Basic Testing - Dead Test

to ensure wiring installation is safe for consumer.
all calculation required to ensure no overload or over-current happening on the circuit.
all load connected (apparatus) are correct.
all protection against over-current are identity with maximum design current.

1.1 Testing Requirement IEE

IEE Regulation 713-02 to 713-12 detail the standard methods or testing required.

The tests should be as follows, and should be carried out in the sequence indicated:

Continuity of protective conductors.(Rp)
Continuity of final circuit ring conductors.
Insulations resistance.
Insulations of site-built assemblies.
Protection by separation of circuits.
Protection by barriers or enclosures.
Insulations of non-conducting floors and walls.
Polarity.
Earth fault loop impedance.
Earth electrode resistance.
Functional tests including the operation of residual current devices.

1.2 Basic Testing on dead circuit or temporary supply not connected

The type of tests are guide under IEE Wiring Regulations and commonly known as DEAD supply test or 'Non supply connected'

Continuity test on protective conductor or 'earth wire'.
Continuity test on ring circuit
Insulation resistance test or 'meggar'
Earth resistance test or 'electrode copper rod resistance test'
polarity test

1.3 Testing equipment or testset required

Electrician or wireman uses many types of test set to perform measurements and readings in electrical engineering. These tests are crucial to ensure circuit installed on premise is safe to operate and avoiding fire incident.

Basic testing equipment use for wireman:

multi-meter (analog or digital type)
insulation resistance testset or known as 'meggar'
socket tester

2.0 Continuity test

Basically this test uses multimeter by applying setting to ohm (or continuity "beep" sound). The value reading is commonly in ohm (Ω) and purpose of this test is to check the conditions of the protective conductor (earth wires) in the circuit whether the line is open or broken. If any of the earth wire during testing reads infinity (∞) (or no sound beep), this means that the earth wire is faulty or broken. This requires immediate attention and effort to recheck or rewired.

Figure above showing a continuity test of socket outlet returns to consumer unit. The protective conductor (earth wire) is measure to ensure the wiring is not open line. Example if meter reads 0.6Ω, this means the earth wire is good.

Figure above showing lighting circuit is perform continuity test.

2.1 Continuity Test on Ring Circuit

Ring circuit is the switch socket outlet under power circuit. The test need to ensure all the socket outlet is complete in loop formation and returns to the consumer unit. The circuit consisting of pairs of L, N and E and all shall wired in a ring formation. The maximum number of switch socket outlet is 10 point controlled by 32A MCB or 30A Fuse circuit breaker.

There are three(3) method to perform this test:

Method 1

Measure resistance at consumer unit from two point. This measures the R1 resistance value of both phase and neutral conductor. The next steps is to measure the R2 resistance value of protective conductor as shown on figure below.

Figure A.2.1 Perform continuity test on LIVE terminal of entire ring circuit. This is upmost important to ensure no OPEN fault on all socket terminal.

Figure A.2.2 Perform continuity test on Neutral terminal of entire ring circuit. Ensure all termination is done properly on all socket outlet.

Figure A.2.3 Perform continuity test on EARTH terminal of entire ring circuit. Best recommend to ensure good continuity is to twist every pair wires connected to the terminals.

Figure A.2.1 Figure A.2.2 Figure A.2.3

R1 (total L Ω) R1 (total N Ω) R2 (total E Ω)

Method 2

This test method require tester to be at all socket outlet.

First step is put a jumper wire between L and E at consumer unit and then measure cable resistance value between the two point on every socket outlet installed in the site as shown in figure on the right.

Method 3

This test method require tester to be at all socket outlet. Measure between socket outlet to ensure the ring circuit is looped correctly by using similar way as shown in figure.

Measure the Total resistance of final ring circuit on A.1 and A.2

Formula; Rt = R1 + R2

Example:

Given measured value R1= 3.5 Ω (L+N) and R2 = 0.7 Ω

Rt = 3.5 + 0.7 = 4.2 Ω

3.0 Insulation Test

The insulation resistance is the cable resistance in individual circuit or entire system. The test is been done commonly at distribution board (consumer unit) but sometimes this test can be done on any cables and electrical equipment. It is important to guard against electric shocks and avoid equipment damage from accidental discharges.

This test is also known as a “Megger” test, is normally used as a “Spot type” test to measure the insulation's dielectric condition of a circuit cables at a given moment in time. Insulation tests on low voltage circuit breakers are also been performed to ensure acceptable levels of insulation resistance between phases and from phase to ground.

3.1 Test voltage requirement

Standard Test Voltage range commonly found in Megger testset :

250 volts (for single phase)
500 volts (for three phase)
1000 volts (for three phase underground cable )

3.2 Test duration

Standard test duration when perform this test is 60 seconds (1 minutes).

