Still confused regarding frame grounding for AC and DC.

[eamarquardt]

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

I don't think Engineer Guy is clear with his description of what type of power we have here.

We have two distinct systems. Single phase, which is actually two 120 volt phases producing 120 volts to neutral and 240 volts between them. They're both 120 volts but 180 degrees out of phase with each other.

The other distinctly separate system is 120 volt three phase which he correctly states is 120 volts to neutral (but a neutral lead isn't used with three phase motors) and 208 volts between phases as they are 120 degrees out of phase (versus 180 out of phase in single phase).

Doubting my version (as Engineer Guy is pretty darned knowledgeable) I just measured the 240 outlet in my garage (lathe, mill, 2 welders, and table saw use 240) and measured 243 volts with a Fluke meter. I also verified with a friend who is a supervisor at a hydroelectric plant on the Columbia river.

A big advantage of three phase motors is that they are self starting w/o any extra windings, capacitors, centrifugal switches, etc. to start them turning like single phase motors.

My lathe and milling machine were designed to run on three phase but residential areas are rarely provided with three phase power. As the motor on the mill would be difficult to impossible to change out and the lathe would be a major PITA to change the motor on I built rotary phase converters using another three phase motor (as a rotary transformer), a time delay relay, a second relay for control of the phase converter starting, a starting capacitor to start the rotary transformer, and finally some motor running capacitors to even out the current on the three legs. See pic in album.

It was interesting to learn that all outlets are switched in the "land down under" and that the hot is in fact 240 single phase.

Cheers,

Gus

[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). If neither terminal is connected to the chassis, if a wire shorts out to "ground" nothing will happen. Some old English cars used to have a "positive ground" which made things a bit interesting when installing an American radio with a negative ground. A special converter. DC 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

[Engineer Guy]

Gus ~

We're in 'violent agreement'. I cited Wikipedia, in part, because that Reference clearly states the reality to most of us, save your Shop: 3 Phase AC isn't run to most Houses. More importantly, it's not an issue within the scope of this RV Park/Trailer Grounding discussion.

If most all Readers here follow my comments, and measure Hot 1 to Hot 2 at their House Electrical Oven; Clothes Dryer; or Hot Tub 240 VAC Receptacle, it will be 208 Single Phase.

Wikipedia correctly notes that 3 Phase [as you have] is an option and, typically, an extra-cost option. It also notes 3 Phase Convertors like your's [very atypical]. 3 Phase Wires + 1 Return can be seen on about any Power Pole one views. However, one will see only 1 Tap - 1 Single Phase - feeding the Step-down, Pole-mounted Transformer going to the average House that doesn't have 3 Phase power. This same 'reality' is true in Oz - at 2x the Household voltage - via the 'Star' wiring cited.

And, as noted in Wikipedia, 3 Phase Power eliminates the power 'loss' in Heating and other Applications [and in your Shop Tools that can't afford such losses].

Of the 3 Phases running down the usual 7,200 VAC, 3 Phase Power Pole Lines, the 'average' House has Single Phase, 230 VAC [that measures 208 net voltage] at up to 200 Amps Mains Service.

I cited what I believe to be 'typical' in order to communicate the 'average' Household/RV Park situation here.

This topic also gets plenty of discussion, and misunderstanding, with the Big Rig Owners who have 50 Amp Power Systems.

[eamarquardt]

the neutral and the ground are bonded together and the ground is bolted to the frame.

Not on the trailer. They should be electrically isolated from each other and only the ground should be connected to the trailer frame. They do come together at the "service point" ie campground power pole. This prevents the frame from being hot from the ground lead should a problem develop. As you point out, should the frame become hot, you may "dance a merry jig" before you stop dancing altogether.

See (not for the faint of heart, trust me):

http://www.ebaumsworld.com/video/watch/80655924/

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?

This is why you should use one of the test plugs to ensure the campground wiring is correct before plugging in. If you do find the campground mis-wired, it should be corrected. If everyone did this there would soon be no mis-wired outlets at "Pappy's" campgrounds and he learn the proper way to wire the outlets.



