In This Article
Ground resistance testing is one of the two core measurements — alongside leakage current — that make up a PCREE electrical safety test, but it gets considerably less attention in most compliance discussions. Understanding what it actually measures, and why a failure here is treated seriously, rounds out a compliance officer's understanding of what a technician is actually doing during a PCREE visit.
What Ground Resistance Testing Measures
Ground resistance testing measures the electrical resistance of the path from a device's exposed metal chassis to the ground pin of its power plug. In a properly functioning device, this path should offer very low resistance — meaning that if a fault causes the chassis to become energized, current flows safely to ground rather than through anyone who touches the device. A high-resistance ground path means that safety mechanism is compromised: a fault condition could leave the chassis at a dangerous voltage relative to a person touching it, with nowhere for that current to safely go.
The NFPA 99 Threshold
NFPA 99 sets a maximum ground resistance of 0.5 ohms between a device's chassis and the ground pin of its power cord. This is measured with a calibrated electrical safety analyzer capable of injecting a test current and measuring the resulting resistance — a standard multimeter continuity check is not an adequate substitute for a proper PCREE ground resistance measurement, since it doesn't apply the test current levels or precision NFPA 99 testing requires.
Why Ground Resistance Tests Fail
The most common causes of a ground resistance failure are a damaged or corroded ground pin on the power plug, a broken or compromised ground wire inside the power cord (often from repeated flexing or being rolled over by equipment carts), a loose internal chassis ground connection, or — for older equipment — a power cord that's been replaced with a non-original part that doesn't properly terminate the ground conductor. Power cords are, in practice, one of the most frequently replaced components after a PCREE test failure, precisely because they take the most physical wear of any part of the electrical safety chain.
Practical note: a device that fails ground resistance testing should be taken out of service immediately rather than scheduled for "next available" repair — an ungrounded chassis fault is one of the more direct paths to a resident or staff electrical injury among PCREE failure modes.
How It Relates to Leakage Current Testing
Ground resistance and leakage current testing are related but distinct measurements that are both part of a complete PCREE test. Leakage current measures how much current is actually escaping the device's insulation under normal and single-fault conditions; ground resistance measures whether the safety path exists to carry that current away safely if it does escape. A device can pass one measurement and fail the other — both are required, and neither substitutes for the other. See our companion guide, Understanding Leakage Current Risks in Medical Devices, for the leakage current side of the testing protocol.
What Documentation Should Show
A complete PCREE test record should show the actual measured ground resistance value in ohms for each device tested — not simply "pass" — alongside the leakage current measurements, the test date, and the technician's CBET credential number. A record showing only pass/fail status without the underlying measured value is the kind of incomplete documentation that draws surveyor scrutiny even when the underlying testing was performed correctly.
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About the Author
PCREE Test Editorial Team
Content reviewed by biomedical professionals with experience in patient care electrical equipment testing, NFPA 99 compliance, and CMS Life Safety survey preparation for skilled nursing facilities.