Three Pole or Four Pole Breaker

[IndiaElecEngg2010]

We have a building which is fed by transformer via main LV Panel, neutral of transformer is earthed locally,

Please suggest which one will be better

1.Three pole breaker at incomer of main LV panel with a neutral link and all downstream breakers Four Pole.

OR

2.Four pole breaker at incomer of main LV panel and Three Pole downstream breakers with neutral link.

 

[rbulsara]

None of them, unless you have some engineering reason or code requirement.

Switching neutral is generally considered a bad idea and at least not permitted in NEC, except in some source transfer switch/breaker or otherwise required for total isolation or some engineering reason.

Rafiq Bulsara

http://www.srengineersct.com

 

[GenSwgrEng]

Use 3-pole breakers through-out. You don't need 4-pole breakers unless you have multiple services or on-site generation. You probably don't need it then, either in most cases.

Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep engineers away from customers, romantic interests, and other people who can't handle the truth.

 

[IndianTechEngg1001]

If we have a system with separate neutral (not connected to earth but earthed at transformer) and also even not linked to any relays system. I am talking about a system of 400V three phase panel which feeds a building. I have seen in UK and Muddle East people using 4P breakers also.

 

[Freeportpower]

In the Uk the arrangement is as follows.

1. Transformer star point brought out to a link in the LV switchboard.
2. Neutral link connected to neutral bus.
3 Neutral bus connected to the earth bar via bolted link (For testing)
4. Earth bar connected to earth grid via bolted link (again for testing).

Therefore 4 pole breakers unnecessary.

4 pole breakers may have a place in certain circumstances but not on a standard LV distribution system.