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 Post subject: Anyone seen a new OSHA requirement that for transformer denergization
PostPosted: Fri Jan 07, 2011 10:23 am 
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Recently a customer had heard that OSHA was requiring transformers to be de-energized prior to operating breakers on the secondary. They asked me about that and I had to tell them I would make some inquires and get back to them.

That is something that I have not seen or come across yet and was wondering if anyone had seen it or heard of it as an upcoming possibility?


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PostPosted: Fri Jan 07, 2011 1:32 pm 
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OSHA takes decades to update their standards, so this is more then likely a NEC requirement for 2011, maybe in Article 450 somewhere.....


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PostPosted: Sat Jan 08, 2011 8:56 am 
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Location: Charlotte, NC
T-Rex wrote:
Recently a customer had heard that OSHA was requiring transformers to be de-energized prior to operating breakers on the secondary. They asked me about that and I had to tell them I would make some inquires and get back to them.

That is something that I have not seen or come across yet and was wondering if anyone had seen it or heard of it as an upcoming possibility?


Have not heard of it and it makes no sense anyways. What is the reasoning here?

In a typical MV/LV substation most often the MV switch on the pirmary side of the transformer has a much lower arc flash hazard than the LV main breaker on the secondary side. Which has led some companies to have a procedure to open the MV switch before operating the LV main.

Maybe this is where your "somebody" became confused. :confused:

Problem with this thinking is often the MV switch is not designed for this duty. In fact there are usually interlocks thee to prevent this sequence. I have actually seen plants override key interlocks to do this because they think it is safer. :eek:

Even if the MV switch is a load break switch and by design can be operated under load they do not like to do it too often, so if this is a common task, those switches will fail. In fact I have a crew out repairing switches like this because of this "procedure" this weekend.


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