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Electrical and Computer Engineering

Electrical Safety 101

 ELECTRICAL SAFETY 101

In Case Of Emergency (Fire, Ambulance, Theft, Safety)
From University telephones: 36111
From any other telephone: 533-6111

Professional Conduct

Graduates of ECE will be professionally responsible for safeguarding people and equipment.  Developing professional safety habits as an undergraduate student is foundational for being a professional engineer in the workplace and in society. 

Electrical Safety

  • Lethal Voltage and Current
    • As little as 50 volts ac can kill under certain conditions. In general anything above 25ma is considered dangerous since it can potentially cause the heart to go into ventricular fibrillation, which can happen in as little time as ¼ second. Currents in the range of 70ma to 300ma are potentially fatal without immediate first aid. With currents through the body of greater than 25ma you may not be able to “let go”. You can use ohms law (E=IR) to calculate body current. Dry skin has a resistance from 100k to 600k ohms. With wet skin the resistance drops to around 1k ohm. With an open skin cut, the resistance drops between 100 and 500 ohms. Thus, one needs to be extremely careful with higher voltages. 120VAC can Kill!
    • If the experiment requires more that 50V (e.g., battery pack or power supply), use insulated tools and wear rubber sole shoes. Only make use of proper cables and connectors.
    • When an activity is complete, or during manipulation, power down equipment, ensure that the equipment is unplugged and that all capacitors are discharged before touching any high voltage leads or the interior of the equipment. 
    • No work other than diagnostic tests using meters, oscilloscopes etc are is to be done on live circuits.
      • Any modification or repair to electrical equipment requires that the equipment be disconnected from all power sources.  Sources of power means ALL sources of potential energy including:
        • Electrical
        • Mechanical items such as springs under tension or heavy objects above ground level
        • Fluid / gas energy stored in accumulators, tanks, etc.
      • If the power connection cannot be disconnected, then the breaker must be opened and locked and tagged according to Ministry of Labour guidelines.
      • Under no circumstances should anyone other than the worker be able to re-energize equipment that exposes workers / students to any energy source.
      • When in doubt, contact the safety officer for clarification.
    • Make sure that equipment chassis, cabinets, or any other enclosures are properly grounded.
    • Do not operate equipment on a wet area.
  • Electrical Equipment and Components
    • Electrical components can cause serious injury.  Make sure you understand electrical components before using them.
      • A resistor that is operated over its wattage rating can burn causing a fire, or explode causing an arc and flying debris.
      • Capacitors can “blow up” proplelling the end cap with enough force to damage one’s eye. This will happen if a polarized or electrolytic capacitor is hooked up in the wrong polarity or connected to a voltage above its rating.
      • Opening an inductive circuit suddenly can cause a large voltage spike, usually for a very short period of time, but may cause the heart to go into fibrillation, depending on conditions.
      • Batteries (mainly 12vdc car type batteries) can explode due to escaping hydrogen gas, which is very explosive. Car battery explosions are very serious and can cause significant injury.  Use extreme care with tools around batteries. Always keep a cap or protective cover over the positive battery terminal. Work in well-vented areas and wear safety glasses and gloves. Always have a neutralizing agent, such as baking soda, available.  C and D cells can also explode, especially  rechargeable Ni-Cad batteries. Appropriate caution should be taken when working with them.
      • Electrical cords–don’t connect multiple electrical strips or cords to make a longer extension cords. All extension cords need to be one cord only.
        • Be familiar with the locations of circuit breakers and fuse boxes
        • Watch for frayed cords and broken plugs. Take these items out of service and have them repaired.
        • Avoid the use of extension cords on the floor as this creates a trip hazard.
        • Never remove the ground pin from a 3 pronged plug.
        • Remove electrical cords from the receptacle by grasping and pulling the plug not the cord.
      • Use only trained and qualified people to construct, repair or modify electrical or electronic equipment.
      • If electrical equipment emits smoke or a burning smell, shut off the power immediately and take it out of service for repair.
      • Use only carbon dioxide, halon, or dry chemical extinguishers on electrical fires.
      • All electrical equipment must be certified by an approved authority such as CSA, ULc, or the Electrical Safety Authority
    • Soldering
      • Splash resistant safety glasses must me worn for all soldering. 
      • Soldering irons must be used with care and always placed in the approved receptacle when not in use.  Soldering irons can cause severe burns, fires and property damage.
      • Solder vapours are harmful. Use a vent hood or fan to remove the vapours.