# How does an illuminated switch light up without a neutral

There are some illuminated switches that operate without a neutral. For a lamp that is lit when the switch is ON, I can envision a circuit diagram that has the switch lamp in series with the switched circuit. But this would create significant additional resistance in the current flowing through the line to the main load. If the switch is parallel to the line, virtually no current should flow since the resistance to the lamp is so much higher than the completed switch circuit.

For switch lamps lit in the OFF position, a switch lamp in series would allow a trickle of current through the actual load, causing a dim glow in a fixture or some current in a motor. This seems wrong.

How do no-neutral illuminated switches work?

They DO pass current through the switch and light at all times - just a few mA. The indicator is wired in parallel to the switch contacts. For most types of bulbs its not enough for the light to turn on.

However with modern LED light bulbs these types of switches (as well as dimmers, and home automation switches) that dont use the neutral can cause the LED bulb to turn on enough to be noticable or flicker.

I believe some of these have a neon bulb in parallel with the switch. This means they draw a small amount of current through any light-bulb the switch controls - however this is too small a current to produce any light in the light-bulb.

A textured polycarbonate moulding designed to allow the glow of the two integral neons to be seen at almost any angle. Easy to install as an addition to existing locations.

• 250Vac
• Double neons provide 360 degree visible glow around frontplate
• Green glow is visible to naked eye
• One or two-way switch wiring

From what I've seen, they pass a small current through the switch (and light), and that current is sufficient to power the illuminated switch light.

I have never looked at a design schematic but do know this. I have seen them fail and on the load side. I had 60 VAC on the load side when off and 120 VAC when on. Removed the switch and the continuity between states show rock solid, 0 ohms off and infinite ohms with a standard Fluke meter. Of course I didn't meg the thing for I don't own an insulator tester or megger, work provides them and for far more important failures. The LED kitchen lights it provided power to was either dim or fully illuminated. I won't deal with a Light Emitting Diode failure at that level, fail on, and just went to Menards and bought a swith without illumantion.

• I must correct my continuity statement. Its so obvious that I am wrong but far more embarrased. I should have stated the switch showed infinite ohms off and 0 ohms when on. Please forgive me. My credibility is damaged and once again appologize. – Steve Harris Jul 5 '17 at 3:21
• 'Tis what the edit button is for... – ThreePhaseEel Jul 5 '17 at 4:01

The current flows through the ground line when the indicator is on. Therefore no neutral is involved.