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Heater element resistance question

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  • Reese
    Recently, our hot tub took a dump, it won t stay on. Keeps tripping the GFCI circuit. Heater elements are usual suspects in spas, but the circ pump turns on
    Message 1 of 11 , Jun 16, 2013
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      Recently, our hot tub took a dump, it won't stay on. Keeps tripping the
      GFCI circuit. Heater elements are usual suspects in spas, but the circ
      pump turns on and runs when the heater and the control panel are both
      electrically isolated. So to continue troubleshooting, how much
      resistance should the heater element have? Should this be similar to
      any other heater element, such as an immersion-type element for a
      water heater?

      It's part # E2550-020XET, says 240V 5.5KW on the label and I measure
      it at 10 ohms. Not 10k ohm or 10m ohms, just 10 ohms. Does that sound
      right? It seems a lot low but resistance heaters like this are new
      to me.

      So if amps = watts / volts, then it draws about 23 amps and if
      resistance = volts / amps, then it I guess it should be 10 ohms,
      if my math is correct. So yeah, I'm asking if someone could check my
      math?

      Reese
    • Stefan Trethan
      The resistance will change with temperature, but 10R doesn t sound wrong. However the mistake you made is that resistance between the two power terminals
      Message 2 of 11 , Jun 16, 2013
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        The resistance will change with temperature, but 10R doesn't sound wrong.

        However the mistake you made is that resistance between the two power
        terminals doesn't really matter if the GFCI trips.
        You should be measuring resistance between ground and either terminal
        to find an earth leakage fault.

        Ideally you would do that with a high voltage insulation tester,
        megger, or whatever you may call it. Not all insulation faults will
        show up on your typical DMM with a couple of volts test voltage.

        ST

        On Sun, Jun 16, 2013 at 8:06 PM, Reese <reeza@...> wrote:
        > Recently, our hot tub took a dump, it won't stay on. Keeps tripping the
        > GFCI circuit. Heater elements are usual suspects in spas, but the circ
        > pump turns on and runs when the heater and the control panel are both
        > electrically isolated. So to continue troubleshooting, how much
        > resistance should the heater element have? Should this be similar to
        > any other heater element, such as an immersion-type element for a
        > water heater?
        >
        > It's part # E2550-020XET, says 240V 5.5KW on the label and I measure
        > it at 10 ohms. Not 10k ohm or 10m ohms, just 10 ohms. Does that sound
        > right? It seems a lot low but resistance heaters like this are new
        > to me.
        >
        > So if amps = watts / volts, then it draws about 23 amps and if
        > resistance = volts / amps, then it I guess it should be 10 ohms,
        > if my math is correct. So yeah, I'm asking if someone could check my
        > math?
        >
        > Reese
        >
        >
        >
        >
        > ------------------------------------
        >
        > Please trim excess when replyingYahoo! Groups Links
        >
        >
        >
      • John Popelish
        10 ohms is in the right range for such a high power heater, though the resistance might a bit higher when it is hot. Your first problem is to decide if the
        Message 3 of 11 , Jun 16, 2013
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          10 ohms is in the right range for such a high power heater, though the
          resistance might a bit higher when it is hot. Your first problem is to
          decide if the breaker is tripping from over current, or because of leakage
          current to ground.

          You need to measure the resistance between ground and the heater element or
          any other load on this breaker, as well as measuring the actual load
          current. The other possibilities are that the breaker is defective and is
          either false tripping of non existent ground leakage, or is false tripping
          on a load current that it should carry.

          Simply replacing the breaker with a new one may be the easiest way to test
          those last two.
          --
          Regards,

          John Popelish


          On Sun, Jun 16, 2013 at 2:06 PM, Reese <reeza@...> wrote:

          > Recently, our hot tub took a dump, it won't stay on. Keeps tripping the
          > GFCI circuit. Heater elements are usual suspects in spas, but the circ
          > pump turns on and runs when the heater and the control panel are both
          > electrically isolated. So to continue troubleshooting, how much
          > resistance should the heater element have? Should this be similar to
          > any other heater element, such as an immersion-type element for a
          > water heater?
          >
          > It's part # E2550-020XET, says 240V 5.5KW on the label and I measure
          > it at 10 ohms. Not 10k ohm or 10m ohms, just 10 ohms. Does that sound
          > right? It seems a lot low but resistance heaters like this are new
          > to me.
          >
          > So if amps = watts / volts, then it draws about 23 amps and if
          > resistance = volts / amps, then it I guess it should be 10 ohms,
          > if my math is correct. So yeah, I'm asking if someone could check my
          > math?
          >


