3000W Chinese Gensets Info.
professor95 wrote: EDIT ADDED 45/5/2013- When this thread started in March of 2005, I never expected to see it survive this long or amass the quantity of information that has been shared here. In...
Forum Discussion
Another shot at explaining neutrals, grounds, grounding, floating neutrals, etc. as related to portable 120 volt gensets and RVs......
The neutral in a 120 volt circuit that goes to earth ground in a residence is derived from a center tapped 240 VAC feed.
Out on a pole is a step down transformer. The step down transformer is fed by two higher voltage wires.
Inside your home is a service entrance panel (SEP). The panel is fed by a two wire, 240 VAC pair of wires. There is a third wire for grounding which also serves as the 120 VAC neutral.
When the first early power distribution systems came about, they used direct current. Problem was it was difficult to change voltages in a DC system since transformers will not work with DC. Long runs of wire with low voltages and high current caused a lot of cable heating and voltage drop.
On the other hand, alternating current can easily convert voltages up or down with transformers. The higher the voltage, the lower the current for the same power (in watts). Example: 1,200 volts x 20 amps is equal to 24,000 watts of power. 120 volts x 200 amps is also equal to 24,000 watts of power. Since the current (amperage) is lower on the HV line, voltage drop due to resistance is significantly reduced. By feeding 1,200 volts into a transformer with (approximately) a ratio of 10 turns of wire on the input to one turn on the output will convert the voltage from 1,200 to 120. You have a transformer outside your house that accomplishes this voltage reduction. This is a schematic of that transformer.
Back to the neutral....
The wire (the center tap) in the middle of the output side of the transformer is truly neutral on a 240 VAC system. In effect, it floats unless there is a complete circuit between the center tap and one of the other legs. To reduce the chance of electrocution in a derived power system (where 120 comes from a center tapped transformer supplying 240 VAC) and to provide a common reference point for the phase differential in a derived system, the center tap was tied to earth ground and called the "common" or "neutral" conductor. Please note the word conductor rather than just wire. This system still prevails.
Quick subject change to a generator, or actually an alternator.
While it is not technically a transformer, it operates on a similar principle. A rotating coil of wire wrapped on an iron core is turned inside a magnetic field (it can also be the other way around). The magnetic field, which has both positive and negative poles (north and south) causes a voltage and current to be induced in the coil of wire. The result is alternating current. The process is shown here. Like the transformer, there is no physical connection between the rotating armature and magnetic field. Thus, the power from the alternator is said to be isolated from any earth ground unless we intentionally make that connection.
If you are still with me, let's change direction one more time and look at something else.
Do you have a 120 volt lamp socket near by? You know, one that you screw a light bulb into. Look at the socket. There is a large, threaded outer metal shell and down in the bottom of the socket is a small tab. Which of these parts are you more likely to come in contact with when changing a light bulb? If you said the outer shell, you get the prize.
Now take a look at the plug on the end of the lamp's power cord. Unless someone has incorrectly changed the cord or plug, you will note one of the two blades is wider at the end. In fact, this plug (called a polarized plug) will only go into an outlet one way. On the wall outlet you will note one slot is longer (wider?) than the other. The longest slot is the one that connects to the neutral wire in a 120 VAC system. The smaller slot is the ungrounded conductor most folks refer to as "hot".
Another question. Which blade on the lamp cord do you believe is connected to the wire that goes to the lamp shell?
If you guessed the wide one, or neutral wire, you get another prize.
Yes, I have still another question.
What do you think would happen if the lamp were plugged into an outlet where the neutral wire was reversed at some point in the circuit and you managed to touch the large metal shell while replacing the light bulb while you were grounded?
If you responded with something like, "I would become a conductor by completing a circuit and I would get the wee wee knocked out of me!", you get even another prize.
In North America we typically use a third non-current carrying wire on 120 volt circuits specifically for shock protection. This wire is called ground or the grounding wire. This graphic shows what could happen if we had a fault in an appliance and there was no grounding wire. Since a RV is considered an appliance (electrically), the same thing could happen.
Ironically, if we were on the other side of the pond, all of this discussion would not occur. Most of the world uses "straight 240", which has no derived neutral.
To tie things, up let's summarize.
This forum addresses specifically a portable genset (alternator). Typically they provide 3,000 watts of power at 120 volts and are plugged into a camper with either a 20 amp or 30 amp 120 volt supply cord.
While we have had some discussion on gensets used for home back-up power as well as units supplying higher voltages and wattages, the focus is on the little Chinese built gensets.
If you want to know more about 50 amp RV connections using 240/120 connections and home back-up power systems, we need to start a new thread.
Since there is no way to assure (or insure) where a portable genset will be placed when used with an RV,
and
the 120 volt power system in a portable genset is isolated from ground (unless wired otherwise),
and
with the exception of the non-current carrying grounding wire, RVs DO NOT have a physical internal connection to ground the vehicle body, frame or anything an individual may easily come in contact with, it is much safer to let the wiring in a RV that is normally associated with neutral in a home power system to "float" with no connection to earth ground.
Look at the graphic of the residental SEP again. Note the neutral or ground bar in the upper right. The SEP in an RV does NOT have the ground(ing) wires and the neutral wires connected to the same buss bar like most residental systems. They are separate of each other and make no common contact in the RV. They are ONLY joined by the external cables from the selected power source when it is safe and appropriate to do so.
