Of course, but what to prevent AC 220v to contact with 5v DC let's say for example in arduino relay ?, 5v DC is connected to arduino board, and arduino board is supply by 36v DC (connected to whole building DC wiring) stepped down with XL4016 to 12v DC, if one of those relay control voltage (5v) make contact with 220v, do you think 36v DC in whole building can become 220v AC ?, and how to prevent something like that ?Yes. Regulations! It is forbidden to run low voltage DC in the same trunking as mains.
based on my explanation, it is good idea to use contactor to contact DC positive to ground when voltage more than 38v DC is detected ?, I think my idea can make 220v AC wire's sub-circuit breaker that cause shorted to 36v DC wire can be tripped is that things happen, also ground and neutral is bonded in main AC busbar, and DC and AC ground is bondedI think there are some very good relays available, that are well designed and safety tested to fail in a way that will not energize the control voltage with mains voltage.
There are some strategies to design a PCB to keep line voltage away from control voltage or, alternatively, connectors and enclosures that allow separation of mains and control voltages.
The point is, you are not the first person to have such a problem so solutions exist. Research them and use the UL or CE listed products and Electrical codes that keep buildings and people safe. I offer no specific solutions because I don't know the codes where you live and I don't know the details of the environment you are operating in.
Yes... it's not a problem, both DC and AC distribution wires insulation is rated for up to 500v, but problem if AC and DC is conducted in electronics devices like relay, voltage sensor, volt and amp meter (powered by 220v AC but measuring 36v DC), etcNFPA state that LV and HV conductors can be ran in the same raceway as long as the insulation on both conductors are rated for the highest voltage.
I think it's compliance with NFPA, at distribution wire, but maybe not in load point, some electronics devices that in contact with both AC and DC isn't certified nor certification is questionable, and some load point panel doesn't have enough separation nor spacing between DC and AC componentsNFPA state that LV and HV conductors can be ran in the same raceway as long as the insulation on both conductors are rated for the highest voltage.