Testing

Testing basics:

Visual inspection of appliances and leads for damage that could allow leakage.

Earthing for earthed appliances - test the earth is a low resistance (below 1 ohm)

Insulation for earthed and double insulated appliances - test for weak insulation by putting 500 volts between the functional conductors (phase + neutral) and earth. To allow a path to earth for double insulated appliances while testing, the meter earth probe is touched on any metal of the appliance - in several places if necessary. We Use leakage insulation test as required.

Leads and power boards test earth - (below 1 ohm) P + N to earth - (above 1 mega ohm) and polarity of each conductor.

Power packs - P + N to output - (above 1 mega ohm)

RCD - RCD tester.

Isolating Transformer - specific tests.

Earth Bonding.

Inspection and testing procedure

On arrival, have the site contact person fill in the site information sheet. This will clarify details of area and equipment to be tested including if there is anything that is not to be tested eg computer servers, computer switches etc.

For computers, ask that staff turn them off to be tested. Do not change the position of, or add any data cables, especially on computer switches etc as this can damage computer servers.

Note whether the appliance is turned on or off at the wall, and on the appliance so that you can leave it as it was after the test. This is very important particularly for fridges etc.

Inspect and test in this order:

Unplug the appliance first for safety.

If the appliance fails any part of the inspection or test, stop at that point and follow the failed appliance procedure.

Inspection

Visually inspect appliances including leads and plug for damage that could allow electrical leakage.

Visually inspect appliances for damage to controls, switches handles, stands, wheels, and all other parts that may cause a danger in any way.

Types of damage or Defects to look for include:

Heat

Chemical

Moisture

Anchor of the lead

Basic insulation exposed. - Basic insulation is the insulation under the outer layer or cover.

Basic twisted - may indicate damaged insulation that could cause a short circuit.

Squashed, cut, or abraded lead - bend the leads to find this.

Tape - no tape is allowed on any lead.

Terminals of sockets spread - causing potential overheating. - Indicated by a loose plug in the socket.

Load label and double insulation sign in place.

Controls are working & identified.

Covers & guards are secured and undamaged.

Ventilation clear.

Any other visible fault, which could cause a danger in any way.

Testing

This is the main part of our service to assure our clients of the safety of their appliances.

Assess each appliance for the correct tests to be preformed and the correct procedures for each test to be effective.

The tests that we do include:

Earth continuity

Earth bonding

Insulation

Leakage.

Leads and power boards

Polarity

Surge diversion

Power pack, insulation to output.

RCD - RCD tester

Isolating Transformer - specific tests

Earth continuity

For earthed appliances Class one only:

Test the earth is a low resistance (below 1 ohm) between the earth pin of the appliance plug and all exposed metal parts. So that in the event of a short circuit to earth, sufficient current will flow to quickly, blow the fuse or circuit breaker. When the tester tests for earth, a voltage is applied between the Earth pin of the plug and the probe. The probe is touched on the metal parts of the appliance. If the earth resistance is low, a current will flow in this circuit, indicating a good Earth if sufficient current flows.

If the Earth test fails, it may be that the probe is not making good electrical contact through corrosion, dirt, or paint on the appliance or the part that the probe is touching, is not conductive, i.e. plastic that looks like metal. Try a different position or scratching through to the metal material in a position that is not normally seen such as the back or underneath.

It may also be that the appliance under test is double insulated or powered through a double insulated power pack -

Printers often have this. - Check. Earth appliances with no accessible conductive parts, (such as an all plastic fan) do not require the earth test because under 3760, we don't dismantle appliances to test. Be extra careful with the visual inspection in this case. Check for dampness or dirt that could conduct around switches etc.

Testing parameters:

Earth resistant's >1 ohm @ 100mA

Plug earth pin to exposed metal parts using the earth probe. (Flex cord and anchor to check for a loose earth connection.)

If the earth test still fails after completing the above procedure, then the appliance has failed the test and no further testing is required. Follow the procedure for failed appliances.

