Understanding GFCIs Developed by NEMA Ground Fault Personnel

Understanding GFCIs Developed by NEMA Ground Fault Personnel Protection Section (5 PP)

What Is to Be Covered? l l l Electrical shock - why have GFCIs How GFCI’s “Think” Proper installation of a GFCI Wiring Errors Grounded Neutral Detection Testing GFCIs March 1999 2

Electric Shock March 1999 3

Occurrences of Electrical Shock 102 - Street & Highway Deaths caused by electrical shock 25 Year Average (1960 -1985) 120 - Farm 120 - Lightning 384 - Industry 474 - Home March 1999 4

Electrocutions - 1983 to 1993 March 1999 5

Effects of Electric Shock 20 15 10 4. 050. 030. 015. 010. 005. 001 March 1999 4 AMPERES AND OVER Heart Paralysis, Serious Tissue and Organ Burning. 050 AMPS TO 4 AMPS. 1 -. 2 Certain Ventricular Fibrillation. 05 -. 1 Possible Ventricular Fibrillation 30 m. A - Breathing Difficult, Fibrillation in small children 15 m. A - Muscles “freeze” in 50% of the population >10 m. A - Let-Go Threshold 5 m. A - GFCI Trip Level 1 m. A - Perception Level 6

Electric Shock Prevention System l l l Isolation (Physical) Insulation Double Insulation Equipment Grounding GFCI March 1999 7

Normal Circuit Operation 6 A N L Equipment 6 A Equipment Grounding Conductor (EGC) March 1999 8

Ground - Fault (Indirect Contact) 6 A N L EGC 12 A 5. 940 A Ground-Fault . 060 A March 1999 9

Ground - Fault (Direct Contact) 5. 90 A N L 6 A Ground-Fault . 1 A March 1999 10

How GFCIs “Think”? March 1999 11

How GFCIs Think l Knowing how GFCIs “Think” will enable you to understand why GFCIs must be installed a certain way n why GFCIs trip under various circumstances n how to logically explain what appears to be illogical tripping n March 1999 12

The Current “Adding Machine” L 6 A Load N 6 A If the current out = current back, the CT shows no output. March 1999 13

Current Adding Machine L 6 A L 240 V Load 6 A N L L March 1999 6 A 120/240 V Load 6 A 14

Current Adding Machine Under Ground Fault Conditions L Load 6 A Ground. Fault N 5. 9 A March 1999 . 1 A 15

The Device is really a DCCI not a GFCI l l l Don’t change the GFCI acronym… Change how you think about GFCIs are really “Differential Current Circuit Interrupters” not “Ground Fault circuit Interrupters” Yes… they trip on ground fault caused differential current, but they also trip on other types of differential current as well. March 1999 16

GFCI Tripping Characteristics March 1999 17

What’s in the GFCI? (receptacle) 120 V Trip Mechanism Solid state circuitry with grounded neutral detection Push-to-test button 15 K resistor Load terminals L N EGC Line Terminals March 1999 Receptacle face on receptacle type GFCIs 18

What’s in the GFCI? (circuit breaker) Trip Solenoid Solid state circuitry with grounded neutral detection Push-to-test button 15 K resistor CB Trip Mechanism Line (breaker jaw) Load “Hot” Load Neutral (to panel neutral bar) March 1999 19

What’s in the GFCI? (Plug-in) 120 V Relay 120 V Mechanical Latching Device Push-to-test button 15 K resistor Load “Hot” Load Neutral Equip. Ground March 1999 20

Proper Installation of the GFCI March 1999 21

Standard 120 V Connection (GFCI Circuit Breaker) March 1999 22

Standard 120 Volt Connection (GFCI Receptacle) 120/240 Vac Source N L 1 L 2 Line Terminals Load Terminals N March 1999 23

240 Volt Load - No Neutral March 1999 24

120/240 V Load March 1999 25

The Adding Machine? 1 A L 120 V N 1 A March 1999 26

Multi-Wire Circuits One leg of multi-wire circuit in use 120 W bulb 1 A 120 V 0 A Switch Open March 1999 27

Multi-Wire Circuits Both legs of multi-wire circuit in use 120 W 1 A 120 V 0 A 120 W 120 V 1 A If what goes out…. Comes back. . The GFCI sees zero total current on the circuit. March 1999 28

GFCI CB on Multi-Wire Circuits March 1999 29

GFCI Receptacle on Multi-Wire Circuits Ø N Ø Use two GFCI receptacles Junction Box Separate Neutrals T March 1999 R Downstream receptacles T R GFCI Receptacles Downstream receptacles 30

Wiring Errors March 1999 31

This “Old House” Problem GFCI installed on one circuit 6 A L 1 N ? 6 A L 2 Second circuit installed and neutral “stolen” from a close-by circuit March 1999 32

Line and Load Reversal on Receptacles Contacts Push-to-test button Load terminals To Downstream Receptacles To Panelboard Line Terminals March 1999 Receptacle face 33

GFCI Circuit Breaker Miswiring Current does not return through the sensor in the circuit breaker March 1999 34

Grounded Neutral Detection 6 A L N ? Neutral grounded downstream EGC ? . 30 A March 1999 35

Testing a GFCI March 1999 36

UL GFCI Tests l Every GFCI must pass the following “in-line” manufacturing tests n n no trip below 4 m. A (no load) must trip at 6 m. A (no load) no trip below 4 m. A (with load) must trip at 6 m. A (with load) must trip with 2 ohm grounded neutral must trip within 25 ms with a 500 ohm fault must trip with “test button” must not trip with “noise” calibration test at 102 V test button at 132 V 1500 V hi-pot March 1999 37

GFCI Testers l Why are testers used? verify operation of the GFCI n check protection of downstream receptacles n l Will not test proper GFCI operation n ALL types of improper installation n Dangerous on 2 -wire circuits n l Will test for some types of improper installation line/load reversal n which outlets are protected by GFCI n reverse polarity n presence of the equipment ground n March 1999 38

Push to Test Button l l Test button indicates proper functioning of the GFCI Does NOT indicate proper installation of the GFCI Push to test March 1999 39

Testing for Line/Load Reversal l l Push the “reset” button on the receptacle Plug a known “test load” into the GFCI receptacle n l l load could be a nightlight, GFCI tester, circuit tester, etc. Push the “test” button (if GFCI trips - then the GFCI is properly functioning) If the “test load” is energized, the GFCI receptacle is improperly installed March 1999 40

GFCI Testers Plug-in testers divert current to the equipment grounding conductor What if there is not equipment ground. . ? Such as in a 210 -7(d)(3) application? March 1999 41

Summary l l l GFCIs have contributed to a 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 Avoid common wiring errors - “Think like the GFCI” Remember that GFCIs detect grounded neutrals downstream - possible source of “nuisance tripping” Test the GFCI by using the test button and a load March 1999 42