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Recent content by cryomark

  1. cryomark

    Common DC bus VFDs-LOTO disconnects

    We'll be making our first foray into a multiple VFD/common bus system soon. Using a single regen unit to control the bus V for 4 reciprocating He expansion liquifiers. These operate in a continuous pulsed regen mode. How is bus isolation usually handled in these systems? Are there interlocked...
  2. cryomark

    Circuit breaker spring tension-effect on operation?

    I have 3 Westinghouse MC3800 frame CBs (~1980 vintage) that were removed from service for various disfunctions. I opened them up to determine if rebuild or replacement was the better option. All had very gummy lubrication which appeared to be the problem with 2 of them. The 3rd has other...
  3. cryomark

    revisit 400A branch on 400A main

    for your reference thread237-122674 I'm re-thinking this installation and wonder about the feasability of the following: The panel board is squareD I line HCW, with a 400A main. Square D literature qualifies it as service equipment. The load is a westinghouse combination starter with switch...
  4. cryomark

    adding 400 A branch on 400 A main

    Thanks to all for your attentions. The panel currently feeds 2-45KVA x-formers(70A CBs), a 60A welding plug, a 25HP vacuum pump/blower skid(60A CB), 2-20A area heaters, a 5HP process air compressor(20A CB) The 480/208-120 xformers are lightly loaded-area lighting,utility 120V, 2 small...
  5. cryomark

    adding 400 A branch on 400 A main

    Must supply 3Ø, 480V to 200HP screw compressor. Starter is westinghouse autotransformer, closed transition. Motor is 209 FLA. The expensive option invloves lots of new conduit and cable run through a heavily plumbed space. Would like NEC refferents and opinions on legality/ advisability of...
  6. cryomark

    Circuit breaker load bolt torque

    Has anyone the installation specs for an old Westinghouse MC3800F circuit breaker? I'd like to know the recommended torque for the 1/2-13 bolt that mounts the 2 hole lug to the load side terminals. The reason- I've a MCC that has exhibited the same symptom of spontaneous circuit breaker trips...
  7. cryomark

    GE Fanuc series 1 SR-20 CNT reset function

    I must reproduce the functionality of a simple Fanuc program in the brand of PLCs we use. No one on site has ever used the GE series, there is only one CPU for two racks, the machines have been in storage for 5 years, we have no handheld programmers or software, I have a hard copy of the ladder...
  8. cryomark

    Best practices-re NFPA 496

    Above article states minimum gage pressure for purged and pressurized enclosures is 25Pa. I have been looking for references and documentation for a convention or common practice of actual operating pressures in typical Class 1, Div 2 applications. Any links or even anecdotal experience will be...
  9. cryomark

    Need definitions RE NEC article 500 & NFPA 496-1998

    Item 1 NEC99 article 500 501-3 (b) (3) In a class 1 div 2 environment, devices without make-break contacts, shall be provided with enclosures. "General- purpose-type enclosures shall be permitted." Definition of general purpose enclosure? We have a commercial 120V AC solenoid...
  10. cryomark

    How slow is too slow for...

    lewish-I think the straight line logic got lost in my background exposition. Sorry. Cooldown mode delivers 5g/s; the single compressor can only take ~2.8g/s, thus the extra must be dumped to atm or the resulting pressure increase adds too much of a heat load to the system. By adding a second...
  11. cryomark

    How slow is too slow for...

    Thanks to all for your response. jraef- the compressor lubrication issue may well end up as the killing factor for this cobble job. lewish-Oxygen deficiency hazard regulations prohibit any intentional venting of cryo gasses in an inhabited area plus the main idea is to recover all of the helium.
  12. cryomark

    How slow is too slow for...

    ...VFD driven motors? I have been drafted for a project, already well on its way to FUBAR, where a compressor may need to run at a small fraction of its' normal throughput. Background novel follows. A small experiment decided a year ago that they wanted to recover the helium being used for the...
  13. cryomark

    Spark plug questions for non-auto application

    Thanks for all the response. To give a bit more background, The device, called an arc cell, is used for real time monitoring of process gas contamination in the compressor discharge of a large liquid helium refrigerator. Everything but He freezes out at our operating temps(4.5 Kelvins). We have...
  14. cryomark

    Spark plug questions for non-auto application

    I'm investigating characteristics of Pt spark plugs for use in a gas contamination detector.(Not gasoline) Our current instrument uses a continuous arc drawn between chisel tip tungsten electrodes powered by a 1KV DC power supply.A spectral peak of the arc varies with the degree of...
  15. cryomark

    flumoxed by flux vector control

    Thanks, rhatcher! The varying load from gas expansion was the cause of over regulation of the VFD output. Fluctuations in the high pressure gas supply and the output sink pressure were complicating matters but when these were factored in, the correlation of "noise" to piston stroke was...
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