Farm generator question

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sw_ross

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In our area for farms the POCO usually provides a meter with a “site isolating switch”
The isolating switch isn’t a service disconnect (no ocpd) just a switch. “Up” is utility power and “down” is generator power (manual transfer switch), or “off” if there’s no generator.

Then you run “service conductors” (3-wire) to the separate structures on the farm and bond ground and neutral at each structure along your grounding electrode at each structure.


image.jpg

If you have a new generator with an ATS sized to feed the whole farm it is usually located by the meter and the conductors are pulled out of the meter, placed on a the load side of the ATS, then properly sized service conductors are run out of the meter over to load side of ATS.

In the example in the photo, depending on a load calculation they might be parallel runs of 250 kcmil with reduced neutral.

I’d be interested in hearing feedback from you guys about how this is setup.
Not a specific question, just looking for comments. I’ll have some questions after listening to the comments.

Thanks!
 
Seems like using an ATS is useless if you have a double-throw switch ahead of it.

Either use the ATS in place of the double-throw switch, or just leave the generator off and have the customer manually start it and throw the switch.


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sw_ross said:
In our area for farms the POCO usually provides a meter with a “site isolating switch”
The isolating switch isn’t a service disconnect (no ocpd) just a switch. “Up” is utility power and “down” is generator power (manual transfer switch), or “off” if there’s no generator.

Then you run “service conductors” (3-wire) to the separate structures on the farm and bond ground and neutral at each structure along your grounding electrode at each structure.


View attachment 21228

If you have a new generator with an ATS sized to feed the whole farm it is usually located by the meter and the conductors are pulled out of the meter, placed on a the load side of the ATS, then properly sized service conductors are run out of the meter over to load side of ATS.

In the example in the photo, depending on a load calculation they might be parallel runs of 250 kcmil with reduced neutral.

I’d be interested in hearing feedback from you guys about how this is setup.
Not a specific question, just looking for comments. I’ll have some questions after listening to the comments.

Thanks!
Click to expand...

Everything there should be a 4, not 3 wire

~RJ~
 
LarryFine said:
Even if the meter switch is not the service disconnect?
Click to expand...

Yes, because when the generator is the power source the conductors are feeders, not service conductors. They are only service conductors when POCO is supplying power. The implications of this (mandatory switch between 3 conductor and 4 conductor run and re-wire bonding when throwing the transfer switch) provide a good argument that either the NEC needs to explicitly address this situation or else the transfer switch practically (from a regulation standpoint) has to be connected after or serve as the service disconnect.
I am a little surprised not to have seen comments about this kerfuffle (shout out to Besoeker) before this.
 
GoldDigger said:
Yes, because when the generator is the power source the conductors are feeders, not service conductors. They are only service conductors when POCO is supplying power. The implications of this (mandatory switch between 3 conductor and 4 conductor run and re-wire bonding when throwing the transfer switch) provide a good argument that either the NEC needs to explicitly address this situation or else the transfer switch practically (from a regulation standpoint) has to be connected after or serve as the service disconnect.
I am a little surprised not to have seen comments about this kerfuffle (shout out to Besoeker) before this.
Click to expand...

The OPs ATS adds a bit to what would be a typical install of POCO owned equipment in areas to the North of me. Then add a likely common gas piping system to those buildings with gas heat. Propane here. I would venture to guess that, unless everything is of new construction, No new farm wide gen install is done "correctly". ATS or not.

The likely hood of all feeder and Service Equipment being updated to 4 wire is nil.
 
I've got a better shot at getting hit by a meteor, than walking onto nec compliant farm wiring around here :( ~RJ~
 
Seldom am seeing ATS but if one were to do so it often is just supplying one building, like maybe the house, and the genset would be installed at the house and not at the site isolating switch.

I have one of those POCO supplied transfer switch/site isolating devices. power is out more frequently than it was when I lived in town. I don't get too excited about connecting my generator unless I know it is going to be off for more than maybe 6 hours. Some think being off a minute is too long I guess. How did the people that first settled the land ever survive without power, worse yet without a cell phone?:D
 
547.9(B) Service Disconnecting Means and Overcurrent Protection
at the Building(s) or Structure(s). Where the service disconnecting
means and overcurrent protection are located at the
building(s) or structure(s), the requirements of 547.9(B)(1)
through (B)(3) shall apply.

