1. Understanding GFCIs Developed by the NEMA 5PP Personnel Protection Technical Committee

2. What Is to Be Covered? Electrical Shock - Why Have GFCIs?
How GFCI’s Operate
Proper Installation of a GFCI
Wiring Errors
Grounded Neutral Detection
Testing GFCIs

3. Electrocutions Associated With Consumer Products
Note the significant decline. In the mid 1970’s time period there were more than 600 consumer product related electrocutions annually and today there are less than 1/3 that number.
Agreement to leave as is for now, the TC is asked to find more recent data on electrocutions.

4. Effects of Electric Shock
20A
4 AMPERES AND OVER
Heart Paralysis, Serious Tissue and Organ Burning
15A
50 mA - 4 Amps Fibrillation
10A 4A
50mA
IEC RCD Standards Breathing Difficult, Fibrillation in children
Muscles “Freeze” in 50% of the Population
Let-Go Threshold
4-6 UL 943 Class A GFCI Trip Level
Perception Level
30mA
15mA
10mA
4-6 mA
1mA

5. Electric Shock Prevention System
Isolation (Physical)
Insulation
Double Insulation
Equipment Grounding
GFCI (solves shortcomings
of above systems)
Isolation
Not possible when using electrical equipment
Insulation
Deteriorates with age
accidentally or deliberately circumvented
Double Insulation
doesn’t protect if equipment is submerged
doesn’t protect cord
Equipment Grounding
deteriorates if not maintained
GFCI
newest part of the protection system
does not depend on other elements of the system

6. Normal Circuit Operation
Equipment N 6A
Equipment Grounding
Conductor (EGC)
Current flows on the line conductor from line to the load
Current returns from the load on the neutral
The same amount of current flows from line to load and returns from load to line
The same amount of current flow from line to load and returns from load to line.

7. Ground – Fault (Indirect Contact)
EGC
5.94A
Ground-Fault
When a person contacts the grounded enclosure of equipment with a fault to the enclosure it is called “indirect contact”
The equipment grounding conductor (EGC) is effective
Current divides and flows to ground based on the impedance of the two fault paths
EGC has low impedance … most of the fault current flows on it
person has comparatively higher impedance … small amount of fault current flows through the person (may or may not “feel a shock”)
.06 A

8. Ground – Fault (Direct Contact)
If ECG is absent (cut off prong on plug) then ALL the fault current will flow through the person. This is called direct contact.
Amount of current determined by impedance of the person
Dry hands or large person has higher impedance than wet hands or small person
.1 A

9. How GFCIs Operate
Knowing how GFCIs work will enable you to understand:
Why GFCIs must be installed a certain way
For Circuit Breaker GFCI: To prevent constant tripping, MUST connect Load Neutral to circuit breaker neutral terminal, NOT panelboard neutral.
For Receptacle GFCI:
If line and load conductors are reversed, per 2010 edition UL 943, no power is available at:
Face terminals or
Line terminals connected to downstream receptacles.
Why do GFCIs trip under various circumstances
Mis-wiring will cause GFCI to trip if:
Ground current is flowing
Neutral is grounded on load side of GFCI.
Portable GFCIs will trip if open neutral is present on the line side of the GFCI.
What conditions causes unexpected tripping
Ground current exceeding 6 mA when a load is applied.
Load neutral is not connected to correct terminals.

10. The Current “Adding Machine”
Load
IIn
IOut
If the current out = current back, the differential current transformer shows no output. L N
Differential Current Transformer
Rrevise text in block to something like “I-out” and “I-in” instead. Label/point to the two 6A currents as I-in and I-out.
Agree with addition of I-in and I-out. Agree to remove 6A.
Show two leads coming from the transformer, and label them “Differential Current”. (Consider showing the transformer this way in all applicable slides).
Do not support.
Current OUT=Current BACK … differential current is zero

11. Current “Adding Machine”
240V
Load
IIN
IOut L1 L2
Differential Current Transformer N
120/240V
Load
IIN
IOut L1 L2
What about a 240V load… current out equals current back… differential current is zero
Same is true for 120/240V systems… current out equals current back.. Differential current is zero
3 phase? - same principles apply
Differential Current Transformer

12. Current “Adding Machine” Under Ground Fault Conditions
Load
IIn = 6A
IOut = 5.9A
Ground-Fault
.1A L N
When a ground fault is introduced another return path is established
Current out (6A) does not equal current returning (5.9A) because .1A is returning through the ground path
The “differential current transformer” detects the difference… the differential current signals the electronics.
Differential Current Transformer
If I-out does not equal I-in, the differential current transformer creates an  output signal.

