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  • Users: abrahamJP
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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

    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...
  8. 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...
  9. 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...
  10. 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...
  11. 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)...
  12. 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...
  13. 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
  14. 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...
  15. 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...
  16. abrahamJP

    Cable Bending Radius

    A cable can be bend 90 degrees if we allow enough space for bending radius ie,12*diameter of armoured cable. My question is whether a cable can bend 45degress or 30 degrees like above if we allow space for bending radius OR what is the minimum limit of degrees that a cable can be bend if we...
  17. abrahamJP

    Taking wire through Concrete

    I am working in a construction site and we need to fix "small watt" bulb all over a concrete core wall as a decoration. But we have forgot to put conduit at casting stage of core wall. Now chipping the wall is only solution.But civil guys not allow to chip more than 15cm,But available size of...
  18. abrahamJP

    Transformer connections and load sharing

    We need a 30W,24v for a toilet device.We have a 240V supply in Qatar.But our supplier who is in US has send us 2nos of RATING 120V/24V 50VA. Is there any way by interconnections I can make it 240V/24v. thanks in advance Abraham
  19. abrahamJP

    Panel Shade as per bs4800

    Anybody has new BS4800 available to know which colour indicated by following shade number; Colour Code - BS4800 , Shade number - 18E55 Thanks in advance
  20. abrahamJP

    Return current through General Mass of Earth

    Hi, I have in mind this question for years,now I got this forum to ask this question. When we model a simple earthing system as in attached PDF,we assume Earth current return to source even when source earth is kilometers away. I understand whatever the current go to earth through earth...

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