          [Non-text portions of this message have been removed]
        • indago
          What is the GFCI 240 volt circuit breaker rated for: 20 amps?   30 amps? ... [Non-text portions of this message have been removed]
          Message 4 of 11 , Jun 16, 2013
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            What is the GFCI 240 volt circuit breaker rated for: 20 amps?   30 amps?



            >________________________________
            > From: John Popelish <jpopelish@...>
            >To: Electronics_101@yahoogroups.com
            >Sent: Sunday, June 16, 2013 2:31 PM
            >Subject: Re: [Electronics_101] Heater element resistance question
            >
            >
            >

            >10 ohms is in the right range for such a high power heater, though the
            >resistance might a bit higher when it is hot. Your first problem is to
            >decide if the breaker is tripping from over current, or because of leakage
            >current to ground.
            >
            >You need to measure the resistance between ground and the heater element or
            >any other load on this breaker, as well as measuring the actual load
            >current. The other possibilities are that the breaker is defective and is
            >either false tripping of non existent ground leakage, or is false tripping
            >on a load current that it should carry.
            >
            >Simply replacing the breaker with a new one may be the easiest way to test
            >those last two.
            >--
            >Regards,
            >
            >John Popelish
            >
            >On Sun, Jun 16, 2013 at 2:06 PM, Reese <reeza@...> wrote:
            >
            >> Recently, our hot tub took a dump, it won't stay on. Keeps tripping the
            >> GFCI circuit. Heater elements are usual suspects in spas, but the circ
            >> pump turns on and runs when the heater and the control panel are both
            >> electrically isolated. So to continue troubleshooting, how much
            >> resistance should the heater element have? Should this be similar to
            >> any other heater element, such as an immersion-type element for a
            >> water heater?
            >>
            >> It's part # E2550-020XET, says 240V 5.5KW on the label and I measure
            >> it at 10 ohms. Not 10k ohm or 10m ohms, just 10 ohms. Does that sound
            >> right? It seems a lot low but resistance heaters like this are new
            >> to me.
            >>
            >> So if amps = watts / volts, then it draws about 23 amps and if
            >> resistance = volts / amps, then it I guess it should be 10 ohms,
            >> if my math is correct. So yeah, I'm asking if someone could check my
            >> math?
            >>
            >
            >[Non-text portions of this message have been removed]
            >
            >
            >
            >
            >

            [Non-text portions of this message have been removed]
          • John Popelish
            I forgot to give you the formula for the resistance, given the voltage and power. R=volt^2/watts So 240*240/5500=10.47 ohms -- Regards, John Popelish ...
            Message 5 of 11 , Jun 16, 2013
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              I forgot to give you the formula for the resistance, given the voltage and
              power.

              R=volt^2/watts

              So 240*240/5500=10.47 ohms

              --
              Regards,

              John Popelish

              On Sun, Jun 16, 2013 at 2:06 PM, Reese <reeza@...> wrote:

              > (snip)
              >
              > It's part # E2550-020XET, says 240V 5.5KW on the label and I measure
              > it at 10 ohms. Not 10k ohm or 10m ohms, just 10 ohms. Does that sound
              > right? It seems a lot low but resistance heaters like this are new
              > to me.
              > (snip)
              >
              > Reese
              >
              >
              >
              >
              > ------------------------------------
              >
              > Please trim excess when replyingYahoo! Groups Links
              >
              >
              >
              >


              [Non-text portions of this message have been removed]
            • AlienRelics
              The resistance will not necessarily change by much. That heater element isn t going to get hot enough to glow, after all, only up to around 100F or slightly
              Message 6 of 11 , Jun 16, 2013
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                The resistance will not necessarily change by much. That heater element isn't going to get hot enough to glow, after all, only up to around 100F or slightly hotter.

                I have a couple of heating elements I use as audio dummy loads. They are air elements, 1kW @ 75V and so about 5.6 ohms. At a full 1kW with no fan, a meter that can only read down to 0.1 ohm does not change its measurement. Close enough for audio.

