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Electrical Safety

To safeguard against injury when using electrical equipment, requirements and standards have been established through the implementation of nationally recognized codes, approval tests, and electrical safety work practices. This is to ensure that you have adequate training and experience when handling electrical equipment.

Electrical Safety Reminders

  • Only licensed electricians are permitted to work on electrical systems and equipment that use or control electrical power.
  • Should a circuit breaker or other protective device “trip”, ensure that a licensed electrician checks the circuit and equipment and corrects problems before resetting the breaker.
  • Report hazards (lack of protective guards or covers, damaged equipment, etc.) to the building manager, Department of Facilities, Environment, Health, and Safety Office. or supervisor immediately.
  • Discard any piece of equipment that gives you even the slightest shock. If the resistance through your body is lowered i.e. standing in water or touching metal, even the slightest shock can be deadly.
  • Take seriously any warning signs, barricades, or guards posted when electrical equipment is being repaired, installed, etc.
  • Do not leave electrical boxes, switch-gear, cabinets, or electrical rooms open when not directly attended. Insulate energized parts when covers have been removed or doors are ajar. The use of cardboard, plywood, or other flammable materials to cover energized circuits is prohibited.
  • Junction boxes and electrical panels need to have proper covers in place to conceal all wiring. Hard wiring should not be exposed/accessible to non-electrical employees.
  • Do not operate electrical tools or equipment in wet areas or areas where potentially flammable dusts, vapors, or liquids are present unless specifically approved for the location.
  • Never use electrical equipment in or around water.
  • Remove any combustible materials, such as paper and wood from the area. Be sure flammable liquids and gases are secured away from the area when the appliance is in use.
  • De-energize equipment before removing any protective covers or guards.
  • Do not use an electrical outlet or switch if the protective cover is ajar, cracked, or missing.
  • Never put conductive metal objects into energized equipment.
  • Remove the cord from the outlet by pulling the plug instead of pulling on the cord.
  • Do not carry equipment by the cord – only by the handle or base.
  • Re-route electrical cords or extension cords so they don’t run across the aisle/corridor or over pipes or through doors.
  • Be sure extension cords are properly rated for the job and used only temporarily.
  • Use extension cords with 3-prong plugs to ensure the equipment is grounded. Never remove the grounding post from a 3-prong plug so you can put it into a 2-prong.
  • Do not overload extension cords, multi-outlet strips or wall outlets.

Factors Involved In Electrical Shock

The Quantity of Current Flowing Through the Body

Current (amperes) is the killing factor in electrical shock, not the voltage. The voltage only determines how much current will flow through a given body resistance. In general, the body’s resistance to electrical shock is minimal, averaging approximately 10,000 Ohms (100,000 Ohms for dry skin to 1,000 Ohms if your skin is wet). At this resistance, even contact with standard 110-volt circuits can be lethal under certain conditions. Refer to the Physiological Effects table below.

OHMS LAW is Current (Amps) = Voltage (V) / Resistance (Ohms)

The Current Path Through the Body from Entry to Exit

Current path through body

Hand-to-hand, hand- or head-to-foot, and ear-to-ear current paths are the most dangerous because it may cause severe damage to the heart, lungs, and brain. This is why it is important not to wear metal jewelry, not to lean against or use both hands-on electrical equipment so as not to become part of the circuit. Step potential is also a concern when the ground is electrified. Shuffle feet to keep them as close together as possible.

The Length of time the Body is Part of the Circuit

Here is a table that shows the physiological effect to your body from exposure to increasing levels of electric current. It also details approximately how much voltage is needed to achieve these current levels based on assumed body resistance (Average ~10,000 ohms).

Physiological Effects Table

Electric Current (1 second contact) Physiological Effect Voltage
1 mA Threshold of feeling, tingling sensation. 10 V
5 mA Accepted as maximum harmless current. Intense involuntary spasms might lead to other injury. 50 V
4-5 mA Current as which a typical GFCI will trip. Designed to protect you
10-30 mA Beginning of sustained muscular contraction (“can’t let go” current). 100 V
75-300 mA Ventricular fibrillation, fatal if continued. 750 V
15000 mA Lowest current at which a typical fuse or circuit breaker trips. Designed to protect equipment

Wiring, Grounding, Insulation

National Consensus Standards For Design And Installation

All installed equipment must be tested and listed or labeled by one of these Nationally Recognized Testing Laboratories

All electrical equipment must be installed and maintained in accordance with the following standards:

National Electrical Code (NEC)® – supported by the NFPA provides electrical safety requirements for wiring methods used in the workplace, for live electric supply and communication lines and equipment for employees in the workplace.

Lockout/Tagout

Lockout/Tagout (LOTO) refers to specific practices and procedures to safeguard employees from the unexpected energization or startup of machinery and equipment, or the release of hazardous energy during service or maintenance activities.

As outlined under the OSHA Standard 29 CFR 1910.147, employers are required to examine machinery and equipment to determine what energy source needs to be controlled (lockout/tagout) and to develop an energy control program consisting of written:

  • Energy control procedures,
  • Periodic inspection, and
  • Training

We are required to adhere to the following standards, 29 CFR 1910.147 and the National Fire Protection Association (NFPA) standard 70E which requires the control of hazardous energy sources. If you need further assistance contact safety@mit.edu.

