Many of the industrial projects I encountered are three phase + neutral. Maybe you could construe as four phases ?
Troubleshoot
- Thread starter Adrian Francis
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drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
"Four phase" [sic] almost certainly refers to a two-phase, split-phase circuit. with two phases 90o apart, each of which has centertapped windings.
I'm not sure about the neutral on that arrangement.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
I'm not, either; I've never seen one in the wild. We'll have to ask somebody from eastern Pennsylvania.
In my over 50 enjoyable years working mostly as an industrial electrician never heard of the extremely common three phase 4 wire systems referred to as four phase. The fourth wire was from the center point of a Y transformer connection such as 480/277 & 208/120 . I helped my dad install a cool custom made transformer back in the 1960's. The old factory had more two phase motors then three phase. Transformer had a 2,300 volt primary and produced both 2 & 3 phase power. I asked my VoTech teacher what that type of transformer is called. He had me ask a sharp teacher that was in his 60's.Told me that was a Scott T connection.
kwired
Electron manager
- Location
- NE Nebraska
Better question might be how much imbalance can be tolerated? That answer can probably vary as well though.
When only loads are three phase three wire or 240 volt line to line on a single phase supply you will have almost perfect balance.
When you figure here in North America there is a lot of 120 volt loads and nearly all of them are connected to multiwire systems it will be difficult to achieve perfect balance other than in situations where all the load is essentially continuous when in operation.
I have worked in several buildings years ago that had 240 volt two phase with a neutral ( ya now called what dumb confusing grounded conductor ).All had the 5th wire that was generated from tap to both phases to provide 120 volts. By around 1975 it started to get difficult to find safety switches with 4 poles with or w/o fuses especially over 100 amps. Back then the fourth pole at least doubled the price and appeared that flimsy manufacturers like Wandsworth were the only companies still manufacturing them. We would order what they called a power pole to a starter to make it a two phase starter. Back then it seemed liked nobody bothered to derate wire due to having over 3 current carrying conductors in a conduit.
kwired
Electron manager
- Location
- NE Nebraska
If you only have the one circuit in the raceway, adjustments still apply but pretty good chance adjusted value still doesn't require increasing the size of the conductor, though back at the time you mention 90 deg conductors weren't the standard issue they are today so that would have had some impact the other direction.
While talking about 90 degree rated wire can remember back in the 1960's when type THHH/THWN started be sold in our area. Wire salesmen dropped off samples to my chief electrician dad who immediately ordered some. Local electrical supply house never heard if it and was mad that they were not notified first. Took a sample of #12 & 14 to my Vo Tech shop teacher. At first he did not like it due to such thin insulation ( we only had type TW wire in shops ). Told him that it was oil & gasoline resistant plus approved for higher temperatures. Only bad things too many contractors used #14 THWN for all of their 20 amo circuits. Can remember placing my hand on a conduit that had two phase 5 wire 100 amp feeders that were warm to the touch guessing to not creating conductors.
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