JWelectric
Electrical Contractor/Instructor
The use of earth return path on utility power is a dying thing simply due to the resistance of earth.
Earth return is never used on the house side of a transformer. Ohm’s law can be used to figure out a lot of the reasons why. The NEC mandates that we can use one rod for an electrode only if that one rod has 25 ohms or less of resistance to earth. Using this 25 ohms as the resistance and Ohm’s Law of voltage equals the current times the resistance we can see that 120 volts divided by 25 ohms of resistance will equate to only 4.8 amps of current flow.
One might ask why I didn’t use 240 volts instead of 120 volts and the answer lies in what would happen should one touch two 120 volt conductors together. It would be impossible to connect 240 volts to a ground rod from a residential panel but even if one could it would equate to only 9.6 amps of current.
Most not all residential transformers across America is fed by 7200 volts and at this voltage only 288 amps of current could flow.
The wires on the highest part of the pole holding the transformer are the high voltage lines. There will in most cases be one, two, or three up top and one a little lower down the pole. The one that is lowest down is the utility neutral.
Looking up at the transformer we will be able to see that one of the higher wires is connected to a fuse then from the fuse to the transformer. This is the supply voltage for the primary of the transformer.
In most cases there will be three wires coming from the side of the can that supplies our homes, this is the secondary of the transformer.
Notice that the bare conductor is connected to the lug in the center, the house neutral or the center tap of the secondary. From this center tap we can also see a #6 hard drawn conductor that runs down the side to the utility pole and disappears into earth. This tap may not be right at the center tap lug but it will be on that neutral conductor somewhere up there. Now pay close attention to that lower conductor on the utility side of the transformer. Can you see that that bottom conductor is also connected to that #6 that is coming down the side of the pole. Yes the high voltage neutral, the low voltage neutral and the grounding electrode are tied together on the top of that pole.
A lightning event is an event between earth and a cloud. The utility wires are hanging somewhere in the area between the cloud and earth. Should the path of the lightning arc include those wires hanging up there in the air then giving that lightning an easy path to find earth is the sole purpose of the earth connection by both the utility and the electrician. The earth connection by either the utility or the electrician plays no role in the use of current in our homes. What makes our homes safe is the bonding of the grounding conductor to the neutral at our service equipment which give a low impedance path for fault current to find its way back to the center tap of the transformer.
The ORIGINAL POSTER has a problem with this center tap conductor. Instead of having two parallel 120 volt paths for current to flow he has one 240 volt series path for current to flow.
Using the air conditioner disconnect we can wire two keyless in series from one terminal to the first keyless then to the second keyless back to the other terminal of the AC disconnect. We have a 240 volt series circuit with on neutral. Put two 100 watt bulbs in those two keyless and turn on the disconnect. Both lights come on and will have a voltage of 120 volts at each keyless, no neutral.
Now change on of the 100 watt bulbs with a 40 watt bulb and turn on the disconnect. The 40 watt bulb will be burning brighter than the 100 watt bulb and the voltages on the two bulbs will be greatly different. This is what is happening with the ORIGINAL POSTERER.
Earth return is never used on the house side of a transformer. Ohm’s law can be used to figure out a lot of the reasons why. The NEC mandates that we can use one rod for an electrode only if that one rod has 25 ohms or less of resistance to earth. Using this 25 ohms as the resistance and Ohm’s Law of voltage equals the current times the resistance we can see that 120 volts divided by 25 ohms of resistance will equate to only 4.8 amps of current flow.
One might ask why I didn’t use 240 volts instead of 120 volts and the answer lies in what would happen should one touch two 120 volt conductors together. It would be impossible to connect 240 volts to a ground rod from a residential panel but even if one could it would equate to only 9.6 amps of current.
Most not all residential transformers across America is fed by 7200 volts and at this voltage only 288 amps of current could flow.
The wires on the highest part of the pole holding the transformer are the high voltage lines. There will in most cases be one, two, or three up top and one a little lower down the pole. The one that is lowest down is the utility neutral.
Looking up at the transformer we will be able to see that one of the higher wires is connected to a fuse then from the fuse to the transformer. This is the supply voltage for the primary of the transformer.
In most cases there will be three wires coming from the side of the can that supplies our homes, this is the secondary of the transformer.
Notice that the bare conductor is connected to the lug in the center, the house neutral or the center tap of the secondary. From this center tap we can also see a #6 hard drawn conductor that runs down the side to the utility pole and disappears into earth. This tap may not be right at the center tap lug but it will be on that neutral conductor somewhere up there. Now pay close attention to that lower conductor on the utility side of the transformer. Can you see that that bottom conductor is also connected to that #6 that is coming down the side of the pole. Yes the high voltage neutral, the low voltage neutral and the grounding electrode are tied together on the top of that pole.
A lightning event is an event between earth and a cloud. The utility wires are hanging somewhere in the area between the cloud and earth. Should the path of the lightning arc include those wires hanging up there in the air then giving that lightning an easy path to find earth is the sole purpose of the earth connection by both the utility and the electrician. The earth connection by either the utility or the electrician plays no role in the use of current in our homes. What makes our homes safe is the bonding of the grounding conductor to the neutral at our service equipment which give a low impedance path for fault current to find its way back to the center tap of the transformer.
The ORIGINAL POSTER has a problem with this center tap conductor. Instead of having two parallel 120 volt paths for current to flow he has one 240 volt series path for current to flow.
Using the air conditioner disconnect we can wire two keyless in series from one terminal to the first keyless then to the second keyless back to the other terminal of the AC disconnect. We have a 240 volt series circuit with on neutral. Put two 100 watt bulbs in those two keyless and turn on the disconnect. Both lights come on and will have a voltage of 120 volts at each keyless, no neutral.
Now change on of the 100 watt bulbs with a 40 watt bulb and turn on the disconnect. The 40 watt bulb will be burning brighter than the 100 watt bulb and the voltages on the two bulbs will be greatly different. This is what is happening with the ORIGINAL POSTERER.