Ask a Question

Disconnecting Circuit breaker during Dielectric tests

It appears to be two questions that need to be addressed.

1.    Will the NSX with a Micrologic (ML) 5.3 E be damaged by a dielectric test when connected?
2.    Should you disconnect electronic voltage measurement devices during a dielectric test this includes a NSX Micrologic 5.3 E (including the external neutral connection) from the switchboard to perform a dielectric test.
The answer to the first question is: The ML 5.3E will not be damaged during a dielectric test provided. You do not exceed the impulse rating of the breaker and are testing in accordance to the relevant standard.

For the second question that is not covered in our user manual as that is that is answering only the first question. For this you need to consider the functionality that a NSX ML5.3 E as an electronic voltage measurement device.

Because the ML5.3E performs voltage measurement there is a high resistance common connection between all poles and neutral. This voltage measurement is designed to be very rugged and can handle the impulse testing without any issue (other devices typically have a much lower voltage impulse rating). In most application where there are only a few NSX breaker are installed clients have found that the dielectric test results are acceptable without removing the NSX. Where many NSX breaker are installed this parallel resistance lowers the measured results from the dielectric test to unacceptable value.

So in conclusion if you are wanting to measure the true resistance across the busbars please disconnect all electronic voltage measurement devices including out ML5.3E (neutral tap included). This can be done by leaving the breaker in the open position (assuming the ML is on the load side) and removing the neutral tap.
Was this helpful?
What can we do to improve the information ?