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  1. #26
    Join Date
    Nov 2009

    Default Re: Whoa, major electrical safety violations

    Quote Originally Posted by NEC View Post
    Ummm, yes I have a masters license. I was curious to how power was cut on a single residence when a transformer tap might feed multiple homes in different areas of the country and with different power suppliers regulations...... It goes beyond the NEC and is not really covered in NFPA-70E.

    I would say that a lateral cut to the home is no more safe either by an electrical contractor or the "Power Company" as long as I follow 70E.

    I would also say that fault current at a residence is seldom more than 10k and arc flash is minimal.
    I have worked on a few different utility properties during my 37 year career during "storm trouble." Every property Ive worked on had similar means to diconnect individual overhead services. You cut the individual service at the point of attachment on the pole or the house. If the service is a midspan tap, that is to say the deadend connection is between poles, the disconnect is still done in the same manner. As I said, UG residential distribution has come a long way in my career. Disconnects are done either in a transformer or a secondary enclosure. Subway, or what i call conventional UG that feeds from manholes is disconnected in the manhole that the service originates from.

    I will preface my next statement with the disclaimer that I am not an engineer. But here goes, available fault current is partially determined by the total KVA of the transformers feeding the services. Obviously distance from the source and conductor size come into play. Lets say you are going to disconnect a single phase 120/208 service that feeds from a 3 phase overhead network. The network is fed by 5-3 phase banks of 225 KVA each and the banks are tied together at the secondaries with the standard malimiter fuses. Your service is 50 ft long and is # 2 stranded CU. What is the avaible fault current should a phase to phase flash occur.

    If you look at NFPA 70e, within the first few pages, you will find that electric utilities are exempt so those regs. dont apply to me. OSHA 1910.269 apply and say I can wear 100% cotton. I am not required to wear FR by osha and I work on equipment with much higher available fault current that 120/240 house services. 70e is a little much, i would be wearing a full flash hood if 70e applied to me.
    Last edited by Edge1289; 11-17-2009 at 09:09 PM. Reason: missing wire size

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