Warning:

Ensure NO LIVE SUPPLY
DO NOT TOUCH both test leads of test set. (DC voltage injected at max 50v )

3.3 Test acceptable value

Standard acceptable value for insulation resistance test shall be more than one(1) mega ohm. (>1M Ω)

3.4 Insulation Resistance Test sequence

Before begin this test, follow the guidelines below:

Unplug any equipment plugged in to any socket outlet under power circuit.
Remove all bulbs, lamp bulbs, switch on light switch under lighting circuit.
Remove any fuse available on any load equipment.
Switch ON all miniature circuit breaker (mcb), close fuse CB
Switch on RCD/RCCB
Place the test lead according to test sequence.

Test sequence for single phase: ( 250 v Test voltage ) a. L – E b. N – E c. L – N

Test sequence for three phase: ( 500 v Test voltage )

a. RYBN to E b. RYBE to Nc. R-Y, Y-B, R-B

3.5 Measure Insulation Resistance (E - L)

Refer to figure on the left showing how to perform insulation test between L and E.

This method can be also used to perform troubleshooting relates to earth fault.

Example reading: N-E : 89MΩ - it is good value .

If value measured is example 400,000 Ω means load is connected or need attention to check further.

3.6 Measure Insulation Resistance (E - N)

Refer to figure on the left showing how to perform insulation test between N and E.

This method can be used to perform troubleshooting relates to earth fault.

Example reading: N-E : 75MΩ, good insulation.

3.7 Measure Insulation Resistance (L - N)

Refer to figure on the left showing how to perform insulation test between L and N.

This method can be used to perform troubleshooting relates to direct short circuit fault.

Example reading: L-N : 195MΩ, good insulation.

4.0 Polarity Test

Where the standard prohibits the use of single pole switching device for the neutral conductor, a test shall be made to verify that all such devices are used only for line conductors. Where the rules required double pole switches, a test shall be made to verify that the poles of such devices are connected correctly to the appropriate conductor.

There are two methods of polarity test been conducted:

dead test - using multimeter and measure ohm value.
live test - using test lamp, testpen or testset equipment.

Measuring the result

You can measure the result by:

continuity sound methods
ohm value
using a testlamp (for live test)

Refer to figure above is known as polarity test.

The polarity test is done on a double pole switch to ensure the polarity of the terminal is correct. The multi-meter shall be ohm value to measure the resistance of the load connected. When the double pole switch is turn ON, the load resistance can read in ohm.

Figure on the left is showing polarity test on a single pole switches connected to a load.

When the MCB and single pole switch is turn ON, the multi-meter shall read 240 volts.

5.0 Earth Resistance Test

Earth resistance are being measured with earth resistance test set equipment and the unit value reading is ohm.

The standard ACCEPTABLE VALUE for earth resistance for Malaysia shall be less than one(1) ohm.

Standard requirement for earth resistance test are:

depth of electrode copper rod shall be at least 3 meter (or greater)
standard material shall be copper rod
the sizing of the main earth electrode conductor shall be at least 16mm.dia (if phase cable is bigger than follow Table 54G Sizing of Conductor.

Earth conductor material

copper
steel

5.1 Earth resistance Formula

Formula;

Re = ( Z + Z1 + Z2 ) ÷ 3

Example :

Given following value of Z=0.3Ω, Z1=0.6Ω, Z2=1.2Ω, find total earth resistance, Re?

Re = ( 0.3 + 0.6 + 1.2 ) ÷ 3

Re = 0.7 Ω

(Acceptable <1 Ω )

5.2 Standard test of earth resistance

Refer to figure on left is side view of earth resistance tests, the L value are the distances of the test spikes (metal) and the cable length during test.

Some earth test set brand and model of the test set is indicated recommended length to perform the test.

L = 10meter, 15 meter or 20 meter depends on test set recommendation stated in the manual.

Voltage of these earth test set are indicated as on manual.

5.3 Top view during earth test

Refer to figure on left, the L of the cable for the test equipment are indicated on the test set. Some brand and model of the test set is indicated recommended length to perform the test.

The green doted line is the test zone area for the earth.

5.4 How to testing on existing earthing

Figure 4.3

This method is used when site have no open soil available but if nearby there is a supply transformer then this test can be done.

5.5 If Re value is greater than >1Ω

The solution to the above problem can be done:

increase the depth of the electrode copper rod.
take measurements during early morning or evening where as not under hot sun.
add earth compound material
change position of the Z, Z1, Z2 to other direction within the green test zone area.

5.6 What is earthing compound?

The Bentonite Earthing Compound is produced from highly hygroscopic grades of Bentonite Powder. It can be used as back fill material to maintain moisture levels in areas of dry and rocky terrain. It absorbs and retains moisture for long periods and tends to reduce soil resistivity to a certain extent.

Adding salt mixed with water as earth compound is not recommended as the salty will damage the copper conductor.

Relate topics : Basic Inspection Basic Live Test Consumer circuit

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