friends, I have one system with two source. One from genset and the other from PLN (national power supply company) that each system has neutral.
The question is
1. Is there any problem if I connect both neutral directly?
2. Is there any spark when I connect both neutral?
3. how is the best solution to connect both neutral?

1.yes
2.at that moment may be not
3.do not

Mr. Ir,
May I ask the following:-
1. Is there any Automatic Transfer Switch (ATS) between these two Sources? ie are they operated in synchornisim.
2. Whether the Genset Main CB is 4 Poles or TP?

thanks Esmail

Omer, there is no ATS only 4 pole breaker. in each output whether genset and PLN...
How about if I open genset breaker first and after a moment I close PLN breaker, manually, let load supply from UPS.

Dear Ir, I bit confused. But let me add the following:-

1. I understand that the Genset is dedicated for essential load as an Emergency power supply which will be operated by hand (only in Manual Mode).

1. The Control Philisophy for a Generatotor that intended to be connected to PLN as emergency power source depends on the local service provider regulations.

3. Usually in your case there should be Electrical as well as Mechnical interlocks between the mains incomer & genset main breaker. ie both Sources will never be in Synchronisim ( will not feeding the same load simultaneously).This measures will ensure that there will be only neutral point to the system.

many thanks for your advice, Omar. Yes you alright in point number 3, both breakers are never feeding load together, they are interlocking each other (pln breaker cannot be closed if genset beaker still close)