Cheers,

Gus

[PcHistorian]

@Gus eamarquardt - I have one of those, (3-light power tester) but I never thought to use it before I plugged in. I haven't done a lot of any 120vac available camping, so "You are right! Thanks for the Advice!" (if I found a problem, I'd probably sneak out to the power box after dark and rewire the damn thing myself.

@Engineer Guy (nice sweater) I like the "Drop the chains" idea. I've seen live wires on the ground after lightning hit a transformer and better the ground getting it than me, while getting in and out of my trailer. Yes, the reason I don't rely on the metal trailer frame for ground is because its purpose is structure, not electrical. Further, not all welds carry perfect electrical connections. That's bit me in the arse on some professional jobs. We replaced everything but the frame on this computer and it would intermittently fail. We tried power monitors, the works. We finally gave up and even replaced the frame and zoom, never another problem. Also, I live in Michigan which means road salt in the winter for snowy and icy roads, and corrosion to any bare metal. Lastly, the tow vehicle (at least mine does) uses a battery negative ground for alternator, engine, starter and battery, and the trailer traffic lights are powered by the tow vehicle. I'm considering charging by tow vehicle. (@Gus, eamarquardt) For these reasons and safety though, I ground individual items, AND run the negative 12v DC wire, And ground the green AC power wires and any device powered by that with metal on the outside. That way I have a common ground assured to each device and each part of the frame is electrically connected together. (Bad electrical connections between pieces of "welded frame" corrode, and that means the frame is gonna come apart. Not me.) I also do my best to have every ground connection fully enclosed, sealed by paint or inside, once again because Michigan salts and any connections showing will corrode. I have enough problems with "Factory connections" corroding off, like I've got two wires to my heater fan switch rusted off (one on the resister bridge side, the other the wires TO the resistor bridge. Means I've got to work on both sides of that connection. :-(

Ah here we go, lastly wiring colors for the house, 120vac. Green is ground, white is common/neutral (larger slot on the outlet), "hot wire" is black (small"er" slot on the outlets). Switching an outlet is not required, but the fuse, breaker, etc... is connected to the "Hot" wire always.

220 vac comes into the house, single phase supposedly with a center tap of "ground" which becomes the neutral/common wire in the house. Horror story, my younger sister's house we found out had never been grounded AS neutral, either from the power company or the box or meter connected to ground or the cold water pipes. Results, one side of the breaker box got more voltage than the other, depending on what the loads per halves were!!! Do it yourself, double check. Story: Edison the man who loved DC and hated AC "Invented" the electric chair (which ran on AC ) just to demonstrate the danger.

Oh and lastly again, if I split a duplex so one is always "Live" and the other is switched I'm supposed to turn the outlets upside down? Is there a code on which one is supposed to be the switched one, the top or bottom one? (what if I mount them sideways? :-S One of mine is not only switched (inside) but it is a 3-way circuit (It's a long way from the door to the head of my bed, full trailer length.)

[rossjools]

, Ooh no! I don't think I ever advocated bonding the neutral and ground together and then to the chassis. If that's how it sounded I apologise, that would be suicide waiting to happen especially here with our 240V supply. What I was saying was to ground the outlets to the chassis and then run that ground back perhaps via the chassis or again perhaps use the chassis as an extra ground back to the external power ground pin on the trailer, just so the chassis and the ground were at the same potential.

If you were in any doubt about the wiring in the camping ground my advice would be DON'T plug in your trailer to it, try and only stay only one night using your onboard battery. If you happen to have a genset use it instead up to genset curfew time then the battery and make sure you earth/ground the genset to the physical ground the trailer is sitting on. Safety in all of this rides very hard on the owner maintaining all grounding points and that's why I check all mine at least every 6 months including 12V lighting earths. By the way, I've never had any 12V lighting problems with my van and I put that down to the maintenance I carry out at regular intervals. Maintenance of any electrical item is a must. If you're not sure how to, ask someone that does know and there is a great deal of knowledge in these forums.

