generator questions

[boltneck]

I have a customer that wants a gen install that has me questioning the best way to accomplish this

200 amp main panel and 100 amp sub panel to a detached garage

garage panel has a 3 wire feeder from the main panel

customer wants to control whole house, havent did a load calc yet but dont think this will be a problem with the mid size gen set he is looking at, as the house has oil heat

what has me confused is this, with a service rated transfer switch, the main panel will then become a sub panel with the neutrals and grounds seperate, correct?

can this be done correctly using the existing feeder to the garage, or will the garage feeder and also the range and dryer 3 wire ckts need to be changed to 4 wire since they now will originate in a sub panel

i need to incorporate the garage panel into the generator because the well pump as well as 2 freezers are fed from the garage panel

 

[ceb58]

I have a customer that wants a gen install that has me questioning the best way to accomplish this

200 amp main panel and 100 amp sub panel to a detached garage

garage panel has a 3 wire feeder from the main panel

customer wants to control whole house, havent did a load calc yet but dont think this will be a problem with the mid size gen set he is looking at, as the house has oil heat

what has me confused is this, with a service rated transfer switch, the main panel will then become a sub panel with the neutrals and grounds seperate, correct?

can this be done correctly using the existing feeder to the garage, or will the garage feeder and also the range and dryer 3 wire ckts need to be changed to 4 wire since they now will originate in a sub panel

i need to incorporate the garage panel into the generator because the well pump as well as 2 freezers are fed from the garage panel

Look at 250.32 (B) and its exception

 

[boltneck]

ok thanks

i was in 250.142 looking at exhibit 250.54

where this install was permitted prior to the 1996 code i am still not sure that this can be considered "existing" since i am now changing this panel into a sub panel

was it ever legit to feed a subpanel from a subpanel with a 3 wire ckt?

 

[ceb58]

After rereading the OP I see something that may throw a wrench into the install. You stated that a well pump is fed from the garage panel. This would seem to void (2) of the exception for 250.32 (B). The exception states that 1,2&3 must be met. This is an example of when to get the AHJ involved before the fact. You alone may have a hard time convincing the customer that there is more to this install than meets the eye.

 

[Dennis Alwon]

I see no problem with the existing 3 wire to the garage-- I don't see anywhere that states the feeder to the detached structure needs to be from a main panel.

 

[LarryFine]

I see no problem with the existing 3 wire to the garage-- I don't see anywhere that states the feeder to the detached structure needs to be from a main panel.

Which would you supply the garage feeder's combined neutral/EGC from, the sub-panel's neutral or its EGC?

Logic says the neutral, for its current-carrying status, but EGC's should originate at the service disconnect.

If the feeder's neutral is bare, I see a second wrench: it could allow regrounding the original panel's neutral.

 

[boltneck]

I think what i need to find out is this,

if the well pump that is in the garage supplies the house with water via a metal pipe, then the install was never code compliant to begin with, and the feeder will need to be changed to 4 wire.

 

[tryinghard]

...was it ever legit to feed a subpanel from a subpanel with a 3 wire ckt?

Not for 220v+, another way to state this is "it was never legit to install a parallel neutral path on items not inteded to cary current". It is the intent of 250.24(A)(5) & 250.142(B) to disban parallel neutral current where it does not belong.

If the trasnfer switch is the service disconnect the rule is the grounded conductor would only bond there and nowhere downstreem unless exceptions are met. The garage in your case may meet the exception but watch out for (2) "There are no continuous metallic paths bonded to the grounding system in each building or structure involved" i.e. water pipe, gas pipe, phone, TV...