Variations in MCB Ratings/Performance

Jul 10, 2007 1 Replies
P

Slightly OT, but might be of interest to the group.



We use a lot of MCB's in our chargers, especially the mobile railway chargers, and recent experiences with various manufacturers seems to suggest that although they all may come with the same nominal rating, some makes seem to perform better than others.



While testing some 29V 200A 3-phase chargers last week, we had 10A 'D' rated MCB's from ABB which would trip on turn-on, but Hager manufactured MCB's didn't show any problem.



Eaton MCB's seem fine also. These are the three main makes that we use.



We have seen this before on some 2-pole units as well, where ABB would not support a transformer load while the others would.



We only use 'D' ratings because of the large inductive load of the mains transformer.



Has anyone else noticed anything similar, with variations between makes?



Peter



-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

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C

Peter,

At the risk of teaching granny etc, it may not be anything in particular to do with the manufacturer. Circuit breakers come in a wide variety of types and include simple magnetic and thermal based trip types,as well as combinations of the two. The key specs are, rated circuit voltage, trip current and curve. The curve relates overcurrent against time to trip and can be quite closely specified for good quality breakers. There are also other parameters, like inertial delay etc.

Manufacturers like Airpax will have data sheets & application notes that explain this far better than I can, but the same nameplate current and voltage rating doesn't really tell the whole story...

Chris

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