,
Ross.

[Engineer Guy]

I'll have to let others go research current Code, due to multi-tasking here tonight.

In our '87 Suburban House, the same Outlet of the flipped-upside-down Duplex Outlet was always the switched one. It's the one nearest the Floor in the inverted Outlet. I didn't do a single Switched Outlet at our Solar Retirement House, so I don't [need to] know current Code.

I use Ye Olde Voltmeter at RV Parks since I can then verify -/+ Voltage simultaneously with 3 'Pin' integrity [H, N & G]. However, no argument that Gus' suggested Tester is handier... I also own several Black Rotary Telephones from the '40s.

I had plans to do my usual 'over-the-top' Wiring through my TV 7 Pin Bargman to add Towing Charging. BDOsborn confirmed what I already knew intuitively. It's hard to get full charging Voltage back through any Wiring. I'd even planned on 2x #4 Wire. That drops the net Wire Gauge to ~2 Gauge. Gus made a good point [taken] prior on lesser current demand as Batteries top off.

My current thinking is to use an adjustable 120 VAC 'Battery Minder', or similar, to really charge, say, 2x 6 VDC Golf Cart Batteries right to Manf. Spec. This can require higher-than-typical Alternator Voltage; in the low 14 VDC range, I recall...

Meanwhile, someone mentioned the brilliant idea of running an Inverter off his Vehicle to allow Power Tool use on his Ranch; my situation, too. So, I'm thinking now of using my 400 Watt Inverter, and a larger one later, to run a Trailer-mounted Battery Minder/Tender off of 120 VAC plumbed back to the Trailer through a separate, safe Plug, as used on Engine Block Heaters, etc.. A Marine Twist Lok should do it. The older OEM Power Center in my Trailer works fine. I don't need an entire, new Progressive Dynamics-type Power Center. Plus, a new one of those doesn't get me remote 120 VAC on the Ranch like a TV-mounted Inverter would.

I've got a nice 120 lb., 3 kW Kipor Genny. But, it's overkill. When I upgrade Tow Vehicles - and have a very beefy Alternator - I could remote start that Vehicle w/Inverter; run the Trailer Hair Dryer or Microwave; and turn the Vehicle off. I could charge while driving, but via 120 VAC -> Battery Tender. Being a budding Boondocker, my need for AC is very sporadic. A hefty Cobra Inverter is $99-. Something like an Ignition-switched Relay would ensure no 120 VAC except when certain, safe conditions are met. I've seen that 120 VAC Power is available on Dodge Trucks now.

Just a thought for right now...

I worked on Instrumentation at Boeing WA. In one of the weirdest situations of all time [to me], the Tide changed the quality of Earth Ground 2x daily in the matrix of Ground Rods under the Building. Research Accelerator Grounding referenced that Ground, which was not a constant. We were measuring microAmps and picoAmps. Ground is not always Ground. That was an Eye opener...

My Avatar is from the MI U.P. The Sweater is from Scotland.

[eamarquardt]

I am acutely that I am sometimes a bit gruff and a PITA, but I try and share what I've learned along the way.

Pain, sometimes, tries one's patience.

Cheers,

Gus

[rossjools]

, Ah yes, Ground. At one point I was in charge of the section that did the earth point testing at RAAF Richmond and we found a similar thing although not nearly so dramatic as that. Before being posted to that Sqn I was with a small communications unit that did a lot of work with the army. We had a supply of 6' copper grounding rods that we knocked into the ground with sledge hammers and then added another 6' length just for good measure. However when we're trailering or caravanning we have to be practical and use what's available so a 2' ground stake would be sufficient to provide a safe enough grounding point for a trailer/caravan. I know I would certainly always ground the chassis of the van to earth, even if I used the grounding stake that came with my genset thus using it to ground both the genset and van.

,
Ross.

