Q's about Back-feeding Electricity from Generator

[Bderick67]

By definition the "neutral" in a alternating current system is the grounded conductor. The "ground" is known as the grounding conductor.

Two most common services(United States) are 480v 3phase, mainly commercial, and 220v single phase for residential. A 480v system has 3 277v legs, whereas the 220v system is made of 2 120v legs. Legs are also often reffered to as phases.

In order to use a single 277v or 120v leg of either system, a path to ground is needed. This path to ground creates a difference of potiental, this is the neutral(grounded) conductor. The neutral is derived at the service, at this point the neutral has to be bonded to the grounding system which should include a ground rod and cold water for residental, the system can be required to be a little more complex for commercial 480v systems.

So in residental panels you should see the neutral bonded to the ground, unless the panel is a sub panel. A subpanel would be fed out of the main panel with a seperate neutral conductor and should be kept isolated within the sub panel.

In commercial 480/277v systems transformers are used to create 208/110v power for general use. In this the neutral is derived at the transformer by bonding the neutral to the building steel and the cold water system, which are equipment grounding systems.

If you were to isolate the neutral in your residents and still run power to everything you will be subjecting all your electrical devises to 220v. So you must have the neutral bonded to ground. As a note though in these panels you will see the neutral bar isolated.

Hope this clears up some confusion.

 

[Jgray152]

I didn't catch this right off

Both neutral and ground are wired to the same place in the panel but are same.

I said

Both neutral and ground are wired to the same place in the panel but are NOT USED the same.

They are wired to the same place but their purposes are different.

 

[johnptc]

By definition the "neutral" in a alternating current system is the grounded conductor. The "ground" is known as the grounding conductor.

.

now i am confused, if the neutral wire was the same as ground you would not need a ground

the way i learned it:

the neutral wire carries current when a 110 volt device is operating the same current carried by one of the two hots. it is not at ground potential except at the main panel and only if the power company set it up that way.

the ground should only carry current in an emergency as to prevent electrical shock and a meter from neutral to the ground wire can often read a difference.

i believe in most systems the neutral is either the center tap on a wye transformer or a center tap from two transformers set up to give a 3 phase delta configuration.

where i am we have 240 volt three phase plus a neutral and a ground, one of the three hot legs is called a stinger and i believe its 177 volts to the neutral.

 

[Jgray152]

The Neutral wire carries the unbalanced load of the circuit. Neutral is nominal 0v while your HOT wires are 120v. There is a GROUND throughout the power grid. Ever see bare wires running down the side of a telephone pole? The electrical company uses the entire earth as a ground (0v) to complete a circuit.

The Neutral only carries current when power from HOT is flowing through a device. Then that neutral wire has current flowing through it and into ground. The amount of current through the neutral is less than the potential current through the hot wire when a device is in between the two. Its like dealing with high and low pressures. Take wind for example, a high pressure will not move unless there is a lower pressure near by. HOT power will not move until neutral is connected to it one way or another.

Like I said, Ground and Neutral are connected to the same area in the panel but are NOT USED the same.

Bare copper is used for a fault to ground circuit and a neutral is an open road for power to flow through when coming from HOT.

http://science.howstuffworks.com/power2.htm

 

[johnptc]

The Neutral only carries current when power from HOT is flowing through a device. Then that nuetral wire has current flowing through it and into ground. The amount of currect through the neutral is less than the potential current through the hot wire when a device is inbetween the two. Its like dealing with high and low pressures. Take wind for example, a high pressure will not move unless there is a lower pressure near by. HOT power will not move untill nuetral is connected to it one way or another.

Like I said, Ground and Neutral are connected to the same area in the panel but are NOT USED the same.

Bare copper is used for a fault to ground circuit and a neutral is an open road for power to flow through when coming from HOT.

why do you say the neutral carries the current to ground rather than back to the transformer ??

It can be stated that Neutral can be grounded, but Ground is not neutral.

( AB website)

 

[Jgray152]

why do you say the neutral carries the current to ground rather than back to the transformer ??

Because in the end of its travel, it leads directly to the earths crust

Your confusing the "terms" with the actual physical wiring.

Ground and Neutral are "Terms" in defining which to use where.

I am trying to not use the word "ground" as defining the bare copper wire in a household since its only a "term". The Neutral wire is a term used to define the difference between HOT (+120v) and Neutral (0v) when in fact, both white and bare copper wire are both (0v).

 

[Bderick67]

now i am confused, if the neutral wire was the same as ground you would not need a ground

The main prupose of a neutral(grounded) conductor is to complete the AC circut. It does this by eventually going to ground. For safety and efficency it is necessary that this bonding point is at the service of the residence or the transformer of a commercail building.

The main purpose of a ground(grounding) conductor is to ground any metal parts of equipment that may become incidently energized. Without this if the metal parts were to become energized a person could become the path to ground. With it if all is working properly, the circut breaker trips.

If you doubt that the neutral is grounded, take a continuity tester an measure between the neutral and ground on an power outlet

 

[four-ever]

Ok so to make sure i understand this correctly , i drew up a little sketch

have a look and see if its ok

Thanks

 

[Jgray152]

Looks good to me. Just make sure you identify what type of plug is on the Generator so you get the correct one. LT14-20 or LT14-30.

If you are making a cable with 2 male ends, make sure you get two LT14-## male ends and one LT14-## Female outlet for the side of the building (if you are going this route). It will make your life easier instead of mix matching plugs.

 

[johnptc]

here is a 50 amp four wire three pole 125/250V male-male twist lock jumper.

It is used to jump from the main three phase service with generator and automatic transfer switch to the house panel.

user beware