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Old 02-01-2009, 04:18 PM   #21
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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.

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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Old 02-03-2009, 09:00 PM   #22
 
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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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Old 02-04-2009, 02:46 AM   #23
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no conductor smaller then a 1/0 can be run in parallel .
Its about time someone stated that.

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Old 02-04-2009, 04:25 AM   #24
 
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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

Last edited by nick; 02-04-2009 at 05:16 AM. Reason: what time is it ive got 5:20 am
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Old 02-04-2009, 08:36 AM   #25
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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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Old 02-04-2009, 07:47 PM   #26
 
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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
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Old 02-03-2015, 12:08 PM   #27
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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.

Last edited by JRaef; 02-03-2015 at 12:11 PM.
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Old 02-03-2015, 12:47 PM   #28
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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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Old 02-03-2015, 01:18 PM   #29
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Old 02-03-2015, 02:12 PM   #30
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Gagh! I didn't see the date!
My bad...

The new mobile app kind of sucks for that reason.

Last edited by JRaef; 02-03-2015 at 03:20 PM.
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Old 02-03-2015, 04:23 PM   #31
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JReaf-

Wye Delta starters are parallel when in RUN, of course the inrush is handled in Start mode.
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Old 02-03-2015, 10:09 PM   #32
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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.
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.

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Old 02-03-2015, 10:13 PM   #33
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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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