[rossjools]

Mmmm. Yes. That guy on the train in India reminds me of a guy I had to transport from Westmead Hospital to the burns unit at Concord Hospital in Sydney's west when I was a member of the NSW Ambulance Service back in 2000. This 28 year old had been train surfing (drunk as, in fact so drunk his mates don't know how he managed to climb on top of the train) in wet weather. As the train pulled out of the station he staggered and his neck caught the overhead supply cable (1200V DC). He had spent many weeks in Westmead ICU and had an entry wound on the left side of his neck and an exit wound on the bottom of each foot. He told me as we drove along that his girlfriend wasn't impressed. I couldn't begin to wonder why and told him so.

Ross.

[PcHistorian]

@general now you guys have me thinking I should have one of those 3 light ac polarity tester things wired in conjunction a DPDT switch with my power in. In all my born days of wiring up polarity reversing DPDT switches, I swear I told myself "I glad I will at least NEVER have to do a polarity switcher with AC." I stand corrected. LOL! Hmmm, it'd be nice if I could do that as a pulse throw relay instead of constant duty. Hmmm.

hmmm. bring my own 2 foot ground rod with me... is steel rerod ok?

Hmmm, remote start TV with inverter... Hmmm. @Engineer Guy:

Yes, more I think about it, inverters need to be next to their batteries. I've been thinking of running a 1500w (surge) inverter in the pickup bed for portable power. (yes, a generator would make more sense at that point. 1200w at 12vdc means 100 amp alternator, for continuous draw. Golf cart batteries you say, instead of marine deep charge. Hmmm...) Then run the 120AC to the trailer. Heck even a 125w, plug in the TV lighter socket, inverter would get the power back to the trailer to top off batteries. Depends how much and how fast you want to do it. I've been considering my 120vac automatic/manual auto battery charger. 10 amps peak output. Just hook it up for the winter/summer and forget it. Problem is it won't fit between my 2x4 studs in the wall. :-(

I have one battery, an ex-standby for alarm systems, 4 amp-hour. Don't know how I'm going to switch it yet. And one of the new Peak battery booster things to use as a 12 volt source. Since these don't work for a run down car battery, I advise everyone to NOT buy one. The only thing it MAY be good for is a cold weather boost, because the battery is cold. I tried it with a "dome light left on over night and a 4 cylender engine" and got not squat from it. (300A yeah, wanna buy a bridge, too? ) And now the damn recharger went. (wall wart variety, built who knows where...) It will fit in between the the studs AND the 1/2 inch particle board wall to be behind my paneling outer surface. The charge port needs the inch more for the plug, though. But since I won't be relying on it for a car start, might as well use it for something... Plus it is portable and has the lighter outlet built in.

@rossjools, I was given a really nice AM/FM/CD/Cassette player, but it uses 240AC 50Hz. Oz voltage. However upon closer examination I noticed it uses 8 "D" cell batteries, meaning 12vdc. So I scrounged a coaxial power input from a broken cordless phone base and opened it up, soldered in onto the battery out power (center terminal to positive) and I now have a sound system, all other jacks standard. :-) (train surfing ?!?! there's one for the bucket list. I'll pass on the drunk part... ;-)

@slow, believe me I was really tempted to do the outdoor, 3 prong, 14ga., extension cords with outlet strip idea, but the more I thought about it, the more I figured it just wouldn't do the Elf Cottage justice if I didn't do the entire interior like a house, AC included. I'm just adding the 12vdc system because it is a trailer for camping and a lot of really neat things use 12vdc. (I found an electric cooler to play with that someone was throwing out. No power cord, just the wire hanging out color coded (red heater, blue cooler) that will be fun restoring, inside the house while the snow is blowing outside.

@Engineer Guy: I have a vacuum tube voltmeter. two digitals, etc... (Are those the "Bell 500" model black rotory? I wish I had the original of the home here. My dad used to work for Western Electric's phone repair depot in Plymouth, Michigan.)) Yooper? I'm a Lowper. Yeah, lots of good wool sweaters come out of Scottland. How close to the ocean was Boeing, WA? (must have been the conductivity due to salt water tides.) microAmps and picoAmps?