Earth Bonding Test

Where equipment such as power points are mounted in metal enclosures, the enclosures must be earthed to provide an earth path in the event of a short circuit. This earthing is called earth bonding because it bonds the metal to earth. Power points are often mounted in parts of desks or moveable partition walls, and connected to a wall socket with a lead and plug. These require testing as a power board with additional earth bond test for any metal enclosure that the points are mounted on or the lead passes through. The earth bonding is checked by doing a normal earth appliance test, while holding the probe on the metal parts

Insulation test

Once an earthed appliance has past the earth test, go on to the insulation test. Our meters automatically go on to this test when the earth test passes. The probe is not required for the insulation test if the earthed appliance has just passed the earth test, as the tester puts 500 volts between phase + neutral and earth + probe. As the earth test has shown that the earth pin of the plug is connected to the earthed appliance with less than 1 ohm, the probe may be removed for the insulation test. This may speed the testing, as the probe can be put on the next appliance while the insulation test is completing.

For earthed and double insulated appliances, the insulation test tests for weak insulation by putting 500 volts between the functional conductors (phase + neutral) and earth. To allow a path to earth for double insulated appliances while testing, the meter probe is touched on any metal of the appliance - in several places if necessary.

Testing parameters:

Appliance switches on.

500v between phase + neutral and earth - for earthed appliances or

500v between Phase + neutral and exposed metal parts for double insulated appliances.

(Minimum of 1 mega ohm) or for appliances with metal covered elements (like on a stove) - minimum of 0.1 mega ohm

Class 11 double insulated (use earth probe)

Leakage

This test is for appliances that require power to activate electronic or contactor type switches.

Details of this test are in AS/NZS 3760

Leads and power boards

Lead and power boards IEC test. Our tester does three tests on leads and power boards.

1. Earth resistance tests between the earth pin of the plug and earth terminal of sockets is below 1 ohm.

2. Insulation between phase + neutral and earth is above 1 mega ohm.

3. Polarity Check that phase, neutral and earth at the plug, are connected through to the correct terminals at the sockets.

Surge diversion

Some leads, power boards, and appliances incorporate surge diversion. This works by having components connecting phase, neutral and earth. When the voltage between any of these conductors rises momentarily above approximately 300 volts (such as during a lightning storm or large load switching), the components lower in resistance and allow current to bypass the normal circuit.

This has the effect of reducing the level of over voltage to the appliance that may otherwise damage the appliance. The components are called metal oxide varistor (mov's)

They vary their resistance down as voltage goes up. When we test anything incorporating mov's with 500 volts for insulation resistance, they will fail the test, as the mov's resistance will go down well under 1 mega ohm.

These appliances are correctly tested with a leakage test.

Power packs

Power packs usually feed appliances that are not designed to be safe with 240 volts, and therefore need to be checked that they will not allow 240 volts through to the output.

Power packs are insulation tested with 500 volts between the phase + neutral and the output, to check that 240 volts is not likely to get through to the output.

RCD - use our RCD tester or our PAT tester incorporating RCD testing. More to come.

Isolating Transformer - specific tests in AS/NZS 3760

The detail of tests and procedures will be covered in the practical training.

Action after completing the inspection and tests:

Appliance passed:

Put a pass numbered tag on asset, 200 mm from the plug so that it is not handled when plugging in or out.

Leave as you found it and tidy up leads better than they were.

Start computers to speed start-up for staff.

Check that vital equipment is on again.

Appliance failed:

For vital equipment, eg fridge or medical equipment notify responsible person immediately and follow instructions with safety in mind.

Tape up the plug with red tape to stop it being used.

Put red tape near damage to indicate position if known.

Write fault on numbered danger tag and place close to the plug.

Fill in failed appliance register.

Put failed appliance in previously designated failed appliance area if practical.

Note: We do not repair appliances, but refer them to the owner for repair or replacement by others. Low value appliances eg leads, power boards etc are normally more economically replaced than repaired.

Give a copy of the fault report to the responsible person each day of testing (2 copies) to keep them up to date with progress.

