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  • Users: cmelguet
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  1. cmelguet

    grounding and bonding of conveyors.

    Hi, I have a grounding question again. Please refer to the attached drawing. At the project we have an overland conveyor of 1km long. At the start of the conveyor we have a 33/4.16 kV 5 MVA transformer substation with its grounding grid designed according to IEEE 80. At the end of the conveyor...
  2. cmelguet

    FRP cable trays

    Hi, I am involve in a project where we are running several 3 phase circuits of 33 kV using single phase conductors arranged in a trefoil formation. The cables are installed on a FRP cable ladder which is no good as a grounding conductor. The circuits lengths is around 1000 m, and all of the...
  3. cmelguet

    33 kv cable joints

    Hi, Does anyone know if the NEC had any restrictions on using cable joints, tape, or preassembled ones.This is for 33 kV, 500 MCM cable trifoil formation runned on above ground cable ladder and also underground cable duct.The length of the circuit is 1800 m. I was told that it is not allow and...
  4. cmelguet

    grounding medium voltage motors

    Hi all, I have two underflow pumps (552 kW each, 4.16 kV) for the thickeners in a mining project. For this size of motors I normally use a two 2/0 AWG bare copper cable to ground the motor directly to the earthing grid. In this case we dont have a grouding grid under the motors because of...
  5. cmelguet

    Grounding and bonding NEC 250 questions.

    Hi, I am from Chile where we have our own standard for low voltage installations, but since they are not updated since 2003,we normally also follow the NEC as a good practice guide. Article 250 of the NEC states: 250.24(C) For 1000 V or less AC Systems, neutral conductor shall be routed with...
  6. cmelguet

    IECEX certified equipment in NEC 505 clasified areas

    Hi, can anyone explain if IECEx certified equipment can be used in hazardous areas clasified under NEC 2011 code 505. From the code it seems that the marking on the equipment needs to be AEx instead of IECEx. This mean the manufacture of the equipment needs to certified its equipment on the US...
  7. cmelguet

    cable ampacity table NEC

    Hi, I am trying to figure out the following: - NEC article 392.80(A)(2)(c)state that for single conductors installed in a trifoil formation with separation of 1 diameter between individual conductors we should use table 310.15(B)(17) for ampacity. This table for example gives you an ampacity...
  8. cmelguet

    welding circuits and a designated ladder cable tray requirements

    Hi, NEC 2011, article 630.41 and 392.10 (B)(1)(b) requires for welding cable to be run on a dedicated cable tray. My question: i have and MCC which supply power to the 63 Amps welding socket, 100 m away. I will use cable tray and conduits to run the cable from the MCC to the welding socket...
  9. cmelguet

    125 Vdc vs 120 Vac for local control stations

    Hi, Anyone knows an standard or document where it states that in a plant is not a good practice to have some local control stations with 120 Vac and others with 125 Vdc?. At the project where I am, it was proposed to have Medium voltage motors with LCS´s control voltage of 125 Vdc and low...
  10. cmelguet

    MCC run, ready light

    Hi, Anyone know an standard that define the colours in the lights on LV MCC modules. I mean the lights that indicate Runnign status, ready status, and fault. Regards,
  11. cmelguet

    transformer voltage ratio

    Hi, There is any guideline from ieee or from your experience to set the maximum voltage ratio for a distribution transformer? I need to decide if install a 33 kV / 0.4 kV 2 MVA transformer or run a 4.16 kv cable from a 500 m away substation, and install a 4.16 kV / 0.4 kV 2 mva transformer...
  12. cmelguet

    NEC interpretation table 430.22(E)

    Hi, I am trying to understand the NEC 2011 table 430.22(E). I would apreciate if someone can clarify. From the table I understand NEC classify motors in Continouos duty, intermittent duty, short time, periodic and varying duty. Also each duty is classify in 5 min rated, 15 min rated, 30-60 min...
  13. cmelguet

    NEC definitions

    Hi, I am trying to get my head clear around the following definitions. Can anyone specify the differences between the following devices to control motor in LV assemblies: Motor controller, Motor combination starter Combination motor controller self protected combination controller Full voltage...
  14. cmelguet

    voltage drop in transformer with motor starting

    thread238-214018 Hi, In the thread 238-214018 Morquea mention a method and rule of thumb to dimention a transformer for motor starting. Basically consist on the following: Calculate Motor Starting kVA = (FLA of motor)*sqrt(3)*(3 phase voltage) Calculate SC level at the secondary of the...
  15. cmelguet

    12 or 24 pulse drive

    Hi, I am working on some MV drive specifications, the idea is to select the same drive for different applications in the plat. I would like to know what to look for in order to decide if to select a 12 or a 24 pulse drive (18 is not possible since the manufacture is already selected). The...
  16. cmelguet

    arc proof vs arc resistance

    Hi, I would like to know if there is any difference in the definition of Arc Proof and Arc Resistance switchgear. To me it sounds the same. I always have understand an arc resistance switchgear as an equipment tested to C37.20.7 or IEC 62271-200. But according to some of my collegues there are...
  17. cmelguet

    thrid harmonics vs transformer grounding

    We are in the process of selecting a grounding criteria for a Dy1 power transformer. We have two alternatives: 1. Use a low resistance grounding of neutral point of secondary. (1500 A) 2. Use a high resistance grounding of neutral point of secondary. (1500 A). (300 or 400 A) My question is...
  18. cmelguet

    current transformer sizing for relaying protection

    Hi, Can someone give a procedure to correctly size a current transformer to be use in protection ?. I guest it should be something like: - pick ratio to be below of the nominal current of the system. - pick accuracy limit factor to be above the maximum fault current. - pick VA of transformer...
  19. cmelguet

    Hazardous Area Clasification Mine Explosives and Pirotecnics

    HI, NEC art 500 states: "The unique hazards associated with explosives, pyrotechnics, and blasting agents are not addressed in this article. I want to specify electrical equipment to be install in an explosive and blasting agentes storage above ground (This are explosives for mine...
  20. cmelguet

    VSI vs CSI VFD topology

    Hi, Can someone explain when I should use a CSI (current source inverter) topology for the inverter of the VSD or when to use a VSI (Voltage Source inverter) kind? Thanks.

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