The practice of grounding, also known as earthing, involves electrically connecting the human body to the Earth’s surface potential. The Earth acts as a vast reservoir of free electrons, allowing the body to absorb these electrons and dissipate any accumulated electrical charge. For those who use conductive products like mats, sheets, or patches to achieve this indoors, the primary concern is verifying that the equipment is electrically functional and correctly installed. Testing procedures focus purely on confirming the integrity of the electrical pathway from the body to the Earth’s potential, ensuring the grounding system performs its intended function.
Verifying the Electrical Source
Before using any indoor grounding product that plugs into a wall, the foundational step is to confirm the electrical outlet provides a functional connection to the Earth. Standard grounding systems rely on the third, rounded hole of a three-prong wall socket, which is wired back to the home’s grounding electrode or rod buried outside. This connection is intended to safely divert excess electricity into the ground.
A simple, inexpensive receptacle tester is the appropriate tool for this initial check. Plugging the tester into the outlet illuminates indicator lights showing if the socket is correctly wired and if the ground pin is properly connected. If the tester indicates an “open ground” or a “hot/ground reverse,” the outlet is not suitable for grounding products and may present a safety risk. A non-functional ground connection means any product plugged into that outlet will fail to connect the body to the Earth’s potential.
If a wall outlet is not used, such as when employing a dedicated external grounding rod or plate, the integrity of that connection must still be verified. This involves ensuring the wire leading from the grounding product to the external rod is securely attached and that the rod is properly inserted into moist soil. Without a verified, low-resistance path to the Earth, the entire grounding setup is ineffective, regardless of the conductivity of the mat or sheet itself.
Measuring Body Voltage Drop
The most direct way to test if the body is successfully grounded is to measure the reduction in the body’s alternating current (AC) voltage. The human body often accumulates a measurable AC voltage from surrounding electrical wiring and appliances, sometimes reaching several volts. When a person makes contact with a properly functioning grounding product, this induced voltage should dissipate into the Earth, causing a substantial drop in the reading.
Setting Up the Multimeter
A digital multimeter capable of reading AC voltage in the millivolt (mV) range is required for this measurement. Set the meter to the AC voltage mode (“V~” or “VAC”), ideally to a sensitive range like 20 VAC or less. Connect the black lead to the “COM” port and clip it to the verified ground point of the grounding product’s cord. Insert the red lead into the “V” port.
Establishing Baseline and Contact
Testing begins by establishing the baseline ungrounded body voltage. The person holds the metal tip of the red lead between their fingers without touching the grounding product. The meter displays the ambient AC voltage induced on the body, which often ranges from 1 to 10 volts or higher depending on proximity to electrical fields. Next, the person makes contact with the grounding product, such as placing a hand on a mat, while still holding the red lead.
Interpreting Results
A successful grounding connection is validated by a significant, near-instantaneous drop in the measured AC body voltage. The goal is a reading reduced by a factor of 20 or more, ideally falling below 0.50 volts, and often into the millivolt range (e.g., 250 mV or lower). While a reading of zero is unlikely due to background electrical noise in indoor environments, any substantial drop confirms that the body is electrically connected to the Earth’s potential and the equipment is functioning correctly.
Essential Tools and Safety Protocols
The process of testing a grounding setup relies on two primary electrical tools: the receptacle tester and the digital multimeter. The receptacle tester, a small plug-in device, is mandatory for quickly confirming that the wall outlet’s ground connection is present and correctly wired before any conductive product is attached. This ensures a foundational level of safety and functionality for the grounding system.
The digital multimeter is necessary for the technical measurement of body voltage drop, acting as the final proof of a successful connection. It is imperative to set the multimeter to the AC voltage setting (V~ or VAC) for all body voltage measurements, as the induced voltage is alternating current. Users must avoid attempting to measure current (amperage) or resistance on a live circuit, as this can damage the meter and create a serious hazard.
All electrical testing must remain non-invasive to maintain safety. Users should never attempt to open or modify wall outlets, plugs, or the grounding product’s cord, particularly the safety resistor built into many grounding cords. The correct use of the tools involves only plugging into the outlet and touching the meter probes to the body and the grounding cord connection point. Adhering to these protocols ensures accurate results without compromising the integrity of the electrical system or personal safety.