@eamarquardt /Gus: Yeah, sometimes pains get us up and out of bed in the morning, and keeps us honest with ourselves. Ooohe Rha. Besides, never shoot the messenger & the only dumb question is the one we didn't ask. Live & learn.

[Engineer Guy]

Yep, the Boeing Plant w/a small Accelerator on site was right near the Water of Gig Harbor WA. So, Salt Water Tide excursions 'just' under the Soil a bit changed conductivity. All measurements are relative to Ground. So, when Ground changes, it matters.

An odd lil 'Rule of Thumb' in the Wild World of High Vacuum [in the Accelerator] was that the current to be measured from an Ionization Gauge had an exponent 2 values lower than the pressure in Torr being measured. So, if the pressure you're measuring was 2.0 x 10 E-09 Torr, the associated current was 2.0 x E-11 Amps, depending on the Emission Current setting at the Ionization Gauge. Heady stuff, but it made one get familiar with what constitutes a good Ground, and how to 'do' Cabling, including Coax, properly.

Another weird one was on the ~5th Story of a Lab Building around Fermilabs IL. You'd think that tying Instrumentation into the Building I-Beam would constitute the 'ultimate' Ground [Lab Engineers did]. No so. As reiterated above, connection integrity matters. I-Beam connections; paint; actual connection to the Soil were imperfect. A 3 Phase Heating Oven was drawing oodles of current, and creating current nodes. We had to 'deconstruct' the set of assumptions, and start from scratch to convince Old Timers that some assumptions were not valid anymore. I vaguely recall that the solution was to run separate, large, parallel Ground Conductors to multiple Ground Rods, and keep them moist. Rod placement the 'proper' distance apart, and by Gutter Downspouts, in a lil 'Well' topped off with Gravel, always works.

The old Phones are actually from Finland, bought in a Pasadena CA Antique Shop Decades ago. They're definitely based on that classic Bell design. Bulletproof. Your Voltmeter sounds pretty kewl.

This is one of the better Resources on Batteries IMO. Golf Cart Batteries have thicker Plates, and can really put up with rough treatment. Each Battery type has it's own associated info on these Webpages, since one set of Guidelines/assumptions [like Charge parameters] doesn't apply to all Battery types...

Deka Golf Cart Batteries

[rossjools]

Hi PcHistorian,
Yes train surfing, and what makes it even more stupid and a real nightmare for Emergency Service people is that all of Sydney's suburban trains aren't like that Indian train; they're all double decker carriages and those double deck electric trains run as far south as Cambelltown and Wollongong and as far north as Newcastle. There have deen a number of train surfing and train planking deaths (where the planker tries to plank between carriages of a moving train) on the Sydney suburban system. When they try to plank on top of a carriage their stomach is about 3"-6" from the o/h cable carrying 1200V DC so if they get it wrong or chicken out they're a goner anyway. If they don't get killed by electrocution they fall and get killed by the train running over them or by hitting their heads on the train or the way base. Just straightout stupid stuff and it's not just the fellas who are doing it, there have been a couple of girls killed too, one only 14 trying to train surf. Sad that kids and even adults seem to have to get their kicks this way.

,
Ross.

[PcHistorian]

I've been playing with lightning rod ground for the last couple of years. The spec is two separate grounds for a lightning rod system. Preferably separate from the building grounds. other wise the resistance from building ground to true ground is going to let the ground in the building (yes entire girder structure and water pipes included, spike.

I've got one of those "bought from radio shack "finland" rotory phones. I had to rewire the ringer and wiring though.

The vacuum tube volt meter I think has some of the tips in a wooden probe vs. plastic or Bakelite ones..

Is there any way to emulate a true ground with a circuit, artificially?
(you mean you sank a well just to put a ground rod in the bottom. Well it should of worked as well as anything, short of running a ground to the power source, at the power company. (or the reactor for fermi.)