3000W Chinese Gensets Info.

Professor,

Can you explain why "grounding is not an issue" when running the gen in the back of a pickup? Is that method theoretically safer than running the gen while it's sitting on the ground? I am thinking back to much earlier posts about grounding rods, open circuits, surge protectors, etc.

Thanks

No, the warnings in those earlier postings still apply. What I should have said was, “Grounding is no more of an issue with the generator sitting in the back of the pickup than any other location.”

Sorry about that omission….. But, you have given me an opportunity to break into another lengthy electricity/RV/generator safety discussion.

You most likely completely understand everything I am about to write. But, let's walk through the system slowly in case there is a reader who might not fully understand.

Conventional 120 VAC power systems, like the one that supplies your house and camper when hooked up in a RV park, have three service conductors. One is a dedicated neutral that is at true ground potential.

Another is the so called hot wire.

The third wire is the grounding conductor. The grounding conductor runs parallel to the neutral conductor and also physically connects to earth ground.

The grounding conductor is not supposed to carry any current unless there is a fault. An example of a fault would be if the hot conductor happened to come in contact with a current carrying material (metal). Without the grounding conductor, which is required to be bonded to current carrying materials easily accessed, there would be a 120 volt potential waiting for you to touch it. When someone does touch it, the circuit is complete and current will flow causing a pretty harsh shock. Now, if the grounding conductor is there, power from such a fault will flow safely to ground and the overload device should trip, or cut the circuit off.

Your camper is very similar, but it is not physically bonded to ground. There is no physical connection between the neutral wire and the grounding wire in the camper’s wiring as you would find in your home's service panel. The two are separate and only connected externally when we plug into “shore power”. In reality, your camper is an appliance that plugs into an electrical supply - just like a blender, TV or toaster oven in your home. The biggest difference is that this is an appliance you can live inside of - thus, your potential exposure to electrical faults is dramatically increased. Again, the only connection the camper has to ground is through the power supply conductors. So, if a fault occurs in the camper electrical system or an appliance in the camper and there is no path to earth ground for the grounding conductor at the supply source, it can make the entire metal framework on a camper hot. An example of the consequences of such a fault might be when an unsuspecting person places one foot on the metal step or grabs the metal door latch and has another foot on earth ground. In this situation we have a complete circuit to ground that can cause a painful, in not fatal, shock (if there is a fault). This happened to me a number of years back while camping at the beach. Fortunately, I was not hurt. But it taught me an important lesson!

Unfortunately, we usually have no control over the condition of the power supply to the camper we encounter in campgrounds. We simply "trust" that it is wired correctly and is safe.

OK - now that we have established what a normal power supply to a camper is and how a fault in that service can hurt you, let's take a look at a generator as a power source.

The key word here is source. In order to make electricity, a gas engine must spin a magnet inside a coil of wire (or a coil of wire inside a magnet). The coil of wire has two conductors. Either one can be called “neutral” and the other “hot”. This is because a generator is not naturally connected to an earth ground. At this point it makes no difference what-is-what in the two wires supplying power to the camper since we do not have a true ground connected. Such an arrangement is said to be isolated from ground. If true isolation does exist, we can stick our finger in either slot of a generator outlet (one at a time, not together), stand on wet dirt with bare feet, and we would not receive a shock. It is sort of like a bird sitting on a wire. Neither one of these two generator supply wires is connected to the generator frame. The frame is said to be electrically “cold”.

The third wire running from the camper - the grounding wire - should end up bonded to the generator frame. But, at this point it is also isolated from true ground. If every thing from the camper’s power cord plug back into the circuit breaker box and to the outlets is OK, there will be no problem feeding from this isolated power source. But, if a fault occurs, where is it going to go?

If you guessed that the fault would make everything in the camper that was originally bonded to the expected grounding conductor, including the camper frame and the generator frame, directly connected to one of the wires from the generator, you get a 100 points.

Now for the second question. Is the above fault dangerous?

The answer to that question is sort of like asking which chamber has the bullet in Russian roulette, or climbing the face of a rock cliff without a safety line. Hopefully, you will never know that there is a potential time bomb ticking away. But, without the expected safety line to ground you have set yourself up to get quite a jolt if you should contact the conductive parts of the camper and the other side of the generator line. This issue is why you will find a grounding connection on the frame of a generator - it is suppose to physically be connected to earth ground.

You may be scratching your head and thinking, “But it would require two faults to get shocked.” This is true, and the odds of having both faults at the same time may seem pretty small. Still, the risk is there since you do not have a true ground from the generator to the camper, or from the camper's frame directly to ground.

Soooooo…… what do you do when powering your camper from a generator? (Actually, the following is desirable for any power source.)

Number one is to be absolutely sure there is no connection between neutral and the grounding conductor in your camper. You do this by using an “ohm meter”. On a camper with a 30 amp 120 volt service, unplug the camper from the power source and hold the camper’s plug so you are looking at the prongs. The “U” shaped grounding conductor should be on the top. In this position, the blade on your right would connect to the power source’s neutral and the one on your left would connect to the hot wire in the power source. Set the ohm meter to the lowest resistance scale (usually 200 ohms). Now touch one probe from the ohm meter to the “U” shaped blade and the other to the blade on your right. You should NOT get a reading at all. No reading means that there is no connection between neutral and the grounding buss anywhere in the camper. Again, this is GOOD. You should also NOT get a reading when checking between the left blade and the “U” blade. You WILL get a reading between the left and right blades (REMEMBER, you are NOT plugged into a power source when you make this test).

If you get a reading indicating a connection between either one of the flat blades and the “U” blade, you have a fault in your camper’s electrical system that should be corrected. This type of fault can go unnoticed because your electrical system seems to work fine.

Number two is to create a true ground between the camper’s frame and the generator’s frame. While a 4 to 8 foot copper-clad rod driven into the ground is desirable, it just is not pratical at a campsite. Still, you can improve your “safety odds” by using one automotive jumper cable with good heavy alligator clamps on both ends. Clamp one end to your camper frame. The connection point should be free of paint and rust. You can also clamp it to the negative terminal on your camper’s battery since it is bonded to the camper’s frame. Clamp the other end to a metal pipe for a water faucet or any metal object driven into the ground. If you don’t have one of these at your campsite, drive a 12” or longer unpainted or galvanized metal tent stake (or pipe)into the ground, the longer the better. Hopefully, there will be some moisture in the dirt to improve conductivity. For those thinking ahead of me - yes, the metal foot on your camper's tongue jack contacting ground is better than nothing. But this is surface contact and the conductivity can be "iffy".

Some may think all of this is ridiculous. Perhaps it is “over kill”. Still, it is better to be informed of the risks involved and to be safe rather than sorry. Personally, I always try to ground my camper’s frame when I set up – even when I am not using a generator.