It is well known that most low voltage equipment is insulation tested at a voltage of 500 V d.c.
However, it is not common knowledge that an insulation tester, claiming to perform a 500 V test, could actually be driving up to 625 Volts into the system under test. This would be a substantial overvoltage for any equipment that is inadvertently left connected to a circuit.
In the past, high test voltages were not considered a problem, since very few appliances contained sensitive electronic components. However, the proliferation of consumer electronics has made a large proportion of common place equipment susceptible to overvoltage. This is the idea that is currently driving the increase in demand for surge protected devices.
Standard insulation testers tend to exceed the suggested test voltage by 10-20%. This will meet the minimum requirements for an insulation tester specification. However, it will still result in the actual test voltage of up to 600 Volts. This will place an extra 100 Volts of unnecessary stress on any equipment connected to the circuit.
Not only does the additional voltage increase stress on the equipment under test. It also increases power consumption during the test, reducing the overall battery life. Anyone performing regular electrical testing will be aware of just how quickly insulation testers run out of juice. Therefore, it is important that additional battery life is not needlessly squandered.
You may wonder why insulation testers provide a different test voltage to the specified value. It is because overvoltage was not, in the past, an issue and having a much higher test voltage was a cheap way of ensuring that the specified voltage is met for all loads. It was considered much easier to design the circuitry to supply a significant excess in voltage than to design complex control circuitry to provide the correct test voltage.
However, with overvoltage and efficiency becoming a concern, noted by the rise in popularity of overvoltage (surge) protection and voltage optimisation devices. We at Megger have made stabilised output voltage control a standard feature in our new line of insulation testers so that the voltage on the dial is what you will inject.
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