2 Phase electric O.o

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Happy holidays everyone:happyyes:
I looked at a side job this past Wednesday, for a GC I know, and its more of a favor.
His "electrician" hacked multiple feeders and stole the wire. building looks like it was wired by Edison him self:slaphead:
after cleaning all the unused junk out, bring everything involved up to current code.
I want to run 1 feed to a 200amp panel in either parallel or series to a existing one. consolidate all branch circuits into a trough. and my run will be about 120ft after I replace/repair the hacking:happysad:
My questions are in regards to the 2phase;
does voltage drop, conduit, and box fill differ because its 2phase?
same with amps, wire rating/derating?
I guess my real question is..... Is their anything I should know about two phase other then general NEC code? Because theirs two sets of conductors per leg?
Its out dated technology and I cant find any material specific to my need.
Thanks everyone :thumbsup:
 

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kwired

Electron manager
Location
NE Nebraska
Do you have 2 phase service from utility, or is two phase derived on site? (derived on site is probably more likely from what I understand)

What do you have for two phase loads? Primarily two phase motors need a two phase supply, most anything else that may have been designed/supplied by two phase power can run on two single phase circuits. If there are no two phase loads to supply, I would not even mess with trying to distribute the two phase system and just go with a typical single or three phase system.

Good luck finding any new two phase distribution equipment, of course since you live in an area where this kind of system was common maybe your luck will be a little better then elsewhere.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
One thing to keep in mind about two phase (either four or five wire) is that if you use the center point neutral (five wire) you have only four CCCs for adjustment purposes. But even four is greater than three and will force you to calculate ampacity adjustments. Four wires of three phase wye is only three CCCs.
 
The building has to auto transforms(adative polarity) which runs the elevator only using 3 phase. The rest of the building is 4 wire 2 phase. In the pictures I attached the CH panel on the right is the one I plan on refeeding. It's the only non~ pushmatic load center in the building.
Isn't two phase essentially doubled up single phase with 90degree polarity instead of the 180?
My goal is to get this done, brought up to code, and do a quality professional install(as should be all out goals while working :) and try not to charge him an arm and a leg. Thank you everyone I stumbled across this sight and live it TYVM
 

kwired

Electron manager
Location
NE Nebraska
Are you replacing branch circuit wiring or just upgrading service/distribution equipment?

If replacing nearly everything why put back outdated methods other then what is necessary to supply any two phase loads that will still be used? If you were to rewire an old house that had all knob and tube wiring would you replace everything with new knob and tube wiring?

Yes your description of two phase is mostly accurate, but for general purpose and lighting loads you could probably spend much less by going with typical single phase equipment. If you want put in two 100 amp panels instead of one single 200 amp panel (or whatever fits your load needs) and you sort of have same thing when it comes to amount and sizes of copper used, but also most likely spend less on that gear then on something designed for two phase.

Again, is the two phase source from the utility, or is it derived on site, and what actual two phase loads will be powered?

Single phase loads supplied by a two phase source is not worth putting back to two phase - especially if nearly all wiring is being replaced, at least I don't think it would be.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I wonder if there is any place in the US other than Philadelphia that still has two phase distribution !
 

kwired

Electron manager
Location
NE Nebraska
I wonder if there is any place in the US other than Philadelphia that still has two phase distribution !

I wasn't certain if they still did. I thought I once read that any two phase services they do supply are simply derived from three phase distribution via "Scott T transformers"
 
My apologies for bad grammar, I posted before I had my coffee lol. The 2 phase has 4CCC with N Center. I considered coming from the 3 phase line side in the elevator disconnect, in mechanical room. However, then I would need 2 new panels, a disconnect, and 40ft of pipe to reroute the run. I posted to brainstorm the best resolve to the situation. I am a licensed electrician, however I am not stubborn, of it a know it all. Theirs a difference between confidence and arrogance :)
 
Augi47, to the best of my knowledge, Philadelphia is the only place in America were 2 phase 250V still exists. And up until last week, I also thought the same as you in regards to the Scott Ts.
 

kwired

Electron manager
Location
NE Nebraska
My apologies for bad grammar, I posted before I had my coffee lol. The 2 phase has 4CCC with N Center. I considered coming from the 3 phase line side in the elevator disconnect, in mechanical room. However, then I would need 2 new panels, a disconnect, and 40ft of pipe to reroute the run. I posted to brainstorm the best resolve to the situation. I am a licensed electrician, however I am not stubborn, of it a know it all. Theirs a difference between confidence and arrogance :)
That is one possible version of two phase, and AFAIK was most common. There was a two phase three wire system as well, where one conductor was common to both phases.

