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PTO Generators Observations
Denwood, there is no transformer connection to the neutral, in fact the neutral is bridged past the transformer.
A part of properly installing transfer switch is making sure that the feed and the load are balanced, ie, an equal amount of current on each leg of the 220V. feed from the genset.
A typical house service panel is not wired with a balanced load in mind, usually it just wired up according to which wire the electrician happened to grab next. If you were to just feed pull down the mains, and backfeed a 220V. circuit like the dryer plug, you could have a balanced load, or you could have the entire load on one leg. Thats the problem.
However, many, many people merely re-arrange the load at the service panel to accomplish a balanced load and then backfeed it from a generator. Several people in my area do this, some even use a SP/ST switch box to disconnect the neutral from the service connection which at least makes the setup a little safer.
Best of luck.
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PTO Generators Observations
Is this the consensus: The opening of the main switch at the main curcuit breaker box (L1 and L2) and subsequent connection to a 220V outlet of a male - male plug hooked up to a generator poses the same threat of back feeding the utility co (on the neutral line only) as a properly installed transfer switch? In other words no threat at all? Now if the main switch is closed while the generator is still plugged in the the 220V dryer plug, thats a different story all together. My take home message appears to be as follows: I can use the 220V male male plug hookup IF the main switch is OPEN and not back feed the utility co. Of course I assume other electrical risks by doing so but these do not include the risk of back feeding the grid and harming a lineman?
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I think the source of most of the confusion around this subject is that most people, including electricians, feel there is no electricity in the neutral wire since it is grounded, in fact nothing could be farther from the truth.
First of all let me say, that in ANY circumstance where the neutral is still connected to the utility company's grid, the potential risk exists, whether or not the mains are open.
Maybe if I give the 'big picture' it will make it clearer. The phenomenon is called stray Voltage.
The electrical utility company causes the problem of stray voltage when they connect the neutral on the primary side of the transformer to the neutral on the secondary winding of the transformer. Why do they do this? Because this is the standard connection specified in the National Electrical Safety Code (NESC) which governs the utilities. The National Electrical Code (NEC), which covers all wiring, requires that the secondary neutral be hard wired to the buildings water system, structure and electrical ground rod.
Therefore, the voltage level of the building structure and water system is elevated to the voltage level of the primary neutral conductor on the utilities electrical distribution network. This voltage can be significant and is the primary cause of Stray Voltage.
The origin of the stray voltage problem lies in the fact that Electrical Utilities do not make a distinction between the function of the Neutral (the grounded conductor) and a Ground. The Electrical Utilities in conjunction with the IEEE has developed the National Electrical Safety Code (NESC). This code requires them to ground the primary neutral conductor at least four times per mile that they distribute electricity. Electrically, the ground rods are actually resistors ranging from 10 to several hundred ohms. The actual resistance depends upon the moisture content and conductivity of the soil. In other words, the utilities are forced to deliberately design their systems to use the earth as a secondary neutral conductor.
The voltage on the primary neutral increases as the distance from the substation increases. Each ground rod tends to reduce the voltage by diverting some of the neutral current into the earth. The current splits between the neutral wire and ground rod in accordance with ohms law. The primary neutral voltage at the end of the distribution line can be 20 volts or more depending on the combined load on the distribution line and the conductivity of the earth. The NESC requires the Electrical Utility to connect the primary neutral to the secondary neutral on each transformer serving a customer. The National Electrical Code (NEC) which governs all wiring requires that the secondary neutral be grounded to the water pipes for every building being served. Effectively the SAFETY CODES require us to hard wire our water system directly to the neutral on the primary distribution side of the transformer.
However, when you connect a generator and put power to the house's wiring, the 220V. gets split, there is 110V. between each of L1 & L2 and the neutral, and 220V. between L1 & L2 directly, but if the conditions are right, or maybe wrong is a better word, there is voltage potential in the neutral itself. If that neutral, which is a continuous conductor all the way through the grid, gets connected by a person's body, like a linesman who thinks he's working on a 'dead' circuit, or telephone wires, or cable TV wires and it becomes a better conductor, guess what? Somebody gets a shock. In a worst case scenario it can kill.
