Case Study: PUWER Regulations applied to a second hand machine.

Our client instructed ESA to assist in bringing a newly acquired machine forward into this millennium. The machine’s functional condition was unknown, many modifications had been done without any documentation and the general machine state meant a full overhaul was required. All this had to be achieved on a small budget in delivering a solution subject to PUWER.

PUWER means Provision and Use of Work Equipment Regulations 1998’, these Regulations place duties on people and companies who own, operate or have control over the work equipment. PUWER also places responsibilities on businesses and organisations whose employees use work equipment, whether owned by them or not.

PUWER requires that equipment provided for use at work is:

  • suitable for the intended use
  • safe for use, maintained in a safe condition and inspected to ensure it is correctly installed and does not subsequently deteriorate
  • used only by people who have received adequate information, instruction and training
  • accompanied by suitable health and safety measures, such as protective devices and controls. These will normally include emergency stop devices, adequate means of isolation from sources of energy, clearly visible markings and warning devices
  • used in accordance with specific requirements, for mobile work equipment and power presses

IMG_0615The mechanical and electrical hazards were assessed for compliance with the above regulation and check to whether they still comply with the latest machinery directives.

The dangerous working parts of the machine were enclosed by a perimeter guard with interlocked gate access points. These access points were mechanically inhibited from opening by a captive key system. The existing electrical interface to the captive key switch had been bypassed. This was due to the increased electrical loading now applied to the system.

The electro-mechanical safety system took the form of an obsolete unit originally made by ‘Fortress Interlocks’. ESA had to back engineer the internal connections for this safety device and prove out the device for safe workings.

Previously the system had solely operated with voltages 230v and above. In integrating this captive key system, these voltage levels were restricted to 230/110v, the interface method changed with the monitoring of the captive key purely done with volt-free contacts to a new PILZ relay. This now meant all mechanical safety would be controlled from this unit only, working alongside the electrical safety controlled via the PILZ unit.

The PILZ safety relay selected reflected the type, frequency and severity of any exposure to the hazards. The classification was defined by the Performance level calculation as laid out in BS EN13849-1 standard and the machine classified as ‘e’ (A continual exposure to the hazards with life threatening severity).

The standard BS EN13849-1 relates to the ‘Safety Related Parts of an Control System’ which takes the old machinery safety standard, BS EN954-1 to the next level when defining the hardware safety elements and involves the frequency of use and the mean-time-before-failure (MTBF) probability’s in the assessments.

Due to the classification, a hardware category 4 PILZ relay was selected. The new relay would need to electrically isolate equipment to be carried over; the equipment had been housed into two untidy enclosures.

Both panels had a mixture of 230v and 24v controlled devices and these control circuits were not detailed in any way providing an obstacle to be overcome when looking for new safety integration.

IMG_0873Our client also requested for these two enclosures to be combined into a single enclosure utilising and carrying over as many suitable devices as possible.

Any devices other than the inverters, utilising 230v control voltages were replaced since the new design and panel layout had to adhere to BS EN60204-1 and utilise SELV (24v dc controls).

We produced a heat calculation for the panel internals and deemed the existing fan and filter adequate for the new enclosure.

The original machine and controls enclosures had no method of emergency stopping, a series of local and field Emergency Stops were introduced. These new safety devices were all dual channel wired to meet with the safety category of the system and provide electrical isolation via the PILZ relay.

Not only did we provide new safety controls that brought the system into IMG_0875this millennium, but we included a series of design improvements:

  • We interlocked the door with a suitable isolator providing additional safe working due to the reduction of risk from electric shock.
  • The new controls design provided the ability to isolate each field motor device for maintenance purposes.
  • We replaced old-fashioned motor control methods, i.e. overloads with modern motor rated circuit breakers. This allowed for a much cleaner enclosure mounting plate layout.
  • Additional timers were supplied to give better reaction between the motors.

With careful consideration to existing equipment ESA delivered a modified control system that not only met with the latest safety standards but was completed with the client’s tight costing constraint.