Grounding Systems Equipment Grounding & Grounded Conductors
Definitions A Grounded or Earthed system is one that is connected to the earth Grounded Conductor is a conductor that normally carries current and is connected to the earth (white) Equipment Grounding Conductor is a conductor that does not normally carry current (except under fault conditions) and is connected to earth (bare copper typically) Grounding Electrode Conductor is a conductor between a common single grounding point and the grounding electrode Grounding Electrode 5/8 dia, 8 long ground rod or other device that is used to make contact with the earth Bond connecting two or more points together
Grounding System
Three Reasons for Grounding
PV Systems & Grounding PV systems are subject not only to induced electrical surges, but to possible direct lightning strikes Metal module frames, metal racks, and conductors connected to grounded electrical systems
Three Parts of Grounding System Grounding Electrode Equipment Grounds Grounded Conductor
Grounding Electrodes 5/8 copper clad rod driven 6 8 feet in the ground Multiple rods may be needed in dry climates and they all should be connected Connects electrical system to earth, dissipates static charges, and keeps all components at same voltage level relative to the earth
Grounding Electrode Most common is 5/8-8 long copper coated steel rod Entire length must be in the ground Use special clamps to make connection Can be driven 45 degrees Can be buried in 30 deep trench Ground mounted PV arrays should have an additional grounding electrode at array location (does not have to be bonded to main DC grounding electrode)
Grounding-Electrode Conductor Conductor from main bonding point to grounding electrode Normally both a DC & AC grounding electrode conductor in systems with an inverter DC grounding electrode must be bonded to AC grounding electrode Smallest allowable size is #8 (conduit)
Equipment Grounding System All exposed metallic surfaces that could accidentally be energized must be connected to ground with Equipment Grounding conductors PV Module Frames Module Mounting racks (if exposed single conductor cable is routed along them) Switchgear enclosures Overcurrent enclosures Metallic conduit Inverters Charge Controllers
Equipment Grounds Interconnection of all metal components and to electrode Conducts errant current to ground Prevents shock hazard Redundant equipment grounds are desirable
Grounding PV modules Copper & aluminum don t mix Oxidation, clear coating & anodizing form insulating surface PV module frames could be energized with high voltage Each module frame requires grounding at indicated location using hardware & instructions provided
Grounding when no hardware or instructions provided 10-32, thread-forming stainless steel screw can be used to attach an IIsco GBL-4DBT lug to module frame at or adjacent to the point marked for grounding
Alternative Procedure If module grounding is to be done with #14 - #10, The IIsco lug is not needed. Use two number 10 stainless steel, flat washers on a 10-32 thread-forming stainless steel screw. Use #19 drill bit to make proper hole for 10-32 screw
Equipment Grounding Conductor Bare copper conductor with no insulation Insulated conductor with green insulation Insulated Conductor with green insulation & yellow stripes Equipment-grounding conductors in DC, PV source and output circuits must have an ampacity at least 1.25 times the Isc from the PV sources at that point in the circuit (use Table 310.16) Insulation rating should be equal to conductors
Equipment Grounds Use Table 250.122 to size grounds other than DC,PV source & output circuits (AC & DC) If circuit conductors have been oversized for voltage drop then grounds need to as well
Grounded Conductors A circuit conductor that is normally electrified and is connected to the earth Ground at only 1 point in DC & AC part of system Insulation on grounded conductor is typically white or use white tape at each splice & termination
Main Bonding Jumper Connects the grounded circuit conductors to the equipment grounding conductor In stand alone systems DC bonding jumper can be installed anywhere; frequently between inverter & batteries With GFP devices bonding takes place at the at the GFP device In utility interactive systems DC bonding jumper is frequently internal to the inverter
GFP or GFDI (Ground Fault Detector Interrupter) Bonding location for equipment grounds and negative conductor
Ground Fault Protection Specialized breaker designed to monitor the current between the grounding system and grounded conductor where they are bonded together If voltage imbalance exists the GFP will open the circuit DC negative conductor must be kept isolated from ground Only point of contact between negative conductor and grounding system should be at GFP device
Isolated Grounded or Negative Conductor