Hazard summary

Workers in industrial workplaces such as office buildings, factories, arenas, shops or offices who are required to work on manual motor controllers (MMCs) or other electrical equipment may be at risk of serious injury or death if the electrical equipment is not stopped, de-energized and locked out and tagged before work starts.

Devices called manual motor controllers are typically used to control motor driven equipment such as commercial heating, ventilation and air conditioning units.

They also serve as a motor starter/controller, and sometimes as a motor disconnect.

Typically, MMCs should be marked with the words “suitable as a motor disconnect.” If they are not marked “suitable as a motor disconnect”, they should only be used as a motor starter/controller.

Using an MMC without the marking “suitable as a motor disconnect” as a lockout point is a hazard because the device contacts could weld together and provide a false sense of locking out.

This could lead to electrical current passing through the contacts even with the device switch in the OFF position.

Without testing to make sure there is zero energy, a worker would not be able to detect whether or not the contacts have welded together.

Here are possible contributing factors to this contacts welded together condition:

  • contamination or corrosion of the contact surface can increase contact resistance, raising the temperature at the points of contact
  • a loose rivet joint, a poor weld, or brazed joint can result in contact heating
  • poor contact alignment which reduces the effective contact area
  • currents that are higher than normal

Care must be taken when installing the switch with the MMC so that it is oriented to correspond with the on/off marking on the switch. If the switch is installed backwards the power could be on when the switch enclosure indicates that it is off.

What you’re required to do by law

Lock and tag the power supply

Under subsection 42(1) of Regulation 851-Industrial Establishments the power supply must be disconnected, locked out and tagged on or near live exposed parts of the installations, equipment or conductor:

  • before any work is done
  • while work is being done

Check to ensure lockout requirements are in place

Under subsection 42(2) of Regulation 851, workers must ensure the lockout requirements are in place before beginning work.

Written procedures

Under subsection 42(7) of Regulation 851, employers must have written procedures for disconnecting, locking out of service and tagging.

Other duties under the Occupational Health and Safety Act

Under subsection 25(1)(c) of the Occupational Health and Safety Act, employers must ensure the measures and procedures prescribed are done.

Under subsection 25(2)(a) of the Occupational Health and Safety Act, employers must provide information, instruction and supervision to a worker to protect the health and safety of the worker.

Related requirements

Other requirements related to electrical work may include sections 40-44.2, 60, 75 and 76 of Regulation 851.

Recommended precautions

To help prevent injury or death from electrical contact:

  • employers must make sure that effective precautions are in place to protect workers (for example, ensure that each controller is used appropriately)
  • work practices should include the consideration of unexpected events, such as equipment failure (i.e. the welding of contacts within a MMC)
  • make sure that contacts are suitable in size and material for the installation
  • support members for electrical contacts should be as highly conductive as possible to help keep the contacts cool
  • always confirm the absence of energy by correctly testing, with an approved device rated for the purpose, prior to contacting any exposed parts
  • remember to consider all electrical equipment and installations as energized until they are proven otherwise
  • do not use an MMC as a disconnect unless it is marked as “suitable as a disconnect.”  Rule 28-602 (3) (1) (b) of the Ontario Electrical Safety Code indicates that MMCs marked as “suitable as a motor disconnect” are acceptable to be used as both a starter and a means of disconnecting.

Contact us

If you need more information about safety requirements, please contact the Ministry of Labour Health & Safety Contact Centre at 1-877-202-0008, Monday to Friday, from 8:30 a.m. to 5 p.m., or webohs@ontario.ca.

This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations, and should not be used as or considered legal advice. Health and safety inspectors apply the law based on the facts in the workplace.