Circuit Breaker MCB

What does it say in the MCB manufacturer's instructions?

Unless specifically required by the manufacturer, the MCB will not be effected by how the load and supply are connected.

However, various Standards, Federal, State and Utility regulations will impact how the MCBs are installed.

In Australia the Standard does not care about the direction of connecttion, only that all the breakers operate in the same direction (i.e. Closed is Up) on all breakers in that DB.

Beyond that, it may have been specified in a particular way at the desing stage, or he\she has their own preferences.

Regards,
Sapper.

Circuit breakers often have connections labeled L1 (L2,L3) and T1 (T2,T3) - it is usual (and may be necessary) to connect the line (live) side to the L terminals.

Your senior customer was correct. As an electrician or an engineer, we always follow the standard procedure to do the connection, either to the MCCB or to the contactor down to the relays. The top is always the incoming and the bottom is the outgoing.

Standardization is the best policy and everyone will knows that the top is always the incoming cable.

Of course, at some time, there is some cases there we need to use the bottom of the MCCB as the incoming. But you need to put some danger tag indicating the incoming cable.

Standardisation is good. But I think the user was looking for a technical reason. Is there any?

MCBs that are made for connection in only one direction are explicitly marked for identification of LINE side (and sometimes LOAD side).

unmarked MCBs are assumed to be made for connection in either direction. i however contend that good manufacturers should mark on the device clearly that it suitable for connection in either direction. MCB users are not always technically trained.

the limitation when specified by the maker is for good reason. the mechanical design of the trip mechnaism, fixed/moving contacts and arc spaces available are some of the criteria for this requirement. the arc quenching that happens during break requires heat dissipation and also has to happen within specified time. this is possible if the arc elongates in the desired direction as the moving pole withdraws from the fixed pole. during this process the flow of energy in the right direction aids and accelerates the opening by creating repulsion forces.

read also -

http://www.maintenanceresources.com/referencelibrary/ezine/eleccircbreak4.html#line