Mixed LV ans ELV is it safe?

[john4703]

I’m trying to work out why my proposed wiring is wrong.

I’ve got a caravan and sometimes it is hooked up to a mains supply. When it is there is a RCCB on the supply and another in the caravan.

I’ve fitted two twin sockets with USB charging ports and they are on a spur. I’ve fitted a 30A double pole switch on the supply side. This is simply because I like to leave the leads that charge my phone and tablet etc plugged in and they have LEDs and it is good to switch them of in some places.

We sometimes go to caravan sites with no mains hook up and I want to fit a couple of USB points that are run off the internal 12v battery.

I thought that using one pole of the switch for the 230v and the other pole for the 12v would work but I wonder if there is any reason not to mix LV and ELV in one switch.

As I see it there is no reason not to use one pole of the switch for the 240v and the other pole for the 12v but it seems wrong and yet I can’t see why it is wrong. The switch must be designed to be safe with a 230v live on one terminal and 230v neutral on the other.

I’d appreciate any sensible advice.

 

[conny]

No you shouldn't. AC and DC should be segregated if run in the same trunking/conduit.
I can't remember which reg, (think it was in the 520's), and one of the reasons is the DC can induce a DC current in the AC circuit I think. I stand to be corrected on the exact reason but pretty sure it is not allowed. Only permissible time may be when the DC is part of the AC control circuit.
Again, I stand to be corrected if I am wrong.

 

[SUNRAY]

I believe Conny is correct.
However I'm not aware of any reason to not use a switch for both circuits. It happens all the time inside equipment. It's also common in PV systems.

If you have doubts, use a 3 pole switch and earth the centre pole to the vehicle.

 

[Harry Bloomfield]

No you shouldn't. AC and DC should be segregated if run in the same trunking/conduit.
I can't remember which reg, (think it was in the 520's), and one of the reasons is the DC can induce a DC current in the AC circuit I think. I stand to be corrected on the exact reason but pretty sure it is not allowed. Only permissible time may be when the DC is part of the AC control circuit.
Again, I stand to be corrected if I am wrong.

Where the two are mixed, the insulation standard of the lower voltage, should match the requirements for the higher voltage. Where it doesn't there has to be some form of segregation. Crosstalk between systems is a potential other factor, but unlikely in this instance.

 

[john4703]

I'd not thought about induced currents. I think I'll do a quick redesign asnd have two separate switches.

 

[winston1]

DC CANNOT induce a current in an adjacent cable. Only AC can do that.

 

[DetlefSchmitz]

DC CANNOT induce a current in an adjacent cable. Only AC can do that.

As usual, I'm not sure what useful point you are trying to make.

 

[john4703]

As usual, I'm not sure what useful point you are trying to make.

I agree, I was more thinking of slight risk that the AC could possibly induce some current in the ELV DC cables

 

[winston1]

.

 

[SUNRAY]

Clearly conny does not understand how magnetic induction works and has given wrong information.

I suggest you check up on exactly what can and what cant affect the current in another cable.

DC cables certainly can affect an AC service.

 

[bernardgreen]

DC CANNOT induce a current in an adjacent cable. Only AC can do that.

Fluctuating DC WILL induce a voltage in an adjacent conductor, and if that conductor is part of a circuit then a current will be created in that circuit.

 

[Harry Bloomfield]

As usual, I'm not sure what useful point you are trying to make.

Once in a while, he does get something right, as least partially. DC will not affect the AC cable, expect perhaps for the switching spike. With no variation in current on the dc cable, nothing will be induced.

 

[conny]

Clearly conny does not understand how magnetic induction works and has given wrong information.

Which is why I said I stand to be corrected.
Diplomacy is definitely not your forte though, that I am sure of.

 

[winston1]

.

 

[winston1]

Once in a while, he does get something right, as least partially. DC will not affect the AC cable, expect perhaps for the switching spike. With no variation in current on the dc cable, nothing will be induced.

Not once in a while. Most of the time.