IET Code of Practice book

IET Code of Practice - 5th Edition Update

In November 2020, the fifth edition of the IET Code of Practice for In-Service Inspection and Testing of Electrical Equipment was published. The new 5th edition includes quite a few changes.

The City & Guilds 2377 qualification has also been updated to reflect the changes to the Code of Practice. The latest C&G qualification based on the 5th edition is City & Guilds 2377-77. This qualification replaces both 2377-22 and 2377-32.

Electrical Tests

The 5th edition has made some changes to the guidance on the earth continuity test, the limit for the leakage test has been changed and the test procedure for equipment with a functional earth has been clarified. These changes have been introduced to avoid unnecessarily failing equipment. The good news is that if you are carrying out the testing to the guidance in the 4th edition, you do not need to make any drastic changes, but you should be aware of the changes to avoid unnecessarily failing equipment.

New Leakage Test Limit

The most significant change is the increase in the limit of the leakage test. Although the leakage test has always been an optional test, most modern PAT instruments automatically carry out a leakage test, or substitute leakage test, as standard on all equipment. The 5th Edition now recommends a limit of 5 mA for all equipment, both Class I and Class II.

Appliance Type Old Limit 5th Edition Limit
Class I Handheld & Portable 0.75mA 5mA
Class I IT, Movable, Stationary & Fixed 3.5mA 5mA
Class I Heating & Cooking 0.75 mA or 0.75 mA per kW,
whichever is greater,
with a maximum of 5 mA
Class II All Types 0.25mA 5mA

The leakage test originates from the compliance tests carried out by the manufacturer which requires certain control conditions and test circuits in order to give accurate results. In practice, it has often been difficult to obtain results that meet the previous limits in the 4th edition. Certain appliance types, such as washing machines and microwave ovens, can sometimes be difficult to obtain a reading below 3.5 mA, so the increase to 5 mA should make testing of this type of equipment much easier and will prevent unnecessarily failing equipment.

Most PAT test instruments will be pre-programmed with the old limits, so if the limits can not be manually changed, it will require some manual interpretation of the test results to apply the limit of 5 mA to any equipment failing at the previous test limit.

Borderline Earth Continuity Readings
test instrument showing a borderline reading

The standard limit of (0.1 +R) Ω, where R is the resistance of the supply cable, still applies for the earth continuity test. However, there are now some additional notes that allow for some leeway on borderline readings.

Borderline readings should not be discounted as a fail if they are within tolerance of the test instrument. All test instruments have a specified accuracy of the readings. Test instruments from different manufacturers may have varying degrees of accuracy, but they are generally expressed as a percentage plus a number of digits, for example ±(5% + 2 digits). When measuring relatively small amounts of resistance, the accuracy to the number of digits is the most significant. An accuracy of ± 2 digits means that the reading may vary by 0.02 Ω but still be within tolerance. So in practice, in this case a test reading that is 0.02 Ω higher than the calculated (0.1 + R)Ω limit should be considered acceptable.

The 5th edition also allows for some leeway for older appliances that have a slightly higher measured earth continuity resistance than (0.1 + R)Ω, up to a maximum of 0.5 Ω. A measurement slightly higher than the limit should be considered acceptable provided that the increase in resistance is due to the design of the equipment and not the deterioration of the earth connection. In practice it is difficult to know if the increased resistance is due to the design or not and the term ‘older’ is subjective. Our advice would be to apply this with some caution and note that it is only readings that are slightly above (0.1 + R)Ω where this would be applicable. Where possible, previous test results should be checked to ensure the resistance has not increased, which would indicate a deteriorating earth connection.

Clarification of Functional Earth Equipment

laptop charger example of Class II FE

Some appliances have an earth connection for functional reasons, rather than for electrical safety. This is usually IT or communications equipment that requires an earth connection to meet EMC (Electro Magnetic Compatibility) requirements. The most common type of equipment with a functional earth are laptop power supplies and other switch-mode power supplies used on IT equipment. Fault protection is provided by double or reinforced insulation, but because they contain an earth connection, they can not be considered as standard Class II appliances. This was previously mentioned in the 4th edition, but this is now further clarified with a new equipment classification of Class II FE (Functional Earth). The 5th edition now explicitly states that this type of equipment should be inspected and tested as Class II equipment.

Class II FE Symbol

There is a new symbol for this type of equipment which was introduced in IEC 62368-1, the latest harmonised product-safety standard for ICT and AV equipment. The symbol is a combination of the double insulated, square within a square symbol, and the existing symbol for a functional earth. The new standard is slowly being implemented and is due to replace all existing IT and audio/video standards by December 2020. The Class II FE symbol is now being used on many new IT power supplies, but older equipment is unlikely to be marked. Some older Class II FE equipment may be marked with ‘ITE’.

Frequency and Appliance Types

Risk Based Frequency

The guidance on assessing the frequency of inspection and testing has always been based on risk assessment, but the 5th edition emphasises this point by providing some sample risk assessments in appendix and the table on suggested initial frequencies has been removed altogether. In our opinion, the frequency table was a useful tool to provide some indication on suitable test intervals, but presumably it was felt that too many people have been relying on the frequency table, rather than carry out a risk assessment.

Appliance Types
equipment types removed

The detailed descriptions of appliance types - hand-held, portable, moveable, stationary etc., have been removed from the 5th edition. The intent is that unless equipment is covered by another inspection and testing regime (such as the EICR), then all equipment comes under the guidance of the Code of Practice regardless of how ‘portable’ it is. Again this has always been the case in previous editions of the Code of Practice, but the removal of the frequency table and the change to the leakage limit to 5 mA for all equipment types, allows the detailed descriptions of the appliance types to be removed altogether.

ES1 / ES2 Classifications

There has also been an introduction of a new classification of ES1 and ES2. These new classifications have been included because a new product standard, BS EN 62368, is being introduced in December 2020. BS EN 62368 covers a broad range of electronic, IT and communication technology products. The new standard is based on Energy Source classifications (ES), which replace the previous approach of protection based on voltages, such as extra-low voltage (ELV) and separated extra-low voltage (SELV). There are some differences, but ES1 is broadly comparable to SELV, with protection against electric shock based on separation and a limited voltage that will not harm a user should a fault occur. Equipment supplied from either a SELV or ES1 supply is classified as Class III. Class III equipment does not normally require testing, so in practice this is just a technical change which will have no impact on those undertaking PAT testing.

Energy Source Effect on Body Effect on Combustible Material
Class 1 Not painful, but may be detectable Ignition not likely
Class 2 Painful, but not an injury Ignition possible, but limited growth and speed of fire
Class 3 Injury Ignition likely, rapid growth and speed of fire

Purchasing the Code of Practice

Now includes a hologram

With the publication of each new edition, inevitably the price increases. The price is now £60! Much like anything else that is massively overpriced, it becomes a target for counterfeiters. Genuine copies now have a hologram on the inside front cover. If you are taking the City & Guilds 2377-77 qualification, you will need a copy for the exam. It is available on Amazon here, or on our website here.