IEC 60204-1: Safety of Machinery – Electrical Equipment of Machines

Moe Lamothe, P.Eng, Lamothe Approvals Inc.

The scope of IEC 60204-1 is as follows: “…applies to the application of electrical and electronic equipment and systems to machines not portable by hand while working, including a group of machines working together in a coordinated manner but excluding higher level systems aspects (i.e. communications between systems).”  A machine is defined in clause 3.33 as “an assembly of linked parts of components, at least one of which moves, with the appropriate machine actuators, control and power circuits, etc., joined together for a specific application, in particular for the processing, treatment, moving or packaging of a material.”  While the definition of a machine would indicate that a piece of electrical equipment with no moving parts is not covered by the requirements of this standard, IEC 60204-1 is the best available guidance for the general electrical construction of a electrical equipment.

Some of the important issues that are clearly indicated in 60204-1 include:

Terminal for Connection to the External Protective Earthing System

The terminal for each incoming supply is to be located in the vicinity of the phase conductor and it must accommodate a copper conductor of the following size (larger terminals are required for aluminum conductors).  Table 1 of 60204-1 is shown below:

There has been considerable controversy over the proper method of terminating the Protective Earthing conductor: it’s colour and the use of green-yellow wire for internal bonding purposes. The following items are extracted from IEC 60204-1, 60950-1, 61010-1.

IEC 60204-1 Forth Edition

The following are relevant definitions and clauses from IEC 60204-1:

Clause 3.42: Protective Bonding Circuit: The whole of the protective conductors and conductive parts used for protection against electric shock in the event of an insulation failure.

Clause 3.43: Protective Conductor: A conductor required by some measures for protection against electric shock for electrically connecting any of the following parts:

- exposed conductive parts;
- extraneous conductive parts;
- main earthing terminal.

Clause 5.2: Terminal for Connection to the External Protective Earthing System

For each incoming supply, a terminal shall be provided in the vicinity of the associated phase conductor terminals (see 8.2.1) for connection of the machine to the external protective earthing system…

At each incoming supply point, the terminal for the external protective conductor shall be identified by marking with the letters PE in order to avoid confusion…

The other terminals used for the connection of machine components or subassemblies to the protective bonding circuit of the machine shall be identified either by the graphic symbol 60417-2-IEC-5019:  or with the letters PE, the graphical symbol being preferred, or by the use of the bicolour combination GREEN-AND-YELLOW.

Clause 8.2.1: The protective bonding circuit consists of:

- PE terminal(s) (see 5.2);
- the conductive structural parts of the electrical equipment and the machine;
- the protective conductors in the equipment of the machine including sliding contacts where they are part of the circuit.

Clause 8.2.2: Protective Conductors

Protective conductors shall be identified in accordance with 14.2.2.

Clause 8.2.7: Protective Conductor Connecting Points

All protective conductors shall be terminated in accordance with 14.1.1. The protective conductor connecting points shall have no other function and shall not be used, for example, to attach or connect appliances or parts.

Each protective conductor connecting point shall be identified as such using the symbol 60417-2-IEC-5019: .  Alternatively, terminals for the connection of the protective conductor may be identified by the bicolour combination GREEN-AND-YELLOW. For use of the letters PE, see 5.2.

Clause 14.2.2:  Identification of the Protective Conductor

The protective conductor shall be readily distinguishable by shape, location, marking, or colour.  When identification is by colour alone, the bicolour combination GREEN-AND-YELLOW shall be used throughout the length of the conductor.  This colour identification is strictly reserved for the protective conductor.

For insulated conductors, the bicolour combination GREEN-AND-YELLOW shall be such that on any 15 mm length one of the colours covers at least 30% and not more than 70% of the surface of the conductor, the other colour covering the remainder of the surface.

In summary of the above clauses, all points where the protective bonding connector(s) are terminated must be identified by PE or and the incoming protective conductor terminal shall be unidentified by PE only. Green/yellow wire should be used for the entire protective bonding circuit and the colour ratio should be a minimum of 30% of either colour.

This termination point shall not have any other function and it is to be identified by the letters ‘PE’. Other terminals used for the connection of components or sub-assemblies to the protective bonding circuit shall preferably be identified by  but the letters PE or the use of the bicolour green-yellow combination can also identify these points.

When identified by colour alone, the protective conductor shall use the bicolour green/yellow combination throughout the visible length of the conductor. On any 15 mm length, one of the colours must cover at least 30% and not more than 70% of the conductor surface with the other colour covering the rest.

Other conductors shall not use the green-yellow colour.

