Three wiring tests are performed corresponding to the standard "OKX" test:
1. The "O" test is a measure of proper hot and neutral wiring. An "O" is printed in the report's wiring column only if the hot-to-neutral voltage exceeds 50 volts.
2. The "K"
test is a measure of proper hot and ground wiring. A "K" is printed in the report's wiring column only if hot-to-ground voltage exceeds 50 volts.
3. The "X" test is a measure of proper
neutral-to-ground wiring. An "X" is printed in the wiring column if the neutral-to-ground voltage exceeds 4 volts.
Isolated Power Wiring
(Recommended by ECRI)
On receptacles that are part of an isolated power system, proper wiring is confirmed by two wiring tests:
1. The "PWR" test is a measure of proper hot wiring. "PWR" is printed in the report's wiring column if the open-circuit voltage across the hot pins is less than 50 volts.
2. The
"ISO" test is a measure of isolation of the hot wiring from ground. "ISO" is printed in the report's wiring column if either hot pin resistance to ground is less than 200 ohms per line volt.
If both power and isolation tests pass, "OK" is printed.
Line Voltage
(Recommended by ECRI)
The voltage delivered to medical devices must be within proper limits for proper equipment operation and to prevent equipment damage. Open-circuit line
voltage is measured between the hot and neutral pins of the probe. Voltages below 100 volts and above 130 volts are considered unacceptable.
Phase Relationship between Receptacles
(Recommended by ECRI)
The phase difference between the probe and power hot-to-ground voltages is measured. The phase is considered "IN" if the shift is less than 30 degrees and "OUT" if over 30
degrees. The phase will be "IN" if the probe and power receptacles are both connected to the same side of the 220-volt line and out of phase, if connected to opposite sides of the 220-volt line. Both
conditions are acceptable, but "IN" is preferred because of lower worst-case leakage path voltages.
Neutral-to-Ground Voltage
(Recommended by ECRI)
High voltage implies either a poor connection
between the power and ground circuits or high line voltage drop because of improper power wiring or excessive loading. This voltage is measured between the probe neutral and ground pins in pass/fail fashion.
A voltage above 4 volts is unacceptable.
Neutral-to-Ground Resistance
(Recommended by ECRI)
Low neutral-to-ground resistance is important for proper operation of fuses and circuit breakers.
Low resistance prevents high neutral-to-ground voltage. The resistance is measured between the neutral and ground pins on the probe. A 60 Hz full wave rectified unfiltered test current of 0.7 ampere peak is
used to generate a voltage across the neutral-to-ground resistance. The test starts at a zero crossing of the test current and lasts for 0.3 second or until the generated voltage rises above 0.5 volt (whichever
comes first). The average generated voltage is used to compute the resistance by Ohm's law. Resistance over 1.0 ohm is unacceptable. The resistance measurement includes:
- Resistance of the neutral and ground screw contacts in the receptacle.
- Resistance of the neutral and ground wires back to the common connection point (usually the distribution panel).
- Corrosion and dirt on the receptacle neutral and ground contacts.
- Corrosion and dirt on the analyzer probe and neutral ground pins.
A short test duration and low test current have been chosen to minimize risk to patients connected to the power system and to prevent false low-resistance values caused by welding. Consequently, this test will
not detect fusing effects caused by poor contacts in the presence of large fault currents.
Ground-to-Ground Voltage
(Required
Low ground-to-ground resistance is
critical to patient safety because it prevents dangerous voltage buildup induced by leakage currents flowing in the ground system. It is measured between the ground pins on the probe and power plug. A 60 Hz
full wave rectified unfiltered test current of 0.7 ampere peak is used to generate a voltage across the ground to ground resistance. The test starts at a zero crossing of the test current and lasts for 4/60 second
or until the generated voltage rises above 0.5 volt (whichever comes first). The average generated voltage is used to compute the resistance by Ohm's law. The impedance limit is 0.1 ohm (0.2 ohms acceptable
for quiet ground systems) for new construction. Existing systems have a limit of 0.2 ohms. The resistance measurement includes:
- Resistance of the ground screw contacts in the two receptacles.
- Resistance of the ground wires between the two receptacles.
- Corrosion and dirt on the two receptacle ground contacts.
- Corrosion and dirt on the analyzer probe and power plug ground pins.
A short test duration and low test current have been chosen to minimize risk to patients connected to the power system and to prevent false low-resistance values caused by welding. Consequently, this test will
not detect fusing effects caused by poor contacts in the presence of large fault currents.
Contact Tensions
(Required
