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Thread: DVRF-5NS switching Electric Towel Warmer

  1. #1
    Junior Member
    Join Date
    Mar 2024

    DVRF-5NS switching Electric Towel Warmer

    I am using the DVRF-5NS to control a 400W heated towel rack (3.33A). This is the towel rack:
    RHEA Electric Towel Warmer from "Paris Mirror":

    Since this is an electric towel warmer, am I correct in assuming that it is a resistive load, like a lightbulb, and it is within the capabilities of this switch (rated for 5A resistive loads)? The warmer is prefilled with glycol liquid, so I assume it must be using a resistive immersion heating element. The switch has a neutral for it's own power.

    This appears to be working fine so far, I just wanted to ensure it is within the capabilities of this switch. Thanks.

  2. #2
    Lutron Technical Support
    Join Date
    Oct 2023
    Hello jb54321, welcome to the Forums. We do not recommend using our smart controls to power anything with a heating element, as if you place it on the Lutron App and/or integrate it with any 3rd party system, and any automations are programmed, it could potentially turn on at unwanted times. Furthermore, the device is only rated for 3 amps (360 watts) of motor/fan loads; it is only rated for 5 amps when used with lighting. See the below spec sheet for more information:


    We hope this helps!

  3. Thanks jb54321 thanked for this post
  4. #3
    Junior Member
    Join Date
    Mar 2024
    Thank you for your reply!

    Putting aside the issue of accidentally turning on at unwanted times for a moment, because that's a potential issue with any load on any smart switch...

    I agree the device is rated for 3A of an inductive motor/fan load. But this is not a motor/fan load - it is a heater, which is an electrically resistive load effectively identical to an incandescent lightbulb, as far as the switch is concerned. The 5A load limit is a function of the load being resistive, not a function of it being a lightbulb, right?

    Imaging a worst case, in case I want to use the switch like this regardless: What is the worst that happens? The switch just stops working? Is there any risk of catastrophic failure (fire/melting) of the switch, or just a dead switch that I'll need to replace if it dies?

  5. #4
    Junior Member
    Join Date
    Mar 2024
    I was dissatisfied with this reply. I am an electrical engineer, so I decided to validate this use-case for myself. I instrumented the Caseta switch with an oscilloscope, and configured it to measure the line voltage, load voltage, and current flow through the switch using a current probe.

    During normal operation, with the switch on, the results look like this:
    Click image for larger version. 

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    As you can see, the Blue trace is current, and the Green trace is Load voltage. The Current is aligned with the voltage, exhibiting a zero degree phase offset. This represents a purely resistive load. The power is computed by the purple line - simply the multiplication of the current and voltage measurements. The resultant average power of ~400W properly matches the advertised rating of the towel warmer, and represents the apparent power (400VA) as well, since the load is purely resistive with a power factor of 1.

    Now, let's look at the moment the switch is turned on:
    Click image for larger version. 

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    Yellow is the line voltage. Green is the load voltage (switched 120VAC). Blue is the current. Purple is computed power. There is no in-rush effect. The solid state switch beautifully turns the load on precisely at the zero-crossing (nice job, Lutron), and there is no observable inrush effect. The load maintains a consistent, resistive current draw for its entire operating cycle, comfortably within the 5A resistive load limit that the switch is designed for.

    Checking in on it again after the towel warmer has fully hit thermal equilibrium, the current is still consistent, and the Lutron switch heatsink has leveled out at <40C, well within acceptable thermal limits.

    Disclaimer, this experiment might not apply equally to all towel warmers. Mine is clearly just a coil that runs current through it to heat up the glycol liquid inside the metal tubes.

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