Additional notes on AS/NZS 3760 2010

Index numbering in red relates to AS/NZS 3760 2003

Section 2

Notes on Inspection:

Note environment of the appliances, which may indicate likelihood of damage. Old Appliances are more likely to be damaged. Check Infrared heaters for reflector corrosion. This will cause over heating of the heater due to absorption of the heat rather than reflecting it out. (Burn danger and damage to internal insulation). Check for unprofessional repairs or modifications. All appliances must comply with standards of construction and any modifications are unlikely to comply with these standards.

Do not pass any modified or home made appliance under any circumstance. Put a failed tag on these and treat them the same as any other failed appliance. The only way these can be made legal is if they are made to a relevant standard and tested by a Certified Testing Laboratory.

Old appliances may have Asbestos insulation and cotton covered cords - these fail because of the hazard of Asbestos if it is exposed. Often on old appliances such as irons, toasters, heaters etc have this type of cord, usually black with a white or red fleck through it.

Check overhead projectors have safety cutout switches working when open - turn on and then open - check for live terminals.

2.3.2 Inspection:

(a) Look for damage that may now or in the future, expose live parts to a person that may directly touch them, or touch other conductive material that could be in contact with live parts eg metal table legs, TV, wall brackets or chair legs etc.

(b) To check that any pull on the flex will not break any internal connections (especially earth - loss of safety) cause a short circuit, expose basic insulation, or live parts.

(c) (l) twists may indicate internal damage

(ll) bend flex if cuts or abrasion is suspected

(lll) tape on cords usually indicate that someone has covered some damage. Tape is not acceptable to repair a cord as it may move or come off, exposing the damage. In addition, damaged cores may short out or break, hidden from view under the tape. That is why it is illegal to tape a cord. This is also sited in the Electrical Regulations.

(d) To warn people not to overload power boards eg by plugging two heaters into it. The maximum combined load of a power board is 10 amps. Equivalent to 2300 watts. Normal wall sockets are rated at 10 amps. Plugging in more load than this is likely to cause over heating marks around the power board, socket pin holes - using heaters through a power board is not a good idea.

(e) So that switches can be turned off safely when required. In addition, switches are not loose, as this could be a hazard if someone moves a switch and the conductors short out behind the switch causing an explosion or livening up the switch that they are holding.

(f) To prevent the possibility of touching live parts directly or with other objects. To prevent mice getting in causing a fire hazard. Check that tools are required to remove or open covers. Some appliances have cut out switches to isolate the live parts when a cover is opened, eg Overhead projectors, (OHP's).

(g) To limit over heating, fire danger & damage to insulation

(h) New plugs have insulation around the base of the pins to reduce the chance of touching a live pin directly or with other small objects, if this plug is not fully into a socket. New cord connections (female end) also have a shroud for the same reason.

2.3.3 Notes on Testing

Strict safety procedures for you and anyone else close by are essential.

No one may touch any appliance under test; keep people back, especially children who may unexpectedly touch some thing.

It is essential that you have shock prevention and treatment knowledge including CPR.

Work in a systematic way and work on one appliance at a time.

Learn all aspects of the test equipment and the exact reasons for every test.

If in doubt - ASK. Add comments if failing an appliance to explain reasons. Once an appliance fails the test, do not proceed with the

next test of this appliance.

Earth continuity Test relies on a good connection of the earth clip on earthed metal. Often this can be difficult due to external insulation

or paint on metal parts. Try underneath appliances where the metal may not be painted.

Some small water heaters may not have accessible earthed metal although all of these are required to be earthed.

They may be tested by putting a wire extension on the earth-clip to reach the earthed element. Directly on the element is usually best

for insulated jugs etc, where there is no other accessible metal.

Check Testing Earth Path?

Picture to be added

When a short circuit occurs from the internal live parts to the metal case of an appliance, the metal case becomes alive - has a voltage

from the case to earth. This voltage could give a shock to anyone that touches the case while simultaneously being in electrical

contact with earth.