The bottom line is anytime there is potential in the neutral beyond your house it's a bad thing.
Best of luck.
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Murf, excellent reply, which I agree with.
A couple of additional points, some areas permit PVC water supply lines from the house to the main, thereby reducing or in effect eliminating the benefit of the ground to the water line connection.
The terms stray voltage and ground potential rise both refer to current flow in the neutral/earth ground system. The purpose of the bonding is to prevent a difference of potential, which can also be called step potential (touch potential). This is defined as the potential difference between two points on the earth. If this voltage (potential difference) is large enough it can kill.
If anyone is interested there is an excellent book called "Ground Currents and Stray voltage" written by O.C. Seevers. Published by the Fairmount Press in 1989. Mr Seevers was a long time engineer with Kentucky Utilities in Lexington, Kentucky.
An additional reference source is the IEEE green book.
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I have to ask the question. If the transfer switches only disconnect as an industry standard how do you disconnect the neutral? Do you need to?
As I read all of this I am more confused about the neutral.
I have 2 10' rods 6' apart with 20'of #6 bare copper 12" down laid out in a grid for the utility and a seperate 10' rod for the gen. How in the world could I possibly back feed a neutral? There is also a ground rod connected at the pole.
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Is there a transfer switch available that lets you switch the main power before the breaker panel to generator power? Why do all these transfer switches make you select which circuits you want to run when you install them? I want to have ALL circuits available to me and just shut off the circuits in the main panel that I don't want to run. And I want the setup to be simple.
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By the way, at the risk of causing a riot after having read this thread, I once had a licensed electrician set up a backfeed for my house where I could plug in a portable generator. A relative of mine is a professional engineer who has built a power plant and puts up commercial buildings. He backfeeds his house. Convincing people to buy a transfer switch for $500 when professionals around us simply "turn off the main" is difficult.
Also - it is true that transfer switches do just that. They just simply ensure that the main is turned off before the generator input is turned on. You take the risk that you could mentally slip and forget to turn off the main when you avoid purchasing a transfer switch.
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Harvey, if you play the lottery, there may be a chance you would win it too. I am curious, did whoever install your transfer switch, rebalance the poles in your breaker box?
Ncrunch, I believe the switches you have been looking at are the northern hydraulic variety. El cheapo. I think they are designed for people, who have a small generator, not big enough for the whole house, AND AT THE SAME TIME, are not aware enough to be able to resist the temptation to run everything in the house at once. They attempt to idiot proof the generator a little, and succeed in making the house very inconvenient. If you just buy a regular switch and choose the circuits you want, you can have all circuits available, just not all at once with a small generator.
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Denwood - yes I think that I might have seen the more expensive switches. Probably you have to call the electric company because you would want the power shut off to the whole house before installing such a switch before the box. And that triggers a visit from your local electric inspector.
The power company will rent you a transfer switch for your whole house (like $5-10 a month). But they will not let you purchase it. I have seen my PE relative once handle handle the live wire coming in to the house. I would never attempt that.
I used to run off a 4KW generator as a backup for years. I purchased an 18HP 10KW generator last summer from Northern tools. I replaced my line into the house with #6 wire and tested it out. It ran great. Ran whole house. Of course I left off pool pump, hot tub, and central air.
My wife is crazy and actually would like to be able to run everything when the power goes out - but costs quickly spiral up when you get to 30KW backup setups.
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I have never heard of renting a switch, but I am not from NY. Here a good switch ran around $200-250 several years back, but you need some extra stuff to install. Any licensed electrician can do the job. To shut off the house, you just pull the meter, no electric company needed, here anyway. The inspector you probably do need. At the time, I asked the stupid question, "If I only have a 50 amp generator, why do I have to buy a 200 amp transfer switch?" DUH, if I had thought for a moment. You have to have a switch big enough to handle the amp service you have from the power company, not the gen set, which is where those cheap northern partial switches save a little money, they don't transfer the whole load.
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