RE: grounding array/sunny boy [RE-wrenches]

Marco, when I refer to ‘grounding the array’ I am referring to PV electrical grounding. This is the grounding of the + or – PV conductor. In most (99.9%) US installations the negative conductor this is grounded at/within the inverter. This electrical ground may be made at only one location. This is done to create a ground loop path in the event of an electrical earth ground fault in the array system. The intent is to ‘collapse’ the array so that high voltage will not be on the array frame or electrical chassis and be a threat to personnel. It also allows for detection of ground fault current by the inverter (or other means of current sensing) to disable the inverter and annunciate the fault. This does not protect against continuous ground current flow, up to the Isc of the entire array, caused by multiple ground faults in the array. There are more effective means of ground fault protection using voltage differential measurement techniques, which do not require PV array grounding, but the NEC won’t allow it. There is much debate over this subject, as the US is the only country that feels it is necessary to electrically ground the array.

I was not referring to the chassis or safety grounding of the PV array frame, structure, conduit, enclosure chassis, etc. This is entirely different than the electrical grounding. Yes, you must ground the PV panel frames to earth ground at multiple locations. Safety grounding is covered in various places in NEC and, in general, may be grounded all over the array field at multiple locations (something like every 6 feet). My only recommendation with safety grounding is to bond all earth ground stakes together and bond them to the primary point of electrical earth ground. This is usually near the building distribution transformer.

Hope this helps and doesn’t cause more confusion.

____________________________________________

Kent Sheldon

Manager, Industrial Power Systems

SMA America

925 513 8813 Brentwood Office (Primary)

530 273 4848 Grass Valley Office

-----Original Message-----
From: Mangelsdorf, Marco [mailto:mmangelsdorf@hei.com]
Sent: Saturday, January 12, 2002 4:14 PM
To: RE-wrenches@topica.com
Subject: RE: grounding array/sunny boy [RE-wrenches]

Kent,

In my effort to get things "perfectly clear" (as Richard Nixon once said while trying to explain his involvement with the Watergate scandal), when you say that you cannot ground the PV array anywhere else, you're not saying to not bond the module frames back to earth ground, right? Or to put it an another way, modules which have metal frames need to have those frames bonded/grounded to earth regardless of the type of inverter or system design, right?

marco
ProVision Technologies
Hilo (hello!), Hawai'i nei