13. What’s in the GFCI? (Receptacle)
Reset Button
Test Button
Cover
Tamper Resistant Mechanism (Optional)
Bridge
Face Contacts
Middle Barrier
Terminals
Terminals
Printed Circuit Board
Base

14. GFCI circuitry with grounded neutral detection
What’s in the GFCI? (Receptacle)
GFCI circuitry with grounded neutral detection
120V Trip Mechanism
Push-to-test Button
15K Resistor
Face
Hot
Load
Hot
Face
Load Terminals
Line Terminals
Load
Shown here is a GFCI receptacle
Line Terminals where conductors from panelboard are terminated
Double pole mechanical latching trip mechanism actuated by a 120 volt tripping coil
Differential current transformer… detects differential current
Electronic circuit asks and answers questions
is differential current over 6mA
is duration long enough
screens out momentary surges, RF interference, etc.
closes trip circuit if differential current exceeds 6ma.
NOTE the EGC passes through, BUT is NOT involved in the detection circuitry
Grounded Neutral detection circuit to detect a neutral on the load side of the GFCI
Push to test button
test circuit from line through differential transformer
through an 15K or so resister (limits test to about 8mA)
creates a differential current causing the GFCI to “detect and trip”
Receptacle outlets on the LOAD side of the differential transformer
Load side terminals for feed-thru capability
Neutral
Neutral
EGC
Receptacle Face

15. What’s in the GFCI? (Circuit Breaker)
Push-To-Test Button
Over-Current trip
Trip Solenoid
Handle (ON-OFF)
Printed Circuit Board
Panel Neutral wire
Trip
Mechanism
“Load Power” Terminal
Primary Current-carrying Contacts
Sensing Coil
“Line” Terminal
“Load Neutral” Terminal

16. What’s in the GFCI? (Circuit Breaker)
Electronic circuitry with Grounded Neutral detection
Push-To-Test Button
Trip Solenoid
Test Resistor
Trip
Mechanism
Sensing Coil
“Line” Terminal
“Load Power” Terminal
“Load Neutral” Terminal
Primary Current-carrying Contacts
Panel Neutral wire

17. What’s in the GFCI? (Plug-in)
Electro-Mechanical Latching Device
Current Imbalance and Grounded Neutral Sensors
Principal difference is what is call “open neutral” protection required by UL on plug-in GFCI’s
If you plug a portable GFCI into a cord or receptacle, its contacts must remain open if the circuit into which it is plugged has an open neutral
If this were not required, a fault could exist and the GFCI would not trip
Open neutral protection is generally accomplished using a normally energized solenoid coil which, once reset, maintains the contacts in the closed position. When power is removed by(either by both or one open conductor), the contacts open.

18. What’s in the GFCI? (Plug-in)
Push-to-test Button
Electro Mechanical Latching Device
Current Imbalance and Grounded Neutral Sensor
15k
Resistor
Load Hot
Load Neutral
EGC
Principal difference is what is call “open neutral” protection required by UL on plug-in GFCI’s
If you plug a portable GFCI into a cord or receptacle, its contacts must remain open if the circuit into which it is plugged has an open neutral
If this were not required, a fault could exist and the GFCI would not trip
Open neutral protection is generally accomplished using a normally energized solenoid coil which, once reset, maintains the contacts in the closed position. When power is removed by(either by both or one open conductor), the contacts open.
Circuitry with Open and Grounded Neutral detection

19. Standard 120V Connection (GFCI Circuit Breaker)
120/240Vac Source L1 N L2
HOT
GND
NEUTRAL
EQUIPMENT GROUND
1-POLE CIRCUIT BREAKER WITH GFCI
DUPLEX RECEPTACLE
240
120
Breaker “plugged” into the panel for 120V power
Note that the neutral pigtail is connected to the panelboard neutral (S/N).
Load neutral must return to the circuit breaker load neutral terminal
EGC could be unconnected and have no effect on the proper operation of the GFCI
NOTE that the CB performs the standard functions of a breaker as well (overload, short circuit, etc.)
Slide 21 – 29 – consider using “Line” instead of “Hot”, since in previous slides we use “L”. Alternatively, if “Hot” is preferred, then  update ALL slides as such, for consistency.

20. Standard 120 Volt Connection (GFCI Receptacle)
120/240Vac Source N L1 L2
Line
Terminals
Load
Terminals
Branch circuit from panelboard connected to the “line” terminals
EGC connected as with any receptacle
Branch circuit conductors feed other receptacles connected to “load” terminals
Cover downstream receptacles with an appropriately marked plate N

21. 240 Volt Load – No Neutral 120/240Vac Source L1 N L2 GND HOT B HOT A
EQUIPMENT GROUND
2-POLE CIRCUIT BREAKER WITH GFCI
250V DUPLEX RECEPTACLE
240
120
Note: Load neutral circuit not used in this circuit
Breaker “plugged” into the panel for 120V power
Note that the neutral pigtail is connected to the panelboard neutral (S/N).
Load neutral must return to the circuit breaker load neutral terminal
EGC could be unconnected and have no effect on the proper operation of the GFCI
NOTE that the CB performs the standard functions of a breaker as well (overload, short circuit, etc.)
Slide 21 – 29 – consider using “Line” instead of “Hot”, since in previous slides we use “L”. Alternatively, if “Hot” is preferred, then  update ALL slides as such, for consistency.

