DC wiring protection

Thread Starter

meowsoft

Joined Feb 27, 2021
494
Is there any best and reliable way to protect DC wiring from 220v or another high voltage current leakage (let's say 220v cable shorted with 36v DC) ?
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
Yes. Regulations! It is forbidden to run low voltage DC in the same trunking as mains.
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 ?
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
Do you think I can make earth switch for DC positive wire in main panel ?, and connect DC positive to earth and cut DC main supply if there is abnormal voltage detected in DC wiring ? (DC neutral was earthed), is this good idea ?
 

MrSalts

Joined Apr 2, 2020
655
I 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.
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
Yes... but my question is DC wiring protection in general
Protection was installed :
- Sub-circuit DC fuse, 150kA, short circuit and over-current protection, no fuse can exceeds 80% wire amp capacity
- Main DC fuse, 150kA
- Main DC MCCB, 50kA
- Grounded-earthed neutral at main negative busbar
- Voltage relay, incorporated with contactor, to cut off voltage source when voltage output exceeds limit (only 34-38v DC allowed)
- 65kA surge arrester at main panel
- Earthing conductor at DC main panel point, doesn't have resistance more than 3.5 OHM to earth

- Also all AC sub circuit is have RCCB, if current from 220v wire leaked to 36v negative wire, RCCB can tripped and voltage relay cut-off main DC sources

problem is, when 220v phase wire shorted to live wire, it can damage entire 36v DC appliance, firstly and absolutely 36v to 12v step down module
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
I 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.
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 bonded
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
NFPA 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.
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), etc

In cable distribution it is have separated conduit nor AC wires have conduit inside conduit (with galvanic isolation, layer two conduit is flexible galvanic pipe wrapped by PVC, galvanic pipe is grounded, to prevents EMI and AC current leakage to DC wire) if in same conduit with DC wire, for distribution wire, there is no problem, only at load side
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
NFPA 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 components
 

Tonyr1084

Joined Sep 24, 2015
6,374
I'm not getting all the sense of urgency here. Good engineering should eliminate all possibilities of HVAC coming in contact with LVDC (High Voltage AC / Low Voltage DC). The very nature of a relay should preclude the chances of shorting one line to another. There are always exceptions to those rules, but in general, it should not happen. I KNOW that cheap relays can be problematic. IF the relay coil becomes shorted but remains functional, when the armature of the relay is pulled down to the magnetic coil, it COULD transfer HV with LV. A good "Contactor" should prevent that from happening. I don't have a drawing of a contactor and I don't know how to draw one. Otherwise I'd post a diagram.

Back to standard relays: The coil should be on a plastic spool insulating it from the iron core, so that even if the coil suffered a catastrophic breakdown there should be no contact between HV and LV circuits. That I have a drawing for.
1631894698356.png
Whether it's SPDT (or SPST not shown) or DPDT, the core of the coil should be insulated from the core windings. So that when the armature pulls down and contact the iron core it should not transfer any energy from the control circuit to the circuit being controlled.

You mention high amperage. This drawing is of the small hand held types of relays NOT meant for high current. For that you may want to go with a contactor instead of a relay. In essence, they are both the same sort of animal; just the contactor is for higher current. And to finally qualify everything I say - I'm NOT an expert on relays. I'm a rather low level electronics guy. The simple stuff.
 
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