How is insulation resistance measured?

Insulation resistance measurement is one of the priority areas in which any electrical measurement laboratory works. And this is not accidental, because it is this operation that is the main link for determining the state of insulation and, accordingly, for ensuring safety when using electrical networks and equipment for various purposes. Let's talk about how insulation resistance is measured.

A special device — a megohmmeter — is used to measure the insulation condition. It consists of a current generator and a voltage measuring mechanism. There is equipment designed for operating voltages up to 1000 V and up to 2500 V.

At the preparatory stage for measuring the insulation resistance, it is necessary:

• check the condition of the megger by testing it with open wires - while its arrow should point to the infinity sign, and also with closed wires - in this case the arrow should stop at 0;
• check with a voltage indicator whether current is supplied to the cables on which insulation resistance measurement is planned;
• perform grounding of the live conductors of the cables to be tested.

When working with a megohmmeter, be sure to use clamps with insulated handles. If the insulation is tested for voltages higher than 1000 V, dielectric gloves should be worn. Do not touch live parts during the resistance test.

Readings from the megohmmeter are taken only when its needle occupies a stable position. To achieve this, it is necessary to rotate the handle of the device at a speed of 120 revolutions per minute. The insulation resistance can be adjusted after 1 minute of turning the knob when the arrow position stabilizes.

When the measurement is finished, ground is applied to the device to release the voltage, only after that the ends of the megohmmeter are disconnected.

Insulation resistance is most often measured in lighting networks. The test is carried out for a voltage of 1000 V, while readings are taken from the insulation of the main lines to the general switchboards, from them to the apartment switchboards, then from the switches to the lamps. The measurement includes checking the insulation of the lighting fixtures themselves.

Regular inspection of the insulation is the main condition for the safe and long-term use of any electrical networks and devices. That is why it is imperative to periodically contact the specialists who perform these works using modern devices and technologies.