Do I need a 4 pole ATS?

[Pierre C Belarge]

Smart
I never said the installation was incorrect.

My only concern is how the transformer is grounded.

I also mentioned I did not believe a 4-pole switch is required.

 

[Smart $]

My only concern is how the transformer is grounded.

...and that seems to be everyones concern.

So ask yourself (as in everyone opposing how the transformier is grounded in my diagram): What purpose does grounding a transformer's secondary serve? My answer to this question is two-fold: 1) To provide a voltage reference, and 2) to provide a low-impedance path for ground-fault current to return to it's source. While the manner this particular transformer achieves its grounded secondary is atypical, the purpose for grounding is satisfied.

 

[Pierre C Belarge]

...and that seems to be everyones concern.

So ask yourself (as in everyone opposing how the transformier is grounded in my diagram): What purpose does grounding a transformer's secondary serve? My answer to this question is two-fold: 1) To provide a voltage reference, and 2) to provide a low-impedance path for ground-fault current to return to it's source. While the manner this particular transformer achieves its grounded secondary is atypical, the purpose for grounding is satisfied.

Can you explain to me how that is so?

 

[Mvillines]

Pierre, help me understand your question. Is it bonding or grounding to earth?

 

[Smart $]

Can you explain to me how that is so?

Real simple... the transformer's X0 terminal, by way of insulated/isolated conductors, is connected to the service ground. Elementary electrical theory

There is nothing in the code that precludes a grounded conductor from being a means of source grounding so long as non-current-carrying metal parts are not connected to said grounded conductor. Take for example an SDS transformer secondary which is bonded at the first disconnect. The grounded conductor between the transformer and disconnect is the means of source grounding.

As I said, the intent is to provide voltage reference and low-impedance path for ground-fault current. The use of insulated/isolated grounded conductors satisfies that intent, provided they are of adequate ampacity and solidly connected.

 

[mc5w]

Here are my concerns:

1. How do you think that you can connect 120Y208 load to one of the generator 120/240 delta windings without an intervening transformer? Among other issues, air conditioner control transformer primary taps would have to be transferred from 208 volt to 240 volts when the transfer switch operates. Similarly, one of the phases would not be able to have 120 volt loads on it.

Another issue is that 2-pole and 3-pole circuit breakers that are connected to to high leg need to be rated for 240 volts ungrounded or corner grounded. A circuit breaker that is rated 120/240 or 120/208 is a violation when connected to the high leg.

2. It is much simpler to reconnect both generator windings 120Y208 volts.

3. For the better generators such as Cummins, you can ( for extra money ) get an oversize alternator that can cope better with bad operating conditions such as a tropical climate or 70% power factor.

3. A delta connected 2/3 pitch generater winding **WILL** have circulating current in it regardless of whether it is 3-wire or 4-wire delta. This is because a 2/3 pitch winding has almost no zero sequence impedance of its own.

The scuttlebutt over at www.eng-tips.com is that a delta-delta transformer runs cooler if one of the winding is opened and operated open delta because of circulating current, even if both windings are 3-wire.

The correct ways to get 120/240 delta out of a generator are:

a. Connect generator for 277Y480 volts and then use a 3-wire T primary 4-wire T secondary transformer using 2 standard single phase transformers.

b. Connect the generator for 120/240 3-wire single phase and 120/240 4-wire OPEN delta. This gives you 2 systems that would match some other building's configuration.

c. Connect the generator for 138Y240 volts and use a balance coil to derive the neutral. This is a single phase version of a zig-zag set using a 240 primary 240 secondary single phase transformer. Overcurrent protection would be similar to a zig-zag set.

These are all things that can be done with a standard 12-lead alternator.

 

[mc5w]

Forgot to add that even if both loads are effectively 240 volts 3-wire, the best things is to connect the generator 138Y240 volts solidly grounded for both windings. You still have to bring the generator neutrals to both buildings evne though not used.

A 138Y240 volts windings is REQUIRED to be solidly grounded using the neutral point because that makes the voltage to ground 150 volts or less.

Also, my experience with ungrounded systems is that they can build up explosive amounts of static electricity if there is any amount of overhead wiring or PVC conduit.

Also, in some state such as New York, an ungrounded system can only exist within a single building. As soon as the power comes from outside of the buillding ( such as a utility service ) or runs from one building to another it must be solidly grounded or resistance grounded.

 

[mc5w]

American Electric Power thinks that a solid neutral transfer switch can backfeed power into their system. Pure horsefeathers conidering that Pacific Gas and Electric has something along the lines of 25,000 solar inverters that have a solid neutral and no backfeed during power failures. These systems are essentially a double ended switchboard application - extremely simplified if 120/240 single phase or 120Y208 volts 3-phase.

A solid neutral transfer switch is permitted by NEC if:

1. The transfer switch is in the same cabinet as the service switch in which case the neutral to ground bond for both the service and the generator are one and the same and the generator is wired with separate neutral and equipment grounds.

2. The transfer switch is immediately adjacent to the service switch which is a similar situation.

3. What you have instead of a transfer switch is essentially a double ended switchboard. If the system is 277Y480 or 347Y600 volts then the service has separate neutral and equipment grounds, is on a dedicated transformer, and there is no neutral to ground bond at the utility transformer, there is only 1 neutral to ground bond at the tie breaker that passes through the current transformer for the master ground fault relay that trips both the service switch and the generator switch, and both the service switch and generator switch need to be 4-pole neutral switching so that each switch's individual ground fault protection can disconnect an upstream ground fault.

Where you MUST have a neutral switching transfer swiitch are:

4. A ground bond is required ast the generator such as when transferring a boat from on board power to shore power.

5. The service and possible also the feeders need ground fault protection for equipment and the system is not set up as a double ended switchboard that does parallel power production.