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What is the definition of the term OSN on electronic trip units?

Published date: 01 September 2020

OSN (Over Size Neutral) means that the neutral protection is 1.6 times greater than the phase protection.

This type of trip unit is used if there is a high level of third order harmonics and multiples thereof (orders 9, 15, etc.).

These harmonics are added together in the neutral and create a high zero-sequence current.

In this case, use of the device should be limited to Ir = 0.63 x In, with a maximum setting on the neutral of 1.6 x Ir.

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