The above Ad will no longer appear after you Sign Up for Free!

If electric companies had to follow code…..

Discussion in 'Lighting and Electrics' started by JD, Mar 7, 2009.

  1. JD

    JD Well-Known Member

    Messages:
    4,061
    Likes Received:
    1,309
    Location:
    North Wales PA
    OK, this may be a rant, but lets face it: Our equipment and livelihood is dependant on how the local electric company delivers power to the building we happen to be in. (Unless you bring your own generator!)

    I witness some of the greatest electrical atrocities when I am riding as a passenger in a car. Inevitably, my eyes are always looking upwards to see what the next thing that will chill me to the bone will be.

    I’ll start with my own house. I have a 200 amp service, which is common. The feed from the service head to the meter base and to the breaker box is 4/0 aluminum. This is the area that the home owner is responsible for. From the service head out is the responsibility of the local electrical company. Ok….

    At the service entrance head, my 4/0 entrance feed cable is bugged onto #6 aluminum triplex! The very visual is almost hilarious. As I have ranted elsewhere, the neutral conductor also serves as the guy-wire. Nice to know it would be the first wire to break if a tree came down on my 100 foot street loop.

    Now, a little math: 200 X 2 X 120 volts tells me that the max load for my house should be 48kw. Following the triplex down the street, I can see that I share a transformer with 4 other homes, each with 200 amp services as well. Said transformer is clearly marked as 20kw !! Hummm… A little more math tells me that the max draw of all the homes is 192kw, which is ten times the rating of the transformer! OK, we all know that homes are not going to use their full draw, but still…..

    The primary on the transformer is a 7kv leg on a 13kv 3 phase Y type distribution. In other words, it ties from one of the (very) hots, to the neutral/ground run which also serves as the neutral/ground run for the secondary triplex, which also serves as a support guy-wire. Hummm… Hoping for no car accidents.

    13kv runs require a larger insulator then the old fashion 1.2kv runs that power companies used in the past. Some of the insulators on my street are the larger insulators normally used for 13kv runs. The rest of them are the old style 1.2kv insulators that look like a whiskey shot glass. Why the mix? Well, as the poles catch fire, they are upgraded to the new insulators! I guess they will ultimately end up with them all replaced.

    About two miles down the street, we have what I like to call the “substation on a pole.” Three very large transformers, each the size of a VW, which downvert the main distribution to the local distribution. This pole is now “S” shaped from the weight, and has been for the last few years.

    I wish I could say it is only a local problem, but over the years and in my travels, it appears it is more the “norm” than the exception.

    I find that these days I start looking at the poles as I near a venue.

    Feel free to add your own observations.
     
  2. mrb

    mrb Active Member

    Messages:
    377
    Likes Received:
    32
    with regard to the drop:
    the power company uses wire with a pretty high temperature rating, and they are paying for the lost power from the voltage drop, so they can get away with smaller wire. #6 is small for 200amp though. Around here they use #2al for 200amps.

    As far as the transformer, 20kva seems a little small. On my street they have a 50kva feeding a dozen houses. These transformers are under rated and can withstand extreme temperatures. The primary is usually fused at 300%, and if it ever blows they will replace the transformer with a larger one.
     
  3. gordonmcleod

    gordonmcleod Active Member

    Messages:
    128
    Likes Received:
    16
    Location:
    canada
    On the neutral at the service entrance panel or in some cases the meter base it is bonded to ground any way so the guy wire neutral is only a reference between points. That is up here the norm
    the feeder is undersized but in free air there is a different rating involved
    I wonder if it was sized for a 100amp service originally
     
  4. TimMiller

    TimMiller Well-Known Member

    Messages:
    1,293
    Likes Received:
    82
    Location:
    Houston, Tx
    I once had a 50k dollar bill from highend, due to the neutral conductor melting down out on the pole. You could tell where they did a really poor job splicing, and caused the rig to brown out, as it was shorting then caught fire. Of course the electric company has a "no fault clause" and said your screwed have a nice day. Around here its the same story with about #8 feeding our houses. 200A service gets a #8 wire. I am waiting for the day it melts. (same story at my girlfriends, and her 200A service not only feeds her house, but her well, and several other distribution points that have around a 125-200A main by themselves). The main service coming in is on a 200A breaker, so that will pop or the wire will melt. Even bigger story, same way at my uncles house. His house consists of 3 panels. The mobile home panel being main breakered at 200A. Just for some of you guys, a mobile home box has a main breaker installed along with breakers for about 10 or so feeder circuits, but on the bottom of the buss bars, there are lugs for attaching on another panel. So from the lugs off the bottom, there is a run of 2/0 that runs into the race way buss. (everyone should have a raceway with panels behind their house). From here the wire is split off to the other two panels, one being the house, the other being the pool. He is the only one i know who has managed to trip his main breaker before, from everything running off of it. So far no wire melting but we shall see.

    There really needs to be a code established for the electric companies. They can actually do what they want as far as what they run, and if their transformer melts down, catches your house on fire, guess what they are not at fault all due to their no fault clause.
     
  5. JD

    JD Well-Known Member

    Messages:
    4,061
    Likes Received:
    1,309
    Location:
    North Wales PA
    Unfortunately, the earth is not made out of copper, thus the term “ground propagation.*” Recently, a farmer lost the primary neutral run. The result was that the bottom end of the transformer had no return other than through the ground path. His animals were getting electrocuted. His grounding rod was hissing and everything in the building that was frame ground measured about 300 volts above the dirt potential. No compensation, needles to say.

    *ground propagation - Basically, the earth is a big resistor. If you stick two metal rods into it a few feet apart, and connect them to a car battery, you can stick a third pole in between the two and measure the voltage with a multimeter. Depending on where you stick the middle pole, you will get a mathematical divide of the source voltage. Of course, soil varies greatly in conduction so it will rarely be liner.
     
  6. FMEng

    FMEng Well-Known Member Fight Leukemia

    Messages:
    1,871
    Likes Received:
    697
    Location:
    Tacoma, WA
    First off, the power company can use smaller conductors on the drop because of the insulation type and because it is in free air, which allows it to dissipate heat readily.

    Secondly, transformers are seldom sized to handle the full rated current of all the disconnect breakers. The NEC recognizes that all of the loads in a building are not used all at the same time. Common types of home loads, such as stoves, ovens, water heaters are computed with a use factor. Some commercial and industrial loads would be calculated at 100%, but not in homes.

    Put another way, if your home's service is 200 Amps, chances are you'd never come close to actually drawing that amount. I'd be surprised to measure half of that with several major appliances running. The power company knows that, so they factor it in when sizing their equipment.

    Electrical service transformers are also built with a huge safety margin. Several years ago, I had the electrical service for a tower site with two FM stations redone. We discovered that the transformer was rated at 40 kVA. The measured load was about 80 kVA. That transformer survived doing that for decades, 24 hours a day.
     
    Last edited: Mar 7, 2009
  7. gordonmcleod

    gordonmcleod Active Member

    Messages:
    128
    Likes Received:
    16
    Location:
    canada
    The only time they get very concerned about the transformer size is usually if the wireing permit is specified with electric heating being installed When I wired my parents new house because of the fact natural gas wasn't available we installed a electric furnace and heat pump system based on its square footage we were compelled under the code to install a 400amp service
    The utility company did have to provide a different pole transformer based on the load
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice