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  1. WDeanN

    480V/60A vs. 480V/100A

    Or hide the welder during the inspection... Remember Peter, with great Power there must also come great Current squared times Resistance.
  2. WDeanN

    Cruise Ship Power

    zog, eleceng - "Real Subs"?? And the Blue Crew did their own work, thank you! SSBN-734 - Blue Crew
  3. WDeanN

    Cruise Ship Power

    Eleceng01, AT LEAST double that for subs, indeed! By the time you climb under the superstructure, open the shore power hatch, dry it out, meg the connections, dry it out again, meg it again, then connect the shore power cables, it took quite a while. On the other hand, we were some of the last...
  4. WDeanN

    Arc Flash Categories

    zog is going to want to shoot me, but here it goes: There is NO restriction that says you SHALL NOT work on equipment above 40 cal/cm. It is a Fine Print Note recommendation in NFPA 70E - 130.7(A). It is a recommendation, not a requirement. That being said, I would recommend adopting the...
  5. WDeanN

    IEEE 1584 & NFPA 70E

    If the software you are using is SKM, I can say that the 70E equations referred to are Ralph Lee's equation, and the 1584 equations are those developed by the IEEE 1584 Committee.
  6. WDeanN

    Arc Flash Reduction Methods On Secondary of Sub-unit

    I call it a myth because there are so many people that think that it is mandated that energized work be shut down if calculations show greater then 40 cal/cm. As I think we have discussed on another board, there is no such restriction in any of the codes. Not in IEEE, not in NFPA70E, not in...
  7. WDeanN

    Arc Flash Reduction Methods On Secondary of Sub-unit

    davidbeach "But if it can't be safely approached while energized, how are the direct measurements to be made to confirm that it has been de-energized." You suit up to the calculated values. Here at my facility, they have embraced the "40 cal limit" myth, but still allow suiting up to the...
  8. WDeanN

    Arc Flash Reduction Methods On Secondary of Sub-unit

    "The quick trip has a padlock secured switch,..." I like this feature. I am generally not a fan of the maintenance switches, because I think it puts the responsibility on the electrician, who may forget to switch it back when he's done. With the locked cover, it can become part of LOTO, and...
  9. WDeanN

    Arc flash calculation for 208V System fed from 125KVA transformer

    "Fault clearing time is 6.083 Second." Try applying the 2 second rule, if you insist on calculating it. Also "The client engineer indicated the above point" I would say do what the client says. If you feel like you must go further, then do so with a footnote, and spell out all of your...
  10. WDeanN

    Arc Flash Reduction Methods On Secondary of Sub-unit

    330 cal!! What’s the boundary on this? Somewhere in the next county? Do you have the option to split the load between transformers? If you can use 3 1000kVA Xfmrs, you will be much better off. I'd suggest the ABB REA flash detector (...
  11. WDeanN

    Unearthed power system on ships

    “Why unearthed power generation & distribution system (say 440 V AC/60Hz) is preferred on ships, rather than earthed power system (common neutral bar).” I can’t speak of ships, but have had a little experience with boats. :) One word – Reliability! It really sucks to have your power go out...
  12. WDeanN

    Arc flash study

    The IEEE equations (D.8) are empirically derived from test data. This means, unfortunately, that they have little (known) physical basis. The equations in section D.8.6, D.8.7 were further derived after additional testing, usually on the behest of some manufacturer, so that they could say...
  13. WDeanN

    NESC Arc Flash Tables vs ArcPro Calcs

    dpc - I know this is probably not necessary, but have you used the multipliers in ArcPro for single phase, three phase, etc? (It's been a while since I've used ArcPro, forgive me) Also, although NESC says they were calculated using "commercially available software" is there a possibility they...
  14. WDeanN

    Arc Flash 208 V panelboard, 2 cycles clearing time in NFPA70E

    Well, I couldn't find the note. I may have been thinking about 130.3(A) FPB, which places the FPB at 4 feet for less than 300kA-cycles. I tried looking through the ROP for 2008 70E, but quickly got lost/distracted/confused by some of the proposals. I'm not sure what to do about PPE. You...
  15. WDeanN

    Arc Flash 208 V panelboard, 2 cycles clearing time in NFPA70E

    I can't find it now, but I thought there was a note in there that you could also base it on kA-cycles, so that if you had a longer clearing time with a smaller fault current, you could also use the tables. Is this maybe in the ROP for 2009 70E? Although, even if this were the case, if the...
  16. WDeanN

    Tips to finding faster CB for the puprose of Minimizing Arc Flash?

    One other note to reduce the AF Category. You quoted 18" for your study. I normally use 24" for LVPCB locations. That's 18" for arms + 6" for distance from front of CB to current carrying parts within the breaker itself. It's still conservative enough to allow full protection, without having...
  17. WDeanN

    Tips to finding faster CB for the puprose of Minimizing Arc Flash?

    Majesus - That was one of the things I prefer about ETAP. They keep circuit breaker data separate from trip device data in their libraries. It's been a couple of years since I used it, but you can chose the breaker, then select your trip device, with ETAP only providing trip devices that fit...
  18. WDeanN

    Tips to finding faster CB for the puprose of Minimizing Arc Flash?

    I may be missing something, but isn't the breaker in this case already operating in the instaneous mode at the available arcing current? I don't know if shaving a couple of cycles off is going to get you much more. You've got a high available fault current. Add some wire or a reactor. Just...
  19. WDeanN

    Arc Flash Reduction With No Main Breaker

    Thanks for the paper, Bob. I've been looking for something similar for many of the Unit Sub locations at my work place. Now to get some of the systems engineers to accept it... On another note, the IEEE needs to start included the publish date in their header for their papers.
  20. WDeanN

    480V power wiring: wiring from hot to ground to get 277V - OK?

    "I agree with dpc, you should tell the person "You have to pull a neutral because if you wire the heater backup like you did the first time – I'll report you to the IBEW local."" Where is he going to get a neutral from??!!! If this is a standard Delta system, like those that commonly feed...

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