We use the LED indicators in substation panels and CT kWh meters for potential indication.
As already mentioned above is that the LED's shown, show the actual parts. These need to be heat shrinked or put in tubing of appropiate voltage rating for the application.
In the substation panels these are put in the actual plastic neon holder casing which are fitted in steel cabinets.
In a meter they are fitted and wiring is often airborne with some minor support.
The flickering of the LED is hardly noticeable and not really an issue for a pilot light anyway.
The 1 N 4007 diode could be omitted but i put it in to make it fail safe and forwhat ever reason a spike may pop the LED.
I have fitted around 1500 kWh meters with 3 LED's each and about 200 of these in our substations as replacements for fading Neons.
No faillures over a period of 15 years.
Also pilot wires and meters are subject to nasty spikes sometimes during lighting, The two resistors will probably absorb most of the energy anyway hence two resistors are used to allowe for surges well above 230 Volts (325 peak).
A thing i forgot to ask Haligan is , were the Neons black after they stopped working ?
Startrek, very good comments and good maths.
Thanks.
To get back to the neons, usually they run well below 1 mA about 600µA at around 70 Volts. (depending upon specs).
So for 110 Volts, 40 Volts at needsd to be dissipated in the series resistor at 0.6 mA
usually a 100 kOhm resistor is used.
For 230 Volts a 220 or 270 k.Ohms ¼ Watt resistor is used.
I have seen many neons with only a 100 kOhm resistor fitted for 230 Volts with very early faillure of the neons.
