Current detective - Revision history

ErnieHorning: Updated terminology, added several safety clarifications, corrected a few technical inaccuracies, and improved explanations while preserving the original design and educational intent.

2026-07-20T17:56:07Z

Updated terminology, added several safety clarifications, corrected a few technical inaccuracies, and improved explanations while preserving the original design and educational intent.

Dirknerkle: /* Outlet Tester */

2018-12-12T16:11:42Z

Outlet Tester

Dirknerkle: /* The Current Detective test plug */

2018-12-12T16:11:08Z

The Current Detective test plug

Dirknerkle: /* Two Outlet Test Plugs */

2018-12-12T16:10:52Z

Two Outlet Test Plugs

Dirknerkle: /* Outlet Tester */

2018-12-12T16:10:35Z

Outlet Tester

Dirknerkle: /* Current Detective Schematic – Leakage */

2018-12-12T16:09:02Z

Current Detective Schematic – Leakage

Dirknerkle: /* Current Detective Schematic – Normal Operation */

2018-12-12T16:08:45Z

Current Detective Schematic – Normal Operation

Dirknerkle: /* Current Detective – Concept */

2018-12-12T16:08:18Z

Current Detective – Concept

Dirknerkle: /* How Much Current Hurts??? */

2018-12-12T16:06:50Z

How Much Current Hurts???

Dirknerkle: /* How Much Current Hurts??? */

2018-12-12T16:05:38Z

How Much Current Hurts???

@@ Line 1: / Line 1: @@
 =Introduction – Current Detective=
-The Current Detective project is a method to monitor the small leakage current that would cause Ground Fault Circuit Interrupt to trip.
+The Current Detective project is a method to monitor the small leakage current that would cause Ground-Fault Circuit Interrupter (GFCI) to trip.
-= Ground Fault Circuit Interrupt (GFCI) or Residual Current Device (RCD)=
+= Ground-Fault Circuit Interrupter (GFCI) or Residual Current Device (RCD)=
 ==What is a GFCI or RCD?==
-It is an electro mechanical device that monitors current flow on the hot and neutral legs of a circuit. When current between the two legs is greater than 6mA, the device causes the circuit to “trip”, or creates an open or break in the circuit, effectively stopping current flow.
+It is an electro mechanical device that monitors current flow on the hot and neutral legs of a circuit. A Class A GFCI is designed to "trip" when the differential current reaches approximately 4 to 6 mA., or creates an open or break in the circuit, effectively stopping current flow.
 ==What Does a GFCI Monitor?==
@@ Line 43: / Line 43: @@
 =Transformer Basics=
-A transformer operates on the principles of “electromagnetic induction”, in the form of mutual induction. Mutual induction is the process by which a coil of wire magnetically induces a voltage into another coil located in close proximity to it. A transformer consists of into of two sections of coiled wire that are separated from each other, a primary winding and a secondary winding. As the AC current on the primary winding goes through the 360º, 60 Hertz cycle, it will cause a current to be generated in the secondary winding. The ratio of primary to secondary windings or “turns” will determine the amount of current passed from the primary to the secondary. Each turn is one loop of the coil.
+A transformer operates on the principles of “electromagnetic induction”, in the form of mutual induction. Mutual induction is the process by which a coil of wire magnetically induces a voltage into another coil located in close proximity to it. A transformer consists of into of two sections of coiled wire that are separated from each other, a primary winding and a secondary winding. As the AC current on the primary winding goes through the 360º, 60 Hertz cycle, it will cause a current to be generated in the secondary winding. The ratio of primary to secondary windings or “turns” will determine the amount of voltage and current is transformed from the primary to the secondary. Each turn is one loop of the coil.
@@ Line 50: / Line 50: @@
 A current sense transformer will pass one “leg” through the coil and the second leg around the coil. The primary winding of the transformer is the single wire. The current sense coil is typically a 2,000 or more “turn” coil. This allows for capture of the primary current in the secondary without impacting the primary.
@@ Line 68: / Line 70: @@
 *Ground
-If you have looked in a residential electrical panel, you may have noticed that the neutral and ground are tied to the same point electrically.
+If you have looked in a residential electrical panel, you may have noticed that the neutral and ground are bonded (tied) together at the service entrance.
@@ Line 102: / Line 104: @@
 * GFCI outlets save lives by monitoring the hot and neutral legs of an outlet to ensure that the current matches within 6mA.
 * GFCI outlets will open the circuit in 25mS to prevent electrocution.
 * GFCIs will detect ground to neutral connection downstream from the outlet.
 * GFCIs will not protect against overload on the hot/neutral unless specifically built to do so.
@@ Line 118: / Line 121: @@
-This design uses a current sense coil with both the hot and neutral leads passing thought it. The ground wire is run outside of this coil. A TLC082 operational amplifier actually provides 2 high gain amplifiers in one unit. One amplifier set for a 100 gain, and the second is adjustable to allow for calibration. The meter in this schematic is a digital voltmeter set to 20volts. The power supply portion of the circuit is 2 9volt batteries to provide portability. This design has no direct connection to the high voltage side. The ground wire could be skipped but accommodations would need to be made to support leakage current to ground for calibration.
+This design uses a current sense coil with both the hot and neutral leads passing thought it. The ground wire is run outside of this coil. A TLC082 operational amplifier actually provides 2 high gain amplifiers in one unit. One amplifier set for a 100 gain, and the second is adjustable to allow for calibration. The meter in this schematic is a digital voltmeter set to 20volts. The power supply portion of the circuit is 2 9volt batteries to provide portability. The amplifier circuitry is galvanically isolated from the monitored conductors by the current transformer. The ground wire could be skipped but accommodations would need to be made to support leakage current to ground for calibration.
 =Current Detective Schematic – Normal Operation=

