putting Lips to a Mic ever killed anyone, but it causes quite a memorable 'bite'. This scenario also often passed current right through the Heart.

Wireless 'everything' on Stage has pretty much eliminated those dangers.