Biomedical Engineering Capstone Design Project
Section III: Electrical hazards
Electrocution/Shock from INSTALLED equipment:
- Test equipment in the lab should bear the CSA or equivalent markings.
- It is possible for a defective piece of equipment to become lethal, should the hot wire touch an ungrounded case.
- An accidental spill of liquid into or around equipment can also be lethal.
- Damaged, modified line cords. Always check apparatus line cords for damage.
Electrocution/Shock from TEMPORARY wiring:
- Experimental apparatus wiring. Always make sure power is turned off when making changes to the wiring.
- Damaged test and interconnection leads. Always check leads before use.
Electrocution/Shock from POWER SUPPLIES or APPARATUS:
- DC power supplies. Outputs are isolated from ground by means of a step down transformer. Connecting any of the outputs to the terminal marked ground (Green) will connect the circuit and power supply to the earth ground through the line cord.
- ENG 306/307 supplies, low output voltage could shock or prove fatal if conditions are right.
- ENG 308 supplies, 60V at 6 Amps and 120V at 3 Amps. The high voltage potential of these supplies create a shock, electrocution hazard.
- Never make wiring changes with power on.
Electrical Shock
- Electric shock occurs when the body becomes part of an electrical circuit. Shocks can happen in three ways.
- A person may come in contact with both conductors in a circuit.
- A person may provide a path between an ungrounded conductor and the ground.
- A person may provide a path between the ground and a conducting material that is in contact with an ungrounded conductor.
Injury and Death
The extent of injury accompanying electric shock depends on three factors.
- The amount of current conducted through the body.
- The path of the current through the body.
- The length of time a person is subjected to the current.
- In addition, you may fall and strike something, or have some other accident as a result of your response to the shock.
Injury < 10ma Death >10ma
Connecting to Human/Animal subjects
Do not use the lab power supplies.
ONLY 9V BATTERIES ARE TO BE USED IN THE INPUT SIDE THAT IS CONNECTED TO THE HUMAN/ANIMAL SUBJECT VIA ELECTRODES.
ISOLATION CIRCUITS AND CLAMPING DIODES ARE MANDATORY.
Transformer Isolation
Optical Isolation
Capacitive Isolation
Clamping Circuit