22. 120/240 Volt Load 120/240Vac Source L1 N L2 GND HOT B HOT A NEUTRAL
EQUIPMENT GROUND
2-POLE CIRCUIT BREAKER WITH GFCI
240
120
NEUTRAL
120/240 VAC LOAD
Breaker “plugged” into the panel for 120V power
Note that the neutral pigtail is connected to the panelboard neutral (S/N).
Load neutral must return to the circuit breaker load neutral terminal
EGC could be unconnected and have no effect on the proper operation of the GFCI
NOTE that the CB performs the standard functions of a breaker as well (overload, short circuit, etc.)
Slide 21 – 29 – consider using “Line” instead of “Hot”, since in previous slides we use “L”. Alternatively, if “Hot” is preferred, then  update ALL slides as such, for consistency.

23. Single Phase 120V Circuit 1A L 120V 1A N
Remember - what goes out must equal what comes back
If it doesn’t there is differential current. 1A

24. Multi-Wire Circuits One leg of multi-wire circuit in use 1A 1A 0A
120V 1A
120V
Many are confused about GFCI’s applied on multi-wire circuits. Remember that as long as what goes out … comes back, the differential current is zero.
In this drawing with one leg of the circuit open, the current flows out on the “hot” conductor and back on the neutral 0A
Switch Open

25. Multi-Wire Circuits Both legs of multi-wire circuit in use 1A 120V 0A
When the switch is closed. If the load is balanced the “neutral” has zero and the differential is between the two “hot conductors”
If the load is not balanced, there is some current on the neutral, but the differential current sensor still sees a total of what goes out versus what comes back regardless of the amounts of current in each wire. 1A
If what goes out…. Comes back.. The GFCI sees
zero total current on the circuit.

26. GFCI Circuit Breaker on Multi-Wire Circuits
120/240Vac Source L1 N L2
HOT B
GND
HOT A
EQUIPMENT GROUND
2-POLE CIRCUIT BREAKER WITH GFCI
240
120
NEUTRAL
DUPLEX RECEPTACLE
Breaker “plugged” into the panel for 120V power
Note that the neutral pigtail is connected to the panelboard neutral (S/N).
Load neutral must return to the circuit breaker load neutral terminal
EGC could be unconnected and have no effect on the proper operation of the GFCI
NOTE that the CB performs the standard functions of a breaker as well (overload, short circuit, etc.)
Slide 21 – 29 – consider using “Line” instead of “Hot”, since in previous slides we use “L”. Alternatively, if “Hot” is preferred, then  update ALL slides as such, for consistency.

27. GFCI Receptacle on Multi-Wire Circuits
Use two GFCI receptacles
Junction Box T R
Separate Neutrals R T
GFCI Receptacles
Downstream
Receptacles
Downstream
Receptacles

28. This “Old House” Problem
GFCI installed on one circuit 6A L1 N ?
GFCI installed on a circuit with a neutral “stolen” from another circuit
6A on L1 switch on L2 open… What does the current sensor see going back on the neutral?
Since it sees 6A, what does the GFCI do? Nothing.
Let’s close the switch on L2… with 6A on L1, but what is going back on the neutral? 0A is the correct answer (provided the loads are the same)
What happens? The GFCI trips
Every time the switch is closed, the GFCI trips
Additionally, this multi-wire circuit doesn’t meet the code rules in NEC (keep all the circuit conductors together).
NOTE: The following are two corrective actions to prevent tripping, either a) add GFCI to L2 with its separate neutral, or b) replace with a 2-pole GFCI device that will protect L1 & L2” . 6A L2
Second circuit installed and neutral
“stolen” from a close-by circuit

29. Line and Load Reversal on Receptacles
Incorrect Wiring
Correct Wiring
To Downstream
Receptacle
To Panelboard
To Panelboard
To Downstream
Receptacle
If the branch circuit conductors from the panelboard are connected to the GFCI “load” side terminals and the downstream receptacles are connected to the “line” terminals ... what happens?
When the GFCI is tripped
A tester plugged into the downstream receptacles shows they are energized.
When a tester is plugged into the GFCI receptacle… it is NOT de-energized.. even though the GFCI has tripped. This page needs to be updated to indicate that the GFCI Receptacle will not have power to the face and downstream terminals when miswired.
it’s intended message is not clear. Consider adding some text/arrows etc. to point out that if the black wire from the Panel board is a) connected to the “LOAD” as shown, it’s “Incorrect,” and that b) if it is connected to the LINE side, that is “Correct”.
UL 943 has been revised to prevent providing power to the face of downstream terminals in the event of a line-load miswire.
In the case of incorrect wiring there will be no power at the face or downstream.