The non-current carrying grounding wire should, whenever possible, be physically attached to earth ground both at the genset and RV. The neutral should not be connected to the genset frame or the frame of the RV.
Whew!! I didn't plan on writing this much when I started.
The neutral in a 120 volt circuit that goes to earth ground in a residence is derived from a center tapped 240 VAC feed.
Out on a pole is a step down transformer. The step down transformer is fed by two higher voltage wires.
Inside your home is a service entrance panel (SEP). The panel is fed by a two wire, 240 VAC pair of wires. There is a third wire for grounding which also serves as the 120 VAC neutral.
When the first early power distribution systems came about, they used direct current. Problem was it was difficult to change voltages in a DC system since transformers will not work with DC. Long runs of wire with low voltages and high current caused a lot of cable heating and voltage drop.
On the other hand, alternating current can easily convert voltages up or down with transformers. The higher the voltage, the lower the current for the same power (in watts). Example: 1,200 volts x 20 amps is equal to 24,000 watts of power. 120 volts x 200 amps is also equal to 24,000 watts of power. Since the current (amperage) is lower on the HV line, voltage drop due to resistance is significantly reduced. By feeding 1,200 volts into a transformer with (approximately) a ratio of 10 turns of wire on the input to one turn on the output will convert the voltage from 1,200 to 120. You have a transformer outside your house that accomplishes this voltage reduction. This is a schematic of that transformer.
Back to the neutral....
The wire (the center tap) in the middle of the output side of the transformer is truly neutral on a 240 VAC system. In effect, it floats unless there is a complete circuit between the center tap and one of the other legs. To reduce the chance of electrocution in a derived power system (where 120 comes from a center tapped transformer supplying 240 VAC) and to provide a common reference point for the phase differential in a derived system, the center tap was tied to earth ground and called the "common" or "neutral" conductor. Please note the word conductor rather than just wire. This system still prevails.
Quick subject change to a generator, or actually an alternator.
While it is not technically a transformer, it operates on a similar principle. A rotating coil of wire wrapped on an iron core is turned inside a magnetic field (it can also be the other way around). The magnetic field, which has both positive and negative poles (north and south) causes a voltage and current to be induced in the coil of wire. The result is alternating current. The process is shown here. Like the transformer, there is no physical connection between the rotating armature and magnetic field. Thus, the power from the alternator is said to be isolated from any earth ground unless we intentionally make that connection.
If you are still with me, let's change direction one more time and look at something else.
Do you have a 120 volt lamp socket near by? You know, one that you screw a light bulb into. Look at the socket. There is a large, threaded outer metal shell and down in the bottom of the socket is a small tab. Which of these parts are you more likely to come in contact with when changing a light bulb? If you said the outer shell, you get the prize.
Now take a look at the plug on the end of the lamp's power cord. Unless someone has incorrectly changed the cord or plug, you will note one of the two blades is wider at the end. In fact, this plug (called a polarized plug) will only go into an outlet one way. On the wall outlet you will note one slot is longer (wider?) than the other. The longest slot is the one that connects to the neutral wire in a 120 VAC system. The smaller slot is the ungrounded conductor most folks refer to as "hot".
Another question. Which blade on the lamp cord do you believe is connected to the wire that goes to the lamp shell?
If you guessed the wide one, or neutral wire, you get another prize.
Yes, I have still another question.
What do you think would happen if the lamp were plugged into an outlet where the neutral wire was reversed at some point in the circuit and you managed to touch the large metal shell while replacing the light bulb while you were grounded?
If you responded with something like, "I would become a conductor by completing a circuit and I would get the wee wee knocked out of me!", you get even another prize.
In North America we typically use a third non-current carrying wire on 120 volt circuits specifically for shock protection. This wire is called ground or the grounding wire. This graphic shows what could happen if we had a fault in an appliance and there was no grounding wire. Since a RV is considered an appliance (electrically), the same thing could happen.
Ironically, if we were on the other side of the pond, all of this discussion would not occur. Most of the world uses "straight 240", which has no derived neutral.
To tie things, up let's summarize.
This forum addresses specifically a portable genset (alternator). Typically they provide 3,000 watts of power at 120 volts and are plugged into a camper with either a 20 amp or 30 amp 120 volt supply cord.
While we have had some discussion on gensets used for home back-up power as well as units supplying higher voltages and wattages, the focus is on the little Chinese built gensets.
If you want to know more about 50 amp RV connections using 240/120 connections and home back-up power systems, we need to start a new thread.
Since there is no way to assure (or insure) where a portable genset will be placed when used with an RV,
and
the 120 volt power system in a portable genset is isolated from ground (unless wired otherwise),
and
with the exception of the non-current carrying grounding wire, RVs DO NOT have a physical internal connection to ground the vehicle body, frame or anything an individual may easily come in contact with, it is much safer to let the wiring in a RV that is normally associated with neutral in a home power system to "float" with no connection to earth ground.
Look at the graphic of the residental SEP again. Note the neutral or ground bar in the upper right. The SEP in an RV does NOT have the ground(ing) wires and the neutral wires connected to the same buss bar like most residental systems. They are separate of each other and make no common contact in the RV. They are ONLY joined by the external cables from the selected power source when it is safe and appropriate to do so.
The non-current carrying grounding wire should, whenever possible, be physically attached to earth ground both at the genset and RV. The neutral should not be connected to the genset frame or the frame of the RV.
Whew!! I didn't plan on writing this much when I started.
