In such a case, it is a good practice to isolate the neutral also.
3 pole mccb circuit breaker generator#
We can use 4-pole breakers or TPN Breakers when the system has two alternative sources and, in the event of power failure from the mains, change-over to the standby generator is done. As such, it is a mandatory practice to isolate the two Neutrals. Even fatal accident may occur due the above reason. 
During this time, if Power Supply Utility Technicians are working, and if they touch the neutral conductors(which is earthed at their point ) they will likely to get electric shock depending on the potential rise in common neutral due flow of current through Neutral conductor as stated above. distribution system ), depending of quantum of unbalance, there will be flow of current through Neutral. If there is power failure and DG sets are in running condition to feed the loads, if there is some unbalance in loads(which is practically unavoidable in L.V. We can use 4 Pole ACB instead of TP for safety reasons.In multi incomer power feeding systems, we cannot mix up the neutrals of incoming powers to other Power Source so we can use TPN or 4P breakers or MCB instead of TP MCB to isolate the Neutral of other power sources from the Neutral of incomer power in use.When we have a transformer or a stand-by generator feeding to a bus, it is mandatory that at least either of the Incomers or the bus coupler must be TPN or 4-Pole Breaker please refers IS 3043.Where to use 4 Pole or TPN MCB instead of 3 Pole (TP) MCB. 4P MCB: It is used where is the possibility of high neutral current (due to unbalance loads and /or 3 rd and multiple of 3 rd harmonics current etc) and Neutral / Earth Protection is provided on Neutral.TPN MCB: It is generally used where there are dual sources of incomer to the panel (utility source and emergency generator source).TP MCB: It is most commonly used type in all ordinary three phase supply.For a three phase distribution panel either TP or TPN or 4P can be used as the incoming protection. For any Distribution board, the protection system (MCB) must be used in the incomer.Where to Use TP, TPN and 4P in Distribution panel: Same type of difference also applies for SPN and DP.However when breaker trips or manually opened, all poles are disconnected.
For the 4 pole breakers, protection applies to current flow through all poles. It is denoted as TP+N which will mean a three pole device with external neutral link which can be isolated if required. TP MCB is used in 3phase 4wire system. For TPN, protection applies to the current flows through only 3 poles (Three Phase) only there is no protection for the current flow through the neutral pole. In TPN opening & closing will open & close the Neutral. TPN means a 4 Pole device with 4th Pole as Neutral. In 4-Pole MCCBs the neutral pole is also having protective release as in the phase poles.ĭifference between TPN and 4P (or SPN and DP):. 4pole MCCB for 4 wires connections, the one additional 4 th pole for neutral wire connection so that between neutral and any of the other three will supply. Application: Three Phase Supply with Neutral. TPN for Y (or star) the connection between ground and neutral is in many countries not allowed. In TPN MCB, Neutral is part of the MCB as a separate pole but without any protective given in the neutral pole (i.e.) neutral is only switched but has no protective element incorporated. Application: Three Phase Supply only (Without Neutral). 3pole MCCB signifies for the connection of three wires for three phase system (R-Y-B Phase). In Three Pole MCB, switching & protection is affected in only three phases and the neutral is not part of the MCB. 
Application: Single Phase Supply to break the Phase and Neutral. In Two Pole MCCB, switching & protection is affected in phases and the neutral. Application: Single Phase Supply to break the Phase only. In Single Pole MCCB, switching & protection is affected in only one phase. Based on the number of poles, the breakers are classified as. Novem84 Comments Type of breakers based on number of pole:
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