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  • Users: enverd
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  1. enverd

    VFD controlling an Air Handler Failures

    Hello All, Recently a new Air Handler Unit was installed and it came with an 9 dedicated VFDs. After the start up there have been constant issues where the first two weekends we had electrical over-current alarm, the weekend after nothing happened and this past weekend the Unit shut itself...
  2. enverd

    Does anyone have a PDF copy of GB19517-2009 national safety technical code for electrical equipment

    need to review for a project in china. thanks in advance
  3. enverd

    Does anyone have a PDF copy of GB19517-2009 national safety technical code for electrical equipment

    Need to review it for a project in china. thanks in advance
  4. enverd

    Motor with Gearbox vs. High Efficiency High speed motor

    I have a situation where I replaced an older motor that was running a process along with a gear box and the set up was controlled with an ABB VFD, we have replaced the entire set up with a new high efficiency high speed (5500RPM) motor but the new motor is still controlled by the existing ABB...
  5. enverd

    phase angle displacement and undervoltage

    I am faced with an undervoltage problem at work where some Air Handling and Exhaust Fan unit, while being fed through VFDs, are tripping breakers. The monitored voltage indicates an ongoing AB = 415V, BC = 417V and CA = 475V. I am thinking that there might be issues with the VFD, control power...
  6. enverd

    Surge Protection w/ Capacitors

    Why is a capacitor typically placed line-to-ground on each phase conductor as a primary surge protection device? Thanks,
  7. enverd

    Short Circuit / Fault Analogy

    If someone would ask you to explain (dummify) what happens in a distribution circuit during a fault, how would you explain it to them? For a lot of people, it is very important to have certain concepts like faults broken down to simple terms using analogies, so please share your understanding...
  8. enverd

    NEC 110.26 Workig Clearance Requirements

    Reviewing 110.26.A.1 and associated table the working space depth is clear on its requirements. However I have been told that if you have two switchboards facing each other at 600V where one of the boards is 3000A and the other is 800A, you have to double the working clearance. As for the...
  9. enverd

    VFDs internal to AC units requiring fused protection

    A contractor sent an RFI (referring to 430.31) indicating that VFDs that are coming with AC units must have fused protection. I am providing just feeders as requested by mechanical engineer, to single point of connection, connecting to VFD which has an integral disconnect. it seems as if the...
  10. enverd

    diesel engine vs natural gas engines

    I have been asked to look into using a natural gas engine generator vs diesel engine, 1000kW for hospital use. By the manufacturers I was told that the NG is a lot more expensive and it needs to be a lot bigger to provide the same power as a smaller diesel engine gen. I am on an OSHPD project...
  11. enverd

    3 legged magnetic circuit fabricated with homogeneous iron core (elec)

    see attached problem about a 3 legged magnetic circuit, how is the distance between leg B and leg A equal to 1d and leg A to leg C is 3d?

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