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Type: Posts; User: Skokian

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  1. Replies
    30$$
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    EIA Resistor Color Code

    An old, old mnemonic for said color code is "Roy G. Biv.

    More here:

    https://www.google.com/search?q=eia+Resistor+Color+Code

    https://en.wikipedia.org/wiki/Electronic_color_code

    Best...
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    277 Vac Electric Shock.

    Firstly, I'm glad that she survived the contact with the 277 Vac source.

    The worst electric shock I ever got was from 277 Vac.

    I've done 480 Vac hand to hand but wasn't shocked much, mainly...
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    52$$
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    Run-Away Motor.

    I agree that if the field of a shunt wound D.C. motor with no load is lost, the motor speed ramps up without limit until the commutator segments start flying away.

    This is a very dangerous...
  4. Two Phase -vs- "Bi-Phase"

    Two phase power is always at 90 degree phase angle. This is widely used in servo systems, especially by the military. It was also a distribution system in the past in certain areas.

    I call the...
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    Transformer Ratios.

    Note that the winding ratio of the 120 Vac to 24 Vac transformer will be less than 5:1.

    This is done to account for the full load voltage drop in both the primary and secondary. Hence, at no...
  6. Back Feed Circuit Breakers.

    Note that not many circuit breakers are U.L. listed for use as power being fed to the breaker's LOAD terminals.

    This may likely also void the manufacturer's warrantee unless the breakers are rated...
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    Service Conductors inside of a building.

    This is a very, very common occurance.

    Namely the power fed to electric fire pumps is very often service entrance.
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    Secondary OCP at the 1st Xformer.

    Would the secondary OCP of the first transformer suffice for the primary OCP for the 2nd one?
  9. Spark Ignition.

    The reason that there are no longer any natural gas fire pump engines is that spark ignited engines were outlawed in NFPA-20 (the fire pump standard) many years ago. This also eliminated gasoline...
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    Melted Coils after Power Interruption.

    We often see this with fire pump controllers, which are normally fed directly by the local utility.

    The problem is when the power comes back, but at a reduced voltage.

    Recall that the pull-in...
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    G.E.I.S. = Gone, Gone, Gone.

    This is very sad news to me; but, not to surprising based on the "Heads Up" [. . . Up their . . .] management of the past couple of decades.

    I worked very closely with several of the engineers at...
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    Single or three Phase.

    This sounds like a 120/208 Vac Open Delta. E.g.: 208 Vac line to line and 120 Vac line to neutral. You would measure 120 Vac from either line to neutral if I have this figured out correctly.
    ...
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    Residential EMT in Chicago.

    For better or for worse, wiring with conduit is far more amenable to future changes.

    It is also better at reducing fire risk when wiring is overheated, although this shouldn't occur if wire and...
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    Bundleng = Bad for Power Wiring.

    We made measurements of bundled -versus- spaced out wiring in large fire pump controller cabinets. These boxes were typically 80" x 72" x 12" (w x h x d).

    The wires were sized per the free air...
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    Include the Reactance in Calculating "Z".

    Note that on higher power circuits (larger conductor sizes) that the wire reactance actually exceeds the resistance. Hence the complex impedance needs to be calculated rather than just the...
  16. Measure the Starting and Running Voltage Drops.

    It does occur on occasion that a dedicated utility transformer is undersized. NFPA-20 requires that the voltage drop at 1.15% of FLA be no more than 5% at the motor terminals. Also note that it's...
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    Vector Impedance Voltage Drop Calculations.

    Note that for larger sizes of conductors, the reactance of the wire becomes important factor. At 400 MCM the reactance can exceed the resistance of the wire. Hence, the complex impedance should be...
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    VFD Overvoltage Tripping.

    Most 480 Vac VFD's will shut down on over-voltage when the capacitors hit 750 Vdc. Note that all VFD's, as far as I know, have to be MANUALLY reset and restarted after an over-voltage shutdown.
    ...
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    Fire Pump Voltage Drops.

    Note that the fire pump wiring must be sized to allow no more than a 5% voltage drop when the motor is running at 1.15% of motor rated FLA. This calculation can be done at 85% Power Factor using the...
  20. Thread: Fire Pump LRC

    by Skokian
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    Transformer sizing must meet both voltage drop requirements.

    Sizing the transformers must be such that it meets both the 15% starting current voltage drop at the fire pump controller inlet terminals and the 5% 115% of FLA voltage drop at the motor terminals...
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    Got it. It's working. Tx. Is there a way to...

    Got it. It's working. Tx.

    Is there a way to do this universally, rather than on a per thread basis?

    Tx. again.
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    I've learned the hard way, that these compressors...

    I've learned the hard way, that these compressors often run their motors well into their service factors. This is also common practice with fire pumps. Note that the compressor is a tank mounted...
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    Good points. I did check the fuses; but, they...

    Good points. I did check the fuses; but, they weren't warm. However, I'll check the wiring connections when I'm back at the site. Since there are no main fuses or breaker in the fuse box in...
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    The two cartrige fuses in the disconnect box are...

    The two cartrige fuses in the disconnect box are FRN-R-20; but, the ones which blow from time to time are 20 amp time-delay plug fuses (edison base) in the upstream eight circuit 120/240 Vac fuse box.
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    NFPA-20 Max. Voltage Drops.

    NFPA-20 (Section 9.4) limits voltage drop during starting to 15% max. of nominal at the controller inlet terminals during normal (electrical) starting, and 5% max. at the motor terminals when the...
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