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Contactor combiner = disconnecting means? (NEC 2014)

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    Contactor combiner = disconnecting means? (NEC 2014)

    We have been arguing about this one a lot recently, and I'd like to put this issue to rest. For NEC 2014, is a UL listed contactor combiner box a "disconnecting means" as defined by 690.17(A)?

    690.17(A) Manually Operable. The disconnecting means for ungrounded PV conductors shall consist of a manually operable switch(es) or circuit breaker(s). The disconnecting means shall be permitted to be power operable with provisions for manual operation in the event of a power-supply failure. ...
    I was thinking that perhaps a contactor combiner might qualify, if it is considered "(8) a dc-rated enclosed switch". Many manufacturers currently offer listed contactor combiner boxes. My concern is that to be in the event of a power-supply failure, such a combiner does not have "provisions for manual operation", it is merely just OFF. Is this a behavior mode that AHJs would accept? What is your personal opinion on this mode of operation?

    New provisions in 690.15, (690.15(C)) state that "the dc output of dc combiners mounted on roofs of dwellings or other buildings shall have a load break disconnecting means located in the combiner or within 1.8 m (6 ft) of the combiner." So, if a contactor combiner does not fulfill 690.17, and 690.15 requires a dc disconnect in the combiner or nearby, this would mean that I need a DC disconnect external to the contactor combiner box also?

    Thanks for your input!

    #2
    There is no place in the NEC that I am aware of that allows a contactor act as a disconnecting means for any applications. Contactors are controllers.

    Furthermore I would say the section you pointed out makes it very clear a contactor would not be acceptable.

    A shunt trip breaker could be acceptable.

    Comment


      #3
      The text says manually operable, so although it seems that being able to manually open it and force it to stay open even if the power comes back.
      But technically you would have to be able to manually close it too.

      Tapatalk!

      Comment


        #4
        690.17(A)(1) allows for the use of "a PV industrial control switch marked for use in PV systems." That sounds like a listed (UL 1741) contactor combiner box type of solution to me.

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          #5
          Switch is still not equal to contactor. But as mentioned, either a breaker or a shunt trip breaker may be OK.

          Tapatalk!

          Comment


            #6
            Thank you all for your responses.

            So, what if you add a "manual override" switch, that controls the contactor's coil circuit? This would be any LV dc switch that could handle the coil current, and probably would be UL508 (industrial control switch). That would enable the coil circuit to be opened in the event of a power failure, but still would not allow the contactor circuit to close, as GoldDigger had mentioned, so technically not completely "manually operable".

            Supposing the above is allowed, some contactors are actually Recognized as components to industrial control switches (category code NRNT2), in which case, if they are part of a UL1741 listed assembly, they should meet 690.17(1), as SolarPro had suggested:

            (1) A PV industrial control switch marked for use in PV systems
            Do you agree/disagree?

            Gracias!

            Comment


              #7
              Equipment listing is increasingly important. Under the 2011 NEC 690.4(D) requires the use of "source-circuit combiners" listed and identified for the application; under 2014 NEC, "dc combiners" in general need to be "listed for the PV application."

              @MWh_Pro, It looks to me like the SolarBOS contactor combiners are set up exactly as you describe. A photo is here and the installation manual is here.

              To understand why listed contactor combiners would have been added in NEC 2014 as 690.17 disconnect types, it helps to review the 690.12 rapid shutdown requirements for PV systems, as well as the 690.11 requirements for dc arc-fault circuit protection. It's difficult to meet either of these requirements in large PV systems with centralized inverters without using listed contactor combiners.

              Here are relevant excerpts from an article we just published, "Understanding NEC 2014 and its Impact on PV Systems":

              Equipment options. While the equipment used to perform rapid shutdown must be listed and identified, it does not have to be listed specifically for the purpose of rapid shutdown of PV systems. For example, string inverters located on a commercial rooftop within 10 feet of a PV array would meet the requirements of Section 690.12, as would microinverters or ac PV modules installed on the roof of a residence. In both instances, if first responders were to shut down power to the premises, there would be no uncontrolled energized conductors beyond 10 feet of the array.