                Anyway, I concur with everything Stefan said. Check leakage to ground with a megger, a typically low voltage DMM will not necessarily show leakage.

                Steve Greenfield AE7HD

                --- In Electronics_101@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
                >
                > The resistance will change with temperature, but 10R doesn't sound wrong.
                >
                > However the mistake you made is that resistance between the two power
                > terminals doesn't really matter if the GFCI trips.
                > You should be measuring resistance between ground and either terminal
                > to find an earth leakage fault.
                >
                > Ideally you would do that with a high voltage insulation tester,
                > megger, or whatever you may call it. Not all insulation faults will
                > show up on your typical DMM with a couple of volts test voltage.
                >
                > ST
                >
                > On Sun, Jun 16, 2013 at 8:06 PM, Reese <reeza@...> wrote:
                > > Recently, our hot tub took a dump, it won't stay on. Keeps tripping the
                > > GFCI circuit. Heater elements are usual suspects in spas, but the circ
                > > pump turns on and runs when the heater and the control panel are both
                > > electrically isolated. So to continue troubleshooting, how much
                > > resistance should the heater element have? Should this be similar to
                > > any other heater element, such as an immersion-type element for a
                > > water heater?
                > >
                > > It's part # E2550-020XET, says 240V 5.5KW on the label and I measure
                > > it at 10 ohms. Not 10k ohm or 10m ohms, just 10 ohms. Does that sound
                > > right? It seems a lot low but resistance heaters like this are new
                > > to me.
                > >
                > > So if amps = watts / volts, then it draws about 23 amps and if
                > > resistance = volts / amps, then it I guess it should be 10 ohms,
                > > if my math is correct. So yeah, I'm asking if someone could check my
                > > math?
                > >
                > > Reese
                > >
                > >
                > >
                > >
                > > ------------------------------------
                > >
                > > Please trim excess when replyingYahoo! Groups Links
                > >
                > >
                > >
                >
              • ljmayes1
                Power = V / R So using your figures: Power = 57600/10 = 5.76kW (pretty close to your 5.5kW). So, I would say 10 ohms is right. Lawrence
                Message 7 of 11 , Jun 17, 2013
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                  Power = V <squared> / R

                  So using your figures:

                  Power = 57600/10 = 5.76kW (pretty close to your 5.5kW).

                  So, I would say 10 ohms is right.

                  Lawrence

                  --- In Electronics_101@yahoogroups.com, Reese <reeza@...> wrote:
                  >
                  > Recently, our hot tub took a dump, it won't stay on. Keeps tripping the
                  > GFCI circuit. Heater elements are usual suspects in spas, but the circ
                  > pump turns on and runs when the heater and the control panel are both
                  > electrically isolated. So to continue troubleshooting, how much
                  > resistance should the heater element have? Should this be similar to
                  > any other heater element, such as an immersion-type element for a
                  > water heater?
                  >
                  > It's part # E2550-020XET, says 240V 5.5KW on the label and I measure
                  > it at 10 ohms. Not 10k ohm or 10m ohms, just 10 ohms. Does that sound
                  > right? It seems a lot low but resistance heaters like this are new
                  > to me.
                  >
                  > So if amps = watts / volts, then it draws about 23 amps and if
                  > resistance = volts / amps, then it I guess it should be 10 ohms,
                  > if my math is correct. So yeah, I'm asking if someone could check my
                  > math?
                  >
                  > Reese
                  >
                • Reese
                  ... A megger, yeah. It so happens I have one of those, bought it to test the transformer in a wirefeed welder a while back... I had forgotten all about it.
                  Message 8 of 11 , Jun 17, 2013
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                    At 02:15 PM 6/16/2013, Stefan Trethan wrote:

                    >Ideally you would do that with a high voltage insulation tester,
                    >megger, or whatever you may call it. Not all insulation faults will
                    >show up on your typical DMM with a couple of volts test voltage.


                    A megger, yeah. It so happens I have one of those, bought it to test
                    the transformer in a wirefeed welder a while back... I had forgotten
                    all about it. I'll give that a shot, see what the answer is.

