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Residual Voltage

Residual Voltage

Residual Voltage

(OP)
Hi

A 3 phase induction motor (440V) has been duly isolated from the mains (main switchboard and local). I would be grateful if someone guided me on the following:

1. Is it possible to find residual voltage on the motor?
2. If so, how can the residual voltage be tested? (proximity/ contact?)
3. If the residual voltage test shows the presence of some voltage, how do we get rid of it for safety?

Many thanks

RE: Residual Voltage

A motor can have residual absorption/capacitive voltage after dc testing.  Should be grounded at least 4 times the duration of test voltage before doing another test.

There may be space heaters with power still applied after the main power is removed.

A motor can create voltage if rotor is being turned (such as motor connected to a fan connected to parallel operating fans through a faulty backdraft damper which causes the motor to spin backwards.

There may perhaps be other causes of induced voltage in the winding from nearby circuits.

A good bet in addition to whatever isolation is established is to hang a ground and keep it grounded for the duration of work.   Also do a live/dead/live check.

But don't take my word for it.   It is not a task to be taken lightly based on input from the internet.  Requires detailed review of the actual installation and the safety practicces of your company and the facility where you are working.

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