Re: Connection of Neutral Conductor

Hi All,

> > Could somebody tell me that the connection of neutral cable after the > isolation transformer? > is it just connected to a functional earth terminal or connected to primary > side supply neutral cable? > > thanks > > Matthew

Define after the transformer? Are you speaking of the next circuit breaker panel. Or are you speaking of in the transformer?

In any case it would be doubtful that it would be connected to the supply side neutral. I do not use 5 wire feeds to isolation transformers, just 4 wire. ( as long as we are talking 3 phase ) The neutral in the isolation transformer should be grounded and that is where the grounded conductor is established for the new feed.

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|> Could somebody tell me that the connection of neutral cable after the |> isolation transformer? |> is it just connected to a functional earth terminal or connected to | primary |> side supply neutral cable? |>

|> thanks |>

|> Matthew | | Define after the transformer? Are you speaking of the next circuit breaker | panel. Or are you speaking of in the transformer? | | In any case it would be doubtful that it would be connected to the supply | side neutral. I do not use 5 wire feeds to isolation transformers, just 4 | wire. ( as long as we are talking 3 phase ) | The neutral in the isolation transformer should be grounded and that is | where the grounded conductor is established for the new feed.

This depends on what kind of transformers are being discussed.

Power distribution MV->LV transformers typically do have secondary neutral connected to primary neutral. This is a major common cause of stray voltage problems that can affect farm animals and cause other strange problems. As long as the primary neutral return path is good, virtually all current returns that way. Break the neutral wire and you now have a ground return. Then every grounding electrode becomes one of many parallel ground paths back to the source substation. Some of those are the distribution grounding electrodes. But with the secondary neutral connected to the primary neutral, the secondary grounding electrodes are also part of the parallel ground path.

IMHO, what the power companies do is a bad thing.

Generally, I believe isolation transformers would have the neutral wire of the secondary connected to the EGC (grounding wire) of the primary, as well as the earthing electrode. The primary winding would then be connected as a 2-wire load to the supply, so if there is a neutral being provided in the supply, it would be left unconnected.

This all ends up creating a singlular grounding network. This is both good and bad. Earth currents can exist, especially when power distribution leakage or lightning strikes are involved. The grounding network provides the low impedance path to avoid applying voltages to high impedance or low current capacity alternative paths (phone wires, people, etc). But if this grounding network gets very large (on the scale of a farm property), it can easily get overloaded by various ground currents passing over very long distances.

The thing is, if you ever did need to isolate the grounding network from one location to another because of residual currents, you sure can't put any other kind of metal (power feeder, telephone, etc) between the isolated segments. If you have to run metal between 2 distant points, also run a grounding wire as well, and have it well grounded with 2 or more electrodes at each end.

The secondary neutral of any isolation transformer creating a separately derived system that is grounded, would then be connected to that grounding network. Ungrounded systems, such as low voltage lighting, would have sufficiently short runs that the lack of ground bonding would not matter.

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