30. GFCI Circuit Breaker Miswiring
120/240Vac Source L1 N L2
HOT
GND
NEUTRAL
EQUIPMENT GROUND
1-POLE CIRCUIT BREAKER WITH GFCI
DUPLEX RECEPTACLE
240
120
Current does not return through the sensor in the circuit breaker
Breaker “plugged” into the panel for 120V power
Note that the neutral pigtail is connected to the panelboard neutral (S/N).
Load neutral must return to the circuit breaker load neutral terminal
EGC could be unconnected and have no effect on the proper operation of the GFCI
NOTE that the CB performs the standard functions of a breaker as well (overload, short circuit, etc.)
Slide 21 – 29 – consider using “Line” instead of “Hot”, since in previous slides we use “L”. Alternatively, if “Hot” is preferred, then  update ALL slides as such, for consistency.

31. Grounded Neutral Detection
GFCI Device 6A L ? N
Leakage Current
1. With CB GFCI, load neutral must be connected to CB neutral terminal and not panelboard neutral. Otherwise, it will constant trip if circuit has load.
2. With receptacle GFCI, conforming to 2010 UL 943 Standard, reversing line and load conductors result in no power available at face terminals or line terminals connected to downstream receptacles.
3. GFCIs trip if miswired or ground current flowing or neutral grounded on load side of GFCI. Additionally, portable GFCIs trip if open neutral is present on the line side of the GFCI.
4. Occurs when ground current exceeding 6 mA. accompanies load start-up. Excessive ground current, (exceeds 6mA.) exists with load causes unexpected tripping.
EGC ?
Equipment
Neutral grounded downstream

32. UL GFCI Tests
Every GFCI must pass the following end-of- line manufacturing tests:
no trip below 4mA (no load)
must trip at 6mA (no load)
no trip below 4mA (with load) at rated voltage
must trip at 6mA (with load) at rated voltage
must trip with 2 ohm grounded neutral
must trip within 25 ms with a 500 ohm fault
must trip with test button at +10/-15% rated voltage
must not trip with noise test of GFCI Standard
calibration test at +10/-15% rated voltage

33. GFCI Testers Why are testers used? Will not test:
verify operation of the GFCI
check protection of downstream receptacles
Will not test:
GFCI calibration
ALL types of improper installation
Danger on 2-wire circuits
Will test for some types of improper installation:
line/load reversal
which outlets are protected by GFCI
reverse polarity
presence of the equipment ground

34. Test and Reset Buttons (Receptacle)
Test and reset buttons verify proper functioning of the GFCI
Test button will initiate end-of-life indication or power denial if product is no longer operational
Push-to-test Button
Reset Button
Test button indicates proper functioning of the GFCI
Does NOT indicate proper installation of the GFCI

35. GFCI Testers
Plug-in testers divert current to the equipment grounding conductor
What if there is not equipment ground....? Such as in a 406.3(D)(2)(b) and 406.3(D)(2)(c) application?
The GFCI will not trip with the external tester. The test button must be used.

36. Benefits of UL943 (GFCI) vs. IEC (RCD)
Increased Safety Benefits
UL943 Max 6 mA - threshold for “let-go” current.
IEC Min 20 mA - threshold current for ventricular fibrillation.
Receptacle End of Life indication
Grounded Neutral protection
Portable units - Load protection if both supply neutral and ground conductors are open together.
UL943 Ground-Fault Circuit-Interrupters (GFCI) vs. IEC Residual Current Device (RCD)
UL943 max 6 mA trips in a current range where human muscles can still “let go” and not contract creating safety concerns. The IEC 20 mA is approaching the ventricular fibrillation levels.
UL943 Receptacles are required to deny power or give a visual indication when the GFCI is no longer providing ground fault protection. The IEC RCD’s do not have this requirement.
UL 943 requires GFCIs to provide protection when the neutral conductor becomes connected to earth on the load side so that a fault current path at the user end could return through the neutral conductor rather than through earth or the ground conductor.
Portable units - Load protection if both supply neutral and ground conductors are open together.

37. Summary
GFCIs have contributed significantly to the reduction in the number of deaths due to electric shock
GFCIs look at the current going out and compare it to the current coming back
Remember that GFCIs detect ground to neutral connections downstream
Test the GFCI by using the test button and a load
GFCIs will not protect between line and neutral
Only Class A GFCIs (6mA) protect from electrocution from “let-go” situations