Ground Plan for Multiple Voltages?

[Lostranger]

I don't know whether to ground all our systems to the chassis. Most of the Gillig's systems are 24v, but it also uses 12v provided by a Vanner. Both those voltages are, of course, grounded to the chassis. Our solar powered, 24v house system is not grounded to the chassis. 120v AC power from our inverter IS grounded to the chassis. Our minimal 12v house needs are currently provided by a small step down transformer, but the APU I'm adding will require considerably more 12v DC to operate its systems. My plan is to install a second house system (smaller battery bank) and charge it with the APU alternator and a single solar panel.

On a different thread, several posters mentioned not grounding differing voltage systems to the chassis. Is it best to run dedicated ground loops for both the 12v and 24v house systems? I don't have a clue.

Jim

[sparkplug188]

I can not think of any reason why you would need isolate the ground loops.  Nearly every new vehicle on the road today steps the battery voltage (12+) down to reference voltages (5+ and 3+) for various sensors and control motors-- all the grounds have 0+ voltage potential and are tied together.  I am curious of the logic behind isolating the grounds.

[digesterman]

Ground is ground, doesn't make a difference what the positive side is. Will be interesting what others have to say.


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[luvrbus]

I never could get clear in my mind they ground to frame but all the gurus say a dedicated ground I know for a fact the Allison World Transmission and the DDEC will give you fits if any other ground are on the dedicated grounds it makes no sense to me  

[Lostranger]

I never could get clear in my mind they ground to frame but all the gurus say a dedicated ground I know for a fact the Allison World Transmission and the DDEC will give you fits if any other ground is on the dedicated grounds it makes no sense to me   

Glad I'm not the only one confused. Looking forward to more input on this one.

Jim

[Seangie]

Jim -

I asked this same question to Mike Sokol at noshockzone.org and this was his response -

The most important connection from your shore power plug is indeed the safety ground wire to your bus chassis. According to both the NEC and RVIA codes, this must be uninterrupted by any switches or contacts. This is typically done by bonding (connecting) your RV's circuit breaker panel to the bus chassis via a heavy wire, usually 6 gauge or so along with bolting the panel to the metal frame. The incoming shore power cable's green safety ground wire is then directly connected to the ground bus bar in the breaker box. What needs to stay isolated from the metal box is the neutral bus (white wires) which separates the ground and neutral bus connections inside your vehicle. And you note, the ground and neutrals are bonded together by the generator or inverter (when running from them), or bonded together back at the campgrounds incoming service panel.

While it seems like the 12-volt DC and 120-volt AC circuits will get their "grounds" confused, they actually live together happily. What you have to be careful of is wiring color since in 12-volt DC wiring the black is negative (ground) while in 120-volt AC wiring the black is hot (120-volts). Yeah, that's caused more than a little confusion at times.

My guess is the only equipment that would have issues with a shared ground is 12-24v sensitive electronic equipment that relies on a specific voltage reading to operate such as the DDEC that Cliff mentioned.  It could possibly give you incorrect readings on gauges as well but this is just a guess on my part.

I am a firm believer in home runs for grounds but that leaves a single point of failure if you ever lose the home run.  In a perfect world with 12v or 24v I think I would have a home run (one positive and one negative) to a terminal block in each section or zone of 12v or 24v supply and ground the block to the frame.

Wondering what the big coach manufacturers are doing...

-Sean

[TomC]

Considering virtually all municipal electrical lines of all voltages and types are grounded through the Earth, the chassis is the same. Electricity only seeks out it's own voltage. Doesn't matter whether it is AC or DC.

In California, there is a twin electrical line coming from Washington and interestingly is DC. You can see the towers off 395 when going north from L.A. towards Mammoth. It is the tower that only has two sets of wires-most towers have three sets for 3 phase AC. Good Luck, TomC

[Seangie]

Tom -

Most of the high power lines that have to carry voltages for long distances are DC because of efficiency.  I think the limit on AC voltage is like 30 or 40 miles or something like that.

