Parallel AC Contactors

GA

This kind of cost cutting is just one of the ways that electric fires get started. Oh and a final point, if in the burnt rubble an insurance investigator finds this dual contact configuration, this pseudo-electrician will be lucky to only lose their license.

JRaef,

I had the same concerned, and have read in one place that if the contactors are fused, then it could be done. Proper specing would resolve 1-2 in your list. As far as equal load on both sides, it's no problem in my application.

have read in one place that if the contactors are fused, then it could be done. Where? To vary this far from an acceptable practice, I want to see chapter, verse and most importantly conditional details before leading somebody to a fire.

Spacing has no bearing on this, I have no idea what that comment was intended to mean. It has nothing to do with spacing, it has everything to do with timing. Fractions of a second count. It may LOOK to you as if the contactors can close simultaneously, but that is virtually impossible, and that split second timing difference will make all the difference in the survival.

Re: "if the contactors are fused..." Now with this extra fusing, you have introduced a new pitfall, what if one fuse blows? Now you have created a situation where only 1 pole of one contactor can burn... even worse. To protect from that, you will have to use a voltage monitor relay on the load side of each contactor. So you then trade one large contactor for 2 smaller contactors and 2 sets of fuses and 2 fuse holders and 2 voltage monitors relays and a power splitter block to connect them and 7 devices to mount and wire instead of one... Where is the savings?

Besides, doing something wrong, then fusing it so it doesn't start a fire, is just bad engineering practice. Please do not do it.

All this said, why are you so adverse to using a large enough contactor? What size motor are we talking about here? What type of application? Because if they are to be used as a bypass arrangement for a soft starter, then it is something that people do. This is because in that scenario, the motor is ALWAYS stopped and started with the soft starter SCRs, the contactors only shunt power around them after it is already running. They are never called upon to start the motor or to stop it, so the high damaging current issues are avoided.

"Other than that, no problems." Tell us what you really think! Ha Ha. Buy the way GA. JHF

Enough is told. What I can add is this type of cost savings (?) proposal may come from finance people, not from engineers.

- MS

While i agree with and appreciate the responses so far, it is well known within the industry to parallel two contacts, even two contactors for high-current, low severity duties like AC1 as per IEC 60947-4. Here is an example:

Of course, this is done by the engineers at ABB Vasteras, with lots of checks and tests. The point is that there are TWO magnets in this.

Let me hasten to add.....such a thing MUST be done by the manufacturer, NOT by the user

If you look further, i believe you will find that these contactors are NOT rated for AC motor starting!

Of course, i did say that ... AC1 duty as per IEC 60947-4 is just heating load. i did not notice any mention of any kind of load by the poster, motor or otherwise.

We now know the reason....that 200A contactors seem overpriced...but still don't know what is the load, what is the frequency of operation, are inching(jogging) and plugging involved, is it switching capacitors .. whatever. Best that the poster elaborates a bit, but all the same... NOT a good idea to parallel two contactors !

Also quite typical though. A new individual asks for engineering help by asking only the question in their mind but none of the relevant background information. We appropriately think of the worst case scenario, since they don't explain what needs to be known to do a proper evaluation. The worst case scenario we describe is not what they are doing so they do their foolish act anyway. All we can do is warn these fools of the consequences.

In this case, my preferred scenario will be for UL to reject this design and this individual has to explain why this rework has to be done. Short of this, I just hope nobody gets hurt.

..." i did not notice any mention of any kind of load by the poster, motor or otherwise."

Oops, you are absolutely right! Sometimes I read things that are not there I guess.

Join the club

If it is any consolation, 90% or more contactor usage is for motor control. Had i not been working on a complex capacitor-switching application, i would probably have jumped to the same conclusion.

The poster now says "EV" which may mean DC motor switching, albeit at low voltage, but another complex application involving blow-out coils etc.

Consider your rating of contactor(if used one) = X

rating of contactors(if used two) = X/2

It is never going to happen that the cost of 2 contactors less than single contactor. You will have additional work cost also for using two contactors. Your idea for cost saving is useless and will affect inverse.

Thank you all for your responses. As far as the pricing issue - I can get two 100A 600V AC contactors for less than a $100.00. A single 600V 200A contactor is around $500.00. There is a huge price jump for contactors above say 120A. Again, thank you all!

Does not make sense. However, which is the brand and make of those contactors?

You all need to relax, no one is designing anything yet. I was asking for some general comments on the subject because I read in an EV application where someone had connected contactors in parallel.

I hope you all realize that exploring your options is an essential part of the design process; jumping to conclusions like a bad girlfriend is less than appealing.

Sometimes posting MORE information is better than less...

If the contactors were on the supply side of a DC input drive, then the induction / inrush issues would not matter because the drive would likely be in an Off state when the contacts close or open, you could probably get away with it.

By the way, $500 for a 200A contactor in an OEM context... someone is making a killing! If you are looking at 48VDC, you have a LOT of low cost options available to you. Make sure you are not basing your assessment on a standard industrial AC contactor; A) it may not have any appreciable DC rating on it at all, and B) it is not likely to be attractive as far as real estate goes.

Relax you say. Well excuse me for showing concern. Apparently unlike you, I worry about people seeing a dangerous proposal getting any kind of approval.

Ah ha .. i think this is where you saw this : ssinc .. yes? if so, even that thread discourages this paralleling.

However, i agree with you that one should explore all avenues, even those which appear at first sight to be ridiculous. That is what brainstorming advocates. Good luck to you.

Hi,

The cost of contactors will go up. In case if any one of the contactor fails to operate

the entrie system fails. So it is not advisible for rugular operation. For limiting the starting current it is OK

N.Prabakaran

Check out vacuum contactors. They are cheap compared to regular contactors. In the larger contactors, they were cheaper that a set of new contacts for regular starters. We used a lot of them to replace large contactors and they were much more reliable. For maintenance, the stroke of the contactor should be checked once a year, it takes about 5 minutes.

Well Ed

You've won the prize....... you get the cigar!

As much as I don't want to be harsh... I find myself having to comment.

What a dumb idea!!!!!

Please tell everyone it is just an idea and you haven't done it!

Please. please read ALL the answers..... and DON'T do it!

cost of two contactors = $500 (maybe) plus cost of fire that follows and damage to buildings/plant and then no further insurance = $25,000,000 (add as many zeros as you like)

Cost of ONE fit for purpose contactor = $1,500 (maybe more)

Sir,

I agree fully with the NO answer as given by JRaef. For a number of years, I worked in a U/L electrical panel shop. Any application such as what you suggested would have to be fully within the application design and U/L listing of the manufacturer's contactors, or be tested and certified to U/L standards on your design. I don't think that either of these is feasible or likely to succeed. If, however, the contactors were to have a common mechanical actuator for all sets of contacts, then it may be remotely possible for such a combination to pass the required tests and receive the required certification/listing.

Probability of this one flying???--less than 0.01%.

--John M.