three phase current

[kcor]

have a question that I hope someone can help me with. If you have a three phase motor that is pulling 28 amps per phase, is the total current equal to 3*28 thanks

[Sleepy Wombat]

How is the motor connected Y or Delta ? Opp's miss read you question... It would be rated at 28 Amps

[kcor]

Thanks That is what I told one of our plant electricans today, and actually got into a argument with him trying to explain why it was not 3*28. Actually offered him a copy of the basic electricity that I used in college, 25 years ago, which was probably not the best way to handle it, but sometimes if someone will not listen, you just have to try and prove it. Would be interested in some good links, if you or anyone knows of any. Will try and attach one that I keep on my desktop. Covert_Amps_Power.pdf

[Sleepy Wombat]

Try the following... http://www.lmphotonics.com/

[mr_electrician]

As my electrical inspector always said, 50% of electricians graduated in the bottom half. Why an electrician that is licensed think that 3 phase means multiplying the 3 readings is scary. Did you carry a sign like this ---->

[kcor]

no, but i wanted to.

[beegee]

In my experience, many electricians tend to have problems with AC, not to mention 3ph or single phase or even worse.. inverters....

[robh]

If you really want to mess with them, throw in the magic number....1.732

[mr_electrician]

Whats so magic about 1.732???? It is the square root of 3 and is used for 3 phase calculations. Not all electricians graduated in the bottom half. I myself was near the top and can do alot more than just bend pipe and pull wire.

[TConnolly]

I'm glad to hear it. The corollary of that statement is that 50% graduated in the top half. But you gotta admit, there were some guys in your class that you wondered about, right? And just to make it fair, I know a few engineers that are down right dangerous with a screwdriver. Nuttin' to get the underwear in a wad about. The phrase magic number is just a phrase, usually used in various industries to refer to numbers that are frequently used. Each discipline has its own set of magic numbers. http://en.wikipedia.org/wiki/Magic_number

[BobB]

Quite an interesting thread going here. I served my apprenticeship as an electrical fitter. Motor winding (some pretty flash ones too) including high voltage and high frequency, re-designing Yankee 60 Hz motors to work on 50 Hz without burning out, transformer (up to 33kV) design and build, welders (high frequency, choke, spot etc), machining (shafts, commutators etc), re-building commutators (big mothers), service work to factories, control circuit design, switch boards (control panels and power stuff - still cannot work with busbar), installation work (hated building sites and still do), some electronics (transistors were new!!!), rectifiers (mercury tube and silicon plate), and many more disciplines. We even did mechanical work from time to time - overhead cranes etc. Also did a lot of marine work including lots of DC stuff, alternators and DC generators on harbour working cranes unloading stuff off ships - before containers obviously. Instrumentation including calibrating temperature and process controllers. No microprocessors in them days. I had voltmeters and ammeters where the needle balanced on a diamond point. Do not bump the meter when the needle was free (not locked) or it cost a lot to replace the movement. dang I am getting old. Even in them days it was hard to find an electrician that could calculate current from volts and va quite frankly. The electrical fitters could of course. I find it sad that the electrical industry has become so "specialised" for want of a better term. You either wire jerk, wire switchboards etc etc. Companies have tended to isolate themselves into certain small market areas and the broad spectrum of training we went through, unfortunately, is now virtually impossible to find in one company or government instrumentality. I am very concerned for the young people of today who cannot get this sort of training and experience. Plenty of sharp young engineers coming out of university these days. Most of them are good for calculating voltage drop (sometimes) and that is about all. Catch plenty of them out with their stuff ups almost everday due to lack of experience and ignorance. They ask "what are your qualifications"? Answer is "a silly old electrical fitter who has fgallen on his backside more times than he can remember but has learned a hell of a lot that way". Boy, don't they look down their noses at you. Then you proceed to pull their specification and/or design apart because it will not work and they look as inexperienced and green as they really are. Have to have dinner now - may return and add a bit later.

[BobB]

Mmmm!!! Osso Bucco and some good big Ossie Shiraz. A lot of the young apprentrices concern me also. Their "get up and go" appears to have "got up and went". Sad when you send an apprentice back to his employer, was with me for a few days for assessment to see if he could learn what I do, and having to tell my friend that only 3 things excited the young fella during the day and got him interested 1) His mobile beeped at him with a message and he sent some drivel back to his mate 2) It was lunch time and he got to go up the road and buy a kebab 3) It was time to go home All he did all day was mark out a control panel door incorrectly from a drawing and I had to re-do it and punch the wrong sized holes for lights etc, ruined the door and cost me money to buy a new one. I did have a young lady here for a couple of days for the same reason and she was good but lacked interest in learning how to use the CAD system. I see a very mixed bag of tradesmen, some of them are very good and well educated and some are only good for wire jerking and nothing else. The saddest thing is that getting a good, varied and thorough training in most parts of the electrical industry is now almost impossible.

[PdL]

Good reading Bob Most of my colleagues in my company went to the same school, and stayed after doing their internship (as well as me) It looks like I was the last one to get an in depth enough education to stay in the job, together with my eager to learn attitude. Amongst the later ones that came to do their internship one managed to stare at the fascinating works of a crimp tool all day, the other didn't know what a relays coil was let alone could wire a Y / delta starter. I once took one guy with me a day on a job. As you say he didn't ask me a single thing. It's sad. I enjoy the commissioning jobs a lot as it is amazing how much you can learn from all disciplines. Ehh ?

[robh]

Most of the times when I have seen it be magic is when doing a 3 phase calc and forgetting to use it, then just before you remember it, someone "magicly" shows up to remind you! I have worked with some very sharp people who have done calcs and when they get done things just wern't right, after working back through the problem theres that darn "magic" number! Pretty common mistake if you have rarely worked with 3 phase stuff.