(1) Conductor Sizing. The supply conductors shall be sized in
accordance with Part V of Article 220.
(2) Conductor Installation. The supply conductors shall be
installed in accordance with the requirements of Part II of Article
225.
(3) Grounding and Bonding. For each building or structure,
grounding and bonding of the supply conductors shall be in
accordance with the requirements of 250.32, and the following
conditions shall be met:
(1) The equipment grounding conductor is not smaller than
the largest supply conductor if of the same material, or is
adjusted in size in accordance with the equivalent size
columns of Table 250.122 if of different materials.
(2) The equipment grounding conductor is connected to the
grounded circuit conductor and the site-isolating device
enclosure at the distribution point.
 
packersparky said:
547.9(B) Service Disconnecting Means and Overcurrent Protection
at the Building(s) or Structure(s). Where the service disconnecting
means and overcurrent protection are located at the
building(s) or structure(s), the requirements of 547.9(B)(1)
through (B)(3) shall apply.

(1) Conductor Sizing. The supply conductors shall be sized in
accordance with Part V of Article 220.
(2) Conductor Installation. The supply conductors shall be
installed in accordance with the requirements of Part II of Article
225.
(3) Grounding and Bonding. For each building or structure,
grounding and bonding of the supply conductors shall be in
accordance with the requirements of 250.32, and the following
conditions shall be met:
(1) The equipment grounding conductor is not smaller than
the largest supply conductor if of the same material, or is
adjusted in size in accordance with the equivalent size
columns of Table 250.122 if of different materials.
(2) The equipment grounding conductor is connected to the
grounded circuit conductor and the site-isolating device
enclosure at the distribution point.
Click to expand...

Was that code in effect when it was installed?
 
Cow said:
Was that code in effect when it was installed?
Click to expand...

Good Q

And how many have had stray V issues bonding the daylights out of what might have been best to rethink the entire distribution?


electricity_wiring.gif

~RJ~
 
romex jockey said:
Good Q

And how many have had stray V issues bonding the daylights out of what might have been best to rethink the entire distribution?


electricity_wiring.gif

~RJ~
Click to expand...
That problem is not limited to farms.

Even if you run 4 wire distribution all around the farm, the fact the POCO uses a current carrying MGN on the primary still sets up potential stray voltage problems.
 
547.9 issues

547.9 issues

Sorry I've been away from this thread for awhile...

My guess has always been that 547.9 set up this "standard norm" for POCO installs in our area outside of the towns (I'm talking about ALL of North Dakota, at least where I've worked), even on properties that aren't agricultural.

My problem with running a 4-wire from the site isolating switch is that it doesn't include an OCPD. You can run a 4 wire and treat the panels in the other structures as sup-panels, but if there's a fault on the EGC that goes all the way back to the isolating switch and there's nothing there to trip!

If you run a 4-wire and then re-bond at each structure then you're creating objectionable current on the EGC, basically paralleling the grounded conductor...
 
sw_ross said:
Sorry I've been away from this thread for awhile...

My guess has always been that 547.9 set up this "standard norm" for POCO installs in our area outside of the towns (I'm talking about ALL of North Dakota, at least where I've worked), even on properties that aren't agricultural.

My problem with running a 4-wire from the site isolating switch is that it doesn't include an OCPD. You can run a 4 wire and treat the panels in the other structures as sup-panels, but if there's a fault on the EGC that goes all the way back to the isolating switch and there's nothing there to trip!

If you run a 4-wire and then re-bond at each structure then you're creating objectionable current on the EGC, basically paralleling the grounded conductor...
Click to expand...
Same around here. Rural POCO's all generally supply a disconnecting means with nearly all single phase services, and most 3 phase 200 amp or less, and it doesn't matter if it is a farm, a single residence, light industry, commercial...that is just what they do. Some those rural POCO's also serve small towns and mostly do the same thing in those towns. Put a meter/main type of device on the pole and everything after that is the customer's property. AHJ here doesn't consider this to not be the service disconnect. Partly because POCO can and have changed out that equipment to something that doesn't meet service disconnecting means requirements.

If you are running a separate EGC (for any reason) you shouldn't have it bonded on the load end in that situation it becomes a parallel grounded conductor and is pointless to consider it an EGC.
 
packersparky said:
547.9(B) Service Disconnecting Means and Overcurrent Protection
at the Building(s) or Structure(s). Where the service disconnecting
means and overcurrent protection are located at the
building(s) or structure(s), the requirements of 547.9(B)(1)
through (B)(3) shall apply.

(1) Conductor Sizing. The supply conductors shall be sized in
accordance with Part V of Article 220.
(2) Conductor Installation. The supply conductors shall be
installed in accordance with the requirements of Part II of Article
225.
(3) Grounding and Bonding. For each building or structure,
grounding and bonding of the supply conductors shall be in
accordance with the requirements of 250.32, and the following
conditions shall be met:
(1) The equipment grounding conductor is not smaller than
the largest supply conductor if of the same material, or is
adjusted in size in accordance with the equivalent size
columns of Table 250.122 if of different materials.
(2) The equipment grounding conductor is connected to the
grounded circuit conductor and the site-isolating device
enclosure at the distribution point.
Click to expand...

Except, the service disconnecting means doesn't appear to be at the buildings.
 
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