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Thread: 240 VAC circuit

  1. #1
    Join Date
    Mar 2003
    Location
    California
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    1

    240 VAC circuit

    I got a temperature controller turning on/off a heater element at 240 VAC, two hot wires. By code does the temperature controller have to interrupt the two hot wires or just one? If the two wires has to be interrupted (using SSR) by code, can you tell me where is it on the code?
    julio@alinesys.com

  2. #2
    Join Date
    Feb 2003
    Location
    United States
    Posts
    386

    Re: 240 VAC circuit

    If a unit switch is to be used as a disconnect it must be marked with an "off" position and disconnect all the ungrounded circuit conductors. 424.19(C), 424.20(A). If the thermostat is not serving as a disconnect then it need not open all the undgrounded circuit conductors. 424.20(B).

  3. #3
    Join Date
    Feb 2003
    Location
    lancaster
    Posts
    164

    Re: 240 VAC circuit

    i understand the answer and agree with the code ?
    could anyone get me an example of not breaking both wire ? i'm a little slow it's cold today. GEO
    THANKS! was not thinking,have only installed 2-pole stats

    [ March 04, 2003, 08:20 AM: Message edited by: vanwalker ]

  4. #4
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    8,790

    Re: 240 VAC circuit

    Most, if not all, 240V line voltage thermostats for electric baseboard heat are designed to control the heater with only a single contact. When these thermostats are turned to the Off position their heating contact and a second contact are both opened to disconnect the heater from the supply.

    [ March 03, 2003, 05:02 PM: Message edited by: jim dungar ]
    Just because you can, doesn't mean you should.

  5. #5
    Join Date
    Feb 2003
    Location
    United States
    Posts
    386

    Re: 240 VAC circuit

    You will find some thermostats are single-line break. They use one line of the 240V 1ph to control the heater and on the load side of the thermostat, have an "anticipator" connected in parallel with the heater, from the load-side of the thermostat contact to the other line. These thermostats are identified in their wiring diagrams as only breaking one side of the load and usually do not have an "off" position but rather a "." knob position. Other thermostats are 2-pole and will have the "anticipator" connected in parallel with the heater across the load side of the stat contacts and usually have an "off" position clearly indicated when both lines are opened.
    I would advise you to use the two pole stat whenever you have a 240V circuit.

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