ace21122112 Posted September 3, 2012 Report Posted September 3, 2012 I work for a company that sells a fair bit of machinery to the US Most is 120V single or 460 3 phase but sometimes its 230V single. Whenever we do go with 230V I have to include a transformer to convert the US voltage which seems to be always 3 wire to 4 Wire with a neutral.. US 230V power is hot-hot-ground with 120 between legs correct? If so is there any reason why 4 wire seem so uncommon.... Is it because the secondary of feeding transformers are delta? Quote
BobLfoot Posted September 4, 2012 Report Posted September 4, 2012 In my experience U.S. 240 Power is 240 VAC L1 to L2 ; 120 VAC L1 to Neut or 120 VAC L1 to Ground ; 120 VAC L2 to Neut or 120 VAC L2 to Ground ; and 0 Volts Neut to Ground. Neut and Ground are usually only ever tied together at the service entrance panel. For 240 volts equipment the two hots {L1/L2} are needed to do the work and the ground is needed for Quote
ace21122112 Posted September 4, 2012 Author Report Posted September 4, 2012 Our machines need 220 as well as 110 sounds like your the same as us just seems strange that always 3 wire is all that's availiable Quote
Mendon Systems Posted September 5, 2012 Report Posted September 5, 2012 230v single phase is always as Bob described it with a phase angle of 180 degrees and a grounded neutral. The problem comes in when someone tries to use the same device on 3 phase. Most 3 phase is 208 volts with a 120 degree phase angle BUT occasionally you can run into some really strange voltage combinations. I ran into one old system recently that was 230 volts leg to leg with one leg grounded and another that was 230 leg to leg with no ground reference at all. It is probably safest to continue doing what you are doing now! Quote
Shiner Posted September 6, 2012 Report Posted September 6, 2012 The single phase application in the US is commonly referred to as an Edison system, obviously named after Thomas. The three phase systems are around, but are diminishing in numbers (at least in my area). Ungrounded systems are still left oveer in old equipment, but anything built new with UL standards will have one side grounded. It seems everyone wants to go to full 480v 3phase or higher as far as motor applications are concerned. I have been given a few reasons for this. Some are uninformed in my opinion but here goes. By not stepping down, you have less losses to pay for (minimal but in large facilities it does add up) and less equipment to pay for (true) and most is dual rated for 480v anyways. You get a better power factor running higher voltages. (???) Motors have more power/torque running higher voltages. (chuckle) In large electrical systems, higher voltages mean less current which means smaller conductors and conduits. (in construction costs this can add up very fast) There are more but I'll let others share either fun facts or funny fibs. We have a number of electrical systems here in Buffalo, mainly because we have some of the oldest electrical systems. For example the last 25Hz facility just got upgraded a couple years ago. Yes, I said 25 cycle. We have grounded B phase systems(corner grounded delta) which were used to try to eliminate the amount of conductors used but can commonly have ground loop issues, High leg systems (wild leg or red leg) where the center of one phase is tapped as the grounded conductor, which gives you the ability to connect 3phase or 1phase loads to one system but causes unbalancing issues and panel layout issues since you can't connect any single phase loads to the B phase. if it was thought of, we had it. Mainly due to the age of some of our system, a lot of experimenting was still going on during the Tesla/Edison battles and believe it or not, over 100 years later some of it is still laying around. Quote
Mendon Systems Posted September 8, 2012 Report Posted September 8, 2012 (edited) The other configuration that should be mentioned here is what is commonly referred to as "wild leg" 230. It is actually a fairly common power system installed at small sites like machine shops that need 3 phase motor power and created by phase converters or transformers. It consists of the normal 230 single phase with two phases at 180 degrees phase angle and 120 volts to ground. The third "wild" phase is a 90 degrees phase angle to the other two and 187 volts to ground. Edited September 8, 2012 by Mendon Systems Quote
OkiePC Posted September 25, 2012 Report Posted September 25, 2012 (edited) I found these nice links showing lots of power distribution possibilities. http://173.247.254.1...istribution.pdf http://www.federalpacific.com/university/transbasics/chapter3.html Edited September 25, 2012 by OkiePC Quote
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