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Old 01-31-2009, 08:23 PM   #1
 
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Default Contactors in Parallel

I'm trying to get some simple electrical theory straight in my head. If I were to wire 2 30 amp contactors in parallel, could I then control a 60 amp load with them? It seems like it would work but I feel like I am missing something.
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Old 01-31-2009, 08:35 PM   #2
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I'm trying to get some simple electrical theory straight in my head. If I were to wire 2 30 amp contactors in parallel, could I then control a 60 amp load with them? It seems like it would work but I feel like I am missing something.
Sure why not? How often do you see feeders that are run in pairs of smaller conductors than single large wires.
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Old 01-31-2009, 08:36 PM   #3
 
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Well no dont do it reason why is if one contactor did not close or hung up you would have a load pull 60 amps on that single contactor not a good thing . best to ya
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Old 01-31-2009, 08:39 PM   #4
 
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Yea that's what I was figuring, sans a equipment failure it seems like it would be ok. But yea if one fails it could be very bad.
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Old 01-31-2009, 08:41 PM   #5
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Well no dont do it reason why is if one contactor did not close or hung up you would have a load pull 60 amps on that single contactor not a good thing . best to ya
I see this done in large equipment all the time. They are always protected by properly sized OCP for just that reason.
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Old 01-31-2009, 08:50 PM   #6
 
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Well RK he needs to explain in detail what hes got but i dont see how overloads would help him if one stays open what is a overload going to do nothing in my way of thinking ? but i maybe out of line ? comments
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Old 01-31-2009, 08:58 PM   #7
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Well RK he needs to explain in detail what hes got but i dont see how overloads would help him if one stays open what is a overload going to do nothing in my way of thinking ? but i maybe out of line ? comments

Well if you had two three pole contactors each fed from a three fuse block with 30 amp fuses feeding a 45 amp compressor motor, if you lost one contactor and the machine tried to run the load from one contactor the fuses would blow, shutting it down.
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Old 01-31-2009, 09:01 PM   #8
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I'm trying to get some simple electrical theory straight in my head. If I were to wire 2 30 amp contactors in parallel, could I then control a 60 amp load with them? It seems like it would work but I feel like I am missing something.
The answer is yes.
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Old 01-31-2009, 09:02 PM   #9
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Why not just get a twin set of contacts to drive the coils of big enough contactors, OL's sized to each accordingly? I believe stackables can run upto 12 contacts.
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Old 01-31-2009, 09:27 PM   #10
 
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Well RK inside you controllers you work on they use 30 amp sets of fuses to fed each contactor and if one drops out the other trips yes i can see that but what did the post say 60 amp load and two contactors thats it . best to ya
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Old 01-31-2009, 09:40 PM   #11
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Well RK inside you controllers you work on they use 30 amp sets of fuses to fed each contactor and if one drops out the other trips yes i can see that but what did the post say 60 amp load and two contactors thats it . best to ya

But, in theory it would be fine. Hence my original answer of "why not?".
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Old 01-31-2009, 09:51 PM   #12
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Wye Delta starters do this as part of normal design.
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Old 01-31-2009, 09:55 PM   #13
 
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Hehe, I didn't mean to spark a huge debate. The reason I'm asking is I have a hobby generator project, and my house has 4 mains, 2 x 150amp and 2 x100 amp. I am building a computer to control everything in the system, stop, start, KW monitoring, I'm also going to build in shedding capabilities, so I would like to control each main. But I'm finding that 100-150amp contactors are very expensive and they are also only single throw. Where as I can get a 30amp DPDT contactor for 10 bucks. However I want to do what's safe. I come from an electrical background, I'm not an electrician but I used to oversee the installation of generators. The biggest being a 1MW unit, so I'm very familiar with it all. I want to save money, but I don't want to risk safety.
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Old 01-31-2009, 09:57 PM   #14
 
