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	Subject - Trouble shooting question CaApprentice I am a 3rd year apprentice. I have only comercial experience and I am applying for a industrial electrician job. It would be great if someont would hepl me answer a few questions on my application. What is the minimum information needed to diagnose, test, and isolate problems in AC power distribution systems? Thank You JimmyDee If I were going in cold and knew nothing about a system, I would have to know the voltage of the system, where the main source of power was located in the plant (switch gear), are they primary metered and do they have their own substation and where was the substation located, where is the sub fed equipment located, if their distribution system was a high voltage system like 4160, 7200, or 12,400 volts, where was the high voltage protective equipment located. Let me caution you about something. If you don't understand what I have just said, the interviewer will eat you alive if you you answer with my answer and don't understand a large plant distribution system. Jim PEI If your interview is with a power company, they consider 4160, 7200 and 12,400 (13,200 or 15KV) to be MEDIUM voltage. Even though I think it is just too high for me. In fact per the IEEE, 600 volts and down is low voltage, above 600 and up through 15 KV is medium. Above that is high voltage. I hope I remembered correctly the break from medium to high, but I am sure 15 KV is considered medium voltage. PEI Sorry, I got carried away and ignored the original question. Your question about troubleshooting large AC distribution systems led me to think of power companys, but you simply said industrial. So, I'll stay generic. Most industrial facilities use PLCs and relay logic to control most of their equipment. I would sign up for an industrial controls evening class somewhere to teach me ladder logic, timers, starters, contactors, relays, pushbuttons, indicating lights, switch types, etc. From that you will also learn to troubleshoot these circuits. Next, I would invest in a good quality Class III volt meter, try to stay away from the traditional 'Wiggy' tester - they have been know to explode when misused on voltages above its rating. If you are really interested in the testing of AC distribution systems, that company will have to provide a DOBLE, Megger fall of potential testing equipment, breaker test unit and so on. You can't afford those. skynrd If you go to automation.com there is a lot of info to be found there and many links to other sites. stedder We do service and maint. work for a factory where they have their own full time electrician (one guy) I guess thats why we're there. But the 25 year employee of theirs is invaluable, most of his work is control systems, motor drives, ladder logic, plc's, relays etc. Even the older machinery has been updated to logic systems (I'm trying to milk him for all I can), these are the areas I would be concerned with along with understanding the different voltages and their properties. Also understanding transformer wiring and rewiring for different uses. lctrc789 Listen to these posts carefully, these guys are right on the money here. I have been in industrial work for twelve plus years and their is a whole differnt operating system then what you are used to anywhere else.. You already know so residential 120/240 single phase, now you are up to 120/208 WYE pahse in some cases as well as maybe some 120/240 Delta systems for power. Well you will have these in industrial applications as well , but you may have 4160 sub stations as well as 13,200 to 4160 or 480 systems or larger.. Plc s and I/O cabintes that control any thing from a computer or a logic controlled circuit to the use of stop /start stations to a Motor control center to many more. I would suggest you take some courses in automation (i.e.) Allen bradley, Plc Logic controls and then remember that many of these use a higher voltage with large switchgears and many motor control applications as well. You have many more different feilds in industrial work, heat trace, PLCs, I/O cabinets,Motor controls,higher voltages,sub stations,and even what you are used to already 120 and 208 etc... I wish you well and always be careful in what you do we are never to old to learn a new application or code... lucky1122 your question to simplify if I might is :What is the minimum info needed to diagnose ,test and isolate problems in power distribution systems? Remember I am trying to simplify here . When troubleshooting a system the first piece of information I must know is what kind of system am I working on? The system could be a floating delta system ,a corner grounded delta system,a Delta system with a mid point ground, these are some systems found in industry. Before I take out my meter, I must know the characteristics of these systems and how they work before I can undertake troubleshooting the system. If I donot I will not be able to read what my meter is telling me.Of course, knowing where and how the power breakdown occurs in a building is essential, but I would still feel that before I could accomplish the most simple task I must be able to read what my meter is telling me.I'll give you an example. Recently I was working in a building troubleshooting a constant pressure pump control fed from a derived system which consisted of a 2phase 4 wire primary, fed into a phase changer converted to a 3 phase 4wire 120/208 VAC system supplying power to the boiler equipment.The control was fed from that system. As I was taking routine voltage checks I read 208 to ground on each phase with the exception of the c phase which was reading at ground potential. I know that a 3 phase wye configuration reads 120V to ground on all legs. What was wrong ? Before you read on see if you would know? I say this to make a point it is crucial to know how systems work . Otherwise , your meter will be telling you something and you wont be able to see it. The problem turned out to be no system jumper between X0 and the equipment grounding connection. A short had already occurred on the C phase(through a lighting fixture) thus grounding the system to potentials reaching 208 volts. So I know all of the other stuff is important, but when it comes to power distribution troubleshooting,I think if I were to pick the minimum info it would be the knowledge of how these systems work and how they are or are not grounded.I can always see the difference between a high side connection and a low side connection on a transformer pot ; But its all based on the information that I know about electrical systems which I take with me to every job. That is my greatest tool when I walk into a building cold. One more thing lets say you walked into a building cold and took your meter to a distribution panel consisting of knife blade switches that are becoming rare in practice but still exist.The system clearly had 4 wires .Lets say you measured your voltage between every wire and the voltage between 1&3 was 240 and between 2&4was 240 but between 1&2 and 3&4 was 170 what kind of system are you working on . Lets say a motor was fed off this circuit and wasnt working correctly. If you know what Im talking about and understand what kind of system that is then you may know what to check first before anything else . good luck in the trade! Afterhrs I have been an industrial electrician for 8 years, before that I was in the Navy for 11 years. The industrial world is completely different as stated above. The most valuable skill in the industrial world is troubleshooting. Time is money! With the JIT (just in time) production system that most manufacturing companies run on now, you can be put you under tremendous pressure at times to get the machinery running again in a timely fashion. Your company can loose up to $100,000 dollars an hour if it can not supply parts, as promised by their contract, to another company! If you have access to a college book store, I would look at purchasing "Electrical Principles and Practices" by Mazur and Zurlis. I would also look at obtaining the folowing items: 1) A great DVM, I use a Fluke 179 2) NFPA 79 3) an "Ugly's" ref. manual 4) an AMP meter (clamp) 5) A great set of hand tools You have now just "scratched the surface" with all the other postings you have read thus far. Now the good news, your conduit skills will be appreciated from time to time. Good luck, Jerry