PV solar farm ungrounded system

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Mou

Member
Location
schenectady , NY,USA
Hi Guys,

I got a question regarding 690.47(c)(3) for ungroundned system.
Does Ballasted PV ground mount solar farm on top of landfill area considered as grounded system or ungrounding system?
The size of the EGC could be based on 250.122 for ungrounded system or higher value for 250.122&250.166 for grounded system.

Thanks
Mo
 
C

Carultch

Senior Member
Location
Massachusetts
Mou said:
Hi Guys,

I got a question regarding 690.47(c)(3) for ungroundned system.
Does Ballasted PV ground mount solar farm on top of landfill area considered as grounded system or ungrounding system?
The size of the EGC could be based on 250.122 for ungrounded system or higher value for 250.122&250.166 for grounded system.

Thanks
Mo
Click to expand...

Grounded and ungrounded has nothing to do with how the modules are mounted. It has to do with the inverter input, and whether or not one of the current-carrying conductors is bonded (in a specific manner) to the equipment grounding conductor inside the inverter.

In a grounded system, one of the current-carrying conductors (usually negative) is bonded to the EGC/GEC through a ground fault detection fuse, and is thusly supposed to be identified either by white or gray wire/tape. Grounded systems usually use inverters with internal transformers.

In an ungrounded system, neither of the current-carrying conductors is bonded to ground, or is guaranteed to have any particular relation to ground. In general, the two polarities "float" at about half of the operating voltage above and below ground. Ungrounded systems use inverters classified as transformerless.
 
G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
A couple of questions in here recently point out that some of us do not understand the difference between a grounded PV array and the equipment grounding conductor. They have nothing to do with each other.

EGC's must be run irrespective of whether the array is grounded or ungrounded.
 
M

Mou

Member
Location
schenectady , NY,USA
Thank you guys for the response. The inverters we use are string inverters Transformer less. If I got what you explained right.
This system is consider ungrounded system and based on NEC2014 690.47(c)(3) I could size EGC based on 250.122 table only.

Is that make scene?
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Mou said:
Thank you guys for the response. The inverters we use are string inverters Transformer less. If I got what you explained right.
This system is consider ungrounded system and based on NEC2014 690.47(c)(3) I could size EGC based on 250.122 table only.

Is that make scene?
Click to expand...

Yes your making a scene. :D (Sorry, couldn't resist.)

Seriously, you are making some sense. However the code section you're referring to concerns the GEC (grounding electrode conductor) not the EGC.

EGCs between array to inverter can be sized to 250.122 (but see 690.43-46).

GEC from inverter to grounding electrode system can be sized to 250.122 with transformerless (i.e. ungrounded) inverters, as you say.

If your AHJ brings up 690.47(D), which is directly from array to electrode, then that has to be sized to 250.166.
 
G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
jaggedben said:
Yes your making a scene. :D (Sorry, couldn't resist.)

Seriously, you are making some sense. However the code section you're referring to concerns the GEC (grounding electrode conductor) not the EGC.

EGCs between array to inverter can be sized to 250.122 (but see 690.43-46).

GEC from inverter to grounding electrode system can be sized to 250.122 with transformerless (i.e. ungrounded) inverters, as you say.

If your AHJ brings up 690.47(D), which is directly from array to electrode, then that has to be sized to 250.166.
Click to expand...
For a combination EGC/GEC don't you have to look at 250.122 and 250.66 and use whichever indicated grounding conductor is larger?
 
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