If the earth connection through the earth wire in the cord and in the building wiring is a low resistance, then a high current will flow in the

circuit as follows. From the power board transformer, through the outside lines and building wiring to the appliance, then back

through the earth wire & building wiring to the main switchboard earth bar, then through the earth/neutral bar link to the neutral bar to

the main neutral and power board lines, back to the power board transformer. The current that flows in this situation, is only limited by

the total resistance of this circuit. This will normally be much lower than the resistance of the circuit when it includes the resistance of

the appliance in normal operation and many thousands of amps will flow until the fuse or circuit breaker opens the circuit.

Because of this low resistance and high current the protective circuit breaker or fuse for this circuit will open the circuit and remove the

voltage.

This must happen very fast (under .4 sec) to reduce the length of time that someone maybe shocked and the time that stray currents

to earth have to cause heating (fire danger). The less the resistance of this circuit, the higher the current and the faster the protector

fuse or circuit breaker will open. This is why a low resistance earth connection to an appliance is very important for safety.

Even when the earth connection is a low resistance, a dangerous voltage will be present on the case of the appliance until the fuse or

circuit breaker blows, due to the resistance of the circuit from the appliance back to the power board transformer.

Picture to be added

The lower the earth wire resistance the less voltage will be present between the case of the appliance and directly to earth.

2. 3. 3. 1

This is to make sure the connection to the accessible earthed metal of the appliance the earth wire and connection of the plug do not have a high resistance which would increase the time it would take for the circuit protection, fuse or circuit breaker to clear a fault. (also see notes on appendix A) As leads, power outlet boxes and RCD'S are often part of the overall circuit of an appliance, it is equally important to check the resistance of the protective earth conductor and connections of this equipment.

The building wiring earth wire must also be of a low resistance to ensure safety. The testing of that does not come under this standard

and if there is doubt that it is OK, then please notify the Responsible Person for them to arrange for it to be checked by a Registered

Electrical Inspector. (Also, see notes on appendix A).

2. 3. 3. 2

When voltage is applied to any conductor or conductive part of an appliance, there is always a chance that the voltage could get past the basic insulation onto an accessible part. If this happens there is the danger of electric shock and, or fire, due to high leakage currents.

In a class 1 (earthed appliance), any leakage current that gets through or past the basic insulation, would normally be conducted back to the building main switchboard and through the earth/neutral bar-link to the neutral. This is provided the protective earth circuit is of a low resistance all the way back to the neutral bar. If it is not, then the voltage and potential for a shock or a fire is high, at the appliance or cord. This is why it is important to have good basic insulation.

In class 2, (double insulated appliances), there is an extra layer of insulation between the basic insulation and accessible parts. For leakage current to get to accessible parts, it has to get through or past two layers of insulation or equivalent of two layers. If this happens, there are no earthed parts to remove the leakage and a dangerous voltage may be accessible. This could occur if the insulation was damaged or bypassed by moisture, water, dust, dirt, or loose metal or conductive parts inside the appliance, eg loose screw. This is why it is important to inspect and test the insulation of cords and appliances.

A leakage test is to detect the level of leakage current, and is one way to test the insulation of an appliance. This test is carried out by connecting the appliance to the Portable Appliance Tester (PAT). The PAT powers up the appliance with normal 240v and measures the current flowing in the phase conductor and the current flowing in the neutral. If the current is the same in both then there is no leakage current. If there is a different current flowing in each conductor then the difference is the leakage current. It is important to connect the earth clip of the PAT to earthed metal and parts of a class 1 (earthed) appliance while doing this test, as resistance in the earth conductor or connectors will cause a lower indication of potential leakage current.

When doing a leakage test on class 2 (double insulated) appliances connect the earth clip to any accessible metal parts. This can often be low voltage outlets, aerials or data outlets. Some appliances have no exposed metal parts. Check these very carefully for conductive material around switches or joints in the casing. Check for mechanical damage - if in doubt, Fail the appliance. Other tests involve wrapping the appliance in a conductive material to do the leakage or insulation test. Remember that if leakage does occur while testing, then parts of the appliance may become alive and be a shock or fire danger. Do Not touch the appliance or any thing that it is in electrical contact with it while testing.