              Listed contactor combiner boxes provide another means of meeting Section 690.12 using off-the-shelf components. Simply locate the contactor combiner boxes within 10 feet of the PV array and find a suitable location for the control switch or button. The contactors will open upon loss of utility power or in the event that the control switch is operated. The voltage and power limits in Section 690.12 still allow for 24-volt control circuits, which can be used to operate contactors in dc combiner boxes and allow for Code compliance in the event that the rapid shutdown is initiated by means other than opening the service disconnect. Another design option is to specify dc-to-dc converters that comply with the rapid shutdown requirements for PV systems on buildings.

              Comment


                #8
                Good information SolarPro and very good article in this months magazine. Here in Massachusetts we are under the 2014 code as of January 1st. The language in 690.12 needs some work and we will be struggling with multiple interpretations until 2017.
                The DC to DC converters I've seen take more than 10-seconds to go below 30volts. They also concern me on how they perform this function...there is no real mechanical break in the DC source circuit in the system. If I were a firefighter...and I'm not...I wouldn't trust anything but a mechanical break in the circuit.

                Comment


                  #9

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                    #10
                    EC&M Article

                    Here is a link to an article in EC&M Magazine this month on this subject: http://ecmweb.com/fire-amp-security/solar-under-fire

                    Comment


                      #11

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                        #12
                        So what is the final verdict on this discussion? Are contactor combiners without a manual DC disconnect acceptable?

                        I can't see how a contactor is Manual Operable?

                        Comment


                          #13
                          The contact combiners I've seen for PV applications can be remotely actuated for rapid shutdown (or similar) and they can be manually actuated locally for fuse servicing (or similar). So it's not an either or situation. The products can do both.

                          As an example, these SolarBOS combiners have a contactor in series with a disconnect. (This is why contactor combiners are prohibitively expensive, which is causing integrators to install string inverters on commercial rooftops in lieu of dc combiners.)
                          Last edited by SolarPro; 02-26-15, 12:19 PM.

                          Comment


                            #14
                            I see that "capacitor bleed down" circuit as a solution to a problem that doesn't exist.

                            The goal is to disconnect conductors, and de-energize equipment on the rooftop. The inverter is unlikely on the rooftop. The DC disconnect in the inverters already does this, by disconnecting the DC side from the inverter. The capacitor stored energy doesn't get out of the inverters, after you shut off the DC disconnect. Unfortunately, if all you do is shut off the AC disconnect (which is what you will most likely want to do), so that you can shut off multiple inverters at once, nothing can stop the capacitor charge from bleeding onto the conductors, array and optimizers.

                            All that this "bleed down" circuit does, is de-energize the capacitors in the inverter. And it only does this, if the inverter is disconnected on its DC side, which already de-energizes the rooftop equipment with or without this add-on kit.


                            Does 690.12 say anything about the voltage inside a piece of equipment, such as an inverter? What about the voltage inside of a computer? Or a power supply?
                            Last edited by Carultch; 02-26-15, 05:26 PM.

                            Comment


                              #15
                              Originally posted by SolarPro View Post
                              The contact combiners I've seen for PV applications can be remotely actuated for rapid shutdown (or similar) and they can be manually actuated locally for fuse servicing (or similar). So it's not an either or situation. The products can do both.

                              As an example, these SolarBOS combiners have a contactor in series with a disconnect. (This is why contactor combiners are prohibitively expensive, which is causing integrators to install string inverters on commercial rooftops in lieu of dc combiners.)
                              Thanks Solarpro...the SolarBOS product does have a specification saying... "Local External Disconnect Handle". Although I haven't seen the product in hand so I'm not sure if such handle is used to interrupt the control circuit to the contactor or actually is a manual means to mechanically open a disconnect "switch" or "circuit breaker" as outlined in Disconnect Type 690.17(A) (1) thru (10)

                              I saw a new ABB product in development for Rapid Shutdown at a Solar Conference this week that was a contactor controlled by 24 volts DC and the disconnect on the face of the combiner box was just interrupting the control power to the contactor. Now I'm not 100% in agreement that this is the type of DC disconnect that 690.15(C) is requiring in reviewing 690.17 "Disconnect Type"

                              I do like the ABB product for field use for Rapid Shutdown...used as a "pass through" only without combining...but when used as a DC combiner I would think a "switch or "circuit breaker" would be the manual operable disconnection means, not a contactor.

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