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

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

3 March 1999 Electric Shock

4 March 1999 Occurrences of Electrical Shock Street & Highway Farm Lightning Industry Home Deaths caused by electrical shock 25 Year Average ( )

5 March 1999 Electrocutions to 1993

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

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

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

9 March 1999 Ground - Fault (Indirect Contact) L N EGC Ground-Fault.060 A 12A 6A 5.940A

10 March 1999 Ground - Fault (Direct Contact) L N Ground-Fault.1 A 6A 5.90A

11 March 1999 How GFCIs “Think”?

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

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

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

15 March 1999 Current Adding Machine Under Ground Fault Conditions Load 6A 5.9A Ground- Fault.1A L N

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

17 March 1999 GFCI Tripping Characteristics

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

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

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

21 March 1999 Proper Installation of the GFCI

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

23 March 1999 Standard 120 Volt Connection (GFCI Receptacle) 120/240Vac Source N NL1L1 L2L2 Line Terminals Load Terminals

24 March Volt Load - No Neutral

25 March /240V Load

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

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

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

29 March 1999 GFCI CB on Multi-Wire Circuits

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

31 March 1999 Wiring Errors

32 March 1999 This “Old House” Problem N GFCI installed on one circuit Second circuit installed and neutral “stolen” from a close-by circuit 6A ? L1 L2

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

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

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

36 March 1999 Testing a GFCI

37 March 1999 UL GFCI Tests l Every GFCI must pass the following “in-line” manufacturing tests no trip below 4mA (no load) must trip at 6mA (no load) no trip below 4mA (with load) must trip at 6mA (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 102V test button at 132V 1500V hi-pot

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

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

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

41 March 1999 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?

42 March 1999 Summary l GFCIs have contributed to a reduction in the number of deaths due to electric shock l GFCIs look at the current going out and compare it to the current coming back l Avoid common wiring errors - “Think like the GFCI” l Remember that GFCIs detect grounded neutrals downstream - possible source of “nuisance tripping” l Test the GFCI by using the test button and a load