Is Overrating of Contactors Normal?greenspun.com : LUSENET : Elevator Problem Discussion : One Thread
I am looking at spec sheets because servicemen told me of contacts prematurely pitting and needing replacement. Manufacturer recommends contacts for 40HP motor, but vendor uses the same contactors for a 50HP motor which draws more current than rated. Their reasoning is wye delta applications switch less power, and that this is industry standard. But I feel that overrating is promoting earlier degradation of contacts. In elevator applications Wye-delta Hydraulic, what is the typical length of time to replace contacts? Thank you. I would appreciate any response.
-- Noel Takahara (firstname.lastname@example.org), September 22, 2004
I'm not an electrical engineer. My opinion is that contact life is more dependant on # starts rather than time in service - to say "six months" really means nothing - some elev's run more than others- seen some I had to replace every 2 months, some every 10 yrs. Other factors are : load on motor when contactor opens or closes. Is car releveling too often - perhaps a pressure leak. In general: sure, elevator co's are going to put the smallest possible contactor on the unit in order to make it more cost effective so that the Customer will buy their unit instead of company "B"'s - check the genral contractors spec's - many now are specifying solid state starters - did yours? If not, Why? I recommend solid state "soft start" unit conversion for you- your problem will disappear.
-- yeahright (email@example.com), September 22, 2004.
The WYE contactor can be down rated, as the WYE current is the square root of 3 multiplied by the direct on line starting current.
As for the time one would expect a set of contacts to last, it does depend on usage, and over/under rating. If the contacts are borderline rated, that is, say 30 Amp contacts for a 30 Amp line current, empirically, they will not last as long as say, 40 Amp rated contacts.
As for the time one would expect a set of contacts to last, it does depend on usage,
-- TW (firstname.lastname@example.org), September 23, 2004.
yes, over-rating contacts is normal. on a regular " across-the-line " starter, you will draw 3-5 times the full load current of the motor until the motor gets up-to-speed. thats why you will find " timed delay " fuses in your service disconnect. on a wye-delta starter, you will draw about 3 times the full load current, but in different stages and a longer duration. you need to convert to a " soft starter ". they offer quite a few benefits over " across-the-line " and " wye-delta ". you voltage curve and amperage draw curve stay stablized and increase at the same level until your up-to-speed. in my opinion, these soft starters offer less wear and tear on your motor, pumping unit, etc.
-- (email@example.com), September 23, 2004.