-Sean

[Audiomaker]

Tom -

Most of the high power lines that have to carry voltages for long distances are DC because of efficiency.  I think the limit on AC voltage is like 30 or 40 miles or something like that.

-Sean

I thought it was the other way around?

[Seangie]

Nope. DC for long runs....Im sure its out there in Google land somewhere. 

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[lvmci]

Heres a good explanation, at first when Westinghouse and Edison were competing for the American system for electricity, DC could only go a mile, that was overcome, Tesla had a third wireless system.

AC current is a specific type of electric current in which the direction of the current's flow is reversed, or alternated, on a regular basis. Direct current is no different electrically from alternating current except for the fact that it flows in the same direction at all times. Alternating current was chosen early in the 20th century as the North American standard because it presented fewer risks and promised higher reliability than competing DC systems of the day. Many of DC's deficiencies were later corrected, but not until a substantial North American infrastructure had already been developed. DC is the European standard.

Electric power distribution requires a circuit, usually represented as two wires leading to a device that uses electricity. In AC current, one wire is negative and the other is either is positive or neutral (ground). The two wires take turns at sending electricity. In North America, AC current uses a standard "rhythm" in which each side gets its turn 60 times each second, thus the 60Hz designation given to standard AC current. This switching of polarity takes the form of a rhythmic pulse in the electrical current that occurs within the normal audible range. This is why you can actually hear this rhythm in circuits such as fluorescent lighting ballasts and audio equipment as a low buzzing tone. This buzz is referred to as "sixty cycle hum". Prior to the 1970s, two AC power schemes were used in North America. One offered energy at 45-50Hz, the other at 60Hz. "Fifty-cycle power", occasionally referred to as "rural power", is now obsolete and the 60Hz standard is now used throughout North America.

In DC circuits, the electricity is always the same polarity, which means that in a two-wire circuit, one "wire", or side of the circuit, is always negative, and the negative side is always the one that sends the electricity. There is no hum because there is no cyclic change in current flow. DC current is more effective for long-distance, high-voltage transmission because it results in less energy lost in transmission, but the cost of converting DC current to AC is relatively high, so DC is typically cost-effective only for long-distance transmission.

Electrical devices that convert electricity directly into other forms of energy can operate just as effectively from AC current as from DC. Lightbulbs and heating elements don't care whether their energy is supplied by AC or DC current. However, nearly all modern electronic devices require direct current for their operation. Alternating current is still used to deliver electricity to the device, and a transformer is included with these devices to convert AC power to DC power (usually at much lower than the supplied voltage) so that electronic devices can use it.

Many good explanations like this one out there,
Lvmci...

[Lee Bradley]

I think Europe uses 240vac 50 cycle.  

AC was adopted because it could be stepped up to very high voltages for long transmission distances and stepped down to lower voltage at the other end. DC had
no similar ability as it doesn't work with transformers.  The DC transmission lines Tom mentioned are very high voltage and is a special case; dedicated supply and load.

For more see

http://en.wikipedia.org/wiki/High-voltage_direct_current

[Lostranger]

Thanks for the info on transmission lines, but I'd love more input on grounding my bus systems. It's only the two DC house system voltages that puzzle me. As I said, the 120v AC is already grounded to the chassis. Should I do the same with 12v and 24v DC house systems? I would have routinely done so until some of the contributions to my charging a 24v system from a 12v source thread seemed to suggest that this was not a good idea.

[Iceni John]

In DC circuits, the electricity is always the same polarity, which means that in a two-wire circuit, one "wire", or side of the circuit, is always negative, and the negative side is always the one that sends the electricity.

Innocent question from an electrical far-from-expert (me):  isn't Positive the side that sends the power out, and Negative is the return path for that power after it has been "used".   Hence, "Negative Ground" in vehicles.   Help, I'm confused!

I'm going to start my conversion's electrical systems soon, so I'm all ears and open to all suggestions.

Thanks, John

[luvrbus]

I saw a 4104 GM burn the guy change most of + ground stuff but forgot a few and it let the smoke out in a hurry when he connected the 2-8D batteries so to me looks like DC power can come from either depending on which is grounded