You must remember that this system is essentially two single phase systems both bonded together at the center taps, but the voltage/currents are not in phase with each other - hence it being called two phase. and it can run single phase loads. It is really only necessary to have this system when you have a two phase motor you need to power. I don't know what kind of expense you will encounter with attempting to obtain two phase gear, but since there is little demand for it I'm guessing it is much more expensive then gear needed to power similar KVA ratings for single or three phase equipment that are produced in much more mass quantities. Keep some of this in mind before deciding what needs to be done.
 
Kwired
I'm only replacing/refeeding the distribution, I don't want to get into rewiring the the building. My load is currently unknown. I didn't have access to half the building. I will tomorrow. Keeping the existing 2? I could use that for any currently unknown loads.I had not considered adding 2 100amp load centers off the existing 200. Thank you very much
Yes the 2 phase is utility supplied
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
I wasn't certain if they still did. I thought I once read that any two phase services they do supply are simply derived from three phase distribution via "Scott T transformers"

Scott T is how they do it, in fact this connection could give any building true 2 phase power.


Also of note, 2 phase has not true neutral. Neutral current doesn't cancel to the same extent, only partly. I think (but mostly likely wrong) its only 1.2 to 1.4 x the sum of current on the other 2 phases but someone will have to confirm.
 

Smart $

Esteemed Member
Location
Ohio
... The 2 phase has 4CCC with N Center.
Technically that's 2? 5W

...Also of note, 2 phase has not true neutral. Neutral current doesn't cancel to the same extent, only partly. I think (but mostly likely wrong) its only 1.2 to 1.4 x the sum of current on the other 2 phases but someone will have to confirm.
It is a true neutral with respect to line conductor sets (i.e opposing rather than adjacent). If a 3-wire circuit supplied identical L-N loads from adjacent lines, the neutral current would not balanced out. The vector sum would be equal to the square root of 2, approximately 1.414 times the line current.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Technically that's 2? 5W


It is a true neutral with respect to line conductor sets (i.e opposing rather than adjacent). If a 3-wire circuit supplied identical L-N loads from adjacent lines, the neutral current would not balanced out. The vector sum would be equal to the square root of 2, approximately 1.414 times the line current.

I was wrong then. Thanks! :)
 

kwired

Electron manager
Location
NE Nebraska
I don't know if there is a proper designation for the points of this system but for this discussion lets call one phase A-B, and the other C-D with both having their midpoints bonded together to make the neutral. If you put line to neutral loads between A and B or C and D they balance out just like on a single phase system. But neutral load from A to N and C to N on same N conductor would be where the current would be additive to the tune of 1.414 factor.
 

kwired

Electron manager
Location
NE Nebraska
Kwired
I'm only replacing/refeeding the distribution, I don't want to get into rewiring the the building. My load is currently unknown. I didn't have access to half the building. I will tomorrow. Keeping the existing 2? I could use that for any currently unknown loads.I had not considered adding 2 100amp load centers off the existing 200. Thank you very much
Yes the 2 phase is utility supplied
What/where are you getting replacement equipment?

I still think getting standard single or three phase equipment to connect non two phase loads to is worth looking at a little harder, especially if actual two phase loads are fairly limited. You mentioned there is an elevator that is three phase - often times from what I have read an elevator is one load that some wish to re-feed with two phase and maybe there is little or no other two phase on the premises - apparently your elevator in this case is no longer original or has had some modifications.
 
The way the mechanical room is set up it's AB red. C is neutral. And DE is blue.
I do plan on using two single phase 100 amp load centers(or smaller) off the existing 200. (Depending on total load I will calculate tomorrow). I had not considered that. TY again.
 
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