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  • Users: bentov
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  1. bentov

    Hydraulic thrust K factor rule of thumb?

    We repair vertical motors, sometimes see premature thrust bearing failure that needs to be explained. Assessing the load requires K factor data on the pump that is often unknown. A recent example: 800hp 1800rpm motor rated 10,300lbs downthrust - on a site visit we recorded production of...
  2. bentov

    MCSF limits for VFD centrifugal application?

    A customer's new pump (Berkeley B3ZPM) will be supplied by a 900ft 4" PVC underground pipe fed by a water district turnout with a "normal operating range" of 17.5-20psi. The pump supplies water trucks (12ft high) and a fire water tank (16ft high) through a back flow preventer (10psi pressure...
  3. bentov

    Multiple sources, voltages, & transfer switches - solid neutral?

    A customer has a 60hp pump supplied by a remote (300ft away) 480/277V service, so the neutral conductor is not present at the pump (ground only). 125ft from that is a 600a 240/120V 3ph 4W delta service supplying (2) greenhouses on separate 200a branch feeder breakers. Next to that service...
  4. bentov

    (yet another!) 277V lighting question

    A greenhouse customer has ordered 277V lighting fixtures (46 x 660W for each of 3 houses), needs to run on a generator for short grows, then roll everything up, take to other sites on a rotating annual basis (so everything is temporary/portable). My task is to provide wiring, etc. One of my...
  5. bentov

    Soft start into a spinning load?

    At our motor repair shop we have 200a 240V 3 phase service equipment, but because our actual operating loads are low the utility supplies us with a whopping 45kva. We routinely rewind motors up to 500hp 480V. The problem is getting motors up to full speed/full voltage for no-load testing. We...
  6. bentov

    Low voltage VFD closed transition synchronous transfer to mains available yet?

    My search continues, just checking to see if anyone knows of something new available that might work (other than medium voltage) . . . anybody tried a synchronizing relay designed for other stuff without destroying a VFD? thread237-369367
  7. bentov

    When is a schematic proprietary?

    During field service at a food processer I asked for schematics, was told that due to a "falling out" with the original construction electrical contractor they are not available - management thought they paid for the job, wiring diagrams should be included, contractor says "my property". I...
  8. bentov

    Safety consequence of missing ground conductor on 480V feeder?

    Got a phone call describing the following system: 480/277 4W meter main, 100a fusible disconnect feeding 1 mile run as follows - 3x350MCM Al 1/2mi to 7.5hp 480V combination panel for 3-phase submersible pump in 16ft deep drainage collector; 3x2/0 Al next 1/4mi to identical setup; 3x#4 Al final...
  9. bentov

    De-rating motor nameplates to match utility load limits

    Sorry if this is covered already, couldn't find it (likely didn't search correctly) . . . Our local utility limits pole mount transformers to 300kva, thus 300hp max motor load. Deep well pumps often teeter on the edge of that (i.e. development testing might indicate "325hp max"). The service...
  10. bentov

    5 minute control power backup for soft start

    We have soft starters that won't reset until 5 minutes AFTER an overload fault with control power on. The cost effective arrangement (fault relay powers shunt trip of main CB) removes power so can't reset. A UPS could of course be used to keep control power on. That seems overkill though (and...
  11. bentov

    Parallelled VFD cabling for submersible pumps

    A 25hp 460V (32fla) submersible in for repair needs a new cable. The old one is OEM special, SO type cord with 3#4 (load), 1#6 (ground) & 3#12 (seal fail & in wdg thermal + common), $30+ per foot. Though installed with VFD controls as a new package, this cable was not shielded. The pump is...
  12. bentov

    Pump station motor control location, minimum separation distance?

    A pump contractor friend of mine made a comment yesterday, about some pump control panels being "too close" to the motors. In this case the VFD panels were about 10-12 feet from the actual motors (not in the way of pump or motor removal or repair though), and the service entrance was another...
  13. bentov

    Industrial data cable wiring practice

    I'm installing a data conduit for my new place (4 buildings on 5 acres, wiring infrastructure spans about 600 feet), going to put (8) Cat 6 UTP cables plus (1) RG6 coax in a 1 1/4" conduit with J-boxes big enough for patch blocks at various locations - won't use much of that capacity initially...
  14. bentov

    EMI/RFI from VFDs in fiberglass enclosures

    If VFDs are installed with EMI-RFI filters and shielded motor run cables, do they still need "Faraday" cage enclosure treatment? If an untreated fiberglass enclosure is used, does the (typically aluminum) interior mounting plate provide any useful directional shielding (i.e. if the plate is...
  15. bentov

    Inductive prox wiring practice

    Literature with 2 wire universal voltage inductive proximity sensors shows control power arriving at a relay coil (A1), then a wire (call it B)from A2 out to the prox, returning from the prox to complete the circuit to the neutral conductor. So, wire B, though not technically a neutral, is...
  16. bentov

    Inductive prox wiring practice

    Need to assemble a simple box with relays to provide another vendor with dry contact signals for position of 10 metal gates spaced 10 ft apart in a 100 ft string. First thought, 120V push-to-test relays, coils wired in series w/2 wire AC proxes - all conductors in a single EMT conduit, nylon...
  17. bentov

    C87600 pump impeller repair filler material

    We have a pump in for repair, expensive impeller has localized cavitation damage (design problem a separate issue) right where the thin leading edges of the vanes leave the hub area at the inlet eye (web has holes clear through, though not at edges so shape is preserved). The rest of it is...
  18. bentov

    4-20mA signal plus VFD motor cables in shared conduit

    I know it's considered bad practice, question is practicality & likely worst case trouble arising . . . We retrofit small (5-15hp 240V) ag drainwater pumps with VFD's (PWM, V/hz) & 4-20mA/24VDC 2 wire level transmitters (pressure membrane piezoelectric transducers), run PID for constant level...
  19. bentov

    Need for shunt trip breaker with soft starter?

    I notice specs for soft start combination controllers usually call for shunt trip breakers to isolate the motor in case of a soft start failure. How is that soft start failure (shorted SCR's, most likely) any different than, say, welded contacts on a regular starter caused by fault current...
  20. bentov

    pressure tank derate or eliminate

    An irrigation supply system for a large cemetary has (3) 30hp split case pumps & a 4,000 gallon steel tank (w/AVC system, lead/lag controller, etc.), formerly used to supply & pressurize a sprinkler/drip system at the end of a 1.2 mile pipeline. A redesign now has a lake at the end of that...

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