Regarding your ground loop tester- what type of injection current does it use? DC impedance is different from AC impedance.
Funny story about that you might enjoy. I was installing new exit lights in a rather old government building many years ago and I had gotten their early on my first day to get a look at the plans and specifications so as to orient myself to the job. The specifications said very prominently that the exit lights furnished were to be standard Edison medium base screw shell lamp holders and the new arrow and EXIT lenses were to be green. The company owner had more than enough exit fixtures left over from a project which got idled by a financial slump before it was finished. The left over ones did everything but cook your breakfast. They had a built in battery back up with a built in charger. They had adapter plates already provided for those huge octagonal concrete embedded boxes. They had your choice of Red or Green lenses included. They were much nicer than the ones that the US General Services Administration (GSA) had specified. I had done a 2 year block of alternative power work by this point in my life so I was familiar with T rated switches. When I saw that Tungsten rated switches had been specified for the few of the emergency lights that were switch controlled I became concerned. Here comes the job foreman down the hall I was working in so I ask "Ronny has anyone checked what the source of the power to these emergency lights is.” You see I didn't know that the outside superintendent had just chewed him up over a small over order issue and that he was in an extremely bad mood. He answers "Just shut the F up and put em on the wall." The next day he gave me my assignment and I nodded my head. He looks at me and asks "Your not talking to me are you." I shook my head no. "It's about yesterday isn't it?" I shook my head yes. He mutters "Well be that way then. Get to work." Off I went and didn't say a word to him for the rest of the 2 weeks that I worked for him. Months go by. I'm sitting in the ready room of the firehouse I volunteered at. We had a shared border with the city in which the government building was located and it seemed that every fire called in for the boundary street was always announced on either jurisdictions radio channel as "Across the street from ### boundary street. Report of a house on fire..." That meant that the fire department that was announcing that call was not due to respond. The side of the street which was "Across the street from" was always in the other departments jurisdiction. For that reason we monitored the city channel along with the county channel and the channel of the adjacent county continuously. I'm sitting their in the ready room watching some movie; I really did know better. You never get to see the end of the movie at the firehouse; and the city radio opens with “Street Box. REICHEL BOX 1735 the ****** west entrance many phone calls smoke on all floors. reports of multiple exits blocked by fire." Then he reads the assignment and gets the answer responding from each unit. As soon as he's done the radio says "Battalion 2 to radio advise incoming units to exercise extreme caution. Power failure in this area traffic lights are inoperative." One minute later. "Engine ## on scene smoke showing from multiple levels Have the first due special service run multiple electrical leads up the east stairway for smoke ejectors and lights." Five minutes later. "Battalion 2 to radio I'm returning all units except the first 2 engines and first 2 trucks for overhaul. We had a multiple floor electrical fire with several exit lights on fire and dripping burning plastic but the circuits been de-energized by the building's operating engineers and we'll be clearing in about an hour."
I go sit down at a desk with a telephone and call the emergency service call dispatcher at my employers office. He was cranky when he answered and I new I'd woken him up. I said "Pauly how would you like to be a hero. He says “What are you up to now Tom?” I tell him that I am withdrawing 1000 dollars from my bank at that the first 100 guys that answer the emergency call out for 8 hours of overtime get either the overtime or a stake and egg breakfast at Denny’s. I drive into the yard at 5 the next morning. Paul tells me he has 70 guys and more returning the messages he left on their phones all the time. We ended up with 65 electricians and 15 apprentices in the yard checking service trucks and ribbing me about how much they will enjoy my stakes. But the guys who knew me were confident that they will have overtime work that day. They had played poker with me or worked a tough job with me and new I am a fairly serious guy about quality and never taking chances with anyone’s safety. I had stopped a job knowing that the company would find an excuse to lay me off because they wanted guys to work right on the edge of an open deck 7 stories up using step ladders that were 10 feet tall without safety harnesses and edge lines. I had earned a reputation of looking out for the guys I worked with.
6 o'clock and the owners rag top Mercedes Benz car pulls into the front parking lot were only management and their good looking secretaries are allowed to park. A couple of minutes later the dispatchers phone rings. He listens for a while and asks “Will 80 do? Their all back here ready to work.” He hangs up and says “Roll every truck over to the Government ******* Office.” I said “I told you I’d make you a hero.” About 2 in the afternoon Ronny comes walking down the hall I’m working in and says “All right I’m sorry. Now please call it off.” I nodded no and as soon as I did, just like on the other floors he’d been on, all of the guys yelled “Just shut the F up and put em on the wall.”
In really old US government buildings the emergency lights were plain vanilla tungsten bulbs supplied by 120 2 volt wet cells in series and tapped to ground between # 60 and #61. When the power fails a rather large double pole contactor would drop out off of the 120/208 AC and onto the 120/240 volt battery bank. What were the charging circuit transformers in those fancy-schmancy exit lights when that 120 volts of DC hit them? A dead short you say? Imagine my surprise. What had tipped me off was the Tungsten rated switches. I had happened upon them in my alternative power work only a couple of years before. You only need T rated switches when they will have to close DC power onto a number of Tungsten filament incandescent light bulbs. Until Tungsten heats it is a momentary dead short and the switches have to be able to close on the DC inrush current of the cold Tungsten filaments. They have a large T stamped into the strap under the UL letters to indicate that capability.
Nobody had stake but we all got 10 hours of overtime out of it.
What then happened was final proof that the owner was a direct descendant of King Midas. He convinced the GSA they needed to give him the job of building them an Uninterruptible Power Supply for the buildings process controls, using their batteries, so that the equipment would remember were it was in the process and could much more easily restarted without a complete re-setup of the job that had been underway when the power failed. He MADE money off the deal when by all rights he should have taken a financial beating for ignoring the specifications that the US General Services Administration had provided and he had contracted to follow.
