Issues with Nova-T dimmer and/or PP-20 Power Pack

I'm a homeowner trying to diagnose a problem with an undercabinet LED fixture installed in 2008. The LEDs are controlled by a Lutron 0-10v slider, which I believe to be a Nova-T NTFTV, in conjunction with a Lutron PP-20 Power Pack to switch 120VAC power fully off. System worked flawlessly for years, but recently developed a problem (within the last year or so).

Sometimes (not always), when an appliance that immediately begins to draw a little power (like a toaster with lighted controls) is plugged in to a kitchen outlet on the same circuit as the LEDs, the lights will flicker momentarily, or (more recently), go off completely and need to be restored by turning the dimmer off and then on. Same thing sometimes (not always) happens when the electric igniter on the gas range is used while the LEDs are on. When the lights go off completely, I can hear the relay in the PP-20 cutting out.

The range is on a different circuit, but the dimmer switch itself is physically very close to the range, like less than a foot to the left. I don't know if there's a shared neutral between the range circuit and the circuit for the LEDs and countertop outlets: there might be, but the two breakers aren't even adjacent to each other in the panel.)

Any thoughts? Could this be the Nova-T dimming control starting to fail, becoming more sensitive to the small voltage dip that happens when the toaster is plugged in, and to interference caused by the spark capacitor in the range operating in such close proximity?

Hard to say but I would guess that the power supply is failing. It is becoming susceptible to voltage droop. I am a little surprised that the ignitor is also having an effect. I would not completely rule out the dimmer yet but I would try the transformer first.

Thanks, Randy -- but just to clarify, do you mean the main power supply driving the luminaires, or the Lutron Power Pack (which I gather is both a 24v power supply and a relay)? The fact that I can hear the relay switch off when the lights drop out is what made me suspect something in the low-voltage control circuit or the Power Pack rather than the main transformer.

The igniter really is the weird part.

Anyhow, I appreciate your input!

Hello Patchen,

Thank you for your post!

Based on the information you provided this appears to be both neutral interaction and possibly amperage issues. Neutral interaction is cross talk between controls that share the same neutral. This explains the appliances. Please see the below app note regarding this:

http://www.lutron.com/TechnicalDocumentLibrary/360283.pdf

Neutral interaction is hard to combat, the best solution would be to run separate neutrals.

Additionally, you could be having an issue with amperage. A main feed to a breaker provides so much amperage, as a rough example lets say your main feed is 30A. If there is a sudden large amperage draw (such as turning on a stove) it can create dips in the voltage, like plugging in a vacuum and the lights dim. That is what could be happening here.

We understand it was working, sometimes the power feeding in can change and suddenly cause issues.

What are you getting from the black to white of the PP-DV when the stove turns out in AC volts? If you get any type of drop this could explain the turn off and clicking. A new PP-DV will more then likely not solve this issue, especially for the long term.

Unfortunately, if it is due to an amperage drop there is really no good solution. Possibly trying the range or lights on a separate phase, but we cannot guarantee it will fix the issue.

Hope this helps!

Julia K.

Thanks, Julia! As it happens, I had an electrician come to look at this; not only could I not reproduce the problem for him, the problem also hasn't recurred in the last two-plus months. Hard to explain, but for now, I'll take it -- and if the problem comes back your advice will be helpful!