Page 72 - Electric Drives and Electromechanical Systems

Chapter 2 Analysing a drive system 65

These general application problems can never be solved by one specific formula; rather,
the requirements of the various equipment must be recognised, and an optimum system
should be selected by careful attention to detail. For example, a system protected to IP54 is
protected against dust and water being sprayed in all direction, though limited leakage is
permitted. If however the system is to be used in a hazardous environment, for example an
explosive atmosphere, different regulations apply, for example BS EN 60079 (2013).
The National Electrical Manufacturers Association (NEMA) system takes a different
approach, by classifying individual cubicles or systems for a specific application, for
example, a NEMA-3 system is defined as being for outdoor use and providing a degree of
protection against windblown dust, rain and sleet, and will be undamaged by the formation
of ice on the enclosure which is equivalent to a enclosure or system rated at IP64 protection.

2.7.6 Hazards and risk
It is a legal requirement, placed on both the supplier and user, that the equipment should be
designed, manufactured, installed, operated, and maintained to avoid dangerous situations.
Within the United Kingdom these requirements are embodied in the relevant Acts of
Parliament, and are enforced by the Health and Safety Executive, which issues a range of
notes for guidance for the designers of equipment. Regulations in other countries will be
covered bynational legislation,and thisneeds tobeconsideredduring the design process.In
understandingrisks,theconceptsofhazards,riskanddangerneedtobeconsideredandhow
they can be determined and designed out of a system.
A hazard is any condition with the potential to cause an accident, and the exposure
to such a hazard is known as the corresponding danger. As part of the design process
an estimate the of damage that may result if an accident occurs, together with the
likelihood that such damage will occur, is termed the risk associated with the hazards.
As discussed in Chapter 11, Cyber-Physical systems, the increasing use of the drives
and controllers interconnected via an network leads to cybersecurity risks, where risk is
for the potential for a threat (a person or thing that is likely to cause damage) to exploit
a vulnerability (a flaw, feature or user error) that may result in some form of negative
impact at either a process or organisational level (GCHQ, 2016; HSE, 2017).
Some hazards are inherent within a design; for example, the spindle of a lathe is haz-
ardous by its very nature. Other hazards are contingent upon some set of conditions, such
as improper maintenance, unsafe design, or inadequate operating instructions. Several
distinct types of hazards can be associated with machine tools and similar systems:
Entrapment and entanglement hazards, where part or all of a person’s body or clothes
may be pinched or crushed as parts move together, including gears and rollers.
Contact hazards, where a person can come into contact with hot surfaces, sharp
edges, or live electric components.
Impact hazard, where a person strikes the machine, or a part of the machine strikes
the person.