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Recent content by Laplacian

  1. Laplacian

    Interchange of main terminals and star point

    There is a possibility the motor manufacturer used less insulation on the neutral end windings, which may result in premature failure if operated continuously in this manner. It may also be less resistant to surges (lighting, capacitor switching, etc.). It is advised to confirm with the...
  2. Laplacian

    Anti-Humans

    Abortion determined safer than birth (sarcasm) -> http://www.reuters.com/article/2012/01/23/us-abortion-idUSTRE80M2BS20120123
  3. Laplacian

    Easy fix for AC Motor Starter Chatter?

    I don't know why you guys are so strong on the UPS recommendation. They require battery replacement or complete replacement every few years. In an industrial environment where preventive maintenance is always "tested", the UPS will likely run to failure resulting in more contactor chatter when...
  4. Laplacian

    Easy fix for AC Motor Starter Chatter?

    If you can't easily get an independent 120V source, a constant voltage transformer (ferroresonant; such as from SOLA) will work well for this application. They are big and lossy, but reliable and maintenance free.
  5. Laplacian

    make and break rating of aux. relay contact

    I have searched a long time for a hermetically sealed relay capable of 5-10A DC break ratings at 135VDC for use in hazardous locations. I recently found some hydrogen filled DC contactors from Tyco and Gigavac with astronomical current and voltage ratings for their small size. We plan to...
  6. Laplacian

    aluminum vs copper rotor construction - real world 800 HP experiences

    It is difficult to quantify the advantages of copper over aluminum. I have seen many aluminum rotor cage failures attibuted to periodic start/stops. Aluminum fatigues faster than copper, and also expands more than copper due to temperature fluctuations. I have seen copper rotor cages fail due...
  7. Laplacian

    Disconnecting Multiple Motors with One Switch?

    How about Electro-switch? They build 12 pole switches up to 400A (600VAC), and 6 pole up to 800A (600VAC). http://www.electroswitch.com/electroswitchesandrelays/default.htm#
  8. Laplacian

    Submerged Cables

    What type of cables are you presently experiencing failures with? Cross linked polyethylene notorious for water ingress? Are these shielded cables? There should not be any issues using cable rated for underground conduit or direct bury service if it was not mechanically damaged during...
  9. Laplacian

    6-Lead Induction Motor - Swap Leads 1 and 4?

    Thanks for the information. The leads were correct, but I would like to purchase a 3 channel scope for future verification. Any recommendations? I found a 4 channel handheld unit, but am not familiar with the manufacturer. Also, how much/fast does the rotor need to turn? On motors this...
  10. Laplacian

    6-Lead Induction Motor - Swap Leads 1 and 4?

    What would be the consequence of inadvertently rolling lead 1 and 4 for example on a 6 lead, wye connected induction motor assuming 1, 2, 3 were the phase leads and 4, 5, 6 were the neutral point. The new configuration would be 4, 2, 3 phase leads and 1, 5, 6 neutral. This is probably a simple...
  11. Laplacian

    Utilization of Electrical Energy in a large Industrial pharmaceutical

    What specifically are you tasked with? In my experience in a similar facility, running at reduced rates always resulted in reduced efficiency. The reason is the plant is designed for peak efficiency at peak load. The base plant operations must still be run, regardless of actual output. If...
  12. Laplacian

    Aluminum cable to copper connectors

    I have seen this type of connection fail after just a few years, but it was an outdoor application exposed to cooling tower drift. The AL had corroded, and pitted away where the CU was in contact. Additionally, the AL oxides swelled in between the connection, forcing the lug away from the pad...
  13. Laplacian

    Hazardous Locations for Other Than Electrical Equipment?

    In the USA, what are the regulatory standards to reference when applying hazardous location requirements to automotive vehicles, for example? NFPA 505 is as close as I can find, but this applies only to special purpose industrial trucks and specifically not automotive vehicles. Intuitively...
  14. Laplacian

    Life of an Electromechinical relay

    MIL-HDBK-217F Is this a protective or control relay? 217F covers control relays. The IEEE Gold Book may also be useful. http://www.sre.org/pubs/Mil-Hdbk-217F(2).pdf
  15. Laplacian

    CT Problem or Bad Wiring

    Shorting meachanism (bar at the CT terminals, or screw in terminal strip) left in place?
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