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Well you got me thinking now RK one load at 60 amp and two contactors which he has so what were going to do is feed each contactor with what ocp device to keep 60 amps to load ? are we saying that parallel fuses gives us protection if one contactor opens ? just say its a resistance type load ? a wye delta starter uses one ocp device not two seperate ocps if you parallel fuse it doesnt give you total amps of 60 amps at a lower ocp comments

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Old 01-31-2009, 10:50 PM   #15
 
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http://relays.tycoelectronics.com/datasheets/ev200.pdf

These are rated DC, I wonder how safe they would be for AC
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Old 01-31-2009, 11:47 PM   #16
 
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http://relays.tycoelectronics.com/datasheets/ev200.pdf

These are rated DC, I wonder how safe they would be for AC
Well dont see ac rating for the contactor but you might be ok now that you got us all interested what is your actual circuit of what you are connecting up ? your using two in parallel with one ocp device to a load or loads ?
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Old 01-31-2009, 11:58 PM   #17
 
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Well dont see ac rating for the contactor but you might be ok now that you got us all interested what is your actual circuit of what you are connecting up ? your using two in parallel with one ocp device to a load or loads ?
Well my plan is to isolate each main, so that the computer can turn each one on and off depending on how much load is placed on the generator. I use phidgets for projects like this, if you haven't heard of them they are awesome USB interface boards and I recommend you check them out.

The mains feed as follows: 150amp for kitchen, guest room, garage, living room and, air handler1. 150amp for den, florida room, bedrooms, and air handler2. 100amp for main house air handler. 100amp for pool equipment. So I would like to use some solenoid contactors either by themselves if the amperage is high enough or in parallel as I asked before. One or one set on each hot leg and an additional set on each hot leg to introduce the generator power to the circuit. I'm probably way reinventing the wheel here, but I just can't bring myself to pay a few grand for a 500amp transfer switch, when I only paid $350 bucks for the engine and another $500 for the generator end.
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Old 02-01-2009, 12:12 AM   #18
 
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Well iam very careful when iam not sure what ones doing , I think your ok as most dc stuff at amp wise will work fine voltage wise with ac ratings as peak voltage of ac goes to constant dc voltage . They look like they can handel lots more than 60 amps was that a 500 amp contact . nice relays i dont see a problem i take back my words . so controlling your loads by a program you have made to operate a generator for power loss are you getting ready for a storm this year or what ? best to ya
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Old 02-01-2009, 09:45 AM   #19
 
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Well iam very careful when iam not sure what ones doing , I think your ok as most dc stuff at amp wise will work fine voltage wise with ac ratings as peak voltage of ac goes to constant dc voltage . They look like they can handel lots more than 60 amps was that a 500 amp contact . nice relays i dont see a problem i take back my words . so controlling your loads by a program you have made to operate a generator for power loss are you getting ready for a storm this year or what ? best to ya
Well my original post was just a theory, my actual loads I am controlling are 100 and 150 amps. not 60. And I would like to have my unit ready for hurricane season. This is a project I've been working on for many years. It just took me this long to find a suitable engine. I got a 30HP engine from a refrigeration trailer for $350 bucks, runs great. So now it's time to get it done.
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Old 02-01-2009, 03:33 PM   #20
 
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Well we have a old transfer switch old 400 amp deal off a job i rebuilt for my house and shop and i run two 17500 kw generac gensets in parallel we also have home bru solar panel for the shop just fun projects i like my own stuff to play with , no computer connections just manual start stop and solar runs 100 % with 12v car batts for mostly small loads its 100 amp max and old ups system from a old job we did. We live in a state which when your out of power for 3 or 4 weeks you must make your own guess you kind of know that living in florida , the company i work for has a yard full of junk switch gear old parts and equipment so we have lots of parts to build from . Nice to talk with a floridian take care let me know how it gos .Sounds like you got it under control with them phidgets nice control boards .

Last edited by nick; 02-01-2009 at 03:41 PM.
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