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Posted By Topic: Voltage marking on MCB's for use in 3 phase DB

Nov 27 2018 21:54

While selecting MCB's and a busbar comb at my wholesaler for a new 3 phase board the manager mentioned that some inspectors were not approving the use of MCB's that did not have a 415V marking on them in boards that had different phases on adjacent breakers.

I'd been selecting from the NHP brand of MCB's as they are lower priced but then noticed they only have the 240V making*, not 240/415V.

Have others come across this aspect?

* However their catalogue says 24V/415V (page 6 of

Nov 27 2018 21:56

Just to clarify, the MCB's were all for single phase loads.

Nov 27 2018 23:05

I looked into this many years ago on a rural 480v centretapped supply. Switch gear can switch 240V. Internal to external is rated 240V so between 2Phases you have a 480V rating. So in your case each contact only needs to switch 220V so where is the issue?
As bad as an engineer decided we couldn’t use 250 V switch gear as the peak voltage was over 300V. Couldn’t understand we work on RMS.

Nov 28 2018 07:36

Once again, inspectors get it wrong.

As long as they comply for the PSCC of the installation, there's nothing wrong with using them.

Nov 28 2018 11:09

"Once again, inspectors get it wrong"

Agree, this time wrong on 2 counts.

2nd is that the mcb ratings are nothing to do with an Inspector; because they are not "mains work" (assuming that what he was asked to do was a "mains work" inspection.