Contractor Role in Inspection & Testing

According to Regulation 712 – 01 – 03, the inspection shall include at least the checking of the following items, where relevant to the installation and, where necessary, during erection. The followings listed below are to be inspected prior to testing.

1) Connection of conductors

2) Identification of conductors.

3) Routing of cables in safe zone or protection against mechanical damage.

4) Selection of conductors for current-carrying capacity and voltage drop, according to design.

5) Connection of single-pole device for protection or switching in phase conductors only.

6) Correct connection of accessories and equipment.

7) Presence of fire barriers and protection against thermal effects.

8) Methods of protection against electric shock.

9) Prevention of mutual detrimental influence.

10) Presence of appropriate devices for isolation and switching correctly located.

11) Labeling of protective devices, switches and terminals.

12) Adequacy of access to switch gear and equipment.

13) Presence of danger notices and other warning signs.

14) Presence of diagrams, instructions and similar information.

15) Erection methods.

2.0 Testing Requirement

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.

Basically there are two (2) type of tests.

No supply test ( Dead test )
Temporary supply test ( LIVE Test )

1 | No Supply Test (or DEAD TEST )

The following test shall be tested without LIVE energized supply.

Continuity Test on Protective conductor ( equipotential, circuit protective conductor )
Continuity Test on Ring Circuit
Insulation Test
Polarity Test
Earth resistance test

A. 1 | Continuity test on protective conductor.

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.

A. 2 | 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:

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 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.

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 1.5.

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

A. 3 | 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.

Test voltage

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 )

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 )

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

Test acceptable value

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

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.

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.

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.

A. 4 | 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.

A. 5 | 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 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 = 0.7 Ω (Acceptable <1 Ω )

Earth conductor material

copper
steel

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.

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.

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.

Conditions when earth resistance 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.

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.

B - Temporary Supply Connected (or LIVE TEST )

After the dead test is completed, the next steps is to tested the completed consumer unit with LIVE energized supply. This is known as temporary connected supply test.

Polarity Test
Earth fault loop impedance Test
RCCB/RCD Tripping Time Test
Phase Sequence Test
Last Point Trip Test (with Socket Tester)

B. 1 | Polarity Test

Polarity under LIVE test condition is simple.

Tools for perform simple LIVE polarity tests:

use electrician tools such as test-pen. To do the test simply point the tip on L label of every terminal or equipment connected with supply switch ON.
using a socket tester
using multi-meter - set to voltage range to measure the voltage supply.
test set such as earth fault loop impedance test set and RCCB/RCD tripping time test set also provide polarity check.

B. 2 | Earth Fault Loop Impedance Test

This test is done during LIVE supply is energized and to perform to check if a fault occurs in an electrical installation, sufficient current will flow to operate the fuse or circuit breaker protecting the faulty circuit within a predetermined time.

The value of the earth fault loop impedance acceptable shall be not more than 100 ohm/Ω (Zs < 100Ω).

Refer to figure on the right is the earth fault loop path.

Formula Earth Fault Loop Impedance

Zs = Ze + ( R1 + R2 )

whereZs = is the system loop impedance
Ze is the external loop impedance (from the suppler side of the consumer unit back to the transformer)
R1 = resistance of phase conductor R2 = circuit earth resistance ( cpc )

Example calculations of Zs value

Given the value of Ze is measured 0.4Ω, resistance of R1 is 4.2Ω, and R2 is 1.8Ω.

Find the total earth fault loop impedance, Zs ?

Solution: Zs = Ze + ( R1 + R2 )

= 0.4Ω + ( 4.2Ω + 1.8Ω ) = 6.4 Ω (Acceptable, Zs< 100Ω )

When Zs value is greater than 100 Ω

The following conditions where Zs is greater and it affects on the electrical system.

RCD or RCCB may not trip and cut off supply according to standard tripping time. (< 40ms )
this indicates poor earthing system on site and needs attention.
Conductor poor termination or wiring improperly done.
conductor poor quality.

Solution:

check and measure again the earth resistance.
Increase the depth of the earth electrode copper rod (if found less than 3 meter).
check earth chamber and all the accessories ensure it properly done.
check all protective conductors (c.p.c) connected ensure proper securing the earth terminal.

