Generator feeding more than one service

[Chris3585]

I am designing a generator system that will serve an existing building and a new addition. The new addition is classified as a separate building and we are bringing in a separate electrical system with a neutral and a ground rod. It is my understanding that since the generator is serving multiple buildings, we have to derive a neutral at the generator and switch the neutral between the normal and generator sources.

Since we are also deriving a ground from the generator, will a parallel grounding path be created between the (2) service grounds and the generator ground?

Thanks,

Chris

 

[RUWired]

I am designing a generator system that will serve an existing building and a new addition. The new addition is classified as a separate building and we are bringing in a separate electrical system with a neutral and a ground rod. It is my understanding that since the generator is serving multiple buildings, we have to derive a neutral at the generator and switch the neutral between the normal and generator sources.

Since we are also deriving a ground from the generator, will a parallel grounding path be created between the (2) service grounds and the generator ground?

Thanks,Chris

Chris, Having two services tied together via a nonswitched transfer switch will create parallel neutral/ground paths. If you have an ATS in each building common with the output of the generator, atleast one of the transfer switches needs to be switched to break the parallel path. If you switch the neutral in both ATS's, the generator will become a seperately derived system and a grounding electrode system will be required. If you switch only one neutral in one of the ATS's, the generator will not be a SDS and a GES is not required.

Using a common grounding electrode conductor between the genset and the buildings grounding electrode system will only put the equipment grounding conductor and the electrode conductor in parallel because the neutral is breaking the common point from the system bonding jumper.

Rick

 

[donselectric]

not being a s/a but
when did a gen become a separate sys ? does the neutrals hit the same lug in the transfer sw... i think you mean transformers being separately derived...
at least thats what i thought but i've been wrong before....

 

[RUWired]

not being a s/a but
when did a gen become a separate sys ? does the neutrals hit the same lug in the transfer sw... i think you mean transformers being separately derived...
at least thats what i thought but i've been wrong before....

From definitions in the n.e.c,
Separately Derived System. A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
Some examples of a separately derived system may include a generator, a battery, converter windings, a transformer, and a solar photovoltaic system, provided they ?have no direct electrical connection? to another source.

Rick

 

[Pierre C Belarge]

Chris, Having two services tied together via a nonswitched transfer switch will create parallel neutral/ground paths. If you have an ATS in each building common with the output of the generator, atleast one of the transfer switches needs to be switched to break the parallel path. If you switch the neutral in both ATS's, the generator will become a seperately derived system and a grounding electrode system will be required. If you switch only one neutral in one of the ATS's, the generator will not be a SDS and a GES is not required.

Using a common grounding electrode conductor between the genset and the buildings grounding electrode system will only put the equipment grounding conductor and the electrode conductor in parallel because the neutral is breaking the common point from the system bonding jumper.

Rick

Rick
Would he not be required to break the neutral in both ATS switches? How would the GE system in one building be sufficient for the other building when the generator is operating?

 

[RUWired]

Rick
Would he not be required to break the neutral in both ATS switches? How would the GE system in one building be sufficient for the other building when the generator is operating?

Think of it like a non seperately derived generator that uses the main bonding jumper in the service equipment, it's the same principle, it would use the main bonding jumper in the building that has the solid neutral switch.

Rick