I was testing a local paper disposal plant that uses Telergon isolators on the three phase motor control centres. Now obviously there is a mechanical interlock ensuring that the panel is de-energised before the door is open. However, after the door was opened I carried out an insulation resistance test on the supply circuit. I noted a low resistance between red and yellow phases. It appears that around 9.6ohms is present between these phases even with the door opened. This was apparent on every Telergon isolator in the plant. I had to disconnect the supply cables to obtain a reading. Because this was a relatively
pressured job, I really didnt have the time to assuage my curiosity! Any ideas?


regards

lyle dunn