PV GROUND FAULT PROTECTION – HOW IT WORKS
NORMAL OPERATING CONDITION
PV MODULE OR ARRAY
WITH COMBINER BOXES
APOLLO SOLAR
T80 CHARGE
CONTROLLER
+PV
IN
PV
CURRENT
GFP
BREAKER
-PV
IN
-BAT +BAT
OUT OUT
CC IN
BREAKER
CC OUT
BREAKER
BATTERY
MECHANICAL
LINK
ARRAY
FRAME
GROUND
GFP
SENSOR
NEGATIVE
BUS
.5A
CONDUIT
RES
SIMPLIFIED
NEGATIVE GROUND
PV SYSTEM
GROUND
BUS
MAIN
EARTH
GROUND
SHUNT
SYSTEM IS ONLY CONNECTED
TO GROUND AT THIS POINT. ALL
RETURN CURRENT MUST FLOW
THROUGH THE GFP SENSOR.
GROUND FAULT IN THE POSITIVE WIRE
(PROTECTION REQUIRED BY UL1741 AND NEC)
WIRE OR CELL
CONTACTS GROUND
PV MODULE OR ARRAY
WITH COMBINER BOXES
PV CURRENT
FLOWS THROUGH
GFP SENSOR
APOLLO SOLAR
T80 CHARGE
CONTROLLER
.5A GFP SENSOR
TRIPS TAKING GFP
BREAKER WITH IT
GFP
BREAKER
+PV
IN
-PV
IN
GROUND FAULT IN THE
POSITIVE BATTERY WIRE
ALSO TRIPS THE GFP
-BAT +BAT
OUT OUT
CC IN
BREAKER
CC OUT
BREAKER
MECHANICAL
LINK
ARRAY
FRAME
GROUND
SIMPLIFIED
NEGATIVE GROUND
PV SYSTEM
GFP
SENSOR
CONDUIT
NEGATIVE
BUS
.5A
RES
SIMILAR PATH IF
SHORT CIRCUIT IS
IN THE CONDUIT
GROUND
BUS
MAIN
EARTH
GROUND
BATTERY
SHUNT
SYSTEM IS ONLY CONNECTED
TO GROUND AT THIS POINT. ALL
RETURN CURRENT MUST FLOW
THROUGH THE GFP SENSOR.
GROUND FAULT IN THE NEGATIVE WIRE
(PROTECTION REQUIRED BY UL1741, NOT NEC)
PARALLEL
WIRE OR CELL
CONTACTS GROUND CURRENT FLOWS
THROUGH GFP
PV MODULE OR ARRAY
SENSOR
WITH COMBINER BOXES
APOLLO SOLAR
T80 CHARGE
CONTROLLER
.5A GFP SENSOR
TRIPS TAKING GFP
BREAKER WITH IT
GFP
BREAKER
+PV
IN
-PV
IN
SIMPLIFIED
NEGATIVE GROUND
PV SYSTEM
GFP
SENSOR
CONDUIT
.5A
RES
SIMILAR PATH IF
SHORT CIRCUIT IS
IN THE CONDUIT
NEC 690.5 states that the Ground Fault
Protection device must:
1) Detect a ground fault
2) Interrupt the fault current
3) Indicate that there was a ground fault
4) Open the ungrounded PV conductors
GROUND
BUS
MAIN
EARTH
GROUND
CC IN
BREAKER
CC OUT
BREAKER
NEGATIVE
BUS
SHUNT
SYSTEM IS ONLY CONNECTED
TO GROUND AT THIS POINT. ALL
RETURN CURRENT MUST FLOW
THROUGH THE GFP SENSOR.
The system may be tested by
forcing a short to the ground
wire near the PV array. It is
wise to use a current limiting
resistor to create the short to
limit damage to the wires. Be
careful of high PV voltage.
The drawing shows that each of the NEC
requirements are satisfied with this GFP device.
GROUND FAULT IN THE
NEGATIVE BATTERY WIRE
ALSO TRIPS THE GFP
-BAT +BAT
OUT OUT
MECHANICAL
LINK
ARRAY
FRAME
GROUND
NOTE: THE CHARGE
CONTROLLER MUST BE ON AND
RUNNING BEFORE THE NEGATIVE
FAULT WILL TRIP THE GFP.
BATTERY
THE IMPEDENCE OF THE
FAULT PATH MUST BE VERY
LOW IN ORDER TO SHARE
ENOUGH CURRENT WITH
THE NORMAL RETURN PATH
TO TRIP THE GFP SENSOR.
23 F. J. Clarke Circle
Bethel, CT 06801
(203) 790-6400
www.ApolloSolar.com
HOW IT WORKS
GROUND FAULT PROTECTION
9-JULY-10
J. PFEIFER