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  1. gepman

    Battery Room Ventilation Fan

    There isn't a lot of hydrogen gas produced in battery charging unless the batteries are overcharged either by rate (current) or potential (voltage). This question of the fan and it's classification is answered in 2008 NEC Article 480.9(A). There will be relatively little volume of hydrogen gas...
  2. gepman

    Liquid Rheostat

    I recently designed a system at a cement plant for a crusher with a liquid rheostat. I used Eletele at the recommendation of the cement plant. They already had one which worked well. Eletele was quite easy to work with and no real language barrier. www.eletele.com.br/Reostatos_e.htm I...
  3. gepman

    EMC Levels in dairy sheds.

    Hi Mark! Here is another research project, http://www.strayvoltage.org/stories/index.php3?Story=20010812_researchers.inc and another http://edis.ifas.ufl.edu/AE019 I have seen similar problems in California but in the Tulare area, where most of the dairies are located, we have several good...
  4. gepman

    MCA for convenience outlet on HVAC equipment

    I don't believe that there is any specific load requirement for a convenience outlet for HVAC equipment. Therefore the air conditioning companies can list the load requirement of whatever transformer or fuse rating which supplies the convenience outlet. The only NEC imposed load requirement...
  5. gepman

    Postive Acting Interlock

    I haven't heard that term before but it may mean the same thing as "fail safe". To be "fail safe" if the wire to the interlock sensor was cut or if you lost power to the interlock sensor the power to the machine should be cut off. Of course there are other ways for the interlock system to fail...
  6. gepman

    4 pole switching neutral

    I agree with waross in how he describes to connect the neutral to ground at the two different sources. I don't see why a 3 pole switch would be any more reliable than a 4 pole switch. I always specify 4 pole switches for a couple of reasons. One is that a 3 pole switch is not always...
  7. gepman

    Generator Cannot Charge UPS

    Jasonarac I just went through the "Event" CSV dump and it does not give a "phase reversal alarm". Typical alarm sequence is: AC power has been restored AC Restored Message sent to registered clients Utility power has failed UPS bypass unavailable UPS switched to battery power AC Fail Message...
  8. gepman

    Transformer Secondary Protection

    alehman A tap of a tap is a good way of looking at it. If the exclusion was introduced in 2005 as you say then perhaps georgeshall's installation was previous to the exclusion and therefore is acceptable as is but he still couldn't make the new tap. Perhaps the reasoning for the exclusion is...
  9. gepman

    Transformer Secondary Protection

    georgeshall brings up an interesting point with the I didn't realize this but I almost never utilize 240.4(B) anyway. I agree with georgeshall but I add that per the NEC articles he quotes your existing system does not meet code (your secondary conductors have less ampacity than the...
  10. gepman

    Generator Cannot Charge UPS

    Jasonarc I didn't see that alarm and the tech support guy with initials MN (who like I said was helpful and I called him to tell him that the problem was solved) told me that the BladeUPS did not have a way to check phase sequence and that is why the frequency measurement is in error. I...
  11. gepman

    Generator Cannot Charge UPS

    If a mistake was made on first power-up sequence then you would have to go through the power up sequence again with the correct phase sequence. I don't know if this requires complete removal of the batteries or if it can be initiated through software. Remember this is a UPS so after initial...
  12. gepman

    Generator Cannot Charge UPS

    My understanding in talking the Powerware UPS tech support is that the UPS does NOT care what the phase sequence is at the input, it just doesn't want it to change. Apparently at the application of power to the UPS it notes the phase sequence and expects it to remain that way. I don't think...
  13. gepman

    Generator Cannot Charge UPS

    edison123, the UPS is for a small data room only but there were two three phase loads, both air conditioners for the data room. The client's comment was that "this explains why the air conditioners never came on when we were on standby power". Apparently they never had a long power outage, at...
  14. gepman

    Generator Cannot Charge UPS

    First I would like to say that I should have stated "We have a client who has a ...", not "We have a ...". I had just gotten a call to go out there the next day and I was in a hurry to post this to give time for answers before the next morning and also have time to call Eaton Tech Support...
  15. gepman

    How to recognize phase A?

    I have been an engineer for many years and not paid much attention to phase sequence, just connected A to A, B to B, and C to C. Of course motor and equipment rotation direction is important. To answer 521AB's question, PG&E (Pacific Gas & Electric Company in California) uses ACB sequence and...
  16. gepman

    Generator Cannot Charge UPS

    We have a 60kW 120/208Y 3 phase generator connected to a UPS through a 4 pole ATS (see attached simplified one-line). The normal power to the UPS is through a 75kVA delta/wye transformer. The UPS is an Eaton (Cutler-Hammer) Powerware Blade 48kw unit with batteries and inverter. The UPS works...
  17. gepman

    Harmonics and VFDs

    I would like to respect DickDV's wishes and put this thread out of existence but I feel like I have earned the privelege of making one last post on this. After the World Ag Expo Show I went sailing up the coast of California from Mexico on a small (45') boat and have been out of internet...
  18. gepman

    frequency inverters to controll flow rates

    If you ask this question in the "Electric motors and motor controls engineering" forum you will get a lot of replies. PWM VFD's put out a lot of noise. My experience is that unless the instrumentation signal is a 4-20ma current signal or similar there will be problems with signal level wiring...
  19. gepman

    Harmonics and VFDs

    As promised here is the report (at least my report) from the World Ag Expo and the VFD vs. Valve shootout. I have attached a picture of the valvecrazy's test setup. The test setup consists of a pool or reservoir from which eight solenoid controlled nozzles spray up into the air and back into...
  20. gepman

    VFD Cable length

    I have used hundreds if not thousands of Allen-Bradley drives and not had a problem with motor and cable burn through when using the maximum lead length tables in their user's manuals when using inverter duty motors. Therefore I assume that the tables are accurate if not somewhat conservative.

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