what is ment by insulation resistance?

Insulation Resistance is a test condition. Two parameters are set depending on the Class of the equipment under test. Class 1 refers to equipment that has a basic earth - ie earth conductor in mains cord attached to the metal case of the appliance, or Class 2 = no earth conductor as two distinct levels of insulation exist.

The insulation resistance in the Appliance Test for Class 1 is set to be greater than 2Meg Ohm [2 million ohms] whilst that set for Class 2 should be above 7Meg Ohm.

In addition to the Insulation Test the 'earth bond' is also tested and should maintain a nominal figure on 100milli ohms [0.1 of an ohm]. These tests are performed as part of an Electrical Test on anything that has a 3 pin plug top and fused no greater than 13A.
[These tests are a legal requirement under the Health and Safety at Work Act 1976; the actual legal piece being the ammended Electricity at Work Regulations 1984. This affects you because although your home is defined as domestic it is the workplace of the 'electrician' who deemed your equipment unsafe].

I suspect, from what you say, you need to get someone who knows what he is talking about to retest. The reason I say that is because there is no actual qualification required to be a tester but the tester should be, in the words of the Act, 'Competent'. I find it strange the 'tester' was unable to explain the requirements test simply to you.

Repair: If is feasible the reading the 'tester' experienced was around 1MOhm and that he read that as a failure. That need not be the case since the Compressor in the fridge is an inductive load and could well lead to a lower reading due the manner in which the test is actually made within the testing device.

As required by the EWR1984 the Line and Neutral Conductors are strapped together [at the test socket] and a voltage not exceeding 1000v at 55uA is applied between the strapped conductors and the earth lead for a time not exceeding 5 seconds. Since the test unit will be based on a comparator with a nominal test standard of 2M it is feasible the measured resistance would behave as though it had circa 2M in parallel with it - ie show around half the expected resistance.

This is not unknown and any tester worth the title would have checked the plug, cable and entry into the fridge compressor to be totally sure the reading was due to faulty insulatiuoin rather than the effects of resistance of the perfectly working bits the cable is attached to.

One other thing you might like to be aware of; IT equipment often has filters within mains side of things. These too can lead to false readings so if you get a false reading on your PC/Fax machine you know what to ask the bloke.

My advice - get another tester in and don't gash the fridge before it's retested.

Something simple, like tightening a few odd screws can make a big difference to readings too.

Paul Beaumont
July 2006

copper conducts
plastics insulate
but , as plastics get old, they can start conducting,
not a lot, you cant use them as wires, but they conduct enough that earth leckage trips in houses trip.
Typicaly on something like a motor, where the moving bits have gotten old, and the insulation is not as good as it was.
can it be repared, only by replacing.
A fridge motor can costs more than a new fridge.

andrew mulcock
July 2006