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Nest contactors running radiant UFRH

Danroonie
Danroonie Member Posts: 8
edited November 2017 in Thermostats and Controls
I am working on heating a 3 room cabin in PA. There is 200 amp service - so plenty of juice to heat it.

The house will only be occupied 1/2 the winter - and internet is available, so an app can tell the 2 nests to call for heat so the homeowner can turn up the heat on the way to the cabin. Each zone has UFH (under floor electric heat) and a less desirable - but fast acting in-wall electric heater (aux) 240V 20 amp. The nest has an aux setting. I got feedback from this forum recommending the contactors but I wanted to get final feedback on the setup. See diagram




Comments

  • HVACNUT
    HVACNUT Member Posts: 6,283
    I would change the transformer to a 50va max and fuse it. Do you know the current draw from the two relay coils, and if the Nest can handle it?
  • ratio
    ratio Member Posts: 3,777
    We covered that in another thread.
  • Danroonie
    Danroonie Member Posts: 8
    HVACNUT said:

    I would change the transformer to a 50va max and fuse it. Do you know the current draw from the two relay coils, and if the Nest can handle it?

    Per ratio's earlier suggestion - the transformer is serving 2 zones- so essentially 50va is available minimum per zone off the 100 va transformer - I've updated the diagram since it was vague. Where would you put a fuse? What would it protect? Thanks!
  • BobC
    BobC Member Posts: 5,501
    i would fuse the output of the transformer, start with a 2a slow blow (might have to go up to 3a) so it doesn't pop on inrush current.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Danroonie
    Danroonie Member Posts: 8
    edited November 2017
    BobC said:

    might have to go up to 3a) so it doesn't pop on inrush current.

    MT0100C has a built-in holder- So 3amp slow blow like this? From amazon I looked at the tech sheet on the seimens site- but it didn't say if 5mm x 20mm is the right size. Tried to get it unsuccessfully at supply Cooper Electric and NAPA auto.

    Thanks Bob and Ratio

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