                    Reese
                  • Reese
                    ... Sorry for the delay, I m currently on vacation and lots of other things were ahead of this in the queue. So I hooked up the megger, which came with a
                    Message 9 of 11 , Jun 26, 2013
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                      At 05:59 PM 6/17/2013, Reese wrote:

                      >A megger, yeah. It so happens I have one of those, bought it to test
                      >the transformer in a wirefeed welder a while back... I had forgotten
                      >all about it. I'll give that a shot, see what the answer is.


                      Sorry for the delay, I'm currently on vacation and lots of other things
                      were ahead of this in the queue.

                      So I hooked up the megger, which came with a manual that was mostly
                      in Chinese so I'm still figuring out how to use it. Here is part of
                      the manual, someone posted it online:

                      http://micromir.ucoz.ru/insulation/VC60B.pdf

                      Testing on the DC side I get a 70-71 M Ohm reading, I can't figure
                      out how to get a reading on the AC side (it's supposed to test up
                      to 750 VAC).

                      So if this 240 volt, 5.5 kw water-heating element should have a 10 Ohm
                      resistance, does ~70 M Ohms resistance with the megger sound right?

                      Reese
                    • Donald H Locker
                      70Meg should be good enough. Up to 750VAC means it can apply that much voltage to the circuit to test for leakage. Many insulations that are OK at 1.5V or 9V
                      Message 10 of 11 , Jun 29, 2013
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                        70Meg should be good enough. Up to 750VAC means it can apply that much voltage to the circuit to test for leakage. Many insulations that are OK at 1.5V or 9V from a normal ohmmeter will break down at operating voltage, so the megger applies enough voltage to make sure it really is OK.

                        Make sure all control circuits are disconnected before testing - the high voltage of the megger can damage low-voltage circuits.

                        Donald.
                        --
                        *Plain Text* email -- it's an accessibility issue
                        () no proprietary attachments; no html mail
                        /\ ascii ribbon campaign - <www.asciiribbon.org>

                        ----- Original Message -----
                        > From: "Reese" <reeza@...>
                        > To: "Electronics 101" <Electronics_101@yahoogroups.com>
                        > Sent: Wednesday, June 26, 2013 4:55:48 PM
                        > Subject: Re: [Electronics_101] Heater element resistance question
                        > At 05:59 PM 6/17/2013, Reese wrote:
                        >
                        > >A megger, yeah. It so happens I have one of those, bought it to test
                        > >the transformer in a wirefeed welder a while back... I had forgotten
                        > >all about it. I'll give that a shot, see what the answer is.
                        >
                        >
                        > Sorry for the delay, I'm currently on vacation and lots of other
                        > things were ahead of this in the queue.
                        >
                        > So I hooked up the megger, which came with a manual that was mostly
                        > in Chinese so I'm still figuring out how to use it. Here is part of
                        > the manual, someone posted it online:
                        >
                        > http://micromir.ucoz.ru/insulation/VC60B.pdf
                        >
                        > Testing on the DC side I get a 70-71 M Ohm reading, I can't figure
                        > out how to get a reading on the AC side (it's supposed to test up
                        > to 750 VAC).
                        >
                        > So if this 240 volt, 5.5 kw water-heating element should have a 10 Ohm
                        > resistance, does ~70 M Ohms resistance with the megger sound right?
                        >
                        > Reese
                        >
                        >
                      • Reese
                        ... Yes, the element is removed from the circuit for megger testing. I took it to an electrical repair place, they said on megger-testing that it had almost a
                        Message 11 of 11 , Jun 30, 2013
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                          At 06:55 PM 6/29/2013, Donald H Locker wrote:

                          >70Meg should be good enough. Up to 750VAC means it can apply that
                          >much voltage to the circuit to test for leakage. Many insulations
                          >that are OK at 1.5V or 9V from a normal ohmmeter will break down at
                          >operating voltage, so the megger applies enough voltage to make sure
                          >it really is OK.
                          >
                          >Make sure all control circuits are disconnected before testing - the
                          >high voltage of the megger can damage low-voltage circuits.


                          Yes, the element is removed from the circuit for megger testing.

                          I took it to an electrical repair place, they said on megger-testing
                          that it had almost a direct short. So either this cheap Chinese megger
                          I bought on Ebay is dingfritz or I'm not using it correctly, possibly
                          a little of both.

                          I guess I need to identify some items of known value and test them, to
                          verify that the megger works properly and that I'm using it properly.

                          Reese
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