Last edit: 01/08/2023
Are you new in the Machinery Technical Standard world and do you feel a bit lost with the terminology?
International Technical Standards are important since they are recognised as complying with the following principles:
- impartiality and consensus
- relevance and effectiveness
ISO and IEC are the two widely recognised international standardisation bodies. In USA, instead, there are many standardisation private companies. That is (one of the many) reasons ANSI exists: to give those companies the recognition of those principles.
But let’s now focus on the terminology used in the documents. Technical standards give both requirements (obligations) and recommendations.
According to [ISO/IEC Directives, Part 2, Seventh edition, 2016]:
“3.3.3 Requirement. Expression in the content of a document conveying objectively verifiable criteria to be fulfilled and from which no deviation is permitted if compliance with the document is to be claimed."
“3.3.4 Recommendation. Expression in the content of a document conveying a suggested possible choice or course of action deemed to be particularly suitable without necessarily mentioning or excluding others”.
The requirements are not expressed with the verb “must” or “have to” but “shall”. Here are all the nuances:
- "shall" indicates a requirement
- "should" indicates a recommendation
- "may" is used to indicate that something is permitted
- "can" is used to indicate that something is possible, for example, that an organization or individual is able to do something
Here some examples of Requirements.
In Section 14 "Grounding – General" of UL 508A, Article 14.1 states:
14.1 An industrial control panel shall have provision for grounding all noncurrent carrying metal parts that are exposed or that are able to be contacted by persons during normal operation or adjustment of the equipment and that are able to become energized due to a breakdown of insulation, loose wiring connection, or electrical disturbance. Grounding (bonding) braids shall be listed according to UL 467 and sized according to 15.1.
In the following example the difference between requirements (indicated by shall) and recommendation (indicated by should) is clearly noticeable.
In Section 184.108.40.206 "Requirements for guards" of EN ISO 12100, Article 220.127.116.11.1 "Requirements for fixed guards" states:
Fixed guards shall be securely held in place either
– permanently (for example by welding), or
– by means of fasteners (screws, nuts) making removal/opening impossible without using tools; they should not remain closed without their fasteners (see ISO 14120).
In Section 7 "Instruction handbook, maintenance and cleaning" of EN ISO 14159, Article 7.1 "Instruction handbook" states:
Information shall be provided so that, after the machinery is installed, it maintains its hygienic integrity (e.g. drainability) and there is adequate access for servicing and cleaning.
Measures shall be described on the use of the machinery so that, when used correctly, the product is not exposed to factors that can lead to contamination. Requirements for monitoring and control of critical hygiene parts shall be identified.
And here some examples of recommendations (non-compulsory statements):
In the following example the difference between requirement and recommendation is even more emphasized since the reccomendation (should) is included in an informational note.
In Article 517 "Health Care Facilities" of National Electrical Code 2020 (NEC), Section 517.42 (E) "Receptacle Identification" states:
The electrical receptacles or the cover plates for the electrical receptacles supplied from the life safety or equipment branches shall have a distinctive color or marking so as to be readily identificable.
Informational note: If color is used to identify these receptacles, the same color should be used throughout the facility.
In Article 430 "Motors, Motor Circuits, and Controllers" of National Electrical Code 2020 (NEC), Section 430.126 (A) "Motor Overtemperature Protection" states:
Adjustable-speed drive systems shall protect against motor overtemperature conditions where the motor is not rated to operate at the nameplate rated current over the speed range required by the application. Protection shall be provided by one of the following means. […]
For motors that utilize external forced air or liquid cooling systems, overtemperature can occur if the cooling system is not operating. Although this issue is not unique to adjustable speed applications, externally cooled motors are most often encountered with such applications. In these instances, overtemperature protection using direct temperature sensing is recommended or additional means should be provided to ensure that the cooling system is operating (flow or pressure sensing, interlocking of adjustable-speed drive system and cooling system, etc.).
In Section 5.3 "Normal conditions for tests" of IEC 60079-29-1, Article 5.3.2 "Test gas(es)" states:
The flammable gas(es) to be used in a mixture with clean air for initial and all subsequent tests shall be selected in accordance with a) to d) with decreasing priority.
a) The specific gas for equipment intended for sensing a single flammable gas only. […]
d) A gas from the manufacturer's list of flammable gases for which the equipment is claimed to be suitable. The choice of this gas should be made by agreement between the manufacturer and the test laboratory.
Finally, it is important to understand three other terms used:
Certification: It is the provision by an independent body of written assurance (a certificate) that the product, service or system meets specific requirements. Certification is also known as third party conformity assessment.
Testing: Testing is the determination of one or more of an object or product’s characteristics and is usually performed by a laboratory.
Inspection: Inspection describes the regular checking of a product to make sure it meets specified criteria.