To test the insulation, a voltage is applied between conductive parts (phase & neutral) and earth. If a current flows in this circuit then the insulation is not high enough. Possible reasons are moisture, water, dust, dirt, or loose metal or conductive parts inside the appliance, eg loose screw. It is required by the standard that the insulation resistance be above one mega ohm (1 m ohm). This will limit the leakage current to relatively safe levels. The tester checks this insulation resistance by measuring the current that flows between conductor parts and earth during the test. It uses Ohms law R = V/I to calculate the insulation resistance.

Metal Oxide Varistors (MOV) are a type of electronic resistor that reduces its resistance as the voltage goes up. They are used in appliances, leads, and power boards as a surge diverter. If a surge (an increase in voltage) occurs, then the MOV, which may be connected between live parts and earth, will reduce its resistance allowing a current to flow to earth. This reduces the voltage of the surge. If a voltage of more than 250v is used to test the insulation of appliances incorporating MOV, then the test will show the lower resistance through the MOV. This is why testing at 250v is allowed.

Some modern appliances incorporate electronic buttons and switches to turn the appliance on. These switches will only turn on when the appliances is powered up with normal 240v. This is why powered up leakage tests are used on these appliances. If an insulation test was done on these appliances using the method as in figure B.1. appendix B, the switch is not able to be turned on and this test would only include the live parts up to the switch. If the insulation past the switch were low then this would not be detected. Older appliances have mechanical switches that don't rely on being powered up to work.

2.3.3.2.1

We cannot determine if a design resistor to earth has a correct value or not. If the appliance has installation resistance below one m ohm then we fail the appliance. Appliance technicians may determine that it is ok and tag it themselves. We do not.

2.3.3.2.2

Residual current devices (RCD'S), RCD'S are designed to detect leakage current and turn off the current if the leakage current gets to high. They sometimes have a design resistor to earth for their operation. Low resistance could be due to a breakdown of insulation or water in the RCD. If it does not pass the normal insulation test or leakage test then we fail it.

Table 1 & 2

Different types of appliances have varying amounts of leakage over their usable life. The amount of leakage allowed, reflects the balance between safety and economics.

Mineral insulated metal-sheathed heating elements are the type commonly used as stoves and jug elements. They are sometimes used in other heating appliances. The mineral insulation has a tendency to absorb moisture from the atmosphere, which can cause a low insulation resistance. This often happens when the appliance is not used for long periods of time. As long as the earth of the metal sheathed is of low resistance and no one touches it, it may be turned on to heat up. This often dries out the insulator, raising the insulation resistance.

2.3.3.3

Power packs are normally double insulated and have no earth conductor. Check for damaged case and signs of over heating. Some types of power packs do have an earth connection.

See appendix E

2.3.3.4

Testing RCD'S. This requires a separate dedicated RCD tester or a tester incorporating a RCD testing function. The RCD is plugged into the tester and the dials set to the appropriate position. The tester is plugged into the power. The test button on the tester is pushed and the time of disconnection is indicated. These are to be as per table 3 (leakage current). This is to ensure that under fault conditions, the time that fault current can flow is limited to reduce danger of electric shock or fire. Some testers have a different testing procedure.

2.3.3.5

The polarity of plugs & cord-extension sockets is only required to be checked if the plug or connector is a rewire able type. It is not always obvious whether a plug or connector is rewireable or not. As the polarity test with our PAT is automatic and fast. We do this test for all leads and power boards. See notes on appendix f.

2.4.1

Print a failed tag and put it neatly on the lead, close to the plug. Tape up the plug to prevent it being used and take the appliance to the area previously designated for failed appliances by the Responsible Person. Leads, power boards, and other old appliances may not be worth repairing as they can often be purchased cheaply.

2.4.2

Print a passed tag and put it neatly on the cord 200mm from the plug. For power packs with no separate plug & lead, put the tag close to the power pack on the extra low voltage cord.

2.5

When required, records will be produced from the downloads from the PAT. This will be handled by the office from the PAT. It is important to down load the information to the office each night after testing, so that in the event of data being lost from the PAT, the loss will be minimal. If the Pat holds several days of data and it is lost this may mean retesting of all the appliances.

