Indicator light wiring question

[VinceBrews]

Hi all,
First post (although I've been reading for a long time - I've learned a lot!

I've building a 50A, 2 element rig. Here's the question. On most wiring diagrams I've seen, the element indicator light (240V) is in parallel with the element (between L1 and L2). I was going to post a picture but don't know how to do this yet...

Question: Could I instead, use a 120V indicator light and connect it between L1 (still downstream of the contactor) and neutral? This would cut down the number of wires going to the panel door because I could daisy chain the neutral between the 2 element indicator light as well as the main power indicator.

If what I'm saying is not clear, I'll create some diagrams.

Thanks for the help guys!
Vince

 

[jeffmeh]

I believe the answer to that is no. If you use a 120v light you might find it lit even when the element is not getting power, as the SSR will leak some voltage. 240v in parallel with the element is the proven method to get it to work correctly.

 

[P-J]

I believe the answer to that is no. If you use a 120v light you might find it lit even when the element is not getting power, as the SSR will leak some voltage. 240v in parallel with the element is the proven method to get it to work correctly.

Excellent answer and right on the money. That issue was one of the problems that surfaced in my thinking when creating wiring diagrams. The SSR's minor leakage current was enough to light the indictor lamp when a 120v model was in place.

Good job!

P-J

 

[VinceBrews]

Thank you gentlemen. I figure there must be a reason no one does it that way.

P-J, perhaps you can help me understand why that is... Why does having the element in parallel with the led prevent the current leak to light up the led? Is it because the element is a much smaller resistance and most of the leak current goes preferentially in the element?

Come to think of it, what is the resistance of an LED? I thought diodes had a voltage drop of 0.7V... How is it that we can hook them up directly across 240V?

Vince

 

[kenh]

Thank you gentlemen. I figure there must be a reason no one does it that way.

P-J, perhaps you can help me understand why that is... Why does having the element in parallel with the led prevent the current leak to light up the led? Is it because the element is a much smaller resistance and most of the leak current goes preferentially in the element?

Come to think of it, what is the resistance of an LED? I thought diodes had a voltage drop of 0.7V... How is it that we can hook them up directly across 240V?

Vince

You can buy LEDs rated for 240V. Inside is a standard LED and the right value resistor for 240V.

 

[VinceBrews]

Is that what they are? An LED in series with a resistor?

 

[lschiavo]

An LED requires only a resistor with DC. I usually set the current to about 15mA via the resistor. For AC, you need to add at least a diode to simulate DC or the LED will fail pretty quickly especially at higher voltages.

I always monitor my control voltage. It is DC already if you are using an SSR. It verifies that your control circuit wants the element to be on. I can see or hear that the element is working.

I don't see where a lamp in parallel with the element would make much difference. I believe I have heard of leakage lighting these as well.