# NC contactor



## ponyboy (Nov 18, 2012)

Put a cheap ice cube relay before it maybe


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## chris.b (Jan 28, 2013)

The coil on the contactor will still have to be energized for the PV system to be connected, right? If the coil fails and either the PV system is not connected or if it fails with coil energized all of the time, it could be bad.


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## wendon (Sep 27, 2010)

chris.b said:


> I have a 60kw generator install that also has a PV system tied into the house. I need to disconnect the PV when the generator is on. The transfer switch has a set of auxillary form c contacts (NC-break-NO). I want to install a NC (coil de-energized) contactor so when the generator comes on, it energizes the coil to open the contactor. I am having a problem finding a NC contactor. I really don't want to do it with a NO contactor because the coil will be energized 99.99999 percent of the time and I am worried about it failing.
> 
> Does anyone know where I can get a NC 120 volt coil/240 volt 30 amp contactor? Am I over thinking this? Will the NO work with no problems?


Try looking for a Deltrol DPDT finger type relay.


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## Wirenuting (Sep 12, 2010)

How about a machine tool relay?
You can get them any size you want & based on the model, you can flip the contact points over as needed.


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## wildleg (Apr 12, 2009)

while I understand why you are predicting eventual failure of the contactor coil due to it being energized 99% of the time, if the intent of the contactor is safety (disconnecting the solar) when the generator is on, it seems like the best design would be NO so it fails in the open position ? (in which case, the NO contactor would be the correct solution ?)


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## oliquir (Jan 13, 2011)

here one on amazon
http://www.amazon.com/Normally-Closed-Lighting-Contactor-933030/dp/B00GFA7B2Y


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## chris.b (Jan 28, 2013)

wildleg said:


> while I understand why you are predicting eventual failure of the contactor coil due to it being energized 99% of the time, if the intent of the contactor is safety (disconnecting the solar) when the generator is on, it seems like the best design would be NO so it fails in the open position ? (in which case, the NO contactor would be the correct solution ?)


If it fails in the open, how would you know if the PV is not connected?
If it fails closed, it won't disconnect, which is what I am worried about.


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## dronai (Apr 11, 2011)

Here in Calif., The Solar system will automatically disconnect if there is a power outage to protect the lineman !!! No contactor necessary. For Generator to start, it is also sensing voltage from the utility side.


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## chris.b (Jan 28, 2013)

dronai said:


> Here in Calif., The Solar system will automatically disconnect if there is a power outage to protect the lineman !!! No contactor necessary. For Generator to start, it is also sensing voltage from the utility side.


Here too, but as soon as the generator comes on there will be voltage to the pv system. It is a whole house generator with service rated transfer switch.


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## JRaef (Mar 23, 2009)

Where are you going to put that contactor, on the AC side of the solar inverter, or on the DC side before it goes into the inverter? Makes a big difference.

If it is going to be on the AC side and is single phase, Allen Bradley makes a 4 pole contactor up to about 85A that has 2NO, 2NC power contacts. Second group down on this page;
http://www.ab.com/en/epub/catalogs/12768/229240/229254/229461/229481/tab3.html

If you planned on putting the contactor on the DC side it gets way more tricky, because it's harder to switch DC than AC, so the contactor cost goes WAY up.


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## dronai (Apr 11, 2011)

chris.b said:


> Here too, but as soon as the generator comes on there will be voltage to the pv system. It is a whole house generator with service rated transfer switch.



But if they are both sensing voltage loss at the utility side, neither backfeeds ? The ATS disconnects, and the Invertor disconnects ? We did a whole house this way. The only way we needed what you are proposing, was if the customer installed a battery back up system that went around that. The Solar guy was going to install a contactor like your proposing.


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## chris.b (Jan 28, 2013)

JRaef said:


> Where are you going to put that contactor, on the AC side of the solar inverter, or on the DC side before it goes into the inverter? Makes a big difference.
> 
> If it is going to be on the AC side and is single phase, Allen Bradley makes a 4 pole contactor up to about 85A that has 2NO, 2NC power contacts. Second group down on this page;
> http://www.ab.com/en/epub/catalogs/12768/229240/229254/229461/229481/tab3.html
> ...


There is a disconnect on the AC side.


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## dronai (Apr 11, 2011)

Edit: I used a 200A metermain with distribution panel, and a main 2 pole breaker out of the service, to my 200A service rated ATS. We don't do separate meters here


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## tates1882 (Sep 3, 2010)

If its a grid tied pv system it should have provisions in the inverter to disable it. Also depending on what gen system your are using the ats may have input for you to inter tie the pv system or at least a set of contacts that you can monitor the state of the pv system with. As an alternative a smart relay and some voltage or current cts and you could build a nice little control circuit. I rarely see a good quality nema contractor fail in the close position with out a ground fault/single phase or similar situation happening first. just my 2 cents


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## chris.b (Jan 28, 2013)

It is a Kohler 60kw with RDT 400 amp transfer switch.


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## tates1882 (Sep 3, 2010)

chris.b said:


> It is a Kohler 60kw with RDT 400 amp transfer switch.


 What about the pv inverter? If you use the ats aux contacts for the gen side of the ats and run them to the inverter, it may have an input to disable it. That would be the simplest solution.


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## chris.b (Jan 28, 2013)

That is what I am doing. I was just having a hard time finding the NC contactor so the only time the coil is energized is when the the generator is on.


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## tates1882 (Sep 3, 2010)

chris.b said:


> That is what I am doing. I was just having a hard time finding the NC contactor so the only time the coil is energized is when the the generator is on.


Its a little un convention but you could use a lighting contactor.
square d
8903LG22V01 
LIGHTING CONTACTOR 600VAC 30A L

For that matter if you get a electrically operated mechanical held contractor the coil should last a lifetime.


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## chris.b (Jan 28, 2013)

tates1882 said:


> Its a little un convention but you could use a lighting contactor.
> square d
> 8903LG22V01
> LIGHTING CONTACTOR 600VAC 30A L
> ...


Latching contactors are very expensive.


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## tufts46argled (Dec 23, 2007)

One possibility is put the PV system in front of the ATS and just feed it from the utilitly voltage!


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## chris.b (Jan 28, 2013)

tufts46argled said:


> One possibility is put the PV system in front of the ATS and just feed it from the utilitly voltage!


Not an option. I found the contactor. $160.


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