Notes:

1.  Most of the electrical safety standards, including 60950-1 and 61010-1, specify that  be used to identify the protective earthing connection point.

2.  If you are  marking your product using a European Low Voltage Directive harmonized standard, then the specific standard you are using for your product will likely take precedence over this requirement.

3.  marking using the European Machinery Directive, the requirement in 60204-1 will take precedence.

4.  This requirement is generally consistent with industry practice in that the protective earthing connection point on such items as switching power supplies (components) is marked with the .

IEC 60950-1 First Edition

Clause 2.6.1: Protective Earthing

The following parts of equipment shall be reliably connected to the main protective earthing terminal of the equipment.

Parts likely to carry fault currents intended to operate overcurrent protective devices:

a)   Accessible conductive parts that might assume a hazardous voltage in the event of a single fault…

b)   Parts required to be earthed to maintain the integrity of SELV circuits…

c)   Parts required to be earthed to maintain the integrity of TNV circuits…

d)   SELV circuits, TNV circuits and accessible conductive parts required to be earthed …if the power source is not a telecommunication network or a cable distribution system

Parts that carry other currents:

e)   SELV circuits, TNV circuits and accessible conductive parts required to be earthed …if the power source is a telecommunication network or a cable distribution system

f)    Circuits, transformer screens and components (such as surge suppressors) that could not assume a hazardous voltage in the event of a single fault…but are required to be earthed in order to reduce transients that might affect insulation…

g)   SELV circuits and TNV circuits that are required to be earthed in order to reduce or eliminate touch current [leakage current] to a telecommunication network or a cable distribution system…

Clause 2.6.3.5: Colour of insulation

The insulation of the Protective Earthing Conductor in a power supply cord supplied with the equipment shall be green-and-yellow.

If a Protective Bonding Conductor is insulated, the insulation shall be green-and-yellow except in the following two cases:

- for an earthing braid, the insulation shall be either green-and-yellow or transparent;

- for a Protective Bonding Conductor in assemblies such as ribbon cables, busbars, printed wiring, etc., any colour is permitted provided that no misinterpretation of the use of the conductor is likely to arise.

Except as permitted in 2.6.2 [Functional Earthing], the colour combination green-and-yellow shall be used only to identify Protective Earthing Conductors and Protective Bonding Conductors.

IEC 60950-1 also provides tables showing the size of protective bonding conductors and terminals.

IEC 61010-1 Second edition

Clause 6.5.1.1: Integrity of protective bonding

The integrity of protective bonding shall be assured by the following means:

a)   Protective bonding shall consist of direct connected structural parts or discrete conductors, or both.  It shall withstand all thermal and dynamic stresses to which it could be subjected before one of the over-current protective means specified in 9.5 disconnects the equipment from the supply

b)   Soldered connections subject to mechanical stress shall be mechanically secured independently from the soldering.  Such connections shall not be used for other purposes such as fixing constructional parts.  Screw connections shall be secured against loosening.

c)   If a part of the equipment is removable by the operator, the protective bonding for the remainder of the equipment shall not be interrupted (except when the part also carries the mains input connection to the whole equipment).

d)   Movable conductive connections, for example, hinges, slides, etc. shall not be the sole protective bonding path unless they are specifically designed for electrical interconnection and meet the requirements of 6.5.1.3.

e)   The exterior metal braid of cables, even if connected to the protective conductor terminal, shall not be regarded as protective bonding.

f)     If power from the mains supply is passed through equipment for use by other equipment, means shall also be provided for passing the protective conductor through the equipment to protect the other equipment. The impedance of the protective conductor path through the equipment shall not exceed that specified in 6.5.1.3.

g)   Protective earthing conductors may be bare or insulated. Insulation shall be green-and-yellow, except in the following cases:

- for earthing braids, either green-and-yellow or colourless-transparent;

- for internal protective conductors, and other conductors connected to the Protective Conductor Terminal in assemblies such as ribbon cables, busbars, flexible printed wiring, etc. any colour may be used provided that no hazard is likely to arise from non-identification of the protective conductor.  The bi-colour combination green-and-yellow shall be used only for identifying the protective conductor and for no other purpose.

h)   Equipment using protective bonding shall be provided with a terminal meeting the requirements of 6.5.1.2 and suitable for connection to a protective conductor

Clause 6.10.1.d): Mains supply cords

Green and yellow covered conductors shall be used only for connection to protective conductor terminals.

Clause 6.10.4.3.d): Protective grounding (earthing) lead

A lead intended for field connection to the protective grounding conductor shall be readily distinguishable from all other leads by being finished to show a green colour with or without one or more yellow stripes.

