Quiz 2 – ‘PAT Testing’ Basics

It is recommended that the test instrument is checked at regular intervals, although annual calibration and the provision of a certificate by the manufacturer or a calibration house is often the norm.

The appliance itself has to identify the type of construction.  Opening the plug and counting the conductors tells us whether there is a 2-core or 3-core flex...not whether it is the correct flex for the item - it could have been changed at some point.

The safety of the item is dependent upon the safety of the socket.  If the socket is damaged, it could make a safe item, unsafe.  Therefore, prior to using the item, the user should check the condition of the socket

By definition, an Extra Low Voltage item has a reduced input voltage and is not powered by the mains supply

The resistance of the flex is influenced by its length.  The longer the flex, the more copper there is, so the more resistance there will be.

"H05VV-F" - for indoor mobile installations and household appliances with medium mechanical strain.  "3G" - 3 conductors.  "NSW24982" - product code.  "1.0mm² " - the cross sectional area of each conductor.

We want the resistance of the earth path to be a little as possible, so a perfect test result would be 0.0Ω.  As a perfect result is unrealistic, we have a tolerance of ≤0.10Ω... i.e. up to and including 0.10Ω is acceptable

The copper used as the conductor has a specified resistance per unit length.  Therefore, as the length increases, so does the resistance.

An earth path is designed to take fault current to ground and away from the equipment user.  Resistance in an earth path will affect its effectiveness putting the equipment user at risk.  As electricity will always take the path of least resistance, low resistance in the earth path is always required.

The key 'safety feature' of a Class II item is two distinct layers of insulation (or one layer of reinforced insulation) around live parts.  Also known as double insulated.

Under fault conditions, we would expect current to pass down the earth path to ground.  If there is too much resistance in the earth path, the fault current will find an alternative path to ground e.g. through the user.

• Current - Amps
• EMF / Potential Difference - Volts
• Resistance - Ohms
• Power - Watts

The 'box inside a box' symbol represents 2 layers of insulation

If a flex has a moulded plug, it isn't possible to open the plug and count the number of conductors.  However, we look at the flex for 3G or 3X to indicate 3-core or 2G or 2X to indicate 2-core.

The industry standard states that an item with a power rating of up to 700 Watts will draw up to 3 Amps.  From 701 Watts to 3,000 Watts it will draw up to 13 Amps.

The only recognised way of identifying whether an item of electrical equipment has been designed as Class II is to look for the Class II construction mark

While an earth path is a safety device, it can be problematic.  It is arguably better to prevent electricity leaking out of the equipment by using more insulation, rather than dealing with electricity which has already leaked out by sending it down an earth wire.

By definition a Class II item is mains powered and has 2 distinct layers of insulation (basic and supplementary) or 1 layer of reinforced insulation.

The duty holder is ultimately responsible for the safety of the site and should determine the date for the next inspection and/or tests based on a risk assessment

Extra Low Voltage (ELV) items are powered by a stepdown transformer or switch-mode power supply with a reduced output of up to 50Vac or 120Vdc