To safeguard against injury when using electrical equipment, requirements and standards have been established through the implementation of nationally recognized codes, approval tests, and electrical safety work practices. This is to ensure that you have adequate training and experience when handling electrical equipment.

Electrical Safety Reminders

  • Only licensed electricians are permitted to work on electrical systems and equipment that use or control electrical power.
  • Should a circuit breaker or other protective device “trip”, ensure that a licensed electrician checks the circuit and equipment and corrects problems before resetting the breaker.
  • Report hazards (lack of protective guards or covers, damaged equipment, etc.) to the building manager, Department of Facilities, Environment, Health, and Safety Office. or supervisor immediately.
  • Discard any piece of equipment that gives you even the slightest shock. If the resistance through your body is lowered i.e. standing in water or touching metal, even the slightest shock can be deadly.
  • Take seriously any warning signs, barricades, or guards posted when electrical equipment is being repaired, installed, etc.
  • Do not leave electrical boxes, switch-gear, cabinets, or electrical rooms open when not directly attended. Insulate energized parts when covers have been removed or doors are ajar. The use of cardboard, plywood, or other flammable materials to cover energized circuits is prohibited.
  • Junction boxes and electrical panels need to have proper covers in place to conceal all wiring. Hard wiring should not be exposed/accessible to non-electrical employees.
  • Do not operate electrical tools or equipment in wet areas or areas where potentially flammable dusts, vapors, or liquids are present unless specifically approved for the location.
  • Never use electrical equipment in or around water.
  • Remove any combustible materials, such as paper and wood from the area. Be sure flammable liquids and gases are secured away from the area when the appliance is in use.
  • De-energize equipment before removing any protective covers or guards.
  • Do not use an electrical outlet or switch if the protective cover is ajar, cracked, or missing.
  • Never put conductive metal objects into energized equipment.
  • Remove the cord from the outlet by pulling the plug instead of pulling on the cord.
  • Do not carry equipment by the cord – only by the handle or base.
  • Re-route electrical cords or extension cords so they don’t run across the aisle/corridor or over pipes or through doors.
  • Be sure extension cords are properly rated for the job and used only temporarily.
  • Use extension cords with 3-prong plugs to ensure the equipment is grounded. Never remove the grounding post from a 3-prong plug so you can put it into a 2-prong.
  • Do not overload extension cords, multi-outlet strips or wall outlets.

Factors Involved In Electrical Shock

The Quantity of Current Flowing Through the Body

Current (amperes) is the killing factor in electrical shock, not the voltage. The voltage only determines how much current will flow through a given body resistance. In general, the body’s resistance to electrical shock is minimal, averaging approximately 10,000 Ohms (100,000 Ohms for dry skin to 1,000 Ohms if your skin is wet). At this resistance, even contact with standard 110-volt circuits can be lethal under certain conditions. Refer to the Physiological Effects table below.

OHMS LAW is Current (Amps) = Voltage (V) / Resistance (Ohms)

The Current Path Through the Body from Entry to Exit

Current path through body

Hand-to-hand, hand- or head-to-foot, and ear-to-ear current paths are the most dangerous because it may cause severe damage to the heart, lungs, and brain. This is why it is important not to wear metal jewelry, not to lean against or use both hands-on electrical equipment so as not to become part of the circuit. Step potential is also a concern when the ground is electrified. Shuffle feet to keep them as close together as possible.

The Length of time the Body is Part of the Circuit

Here is a table that shows the physiological effect to your body from exposure to increasing levels of electric current. It also details approximately how much voltage is needed to achieve these current levels based on assumed body resistance (Average ~10,000 ohms).

Physiological Effects Table

Electric Current (1 second contact) Physiological Effect Voltage
1 mA Threshold of feeling, tingling sensation. 10 V
5 mA Accepted as maximum harmless current. Intense involuntary spasms might lead to other injury. 50 V
4-5 mA Current as which a typical GFCI will trip. Designed to protect you
10-30 mA Beginning of sustained muscular contraction (“can’t let go” current). 100 V
75-300 mA Ventricular fibrillation, fatal if continued. 750 V
15000 mA Lowest current at which a typical fuse or circuit breaker trips. Designed to protect equipment

Wiring, Grounding, Insulation

National Consensus Standards For Design And Installation

All installed equipment must be tested and listed or labeled by one of these Nationally Recognized Testing Laboratories

All electrical equipment must be installed and maintained in accordance with the following standards:

National Electrical Code (NEC)® – supported by the NFPA provides electrical safety requirements for wiring methods used in the workplace, for live electric supply and communication lines and equipment for employees in the workplace.

Lockout/Tagout

Lockout/Tagout (LOTO) refers to specific practices and procedures to safeguard employees from the unexpected energization or startup of machinery and equipment, or the release of hazardous energy during service or maintenance activities.

As outlined under the OSHA Standard 29 CFR 1910.147, employers are required to examine machinery and equipment to determine what energy source needs to be controlled (lockout/tagout) and to develop an energy control program consisting of written:

  • Energy control procedures,
  • Periodic inspection, and
  • Training

We are required to adhere to the following standards, 29 CFR 1910.147 and the National Fire Protection Association (NFPA) standard 70E which requires the control of hazardous energy sources. If you need further assistance contact safety@mit.edu.