Contactor burning

Discussion in 'Electrical Forum discussion & Blog' started by iwen, Jun 13, 2010.

  1. iwen

    iwen New Member

    Messages:
    1
    Location:
    Blantyre, Malawi
    A supply of 110v was supplied to a 220v contactor, after sometime the contactor got burnt, why? does it mean a 220v contactor could not withstand 110v power? please help.
  2. leejosepho

    leejosepho DIY scratch-pad engineer

    If 110/120 volts were sent into a coil (the magnetic part of the contactor) expecting 220/240 volts, the coil might not have been able to hold the contacts closed tightly enough to keep them from getting hot (like a loose connection). However, I would doubt the coil was expecting 240 volts in the first place since control voltages are usually only 120 VAC or 24 VDC (even when the circuit being controlled has a higher voltage). But if only 120 volts were sent through a contactor (irregardless of conrol voltage) and on to a piece of equipment or device needing 240 volts, the contacts might have somehow been strained or overworked while trying to help get enough power to the choked piece of equipment.
    Last edited: Jun 13, 2010
  3. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    Lee, check the OP's location.
    Also, in a motor starter or in a commercial/industrial setting a contactor coil may very well be 240v, and typically is. If you have a straight 240v single or three phase load why bring a neutral in just to power the coil?


    iwen, it is either what Lee said about the contacts not closing properly causing a high resistance situation, or more likely the 240v coil getting 120v simply overheated due to the wrong voltage.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,677
    Location:
    Cave Creek, Arizona
    The amperage through the contactor determines whether it has the capacity or not, NOT the voltage. A 220/240 feed is just TWO 115/120 lines so each contact in the the contactor is actually handling the lower voltage anyway. Improper coil voltage and how the coil activates the contactor will usually be the cause of it failing.
  5. leejosepho

    leejosepho DIY scratch-pad engineer

    I understand, and I have worked on many.

    In my last project, I did not want to run 480 through the control pendant.

    Attached Files:

  6. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Why? .
  7. Ian Gills

    Ian Gills Senior Robin Hood Guy

    Messages:
    2,777
    Location:
    USA
    I'd like to know where you get 120 volts from in Malawi. I like Blantyre, but it was good ol'
    240 volts the last time I was there eating my chicken and chips with helpings of Nali sauce.
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,051
    Location:
    New England
    If the coil is designed for a specific voltage and you apply one below the minimum for the range allowed, you risk two things: either the coil won't be able to close the contacts at all, or, if it does, it doesn't provide the proper pressure to ensure a good, low resistance connection across the contactors. If you need a smaller control voltage, buy a different contactor. As to contact ratings, as long as you don't try to exceed the ratings, either voltage or current, one with higher contact ratings than you will use is often a good thing (except for cost and size). Many items using a contactor have a start-up surge, and the average current is much smaller than the peak, so a larger contactor than you think may mean much longer life.
  9. leejosepho

    leejosepho DIY scratch-pad engineer

    Anything I say here is likely going to be spun into something to try to make me look incompetent, ignorant or even stupid, but oh well ...

    First, because the only thing I actually know how to do with *3-phase* power is that of wiring and connecting contactors and motors. But beyond that, I needed control voltage and pendant wiring for a 110-volt double-acting hydraulic valve (for leveling the beam hanging on the hook) as well as for the reversing starter for the turn motor for the drums and straps ... and along with that, I needed a 12-volt circuit in the pendant for starting the hydraulic pump in conjunction with the aforementioned valve ... and I already had 120VAC available since it was needed for charging the hydraulic pump's and air compressor's battery. But of course, maybe 480 for all of that would have been much easier for a real electrician, eh?!
    Last edited: Jun 14, 2010
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Lee

    I am not sure that I fully understand what you are saying here. No I am not trying to make you look incompetent in any way just trying to understand what you are saying.

    This is what I understand you to have said.

    In the control pendant for the overhead crane you have installed 12 volt circuits for charging batteries. Is this what you are saying?

    These 12 volt circuits for charging batteries are for internal combustion engines that operate an air compressor and hydraulic pumps. Is this correct?

    It would help if you would take the time to explain just what you are lifting and what is being done with the product that is being lifted.
  11. leejosepho

    leejosepho DIY scratch-pad engineer

    I do not believe a single word of that!

    What would that have to do with anything?!

    In any case ...

    What you see there is half of a septic tank coming out of its form. If it is a top half, it will need to be turned on its side so it can be coated inside ... then turned back and moved to a staging area where it can be set on the floor and released so it can be taken on out to inventory. If it is a bottom half, it needs to be turned rightside-up and hoisted over and released in the staging area ... and to complicate things, the clamp holding it has to adjust to fit five different sizes of tanks ... and that is where the 12-volt air compressor comes in. With its battery supplying power up on the beam, it (the compressor) sends air down from the beam to power the cylinders that close and lock (via air checks and rod locks) the clamp.

