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Thread: Drying out Wet Bus Duct

  1. #1
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    Drying out Wet Bus Duct

    Has anyone ever heard of or used a "baking" method to dry out bust duct that had water intrusion? If so, who are the companies that perform this type of work? I do know that manufacturers do not extend their warranties on bus duct that has been "baked" or dried.

  2. #2
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  3. #3
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    The problem with drying busway is.

    It can take considerable time.
    The dirt that deposits on the insulators and exposed busway (in joints and at openings for switches/ CBs) is a conductor dry it may read acceptable or close to acceptable, with an increase in humidity this dirt can become a conductor.
    The steel casing will continue to rust.


    I have the NEMA specs in the office I forget what NEMA stance on this is. But most manufactures are in business to sell busway, so accepting drying might be unacceptable.

    Having said all this, I have worked with firms that dried busway.
    Stripped all switches and buckets.
    Dehumidifiers and heat in every electrical closet.
    Energized busway at LV with a variac and increased voltage over a period of time as megger readings improved.

    I prefer replacing.
    Brian John
    Leesburg, VA

  4. #4
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    Quote Originally Posted by brian john View Post
    The problem with drying busway is.

    It can take considerable time.
    The dirt that deposits on the insulators and exposed busway (in joints and at openings for switches/ CBs) is a conductor dry it may read acceptable or close to acceptable, with an increase in humidity this dirt can become a conductor.
    The steel casing will continue to rust.


    I have the NEMA specs in the office I forget what NEMA stance on this is. But most manufactures are in business to sell busway, so accepting drying might be unacceptable.

    Having said all this, I have worked with firms that dried busway.
    Stripped all switches and buckets.
    Dehumidifiers and heat in every electrical closet.
    Energized busway at LV with a variac and increased voltage over a period of time as megger readings improved.

    I prefer replacing.
    We used a welder once to dry out a 250' long buss duct that was soaked when an old metal roof started leaking right into it at first it just blew the 3k amp fuses at night when the plant was shut down, so when we can in on Monday we had no power for the MDPs fed from it, and when we investigated as to why the fuses failed well it was self evident when we walked the duct down and found water all over the place about at the 235' mark of the run, the amount of ruse that ran into the buss is what got the fuses so we had to open that section and clean it out and we had 4 or 5 insulator knobs we had to replace, so our plant EE came up with this idea if a welder can be used to thaw out frozen water pipes in a house or underground, it should work for this, we removed the cables feeding it from the service and bonded A to B together at the east end with a jumper from C to the building steel and took one of our Hobart motor generator welders with a very high amperage capacity (1200 amps) over to the other end and lugged B to C, and bonded the work lead to the building steel and the stinger lead to A to put all three phase in one big series run, with the amperage all the way down we slowly brought it up till the IR thermometer read 150° we kept an eye on it and let it bake for about 4 hours, after that we megged it out, put a large drip pan over the buss at the leak point which had stopped because the storm moved on, and put it back in service, lasted about two years before it just let go and started a ball of arcing that literally burned all the way up to the point of the multiple parallel 1k MCM conductors that just fell apart, funny thing was only one of the three fuses opened in all the arcing, and there was no buss-way anymore all splashed on the floor as melted globs of copper and tin from the casing, all we could do was used welding glasses while manning CO2 extinguishers to put out the little fires that was breaking out from a few stock piles of cardboard stock for shipping box's
    Last edited by hurk27; 04-30-12 at 10:27 PM.
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  5. #5
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    We were called to a site where a contractor Hi-potted the busway hoping that would dry it out. 64kv on 600 VAC busway.
    Brian John
    Leesburg, VA

  6. #6
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    I think there is a big difference between prolonged submersion and incidental exposure to water.

    I am very suspicious of being able to ever reuse something that has spent 2 weeks under water.

    Something that had some water drip on and into it is something that can probably be reused in most cases, with possibly some minor repairs.

    There is a wide range of situations that span the gap between those I mentioned above. I am not sure there is anyway someone from the outside looking in can tell you what the appropriate solution is.

    I am somewhat suspicious of using heat. I would be inclined more toward draining the water out and then rinsing the inards out with IPA, followed by forced air drying. But, that is a lot more work than just applying heat, and may not be all that easy to do in some cases.
    Last edited by petersonra; 05-01-12 at 09:46 AM.
    Bob

  7. #7
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    What is IPA? Google drew a blank.
    "Electricity is really just organized lightning." George Carlin


    Derék

  8. #8
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    Isopropyl Alcohol
    /mike

  9. #9
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    Quote Originally Posted by brian john View Post
    We were called to a site where a contractor Hi-potted the busway hoping that would dry it out. 64kv on 600 VAC busway.
    Perhaps he was trying to fail the bus, so there is no question.

    (Hi-Pot equipment drives no substantial current, which is needed to produce heat. See the examples of welding machine use for that purpose, where voltage low and current high. Exact opposite of Hi-Pot equipment.)

  10. #10
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    Quote Originally Posted by petersonra View Post
    I think there is a big difference between prolonged submersion and incidental exposure to water.

    I am very suspicious of being able to ever reuse something that has spent 2 weeks under water.

    Something that had some water drip on and into it is something that can probably be reused in most cases, with possibly some minor repairs.

    There is a wide range of situations that span the gap between those I mentioned above. I am not sure there is anyway someone from the outside looking in can tell you what the appropriate solution is.

    I am somewhat suspicious of using heat. I would be inclined more toward draining the water out and then rinsing the inards out with IPA, followed by forced air drying. But, that is a lot more work than just applying heat, and may not be all that easy to do in some cases.
    One of the worse busway explosions I have seen was a drip on a 90 degree elbow. Blew up (vaporized) 30' of busway and blew every 90 degree bend out the full lenght of the run (maybe 8-10). The straight portions meggered OK, but all was replaced.

    Hard for the average contractor to dip 285' of 4000 amp busway.

    Drying has been used for years, I am not a big proponent of drying, but it seems to work, WELL until it goes boom.
    Brian John
    Leesburg, VA

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