@@ Line 136: / Line 136: @@
 =Outlet Tester=
-[[image:GFCI_and_Outlet_tester.jpg|649x456px]]
+[[image:GFCI_and_Outlet_tester.jpg|724x456px]]
 The 3 prong outlet testers use neon bulbs between the hot, neutral and ground to validate wiring and indicate problems. These testers may allow 2 to 5 milliamps between the hot and ground. To a GFCI, this will appear as leakage.

@@ Line 150: / Line 150: @@
 This circuit calls for a controlled calibration. A combination of a resistor and neon bulb with a known current draw will provide leakage current of a known quantity to allow the calibration. This will create a small controlled load from hot to ground (leakage).
-[[image:Leakage amp test plug.jpg|345x260px]]
+[[image:Leakage amp test plug.jpg|545x460px]]
@@ Line 158: / Line 158: @@
 * 1.9 milliamps current (designed)
 * 30K ohm resistor
 =Reference material=
 [https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf]

@@ Line 142: / Line 142: @@
 =Two Outlet Test Plugs =
-[[image:GFCI  with 2 test plugs.jpg|624x356px]]
+[[image:GFCI  with 2 test plugs.jpg|724x456px]]
 Two outlet test plugs will allow approximately 5milliamps from the hot to the ground wire. Again, the GFCI would consider this leakage current. This will be close to tripping the GFCI.

@@ Line 136: / Line 136: @@
 =Outlet Tester=
-[[image:GFCI_and_Outlet_tester.jpg|449x256px]]
+[[image:GFCI_and_Outlet_tester.jpg|649x456px]]
 The 3 prong outlet testers use neon bulbs between the hot, neutral and ground to validate wiring and indicate problems. These testers may allow 2 to 5 milliamps between the hot and ground. To a GFCI, this will appear as leakage.
 =Two Outlet Test Plugs =

@@ Line 130: / Line 130: @@
 =Current Detective Schematic – Leakage=
-[[image:Current detective - Leakage.jpg|555x323px]]
+[[image:Current detective - Leakage.jpg|755x523px]]
 In an operation with .01 amps of leakage; the sense coil will output the difference of the 2 phases of power. This current will be converted to voltage by the 1K across the coil. This voltage will be amplified 100 times by the first amplifier. The second amplifier is adjusted to have 1 volt reading equal to 1 milliamp of leakage. Keeping in mind that greater than 5mA of leakage is a GFCI “trip”.
 =Outlet Tester=

@@ Line 124: / Line 124: @@
-[[image:Current detective - normal.jpg|568x297px]]
+[[image:Current detective - normal.jpg|768x497px]]
 In normal operation, the current on the hot lead and the neutral legs will be equal. The sense coil output will be zero since the 2 different phases are 180º out of phase and will cancel out each other. The meter should read 0 volts when calibrated.
 =Current Detective Schematic – Leakage=

← Older revision		Revision as of 16:08, 12 December 2018
Line 115:		Line 115:
	* The goal is to make something simple to build and operate.		* The goal is to make something simple to build and operate.

−	[[image:Current detective - Overview.jpg\|~~624x205px~~]]	+	[[image:Current detective - Overview.jpg\|824x405px]]

@@ Line 18: / Line 18: @@
 (NEMA)
-[[image:Effects of electrical shock.jpg|254x522px |center]]
+[[image:Effects of electrical shock.jpg|254x522px]]
 * 0.5–2mA