Measurements shall also be made between the earth point on all mains sockets in the scanning room and the ERB. If any devices are plugged into sockets outside the scanning room and then used within the scanning room, these should be supplied from the same phase as any sockets within the scanning room, and the touch voltage on the earths of these sockets also measured. The touch voltage should be less than 10 mV,AC or DC. If a voltage greater than 10 mV is found, the measurement should berepeated using an IEC filter. If the touch voltage is still above 10 mV, the source of the voltage should be investigated.
Once it has been established that there are no significant touch voltages present, the bonding resistance should be measured. A battery operated four-wire milliohmmeter should be used, in order that the meter can be kept at a safe distance from the midline of the field during the measurement. The meter shall have a resolution better than 10 milliohms, and be capable of performing the measurement at a current greater than
100 mA.
The resistance between the ERB and all accessible conductive surfaces of installed equipment should be less than 100 milliohms. The resistance between the earth point of all mains sockets and the ERB should also be less than 100 milliohms.
Any portable devices shall be plugged directly into a conveniently located hardwired socket.