CSA International has a different interpretation:

CSA's interpretation is that the requirements of CSA C22.2 No. 1010.1 and the Canadian Electrical code take precedence over the requirements of IEC 60204. Therefore, there should be only one PE terminal except where the ground connection passes through the equipment to another device. This second ground connection to the other device can also be identified as such.

The PE terminal symbol should be at only these external connection points to signify the location for the external ground connections. The wire from the external ground connection point to the enclosure must be green-and-yellow. For North America, it can be green only since this is a North American deviation. For internal bonding connections, it can be green or green/yellow, or any other colour. The only stipulation is that green/yellow not be used for any other purpose.

Comments:

There is obviously some controversy, but the best approach is to follow the concepts outlined in IEC 60204-1: use green-and-yellow for the entire bonding circuit.

Overcurrent Protective Devices

IEC 60204-1 Forth Edition

The rated short-circuit breaking capacity of an overcurrent protective device must be at least equal to the available fault current at the point of installation. This means that the I²t withstand capability of the fuse or circuit breaker must be greater than the available I²t on the incoming power line.

For cord-connected equipment, usually the branch-circuit protection device will provide adequate protection but it may be necessary to use high-interrupt capacity fuses. This is particularly true of the smaller IEC fuses with glass bodies. They are prone to exploding or arcing from end to end under severe short circuits with the result that adequate protection is not provided.

Two situations merit special attention:

a)      Permanently connected equipment may have much higher branch circuit protection making it necessary to use protection device rated 10,000A or better.

b)      DC powered equipment – DC is particularly adept at arcing across a small gap such as that presented by a 5 x 20 mm fuse.

IEC 60590-1 First Edition

Unless appropriate short-circuit backup protection is provided, protective devices shall have adequate breaking capacity to interrupt the maximum fault current (including short-circuit current) which can flow.

NOTE – If fuses complying with IEC 60127 are used in PRIMARY CIRCUITS, they should have high breaking capacity (1,500 A) if the prospective short-circuit current exceeds 35 A or 10 times the current rating of the fuse, whichever is greater.  

For North America, fuses providing branch circuit protection must comply with one of the following standards:

a)      UL 248-4 (CSA C22.2 No. 248.4) Class CC fuses; 

b)      UL 248-8 (CSA C22.2 No. 248.8) Class J fuses;

c)      UL 248-10 (CSA C22.2 No. 248.10) Class L fuses;

d)      UL 248-10 (CSA C22.2 No. 248.10) Class R fuses; or

e)      UL 248-15 (CSA C22.2 No. 248.15) Class T fuses.

The standards listed above provide a very high breaking capacity of at least 200,000A.

In general, fuses should be acceptable for the application and not explode in the product, or should be high breaking capacity fuses.

Emergency Stop Functions

 IEC 60204-1 Forth Edition

There are three defined categories for stop functions:

-  Category 0 – stopping by immediate removal of all power.

-  Category 1 – a controlled stop with power available to the machine to achieve shutdown.

-  Category 2 – a controlled stop with power left available to the equipment.

For Category 0, the stop shall override all other functions, power to the equipment shall be removed as quickly as possible without creating other hazards, reset shall not initiate a restart, it shall have only hard-wired electromechanical components. A Category 0 control cannot use hardware or software or the communication of commands over a communication link to achieve its intended function.  

Control Colours

IEC 60204-1 Forth Edition

The following colour coding of actuators should be used:

Function	Colour (allowed)	Colour (NOT allowed)
Start / On	White (preferred), grey, black or green (permitted)	Red
Emergency Stop	Red (mandatory)	All other colours
Stop / Off	Black (preferred), grey or white	Red (permitted but is not recommended), green

Conductors

IEC 60204-1 Forth Edition

The following tables will provide some guidance with respect to wire temperature, wire size and wire insulation types that are acceptable. Maximum allowable temperatures for copper conductors are shown in the table below:

Comments

IEC 60204-1 provides a significant amount of additional information with respect to wiring space and the routing of cables. For anybody with electrical equipment construction needs beyond the most basic boxes, it would be very beneficial to acquire a copy of IEC 60204-1. Also available are two part 2 standards, which cover the accepted terminology and schematic symbols. 

Moe Lamothe is the president of Lamothe Approvals Inc. (Georgetown, ON, Canada). He can be reached at info@lamotheapprovals.com.

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The copyright for all of the text, tables and illustrations remains with Lamothe Approvals Inc. Permission is granted to print or reproduce this document provided that it properly attributed to Lamothe Approvals Inc.

Prepared May 2003