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DPST vs SPST

  1. Aug 21, 2009 #1
    Hello,

    I have a 240v water heater with a machincal timer which went bye-bye after I installed it over 15 years ageo. Those darn plastic gears finnaly broke. So I bought a Intermatic EH40.

    The line is 240v with 3 wires (white, black, and ground) which matches the water heater wires.

    But because the EH40 is a DPST and my old switch was a SPST, i'm having a brain freeze about how to connect it. I'd rather not return the unit.

    How do I connect my water heater to the new timer/switch?
     

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    Last edited: Aug 21, 2009
  2. jcsd
  3. Aug 21, 2009 #2

    Danger

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    Welcome to PF, Osiris.
    If I understand the question correctly, you can just leave the neutral (white) line intact, and splice one side of your DPST into the hot (black) line.
    Better wait for an electrical expert such as Berkeman to respond before taking my word for it, though. If in doubt, the best thing is to have a professional electrician or appliance repairman come in and do it for you. There's no point in taking chances.
     
    Last edited: Aug 21, 2009
  4. Aug 21, 2009 #3


    Thanks for responding so quickly. I've done this before years ago but I'm a little rusty. I think your suggestion sounds right. I have some friends who do this but they are hard to get a hold of.
     
  5. Aug 21, 2009 #4

    Danger

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    Bye the by, your illustration didn't appear when I first read this. Even now, though, I can't quite understand it. The combination of a foreign language and incomplete circuitry is really confusing me. What the hell is a 'charge area'? :confused:
     
  6. Aug 21, 2009 #5
    Yeah I know. There is English on other pages but when it comes to the circuit layout, it goes foreign. Nowhere in the box does it show an English representation.

    But here is the full PDF http://www.intermatic.com/~/media/files/intermatic/products/instructions/timers/eh10%20-%20english.ashx [Broken]
     
    Last edited by a moderator: May 4, 2017
  7. Aug 21, 2009 #6

    dlgoff

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    The switch in your attachment is a DPST. Is this the one you are wanting to replace? As shown, it will work correctly. The two poles are terminals 3 & 5 with a single throw to terminals 4 & 6 respectively.
     
  8. Aug 21, 2009 #7

    negitron

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    It doesn't say "charge area" it says:

    CHARGE
    CARGA

    That's the French/Spanish, respectively, for the power supply/mains voltage.
     
  9. Aug 21, 2009 #8

    Danger

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    Oops... :redface:
    Once again, my brain misinterpreted something that my eyes saw just fine. I run into that problem a lot, and have gotten into some serious trouble due to it upon a couple of occasions. (Honestly, I didn't see the wedding ring...) :uhh:
     
  10. Aug 21, 2009 #9
    Ok, so I attach the load to 4 & 6 and do the jumpers too? Thats where I'm getting a little confused. With the old SPST box there were just 3 pins. So on the DPST each pin is not tied to anything else. So the jumpers is what bridges them, right?
     
    Last edited: Aug 21, 2009
  11. Aug 21, 2009 #10

    dlgoff

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    Where are you located? In the US, black is the source (115volt), white is the return/neutral, and green is the safety ground. In this case you only need to switch the source wire. So you could do this with just a SPSP switch. If you are using a 230volt source, then you would have two sources (Line 1=115volts and Line 2-115volts) and would need the DPST switch. However if you are in Europe then you will have a single source of 230volts I think and would not want to advice you without seeing what you have.
     
  12. Aug 21, 2009 #11

    negitron

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    In this case, one line should be black and the other red. The neutral, if present, will still be white and the ground will be green or bare copper.
     
  13. Aug 21, 2009 #12

    dlgoff

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    Yes. I failed to mention the colors for two lines. Thanks for the catch.
     
  14. Aug 21, 2009 #13

    vk6kro

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    The load is the circle on the bottom right.

    The timer is the rectangular box on the top left. This switches the two contacts shown.

    Incoming power is the lines marked "Ligne 1 and Ligne 2".

    The timer gets its own power from the unswitched lines, of course.

    Switching both power lines is a safety feature, but follow your local code.
     
  15. Aug 21, 2009 #14

    Danger

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    Osiris did, though, in the original post, specify that the 3 wires were white, black and ground.
     
  16. Aug 21, 2009 #15

    negitron

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    Then he's probably not in the US. My post specified the US color code for 240 V split-phase wiring.
     
  17. Aug 21, 2009 #16
    The diagram seems to make sense for a 240 system with two sides at +/- 120 V, but I'm wondering how the OP's original circuit was wired with only a SPST switch. Are there any locations where there is a single-sided 240 V supply voltage?

    If the original circuit was somehow simple enough to use an SPST switch, then I would think recreating the same connections on one side of the new switch should be equivalent, since a DPDT switch is just two SPST switches ganged together.

    By the way, for those who couldn't read it, the text in the lower left says "To interrupt the two sides of a charge of 240 V" (I'm guessing "charge" is better translated as "voltage", but I can't say for sure.) The box at the top left is roughly "timer feed". "Ligne 1/2" are simply "Line 1/2".
     
  18. Aug 21, 2009 #17

    vk6kro

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    Yes, a lot of countries (including Australia) have a line that is one phase of a 3 phase system and the neutral of the 3 phase system brought into houses. The neutral is approximately at earth potential, but may have a few volts on it relative to Earth. An Earth wire is also used and all exposed metal on appliances is attached to Earth.

    So this may be 240 volts rms relative to earth on only one line. It is, however, traditional to switch the neutral line as well as the active line for appliances. Lighting is usually only switched in the active line.

    There is no 120 volt line.

    Higher power is available if all 3 phases of the 3 phase line are brought into the house (or factory). In this case, the voltages are all 240 volts relative to earth but about 400 volts relative to each other. This costs extra for the wiring and more expensive power meter.

    The American system is actually unusual, but makes perfect sense.

    Incidentally, I fed "charge" into Google language translator and got the following:
    1. burden
    2. load
    3. loading
    4. cargo
    5. office
    6. charge
    7. onus
    8. trust
    9. onslaught
    So, it can mean something different in French to the same English word. I'd pick "load".
     
    Last edited: Aug 21, 2009
  19. Aug 21, 2009 #18

    Danger

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    That PDF gave me a headache. :frown:
     
  20. Aug 22, 2009 #19
    Thanks everyone for responding. I really appreciate it.

    I'm in the Northeast US and my house was built in 1969. The line is 240v (238 really) coming from the romex, White, Black and Green ground. I orignally bought a SPST 15 years ago and it was easy to wire. In fact I have done a lot of electrical work like replacing bad throw fuses, adding digitial thermostats for my electric baseboard heaters which are also 240v to wiring recessed lighting, but I'm not a licensed electrican, just an enthausiast with common sense.

    I got the new DPST at a great price and it was about half the price of the SPST from the same company. It is strange that the wiring diagram was not in English thought...

    So in wiring up the new DPST switch I would use pins (screw contacts) 4 and 6 as dlgoff suggested?
     
    Last edited: Aug 22, 2009
  21. Aug 22, 2009 #20

    vk6kro

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    Yes, input on 3 and 5 and output from 4 and 6.
     
    Last edited: Aug 22, 2009
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