Could someone confirm if I’m interpreting rule R.30 correctly here? We want to drive two 12volt LED strips off an automation direct relay. It looks like R.30 would consider the combined strips a single custom circuit that we control on the relay.
If not would it count as two low-load custom circuits which can also be driven off a single relay? Each strip draws approximately 500mA max.
We would use 18 gauge wire and a 20amp fuse, which seems to meet the wire gauge requirement.
We are thinking of wiring it like this:
Wiring both LED strings through one relay is allowed as you noted. However, the wiring is incorrect. The black and red wires from the PDP would go into the relay input terminals, and the LEDs would be connected in parallel as you show, but both to into the output terminals of the relay.OK, I see now that you have the inputs at the top and that the relay port provides enough voltage and current to switch the MOSFET directly; it doesn’t need the 12V as I thought.
The relay’s actuation coil still has to have a ground line. As pictured, the only possible routes to ground are the relay port of the RIO or the LEDs, neither of which seems likely.
Also note that as this is a custom circuit, you do not have to use the spike or AD relay. You can use a much less expensive 12V relay module which could be controlled through a DIO pin.
You are controlling two units in parallel with one source. You add amp draw. 1 strip is 500ma. Then 2 will be 1000ma or 1amp. If relay is rated at 500ma, you will burn the contacts of relay.
Fuses are used to protect the units, not the wire. You should calculate in rush time & amp for the right fuse. If 1 unit pulls 500ma and 2 units are 1000ma then using a 20000ma fuse, is a very bad idea. A 1a or 2a fuse is better.
It would be best to fuse each unit by them selves. Maybe 1amp fuse per unit.
The strongest part of any machine is its weakest link. It can only be as strong as weakest part. If you have a motor that can push 1000hp but you have a clutch that can do 500hp. Then the most that motor can out put is 500hp! #16 wire can handle 5amp. You are putting 20amp on a #18. For a circuit that should never draw more than 1amp.
The three AD relays (legal for for small actuators and custom circuits) and the relay I linked (legal for custom circuits only) are all rated at least 10A.
The automation direct relay is rated for 12 amps, and the 18 gauge wire is rated for 20 amps per rule R.53. So, it seems like a 10 amp fuse will be sufficient to protect both relay and wire. A 20 amp fuse could put the relay at risk.
Either way , I think the LED strip would become an open circuit if we tried to pump 20 amps though it, but I will try to find a compatible 10amp fuse.
