Electrical safety testing of equipment is covered by AS/NZS 3760:2010 In-service safety inspection and testing of electrical equipment.
This article describes how to test earthing continuity of amateur equipment. It is only one of several tests described in (AS/NZS 3760:2010), but it is most relevant to ham equipment, especially so-called ‘boat-anchor’ equipment.
Most appliances that hams will encounter fall into one of:
- Class I equipment (basic insulated, protectively earthed equipment)
- Class II equipment (double insulated equipment).
Class II equipment will be marked as such or more commonly, the Double Insulated symbol below will be on the rating plate. If there is not evidence that an appliance is Class II, treat it as Class I.
Above, the Double Insulated symbol appears on Class II equipment.
One of the tests prescribed for Class I equipment is a test of Earthing continuity.
Class I equipment – testing earth continuity
The test of earth continuity is to ensure that all exposed metal is properly connected to the appliance earth pin.
The equipment required to perform the test is either a ohmeter suitable to read around 1 Ω, or a portable appliance tester (PAT). Most ham shacks should have a suitable ohmeter.
Above is the test setup using an ohmeter. One terminal of the ohmeter is connected to the earth pin of the cordset, and the other is used to probe all exposed metal to measure resistance. (AS/NZS 3760:2010) requires resistance is less than 1 Ω.
If the equipment does not meet this requirement, tag it so that it will not be used as it is dangerous, then have a competent person repair and test the equipment.
A great deal of equipment was imported that was designed for Japanese or American standards at the time, and is unsafe by Australian standards then and now.
Above is an extract of the circuit of the very popular Yaesu FL2100Z amplifier. Note the two wire mains cord and 2 pin plug top. This is a Class I appliance and the chassis MUST be connected to a 3 pin plug top earth pin, and with a resistance of less than 1 Ω.
AS/NZS 3760:2010 In-service safety inspection and testing of electrical equipment.