Reason for Early make late break?

Simonslimline · Dec 30, 2013

Just wondering if anyone could explain the reasons why this is used in some circumstances.

I noticed it has been mentioned in the main forum and has got me interested.

Cheers

telectrix · Dec 30, 2013

generally it's where the N breaks after the L, and makes before the L ( or L1,L2,L3 for 3 phase.) with reference to multi pole switches/isolators.

Simonslimline · Dec 30, 2013

Would this be to stop arcing?

telectrix · Dec 30, 2013

might be totally wrong here, but i think it's more to do with preventing the L conductors becoming "live" with an open circuit N. where all the N conductors in the circuits would be "live" through the load/s during the time the N was O/C. tony, malcolm or darkwood will correct me if i'm wrong.

D Skelton · Dec 30, 2013

The reason for late break-early make neutrals is to prevent the star point from floating, thus creating damaging and highly disruptive surges (up to 400V) across phases, even if only for a fraction of a second.

When you have seen the display of fireworks first hand that can sometimes ensue as a result of a floating neutral, you realise the importance of the LNB-ENM switchfuses/disconnectors lol.