Table 4.

The Intervals for testing will be determined and advised to you.

Notes on Appendix's: Our PAT does each of these tests by connection the appliance to the PAT and then running the tests. This is often a different procedure to that shown in the appendix. The types of test for each appliance are still carried out by the PAT. If the appliance passes all of the required tests, then a pass tag is printed.

Appendix A. The earth conductor is vital for safety of class 1 appliances.

A2. Our PAT is capable of many varied test parameters. The parameters that are set for various types of appliances under test are set to optimize the safety and efficiency of the test. Do not change these without discussion with me. (Bruce). However suggestions are welcome.

A3. Rotating metal parts could include the chuck of a drill etc.

B1. A leakage test is used where there are electronic switches that require mains power to close. In this way, all of the insulation of the live parts within the appliance will be tested. A leakage test may also be used where using a high voltage insulation test may damage sensitive equipment.

B2. If there is leakage currents during this test then a dangerous voltage may be present on the appliance. Do not touch the appliance during testing.

B3.1 PRCD = Portable RCD

B3.2 Put the earth clip on any metal that may become alive due to a fault.

B3.3 We use 250v for testing leads and power boards incorporating MOV Surge diversion.

Figure B2 Legend 2 should read: Test active and neutral to accessible metal parts.

C1. Isolating transformers require the exact tests as shown in this appendix. Some of our PATs have Help screens that will take you through this. Or call me.

D1. Operation of our RCD tester gives a time for the RCD to disconnect under fault conditions.

E3 (c) Testing of power packs for insulation between supply conductors and out put conductors may be difficult due to the tiny size of some output plugs. Be careful no to damage these plugs with the earth clip.

F. Cord sets with two core figure 8 plugs have no polarity requirement; these require a visual inspection only.

Appendix J

J1 Basic Electrical Principles:

This information can be obtained from books and websites, including our Website as above.

The knowledge required for competent appliance testing technicians includes: Atomic structure - Electrons surrounding the nucleus

Electron movement - Electrons can move from atom to atom if an external force is applied.

Conductors & insulators - materials have various degrees of insulation or conduction. Electrons held strongly or weakly.

Current flow - amps - Electrons moving from atom to atom around a circuit.

Electrical force - volts - Magnetic or a chemical force causing electron imbalance between atoms.

Conductor and insulation resistance to current flow - ohms - heating effect - current control.

Appliance principals of operation to be considered: The circuit - basic insulation, earthed appliances & double insulated appliances- heating - transformers - motors - electronics - earthed appliances (class 1) double insulated (class 2) - MOV (metal oxide varistor)

Reason for protective earth.

Reason for double insulation.

J2 Circuit Protection From Over Current And Leakage Current:

Causes of over current

Short Current

Heating or fire caused by over current

Size of conductor - small wire = high resistance.

Loose terminals (heating effect)

Fuses

Circuit breakers

RCD'S

J3 Electrical Safety:

Causes of fire

Effects of current flowing through a person's body- shock - burns

Treatment for electric shock and burns

Conduction of water - dirt - dust

Safety Precautions:

Clearance from test area and equipment (yourself & others)

Isolate first, then visual check

Damage to Insulation in Leads & Appliances

Broken earth wire or loose connection

Broken switches

Exposed basic insulation

Exposed conductors

Name of conductors & Colour Code:

A = Active = P = phase = L = line or live - red or brown. In three phase conductors the colours may be any colour except green, yellow or green with yellow stripe. Switches fuses and circuit breakers are always in the phase conductor.

E = Earth green or Green with yellow stripe - connected to the earth at every building and power suppliers transformer - no switches, circuit breaker or fuse anywhere in this conductor.

N= neutral - black or blue connected to earth at every building and power suppliers transformer (this is called neutral because it is connected to earth and normally has neutral voltage (very low) to earth. No switch in this conductor except in some appliances with double pole switches. Only allowed to be switched if the associated phase conductor is also switched at the same time.

J4 Read all of AS/NZS 3760 2010

J6 Regulations - see legalisation

Have a great day

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