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120v vs. 24v for control wiring

pcloadletter
pcloadletter Member Posts: 38
in THE MAIN WALL
Most of the various boiler controls/sensors/accessories come in both 120v and 24v versions depending on how they will be wired into the system, e.g. Pressuretrols, Vaporstats, LWCOs, autofeeders, etc.



I have a Peerless oil boiler with a Midco gas power burner and 120v LWCO

wired into the burner power feed. I'm thinking of adding an auto water

feeder and I assume it would be a 120v model wired into the same burner

power feed as opposed to a 24v model wired into the transformer.



This got me to thinking, are there any basic rules of thumb about wiring such devices on the high vs. low voltage side? I guess it really depends on the configuration of your boiler. But if you were to install a boiler from new and could set things up any way you want (while adhearing to code), what devices would be wired on the high side vs. the low side?

Comments

  • SWEI
    SWEI Member Posts: 7,356
    The majority of safety devices

    are just dry contact switches which will work with either voltage.  The majority of modern controls run on 24V, which reduces shock hazard and allows mechanical licensees to install and modify them.  Some secondary safeties and older systems run on 120V.  Depending on the sequence of operations and the risks presented by an improper shutdown, it may be better to interrupt one or another in a particular design.

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