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Old 13-11-2009, 04:39   #1
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Reverse-Polarity-Indicating LED - Path to Earth (Ground)?

Hi, I would like to connect 2 indicating leds to my polarity switch.
a green one with wires from the live to the earth
and a red one with wires from the neutral to earth

so that the green is on when the polarity is ok and the red one is on when the polarity is reversed (meaning the neutral is live).

To do this I have bought two 240 volt leds, 1 red and 1 green

I wired it up and it works perfectly.....

but now i read that I may have created a path for stray currents by not putting two 8000 Ohm resistors in the circuits. (8000 Ohm for 240v instead of 25000 Ohm which is for 120v)

Here is a quote from our forums....
"RPI’s are wired in series with a (minimum) 25,000 Ohm resistor (unless they utilize a momentary contact “push-to-test” button), to prevent a path for stray currents via the grounded Neutral wire."

So my question is... Why do I have to do this with an led running in an A/C circuit. It must have a resistor built in so that it can handle the 240 volts. If it has a resistor built in then it must be big enough to stop the stray currents by the fact that it is allowing a 2v (i guess) led to run in a 240v circuit.

Does this all sound reasonable or am I missing something?
Fuss is offline   Reply With Quote
Old 13-11-2009, 11:29   #2
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The 240v led has a built-in current limiting resistor, which is probably on the order of 50k ohms for a 5 milliamp led.

The trend in boat wiring is to put in ground fault interruptors both on the boat and on the dock, which will trip if stray currents (like the one you are creating with your green led) are more than a few milliamps. A green led between the load and earth will increase the frequency of spurious trips--better to wire it between the load and neutral wires and call it a power indicator.
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Old 13-11-2009, 15:09   #3
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Thanks Don ,
So this means that 240v leds all have a resistor so they should be ok.
I don't understand the part about the green led because that also has a 50k Ohm resistor, so surely this is ok too?.
Thanks again for the reply
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