three phase contactor

[nidanaya]

can somebody tell wheather a 30 A contactor can withstand 130A for few miliseconds?

 

[Skogsgurra]

If the 30 A is for motor load, it should be able to take the starting (locked rotor) current. That is at least six times, often up to eight times, rated current - or 180 - 240 A.

When you say "for a few milliseconds", I get a feeling that it is about switching capacitors. There, the peak current can get very high and kills contactors. How do you know that the peak is 130 A?

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

Given that this is only 430% current and that your other thread is about motor windings, I'd venture to guess (because your lack of information leaves no other choice), that this is a motor starting application. If a contactor shows a motor rating, in HP or kW, then that is the determining factor, because as skogsgura said, it will be designed to handle the locked rotor current of the given motor size for at least 10 seconds as well as the 10-20x magnetizing current for one cycle or so. If however your contactor makes no mention of a motor rating, then you cannot assume anything about it.

If it is a capacitor switching application, you should get the capacitor switching duty rating from the contactor manufacturer. You cannot assume anything about a contactor's ability to switch capacitors without testing, because with capacitors, there is more damage from OPENING the contacts than from closing them.

You could also tell us more about what you have and what you want to do so we can avoid a game of "20 questions".

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[controlsdude]

All contactors have different part numbers depending on what current/voltage/ duty cycle or situation that you want it to operate in just like when you select different grade of steel (since your mechanical this example fits). Select a manufacturer and part number for a 30a contactor and attach a cutsheet, then we can tell you this info, or the cutsheet will tell you this info.

 

[ScottyUK]

The IEC world makes things easier to select the correct contactor rating for your application by assigning codes to switching duties. As a rule-of-thumb, AC-3 rating is one frame size larger than AC-1, and AC-4 is one frame size larger than AC-3.

Alternating current:
[li]AC-1 Non-inductive or slightly inductive loads, resistance furnaces. Power factor 0.7 - 0.8 (slightly inductive).[/li]
[li]AC-2 Slip-ring motors: starting, switching-off.[/li]
[li]AC-3 Squirrel-cage motors: starting, switching-off motors during running. Power factor 0.4 - 0.5 (AC-3).[/li]
[li]AC-4 Squirrel-cage motors: starting, plugging, inching.[/li]
[li]AC-5a Switching of electric discharge lamp controls.[/li]
[li]AC-5b Switching of incandescent lamps.[/li]
[li]AC-6a Switching of transformers.[/li]
[li]AC-6b Switching of capacitor banks.[/li]
[li]AC-8a Hermetic refrigerant compressor motor control with manual resetting of overload releases.[/li]
[li]AC-8b Hermetic refrigerant compressor motor control with automatic resetting of overload releases.[/li]


Direct current:
[li]DC-1 Non-inductive or slightly inductive loads, resistance furnaces.[/li]
[li]DC-3 Shunt motors: starting, plugging, inching. Dynamic breaking of d.c. motors.[/li]
[li]DC-5 Series motors: starting, plugging, inching. Dynamic breaking of d.c. motors.[/li]
[li]DC-6 Switching of incandescent lamps[/li]

 

[LionelHutz]

Almost any decent 30A contactor will withstand 130A for a few milliseconds, assuming you're using withstand as it's commonly used, where the 130A current event occurs while the contactor remains closed.

 

[jraef]

"Decent contactor" must be defined to not include DP ("Definite Purpose") contactors. Technically you cannot use them in the field anyway so the point should be moot, but hardly anyone pays heed to that I'm affraid. The lure of cheap makes for turning a blind eye.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[LionelHutz]

I'd have no problem with expecting even a definite purpose contactor to withstand a 130A current surge for a few milliseconds. Not switch it, withstand it.