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  1. abrahamJP

    ACH required for a Closed Office Space

    I am trying to learn hvac design etc... I have a doubt as per Ashrae 62.1, is there an ach defined for an office space...it is not directly given.. Problem is that one web site saying it is 2-3 ach .....when I put this this in a small office space of volume (108 cubic meter), I get...
  2. abrahamJP

    earthing

    Hi, For a big shopping center, which has 30 LV Transformers(11KV/415V-system fault level-250mva) in Ground floor Transformer rooms-While designing earthing system how much fault current to be considered- 1)Only One transformer or 2)Fault curent based on Probability of Failing, since 30 is a...
  3. abrahamJP

    Why Short Circuit & Overload Segregation for Electronic trip unit based Circuit Breakers

    Hi, This may be a hypothetical question,But I am glad if somebody can share their insight on it. If for Electronic trip unit type ACB acts and trip in same manner for Short Circuit and Overload the why we have to segragate on basis of Overload and short cirucit. For eg: a 2500A breaker set to...
  4. abrahamJP

    1 SECOND & 3 SECOND SHORT CIRCUIT RATING

    1.What is the difference in 1 second & 3 second rating.For eg: 65ka,3 second. 2.In our plant,11 kv primary feeders (main incomers)busbars is rated for 25ka,3 seocond. But in 11kv secondary feeders(to hv equipment),25kA,1second is allowed.How we can know from theortical point of view,1 second...
  5. abrahamJP

    Transformer Rating & 0.8 PF

    Hi, In GCC Countrie's regulation ,there is a guideline which says Transformer to be rated(KVA) 25% more than Maximum Demand(KW). How this value came from.If Power Factor is 0.8(1500KVA*0.8=1200KW),this could be possible.But with Capacitor Bank ,a must we get power factor more than 0.92 minimum...
  6. abrahamJP

    long busbars support calculation basis

    I had seen busbars going from Transformer to Nearby panels (4000A,415V) supported by very rigid pillars.I asked suppliers then why you suggest such huge supports..Their answer was to protect against high short current stress. Now consider new situation where I encounter is of Bus bars from LV...
  7. abrahamJP

    What is Earth Resistance

    But following document mentions if HV & LV Separte keep 8mts distance from Earth Pits; https://library.ukpowernetworks.co.uk/library/en/g81/Installation_and_Records/Earthing/Documents/ECS+06-0023+Secondary+Distribution+Network+Earthing+Construction.pdf that is my concern. best regards Abraham
  8. abrahamJP

    What is Earth Resistance

    Thank you very much for enlightning answers. One question can I ask witout strating another thread; Is there any thumb rule for distance between HV and LV Earth pits?for 11k,allowable GPR is around 300V as per IEEE ,I read. But if there is any distance to be maintained by thumb rules something...
  9. abrahamJP

    What is Earth Resistance

    I have two questions regarding earth resistance; 1.For single electrode R=(rho)/2(pi)[1/r] ->here why ressitivity of copper rod (material -copper) has not considered,but only resistivity of soil is considerd? 2.For concrete encased electrode,earth ressitance less than rod alone-How since...
  10. abrahamJP

    FINAL DISTRIBUTION BOARD ISOLATOR RATING

    I couldnot exactly remember which BS standard,but it mentions maximum incomer isolator possible for a distribution board is 125A.Whether such a rule exists-When I look to well known manufacturers productline,I can see it exists. My question is on what basis such a rule is made? choice 1...
  11. abrahamJP

    Step Voltage-Earth rods around the building

    Hi, I have a building with three 11/6.6kv, 5MVA transformers with MCC's as loads.Proposed Grounding system is a single row of ground rods at every 8 meter around the periphery of a building interconncted by a cable (of suitable earth fault current carrying capacity). I want to put this...
  12. abrahamJP

    ACB drawing out space

    Thanks for all thoughtful replies-It helps to gain a partial understanding of subject. My thinking was this code design was based on old acb standards-not either on considering new electronic trip units or "maximum power,minimum volume concepts" prevalent in switchgear industry.Still question...
  13. abrahamJP

    ACB drawing out space

    I live in middle east,may be a remote place for you-but my question is beyond codes if acb depth is 450mm,what additonal space I should allow for 1)safe working 2)is some arc/shock hazard etc come into this picture to take away precious space of architects regards Abraham
  14. abrahamJP

    ACB drawing out space

    Hi, Is there any standard or documents available to get an idea of approximate front space required for drawing out of ACB (low voltage) like for example-for 1600A ACB ,750mm space is required infront of switchgear. Now I would like to know 5000A ACB, what is the minimum distance required...
  15. abrahamJP

    Meaning of short circuit MVA

    Hi, Given datas: 11kv,350MVA Fault level & 11kv is feeding to 11kv/400v,500kva with%z=5%; Transformer; ------------------------------- Now to calculate Impedances; primary impedance-->(11000^2)/350-->(equation1) secondary side impedance-->(5)*400/(100*500)-->(equation2)...
  16. abrahamJP

    Transformer Connection Question

    Dear Sirs, I have a sample question from one theory paper here; A Three phase transformer is made of 3nos 10kva single phase transformers connected in delta.When only two phases(instead of three phases) are feeding,what will be the output? My answer was 2/3*30=20KVA.But answer seems to be...
  17. abrahamJP

    FAULT LEVEL

    Hi, 1500kva thanks
  18. abrahamJP

    FAULT LEVEL

    Hi, We have 11kv,250mva fault level given by utility.Then we have a Transformer 11/0.415kv,%z-6% transformer.My question is what wll be Fault MVA at 0.415kv. thanks in advance Abraham
  19. abrahamJP

    Cable Joints

    Hi, I need to make a cable joint between Rubber Insulated cables(for use in sump pits) and xlpe/pvc cables. This happened because sump pump supplier supplied a short run of cable so not reaching to panel board which 40 mtrs away. This joint comes after sump pit and in trays.So xlpe/pvc cable...
  20. abrahamJP

    Welding Strength

    Hi all. I have to connect an Electrical tray to Building steel using a slotted channel. This slotted channel is to be welded to Building steel using simple weldng rods. if width of slotted channel is 5cm and entire this thickness can be welded. My question is how much Newtons,such a simple...

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