Category: Science > Instruments and Methods
Asked by: jelem2000-ga
List Price: $40.00
21 Nov 2005 11:28 PST
Expires: 21 Dec 2005 11:28 PST
Question ID: 595858
In an upcoming cout case the police got a seach warrant by using a thermal imaging camera (Raytheon Palmir 250)They said that the electrical wire going to the house was anormaly hot. There was 15 lamps on in the house.Each 1000watts sodium high pressure.The wire going to the house is about 300ft long, it is new and is rated 400amps. I do not beleive that 15000watt would generate enough heat in a 400amps wire so that it would be visible on that camera. I also would like to know how many amps would go through the same wire if all the electrical appliances were in use in the house instead of the lamps.Of how many degree would that increase the temperature of that wire. Thank you
Answered By: redhoss-ga on 21 Nov 2005 13:36 PST
Hello jelem2000, I think your reasoning is sound and that you have a very legitimate complaint. I have found information that you can use to prove your point. First we need to know what wire size is used in a 400 amp service. This is found here: http://www.cinergypsi.com/pdfs/Permanent_Overhead_Service_for_Manufactured_Mobile_Homes.pdf Look on page 2 at the chart titled "Customer Wire Sizes". I will assume you have copper wire in your service. The two "hot" wires would be 500kcmil. Now we need to know what the temperature rise would be for the amount of current as stated in your question. This is found here: http://www.tycothermal.com/assets/NorthAmerica/English/Documents/Engineering_Specification/Products/216/011-ENGDATA-0101.pdf Look on page 11 at the chart titled "Sheath Temperature Rise Type MI Single Conductor 600 Volt Free Air Conditions". Your wire size (500kcmil) is shown at the far right. It is the largest conductor shown. I will assume that you are operating the lights at 120 volts. This is the worst case. If you are operating at 220 volts, the current would be 1/2 what we are going to calculate. So, for 120 volt the amperage would be 15,000 watts/120 volts = 125 amps. Assuming that all the lights are powered by the same conductor, which is probably not the case and is the worst case. Reading from the chart that should produce a temperature rise of 5 degrees centigrade or 9 degrees farenheit. If you were operating all of your electrical appliances, lets say that you might be drawing 300 amps or 150 amps per conductor. Again, from the chart that should produce a temperature rise of 7.5 degrees centigrade or 13.5 degrees farenheit. So, you can see what all of this leads to. It would be absolutely impossible to tell from the temperature of your service wires what appliances you are operating in your home. Also, I don't care how accurate the instrument is that they used to take these readings, a difference of 2.5 degrees centigrade is a very minute difference. They would have to monitor your usage over a long period of time to get day to day and seasonal variations in your usage to have any chance of predicting what appliances you might be using at any given time. However, as we both know, the police don't always have to prove their case scientifically. I think that any reasonable person would come to the same conclusion that you and I have come to. Will that happen in court is anyone's guess. Let me know if there is any of this that you can't follow. Please ask for a clarification and I will try and explain a different way. Good luck in court, Redhoss
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From: hedgie-ga on 25 Nov 2005 16:55 PST
Good, well documented answer. Just one point is not clear: "Assuming that all the lights are powered by the same conductor, which is probably not the case and is the worst case..." I understood from electrical wire going to the house was anormaly hot that they measured temperature of the external wire, going from the post to the house. Then all load, all lamps, were on that conductor. Incidental comment: It seems likely that warrant was issued based on pattern of the power consumption, as described/mentioned here: In court records, a number of suspects have blasted the detectives' power comparisons as bogus, arguing that Grant and Goodpaster unfairly compared their electrical usage to that of smaller homes with less square footage and purposely failed to take into account factors such as the existence of jacuzzis, swimming pools and other items that raise power consumption. http://www.kubby.com/000120Search-unwarranted.html I recall a case in which electric utility provided such data to the police, and that act of 'cooperation with police' was found to be improper, violating presumption of privacy. Considering that precedent, police may have been tempted to lie about the source of the power data. They perhaps invented the infra measurement as a cover, to hide real source of data. The story does not fit, but real issue seems to be not technical but constitutional. Is the 'power consumption pattern' , no matter how obtained, a reasonable cause for a warrrant? Perhaps, as a protection, people will start applying for a permit ot install a hot tub? I would start thinking about moving out of the police state. Where do you live now? In Sudan, Saudi Arabia ..?
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