Last Revised: April 12, 2024

Revision 3/2020

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This Fact Sheet applies to equipment and appliances used in a laboratory. It does not address computers or other office equipment used in non-laboratory settings.  This Fact Sheet provides some basic guidance for commonly encountered electrical concerns in laboratories.

Extension Cords and Power Strips

Extension Cords

Use extension cords for temporary (less than three months) use. Situations that require extension cords for greater than three months are considered permanent installations and must be addressed through upgrades to building wiring systems. Extension cords must be appropriately rated for the intended load.

Do not place extension cords in foot traffic areas or under equipment. Length shall be the minimum required for the specific application but shall not exceed 15 feet. Ground wires are required for all extension cords (i.e., the cord should have three prongs).  Extension cords must be plugged directly into a receptacle and cannot be daisy chained.

Power Strips

Power strips/surge protectors must be listed or labeled by a nationally-recognized testing laboratory such as Underwriter’s Laboratories Inc. (UL) and have a built-in circuit breaker to protect against overloading.  They must be plugged directly into a receptacle (not daisy chained or plugged into extension cords) and must be rated for the current and voltage connected to them.  

Single-Conductor Wires and Terminal Connections

Single-Conductor Wires

Single conductors shall not conduct greater than 24 volts. Code single conductors red or black and keep them as short as possible. Single conductors shall be a single continuous length of wire unless spliced or joined in a grounded electrical box that provides appropriate strain-relief. Wire nut or other connections that are not housed in a grounded electrical box are not permitted.

Terminal Connections

All electrical connections at the supply end (bus bars) for 24 volt or greater services shall have strain relief and be enclosed. Label the enclosure with the voltage.

Plug style connections are permitted if the conductor is fully insulated and the conducting wire is not exposed when disconnected.

When possible enclose electrical connections in a protective housing. Insulate high temperature (>1808C) connections, such as furnaces, with 3M 69 Class "H" glass cloth tape (call Chemistry department or LRSM stockrooms for availability).

Exposed energized connections are not permitted.

Electrical Equipment Modified by or Built by Lab Workers

Electrical Equipment Modified by or Built by Lab Workers

Download the policy “Electrical Safety - Research Labs and Support Shops.

This excerpt (Section 11) from Penn’s Electrical Safety Program defines practices and procedures to be implemented for electrical equipment that is not listed or labeled by a nationally-recognized testing laboratory (NRTL). Typically, this will include research related equipment that is custom built in-house or NRTL-listed or labeled equipment that has been modified which invalidates the listing or labeling.

Power Supply Use for Experiments

Power Supply Use in Experiments

For experiments where a power supply is used to induce an electrical current to the material being tested, you must develop a Hazard Control Plan (HCP) which describes the step-by-step procedures for safely conducting the experiment. Ensure anyone involved in the experiment is trained on the HCP, and document that they understand and will follow it.  EHRS must review and approve HCPs for all experiments having the potential for an exposure to more than 5 mA of current.

Consider the following recommendations when writing your Hazard Control Plan:

  1. Ensure the power supply is de-energized (unplugged) prior to any work on the wiring or other components of the experiment.
  2. If there is potential for catastrophic failure that could cause the device to eject parts while energized, a clear shield should be installed between the testing setup and lab personnel involved in the experiment.
  3. Standard laboratory attire consisting of a lab coat and safety glasses must be worn while the experiment is conducted.
  4. Since there is potential for an open arc/spark, keep flammable liquids that can produce vapors away from the experiment area.
  5. When the power supply is energized, always keep one hand in your pants or lab coat pocket. Remove all metallic jewelry and insure pockets are free of metallic objects. Only work with electrical lab equipment using one hand. If contact with an energized conductor should occur, with a hand in your pocket, there’s less likelihood an electric shock would travel across your heart. The pathway to ground will likely be down your leg or through another part of your body, bypassing your heart.
  6. If there is arc fault and/or ground fault detection built into the power supply, there should be some kind of test button on the equipment. Include weekly testing of the protection circuitry as part of the lab’s operating procedure.
  7. As an additional precaution, consider use of a non-conductive rubber mat on the bench top and an insulated floor mat to stand on. These items will be good to have around the lab anyway for any future experiments where the high voltage equipment may be used. Grainger is in Penn’s online purchasing system, and products purchased through them are available at a discount.  Two example products are:  Notrax Switchboard Mat and Knipex Insulated Mat
References and Related Resources