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  • Users: JBD
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  1. JBD

    Protective relay behaving badly

    Burnt2x - the motor is being protected by a Multilin 269+ relay. The IFC relay 51 function is for cable feeder protection only.
  2. JBD

    Protective relay behaving badly

    CT's are scheduled to be evaluated at the next system shutdown. The only other device in the circuit is an ammeter and switch. Total lead length is just under 10 ft. Only one of the three relays trips. The problem follows the same relay even as it is moved from Phase A to B to C. I was hoping...
  3. JBD

    Protective relay behaving badly

    Can any one help with a GE IFC53 relay that trips for no apparent reason. The system is a 4160V air break circuit breaker with (3) IFC53 relays for 50/51 phase protection. The settings for the IFC53 are 400:5 CTs, Tap setting = 4(320A), Time dial = 4.0, and Instantaneous = 70(5600). This...
  4. JBD

    IEEE 1584 & NFPA 70E

    NFPA 70E is the law (as enforced by OSHA). 70E says what you should do. Anything in an Annex is reference material only and not enforceable. IEE1584 is a simply one of several tools that can be used to comply with 70E.
  5. JBD

    Single Phase or Three Phase

    A phase is not a single conductor or reference point. Phases require two points either usually Line and Line. A 1-phase system has 1 set of L-L conductors, a 3-phase system has 3 possible sets of L-L conductors, and the very rare 2-phase system has 2 sets of L-L. You probably don't refer to a...
  6. JBD

    Transformer Winding Type

    dpc I believe the primary builder of dry type transformers in the US is ABB, I can't think of any major still building their own. I still think that for most applications <5000kVA and <35kV whatever is standard is usually fine. Of course special applications (ie.e furnaces) will always need...
  7. JBD

    Transformer Winding Type

    Unless you are a utility or you want to have a specially built transformer it does not matter. Most purchasers chose a manufacturer first and then accept their standard offering. Do you have a particular reason for asking?
  8. JBD

    Arc Flash PPE Assumptions

    IEEE 1584-2002 is a methodology to determine the amount of incident energy in an arc flash. IEEE 1584 does not make PPE recommendations NFPA 70E is the proper place to go for implementing PPE and other electrical safe work practices based on the arc flash incident energies. Arc flash incident...
  9. JBD

    New to Short Circuit / Arc Flash Study

    I have no emotional involvement. But, I do wonder why you seem to put more faith in the IEEE 1584-2002 calculations for <250 systems than IEEE does. What would you tell a customer when the IEEE calculation for their 300kVA transformer is >8 cal/cm^2 but that NFPA 70E considers it to be a hazard...
  10. JBD

    New to Short Circuit / Arc Flash Study

    You can not simply follow only IEEE 1584 when you are creating an Electrical Safe Work Practice. IEEE 1584 is simply a tool for determining the incident energy from an arc fault, it makes no recommendations as to any action to be taken. You must go to NFPA 70E to find the correct hazard...
  11. JBD

    New to Short Circuit / Arc Flash Study

    old field guy, Personally I do not think NFPA 70E task tables are always conservative. I also do not think that calculations are always conservative either (IEEE 1584 admits that it's formulas are not "as accurate" <250V). My point is that some times an educated judgement must be made, and...
  12. JBD

    New to Short Circuit / Arc Flash Study

    rbulsara, You have not answered my question about how you would reconcile the differences in my examples. I am not advocating using tables instead of engineering calculations. Again for example, that the IEEE standard says a 112.5kVA 208V 3%Z transformer is not important and to ignore it, but...
  13. JBD

    New to Short Circuit / Arc Flash Study

    rbulsara, If you think that the NFPA 70E tables are conservative, then how do you reconcile the different ways that IEEE and NFPA handle a 150kVA 240V 4%Z d-d transformer? By the way, I make my living performing systems studies including arc flash. I am a advocate of IEEE 1584-2002 methodology...
  14. JBD

    New to Short Circuit / Arc Flash Study

    IEEE 1584-2002 says you can ignore the 208V secondaries of transformers smaller than 125kVA. NFPA 70E allows you to define 240V circuits with 10kA max fault current as hazard category 0. rbulsara, I am not an advocate of the NFPA70E task tables, especially as they are currently written...
  15. JBD

    New to Short Circuit / Arc Flash Study

    rbulsara, You are missing my point. I fully support NFPA 70E and IEEE 1584-2002. Although, I don't believe the values in the NFPA are always more conservative. I am trying to point out the 125kVA and 208V max limits in IEEE are in conflict with the 240V and 10kA limits in NFPA 70E. Someone...
  16. JBD

    New to Short Circuit / Arc Flash Study

    I am aware of the procedures and limitations of IEEE 1854-2002 and NFPA70E. I firmly believe in the need for protection against injuries caused by arc flash. My point is that IEEE based their limit of 125kVA and 208V primarily on anecdotal rather than on actual evidence (in one set of data, I...
  17. JBD

    New to Short Circuit / Arc Flash Study

    Page 1 of IEEE 1584-2002 says "Single-phase ac systems and dc systems are not included in this guide." I have never seen any test data to support the 125kVA size. In fact, on this issue IEEE 1584-2002 does not use definitive language. On page 25 it says "systems fed by transformers smaller than...
  18. JBD

    New to Short Circuit / Arc Flash Study

    IEEE 1584 says to ignore 125KVA and smaller 208V transformers, but they offer no reason for choosing this size and voltage limits. NFPA70E implies (look at their task tables) that 240V max systems with available fault current of 10kA maximum will never exceed a hazard category 0. Notice how...
  19. JBD

    Transformer Taps

    I am getting a transformer from China, and the nameplate shows taps of: 1, 2, 3, 4, and 5. I am familiar with US transformer nameplates that have taps like: C, D, E, F, and G and are shown with their relative positions on the windings. Comparing the nameplate voltages I know that the US nominal...
  20. JBD

    TRANSFORMERS

    I have done this type of installation before without any problems. If you are going to purchase the transformers, consider going with 600V instead of 480V. This way you will have less of a voltage drop. It is a little cleaner than messing with the taps.

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