# Contactors in Parallel



## randomkiller (Sep 28, 2007)

alanblinkers said:


> 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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## nick (Feb 14, 2008)

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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## alanblinkers (Jan 18, 2009)

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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## randomkiller (Sep 28, 2007)

nick said:


> 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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## nick (Feb 14, 2008)

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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## randomkiller (Sep 28, 2007)

nick said:


> 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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## InControl (Mar 20, 2007)

alanblinkers said:


> 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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## Rockyd (Apr 22, 2007)

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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## nick (Feb 14, 2008)

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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## randomkiller (Sep 28, 2007)

nick said:


> 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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## brian john (Mar 11, 2007)

Wye Delta starters do this as part of normal design.


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## alanblinkers (Jan 18, 2009)

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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## nick (Feb 14, 2008)

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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## alanblinkers (Jan 18, 2009)

http://relays.tycoelectronics.com/datasheets/ev200.pdf

These are rated DC, I wonder how safe they would be for AC


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## nick (Feb 14, 2008)

alanblinkers said:


> 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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## alanblinkers (Jan 18, 2009)

nick said:


> 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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## nick (Feb 14, 2008)

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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## alanblinkers (Jan 18, 2009)

nick said:


> 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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## nick (Feb 14, 2008)

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 .


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## MechanicalDVR (Dec 29, 2007)

alanblinkers said:


> 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.


 
I don't want to piss in your cornflakes but you can't make chicken soup from chicken **** is an addage to live by. Cheaping out on parts never works out in the long run. Bite the bullet and do it right the life you save maybe your own.


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## alpadrino (Feb 4, 2009)

no conductor smaller then a 1/0 can be run in parallel . second you would need 60 amps not two 30 amp


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## TOOL_5150 (Aug 27, 2007)

alpadrino said:


> no conductor smaller then a 1/0 can be run in parallel .


Its about time someone stated that.

~Matt


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## nick (Feb 14, 2008)

alpadrino said:


> no conductor smaller then a 1/0 can be run in parallel . second you would need 60 amps not two 30 amp


Well hes not parralleling anything he change his mind after a few post , that was the original problem as two contactors were in parrallel but this whole post is screwed you dont parallel contactors !! if you do show me a schematic ive never seen it and show me parallel fuses or oc protection in parallel to protect a motor? give me a web page maybe i can learn something new ? Hes got 500 amp contactors now each fused for each load read the post you can do that ok , but i would just put a transfer switch in one time myself . When you see multipule contactors in a motor controller/ starter a wye /delta were just changing taps on the windings if its a partwinding motor its changing the taps or windings on the motor its not parralleling anything ? part winding starter you have two sets of heaters but just one contactor at one time is on line . comments


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## randomkiller (Sep 28, 2007)

nick said:


> Well hes not parralleling anything he change his mind after a few post , that was the original problem as two contactors were in parrallel but this whole post is screwed you dont parallel contactors !! if you do show me a schematic ive never seen it and show me parallel fuses or oc protection in parallel to protect a motor? give me a web page maybe i can learn something new ? Hes got 500 amp contactors now each fused for each load read the post you can do that ok , but i would just put a transfer switch in one time myself . When you see multipule contactors in a motor controller/ starter a wye /delta were just changing taps on the windings if its a partwinding motor its changing the taps or windings on the motor its not parralleling anything ? part winding starter you have two sets of heaters but just one contactor at one time is on line . comments


 
Step away from the conduit and spend sometime in the service world and you will come across things you have never imagined.

As for this post, I agree he should be using equipment engineered for the purpose at hand, there is no need to reinvent the wheel.


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## nick (Feb 14, 2008)

*dumb construction electricians*

Well RK you may have seen this but i just cant see two contactors operating in parallel on a motor for what reason and at lower amperes than then the motor flc load that meaning two 30 amp sets of fuses will not give you 45 amps to a motor or load it just doesnt make sense , can someone explain in detail so i can understand RK ? I would like to know and yes we have never done service work before, is this factory equipment because to me its a unsafe practice .comments best to yas :huh:


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## JRaef (Mar 23, 2009)

You can parallel contactors for resistive loads, you cannot parallel contactors for any sort of inductive load, ie motor, transformer or power supply. The reason is, there is no way that two contactors will close at EXACTLY the same instant, and the inrush current that magnetizes any inductive element will destroy the smaller contacts in short order. Magnetic inrush can in theory be as high as 2200% of the rated current for a few cycles as the magnetic field establish and impedance drops it down. That time period is short, but longer than the delay you would see between two contactors closing. Contacts rated for AC inductive loads take this into account in their design, but only for their rated current. When you parallel them to use lower current ratings on the contactors, you are eliminating that design allowance and subjecting the contacts to excessive heat, arcing, and vaporization of the contact materials. The only way to avoid that is to size EACH of the parallel contactors for the full load, and what would be the point of that?

Addressing other comments: Wye Delta starters appear to be doing this, but do so in a different manner and sequence. Sometimes you see this done on but it is generally on large resistance heater controls. On most resistive loads, there is no inrush so it doesn't matter. This is also done on bypass contactors for soft starters, but in that case the SCRs have already dealt with the magnetic current, the contactors are used just to bypass the slight voltage drop across the SCRs after the motor is at full speed. But if you read the manuals for those that do this, they will tell you that you cannot use that type of parallel bypass to start the motor across the line if the soft starter fails. 

The point is, if you have absolute control of exactly what parallel contactors are being used for, you can engineer them into a system, but for something like this, no.


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## Hawkrod (Mar 19, 2012)

And just another thing to make things more elegant (complicated), I like using old school Square D multi pole contactors like an 8903LX latching contactor. You can set some contacts for NO and some for NC. When it switches it turns some on and some off. They are quite adaptable but I wouldn't use them for the reasons offered above against splitting the load and only present it as a hypothetical.


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## Jlarson (Jun 28, 2009)

Zombies!


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## JRaef (Mar 23, 2009)

Gagh! I didn't see the date!
My bad...








The new mobile app kind of sucks for that reason.


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## Bad Electrician (May 20, 2014)

JReaf-

Wye Delta starters are parallel when in RUN, of course the inrush is handled in Start mode.


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## dmxtothemax (Jun 15, 2010)

alanblinkers said:


> 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.


YES !

But like anything
it might not be the best way to do it
Depends entirely on the specific application

But loosely on a technical level, it will work.

:thumbsup:


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## dmxtothemax (Jun 15, 2010)

JRaef said:


> The new mobile app kind of sucks for that reason.


 
So your having trouble with the new refinements ?

Any one out there who think it is working ok ?

I switched mine off !

Somehow not compatible with my system.


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