You need to say whether it's a 150 amp service or a 1200 amp service it has to be one or the other.
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A 1/0 copper conductor with an insulation factor of 90 degrees C is rated at 155 amps. There is no ground wire stated for a 150 amp service so the next size up is a 200 amp service. The ground wire for this size is #6 bare AWG.
Without knowing what types of loads that are coming off of the distribution a reduced neutral can not be recommended. The neutral will be the same size as the service conductor which is 1/0.
Wire size for any piece of equipment is based on the equipments load amperage. The higher the amperage that larger the wire size has to be. For motor loads the motor's amperage has to be increased by 25% to size the conductor. Example, a 10 amp motor load current plus 25% equals 12.5 amps. This would boost the wire size from a #14 to a #12 conductor. This additional amperage increasing is also used for transformer conductor sizing.
There is no standard size ground wire for 120 volts. Wire size is determined by the amperage.
Over 800 amp service requires 00 bare copper wire. There is a code change coming for service grounding conductors in the next electrical code book edition.
A big motor needs thick cable, a small motor will only need thin cable. To be specific it's necessary to know the motor voltage and power.
500 mcm
six awg
A conductor used for grounding of the main service should be a single wire. The code book has a table that states the size of ground wire for different service panel amperages.
A 200 amp service panel will require a # 4 bare copper ground wire.
Yes, NEC has an entire chart on grounding.
A 100 amp residential service requires a size #8 copper wire, it should be insulated in green.
For Service Entrance Cable 600 kcmill (Thousands of circular mils).
500 mcm
six awg
250 mcm
500 mcm
A conductor used for grounding of the main service should be a single wire. The code book has a table that states the size of ground wire for different service panel amperages.
A 200 amp service panel will require a # 4 bare copper ground wire.
Yes, NEC has an entire chart on grounding.
200 amp service in chicago uses 3 aught.
For a 200amp service you need number 4 copper
300