My recent experience was with safety contactors so Jonathan is right. I do not know whether the contacts-in-series trick can be done with other types. However, I think that the mechanism of action here includes arcing. In other words, placing several contacts in series doesn't eliminate arcing, it merely reduces the maximum duration of the arc to the time it takes for all of the contacts to open. When the first one opens, an arc will start and there will be a voltage drop associated with it. When the second one opens, there may then not be sufficient remaining voltage to sustain an arc across BOTH sets of contacts and if so, the arc will cease. Sean On Tue, Dec 21, 2010 at 8:07 PM, Jonathan Hallameyer wro= te: > Ive seen the ratings for series contacts in the Rockwell automation > contactor catalog, they are talking about in a multi-pole contactor > (I.E, one meant for 3 phase AC with all the contacts put in series for > whatever DC load) =A0 And the particular ones I was looking at was > "safety" contactors where all the contacts were positively linked, > along with aux contacts for feedback, so the opening and closing of > those should be as coordinated as you'll get with a mechanical switch. > =A0I'd imagine different drop-out speeds could indeed be an issue with > separate 1-pole contactors. > -Jon > > On Tue, Dec 21, 2010 at 3:43 PM, Mark E. Skeels > wrote: >> Did the switch timing differences between the contactors have any >> bearing on the outcome? >> >> Mark Skeels >> Engineer >> Competition Electronics, Inc. >> TEL: 815-874-8001 >> FAX: 815-874-8181 >> www.competitionelectronics.com >> >> On 12/21/2010 1:22 PM, Sean Breheny wrote: >>> Hi Dave, >>> >>> If you find such a thorough explanation, please let me know :) >>> >>> We (coworkers and I) had an issue where we had to find a contactor >>> which could switch 60VDC and 80 Amps peak. Using the ratings at face >>> value, we were going to have to use a contactor which was the size of >>> a lawnmower engine (and no doubt cost several times as much). However, >>> after working with the applications engineers at the company (I think >>> it was Rockwell Automation/Allen Bradley), they were able to tell us >>> that we could put several contacts in series and effectively raise the >>> interrupting DC voltage and current specs of the contacts by doing so. >>> =A0 We provided them information on how the 80 Amps current was only in >>> 0.5 second pulses and in-between the current was no more than 10 Amps. >>> I do not remember whether they took that into account or not. >>> >>> I have since seen a few contactor catalogs which give tables showing >>> the ratings when you have 2,3,4 etc. contacts in series, but certainly >>> no great discussion of the whys and hows. >>> >>> We didn't have a reactive load but most contactors have not only >>> voltage and current ratings but also a maximum L/R ratio for the >>> circuit. If you have a good handle on what the inductance is, you >>> should be able to see if this rating is being exceeded. >>> >>> Is this an AC or DC application? >>> >>> The whole Ipk * Vpk> =A0kVA thing sounds bogus to me. Sounds like you >>> need to find a different engineer to talk to at that vendor. >>> >>> Sean >>> >>> >>> On Tue, Dec 21, 2010 at 2:07 PM, David VanHorn =A0= wrote: >>>> Can anyone point me to a clear, well written guide to relay >>>> specifications, particularly with regard to reactive loads? >>>> >>>> I'm looking at a relay in a design, and it's not clear whether or not >>>> it is being used within spec. =A0Inrush current is ok, but peak voltag= e >>>> is high (few uS at opening). >>>> One source tells me that because Ipeak * Vpeak is larger than the kVA >>>> rating that there is a problem, but it doesn't make sense to me in >>>> that Ipeak and Vpeak cannot occur at the same time. =A0My Ipeak and >>>> Vpeak measurements are under absolute worst case conditions, measuring >>>> many times with the scope, and taking the worst observed value. >>>> >>>> The more I dig, the fuzzier the ratings seem to become.. >>>> -- >>>> http://www.piclist.com PIC/SX FAQ& =A0list archive >>>> View/change your membership options at >>>> http://mailman.mit.edu/mailman/listinfo/piclist >>>> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .