Running a portable generator with the street power on.

[nerspellsner]

Most standby generators should be run under load every so often. Most transfer switches do not switch the neutral. Does running a generator connected to a house and the street power on harm anything with the street neutral and the generator neutral connected together at the transfer switch?

 

[iwire]

No, assuming there is a properly wired transfer switch.

With only the neutral of the generator connected to the utility you do not have a complete circuit between the generator and the utility so there is no way for the generator to effect the utility side.

 

[tshea]

HEre's something else to keep in mind...make sure the end of the neutral wire in the transfer switch is pointing up. We don't want the extra electrons to fall out :lol: :lol: :lol:

 

[nerspellsner]

Can the generator be damaged by the voltage from the street neutral? In this situation a Gentran 10 circuit transfer switch is installed. Some loads are powered from the street and some powered from the generator at the same time. There are 2 neutrals from two separate systems connected together with voltage on both of them.

 

[tshea]

No, assuming there is a properly wired transfer switch.

With only the neutral of the generator connected to the utility you do not have a complete circuit between the generator and the utility so there is no way for the generator to effect the utility side.

Here's the answer in bold.

You do not have a complete circuit.

The toggles on the GenTran are on-off-on switches. IF the panel is wired correctly there is NO current flow on the neutral (white wire) from the generator because the generator power circuit to the load is NOT complete.

 

[nerspellsner]

Thanks for the answers. I guess there is no way a generator can be damaged by the street neutral if both the street power and the generator are feeding the panel at the same time. I understand that there is not a completed circuit between the generator and the street. I was unsure about the two neutrals (not the grounded conductor in a two wire circuit) carrying the unbalanced load of 2 separate 240 feeds being connected together and maybe damaging the generator some how.

 

[hardworkingstiff]

Thanks for the answers. I guess there is no way a generator can be damaged by the street neutral if both the street power and the generator are feeding the panel at the same time.

The wording of this sentence makes me wonder if we are having a failure to communicate?

If the transfer switch is wired correctly they will not both be feeding the panel at the same time. The neutrals maybe electrically tied together, but only one source will actually "feed" the panel.

 

[nerspellsner]

The neutral conductor from the generator goes to the neutral bar in the main panel panel. The neutral conductor from the street also goes to the neutral bar in the main panel. When a connection is made from the running generator to the main panel, and the street power is still on, the main panel has two active neutrals connected to the same bar from two different systems. They are most likely operating at different voltages, 118v from the generator and 124v from the street.

 

[hardworkingstiff]

The neutrals are connected. They have no difference of potential. The street power stops at the transfer switch (the ungrounded conductors). They (should) go no farther.

The ungrounded conductors of the two systems should be isolated from each other, and only on set is connected to the load. (With a transfer switch for the whole panel).

If you are having some problems, share them with this Forum and I can just about guarantee someone will have a solution.

 

[nerspellsner]

It is not a whole panel transfer switch. It a gentran 10 circuit transfer switch.

 

[iwire]

nerspellsner.

If you hook up only the neutral from any source to a lamp will it light?

No

Why?

Not a complete circuit.

This same thing applies to the interconnected neutrals from two or more sources.

When a connection is made from the running generator to the main panel, and the street power is still on, the main panel has two active neutrals connected to the same bar from two different systems.

No, you have one 'active' neutral and the other is just a conductor that does nothing.

They are most likely operating at different voltages, 118v from the generator and 124v from the street.

Imagine the generator is just a portable one drop it on the ground right beside an outlet powered from the utility service.

Do not connect it to any thing but go head and start it up.

Get out your meter.

Measure the generators output and find its running at 124 volts

Measure the voltage at the service supplied outlet and find it's running at 118 volts.

Now measure the voltage between the neutrals of the generator and the service neutral. You will find 0 volts.

Why 0 volts when one circuit is 118 and one is 124 volts?

Because there is no complete circuit to measure.

You are trying to measure between one conductor from two different sources.

Hook the meter from the 'hot' of one source and the neutral of the other source and you still have 0 volts.

If you actually try this with a typical digital meter you will get some readings but these will be erroneous due to the meters sensitivity.

The only time one source will effect the other is if you tried to connect both the neutrals and hots from both sources at the same time.

Having the neutrals tied together from two sources is the way the majority of generators are wired.

You can get a transfer switch that will switch the neutrals but that is only required in a few applications.

One last thought.

If you took you meter and placed one lead on a 9 volt battery and the other lead on a 1.5 volt battery would your meter find any voltage difference?



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