    But before any of that can happen, and after the clamp has been engaged around the tank in its form, the beam's hydraulic system is used to level the load so the tank will not be stressed and broken when first lifted. So, and with the air controls directly on the clamp, the first control at the pendant is a DPDT switch for controlling the 12-volt hydraulic pump (on/off) and its 110-volt hydraulic direction valve.

    The other control at the pendant is an SPDT switch for the beam's turn motor.


    table.jpg pendant.jpg


    The only thing I know to actually be wrong here is my mis-use of one green wire.
    Last edited: Jun 15, 2010
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,051
    Location:
    New England
    One thing we always did (but it was DC controls) on relays or contactors, was insert a diode to prevent the coil from chattering upon release when the coil field collapsed. May not be relevant or as easy to do with an a/c circuit. The bigger the coil, the more current, the more chance it could create enough of a pulse to create problems.
  13. leejosepho

    leejosepho DIY scratch-pad engineer

    That kind of problem is beyond my knowledge or experience, but the one somewhat similar problem I did have was with the DPDT spring-to-center on/off/on toggle switch (12VDC) that did not always start the hydraulic pump and trigger the directional valve simultaneously unless it was toggled quickly and completely. The pump would start, but then the valve would chatter whenever an operator in training was being timid or someone was trying to get just a very little bit of movement-for-balance at the hook ... and the most challenging factor there is the fact that the tops of tanks have baffles inside (big on one end and smaller on the other) that always cause them to be out-of-balance (and there is no room for error in the first couple of inches while first beginning to lift either a top or a bottom from its every-so-slightly-tapered form).
  14. leejosepho

    leejosepho DIY scratch-pad engineer

    Why? Does his or her location mean s/he cannot ask about any voltage other than 220/240?
  15. sbrn33

    sbrn33 Electrical Contractor

    Messages:
    31
    Location:
    Fremont, NE
    9 out of 10 times this is a burnt coil not any real problem with the actual contacts or mechanism. Low voltage to the coil for a while will burn em up.
  16. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    If I understand this correctly we have an overhead crane that is powered by 480 volts.
    This crane has two 12 volt direct current electric motors that operate an air compressor and a hydraulic pump.
    The operation of the crane and both the compressor and hydraulic pumps are controlled by a pendant that hangs from the crane which the above drawing is supposed to be of.

    Well I am going to leave this one alone as I just don’t see the crane lifting and lowering with only two wires to the motor controler but will ask why these tanks that are designed to be buried underground must be handled so delicately? Are they not reinforced by some sort of rebar?
  17. leejosepho

    leejosepho DIY scratch-pad engineer

    Ah, so I was wrong ... but is it the low voltage that actually does the damage or is it the fact that the coil is straining *because of* the low voltage? I presently have a small 12VDC fan (out of a computer power supply) being supplied with 7.5VDC to cool my modem. I did that because I do not want the fan running at full speed. Is that fan now likely to fail early?
  18. leejosepho

    leejosepho DIY scratch-pad engineer

    Yes, and that bridge crane has its own wireless controls for travel, lifting and lowering and speed.

    No. What we have here is an I-beam hanging on the crane's hook, and everything I have mentioned is on that beam. Here is a picture from one of my early tests during fabrication:

    testpic4-.jpg

    Only the hydraulic pump and leveling system are in this picture, and a 480V turn motor and the compressor and control pendant were added as my work continued.

    Ultimately, I installed a cord reel to bring 480V down to the hook and power everything on the beam from there.
    Last edited: Jun 16, 2010
  19. leejosepho

    leejosepho DIY scratch-pad engineer

    Cool!

    Certainly, but the concrete is only a little over 12 hours old when the halves are pulled from their forms.
  20. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Cool Dude and thank you for the explanation. I was having a hard time with the pendant and thinking it controlled the crane as well as the beam.

    I can also understand the pulling of green concrete in only 12 hours of pour. Having done some work at a similar plant I suppose I was thinking of your plant being like the one I did service work at. There they had break away molds that were opened in the yard.
Similar Threads: Contactor burning
Forum Title Date
Electrical Forum discussion & Blog Burning Smell & Banging When Turn Dryer On Mar 27, 2012
Electrical Forum discussion & Blog Pole transformer exploded - danger from burning transformer oil w/ pcbs? Dec 24, 2008
Electrical Forum discussion & Blog Recessed lights burning out Oct 28, 2008

Share This Page