Figure above showing the earth fault loop impedance is been tested at consumer unit (distribution board). The test readings shall be below 100 Ω.

Figure 6.2

Figure above right also doing earth loop impedance test on ring circuit. Commonly the earth loop impedance testset is plugged into any socket outlet and then prest TEST button to obtain the value about 0.4Ω to 0.6Ω

Referring to table below, the maximum value of Zs is indicated.

How to find fault current

Formula; If = Vn ÷ Zs

Where;If - fault current leakageVn - nominal voltage suppliedZs - value of earth fault loop impedance

Example fault current calculations

Given Vn is 240 volts and earth fault loop impedance on site is 34Ω, calculate the earth current fault?

Solution : If = Vn ÷ Zs

If = 240v ÷ 34Ω, = 7.05 A

B. 3 | RCD/RCCB Tripping Time Test

This test requires to ensure the protection device able to operate in specific time to quickly disconnect the incoming supply.

Standard test value is:

< 50 milliseconds (IEE standard)
< 40 milliseconds (Malaysia standard)

Test instrument: RCD/RCCB Time test set (refer on Test equipment topics)

Test method: Set test cycle button to 0° and 180° deg repeat all test below 3 point.

No trip test (Time taken shall be not more than 2000 ms.)
Rated Trip test (RCD/RCCB should trip during this time, take value) Acceptable results should be <40ms (MS)
Fast Trip test (RCD/RCCB should trip during this time, take value) Acceptable results should be <40ms (MS)

Warning: Wrong wiring installation may cause damage to your test equipment.

RCD test can plug into a switch socket outlet (SSO).

B. 4 | Phase Sequence Test (for 3 phase system)

The phase sequence test is need to ensure the three phase supply order is correct, which is clock wise direction.

Test equipment is known as phase sequence tests.

Phase sequence meter is used for detecting the sequence of the supply in three-phase electric circuits. Since the direction of rotation of three phase electric motors can be changed by changing the phase sequence of supply.

Correct phase sequence is clockwise rotating direction. (Correct order : R-Y-B-R )
If any of three phase line is reversed, the test set will shows anti-clockwise rotating directions.

Figure above is an old method of perform phase sequence test. This test methods has obsolete over the years due to many modern test equipment are available in the market today.

Figure above showing how phase sequence tester is been used and clip on to an isolator terminal.

Picture above is the example of rotating disc type (left) phase sequence tester and the LED lamp type (right) phase sequence tester.

B. 5 | Last Point Trip Test (optional)

This test is optional, basically is to ensure the RCD/RCCB will be able to trip due to earth fault from the furthest circuit or point from consumer unit. This way any sudden fault may be able detected by the protection device.

Items use to perform the test:

1no. 100 watt lamp bulb, two(2) x long pole insulated (or wood pole).
or socket tester (refer to test equipment topics).

Lamp bulb method:

ensure using insulated long pole or wooden pole with red and black cable,
this is done for lighting point, point one red cable on Live (L) terminal and black cable to the Earth (E) terminal, this will cause earth fault and trip the RCD.

Figure above is another test methods by using two long pole to perform test trip with a 100w bulb. This test should be performed on lighting terminal or ceiling rose.

Using Socket tester to perform last point tripping test.

Refer to right picture is the socket tester with three indicating lamps and a red color test trip button.

How use socket tester

plug in the socket tester to switch socket outlet (SSO)
switch on the socket switch
Look at all the three indicator light, if polarity is correct then all LED should lite up.
To perform tripping test simply press the red button , this should cause the RCD/RCCD to detect a fault and causes supply to cut off.

Inspection & Testing Form (IT Form)

This is the standard Sarawak form for Inspections & Testing under Electrical Inspectorate Unit (EIU).

List of test equipment for Testing work requirement

Multi-meter -analog or digital (prefer digital) or clamp meter
Earth resistance testset complete with test spike
insulation resistance testset
Earth fault loop impedance testset complete
RCD/RCCB tripping time test
phase sequence testset
socket tester
test lamp incandescent 100 watt lamp bulb

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