Voltage Ratings: 110/115/120, 220/230/240 or 440/460/480

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Engineer
I've actually proposed the full 6 coil 'hexaphase' setup for things like apartment buildings ...
It would also be handy for large DC loads such as VFDs and battery chargers -- you could hook up six phases to a six-pole rectifier and end up with so little voltage ripple that you'd hardly need a filter capacitor. (although the current ripple and the third harmonic might be problematic)
 

Besoeker3

Senior Member
Location
UK
Occupation
Retired Electrical Engineer
It would also be handy for large DC loads such as VFDs and battery chargers -- you could hook up six phases to a six-pole rectifier and end up with so little voltage ripple that you'd hardly need a filter capacitor. (although the current ripple and the third harmonic might be problematic)
We have those for aluminium anodising plants. These were 24-pulse systems. The lowest harmonic was the 25th.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
240/120V three phase delta is another name for 'high leg' delta. This is a 240V delta with the mid point of one phase coil tapped and grounded to provide 120V line to 'neutral'. But you only get 2 of the 3 phases giving 120V to the grounded conductor; the other phase gives 208V to the grounded conductor. The 208V is simply not used.

The grounded conductor is 'neutral' to the two 120V phases, but not 'neutral' to the complete 3 phase set.

You of course cannot have all three phases at 120V to the grounded conductor in a nice symmetric three phase arrangement while at the same time getting 240V phase to phase.

There are variations on this form of service, eg. and 'open delta' which is used with mostly 120/240V single phase loads, with a 'stinger' to provide the 3rd phase for a small amount of 3 phase loading. Another version is a symmetric 240V three phase system tapped for grounding and to provide for a small amount of 120V loading.

-Jon
And of course I know all that. My point was that if there is a true neutral for a 240V three phase system, the voltage from all three phases to neutral cannot be 120V.
 

jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
240/120V three phase delta is another name for 'high leg' delta. This is a 240V delta with the mid point of one phase coil tapped and grounded to provide 120V line to 'neutral'. But you only get 2 of the 3 phases giving 120V to the grounded conductor; the other phase gives 208V to the grounded conductor. The 208V is simply not used.

The grounded conductor is 'neutral' to the two 120V phases, but not 'neutral' to the complete 3 phase set.

You of course cannot have all three phases at 120V to the grounded conductor in a nice symmetric three phase arrangement while at the same time getting 240V phase to phase.

There are variations on this form of service, eg. and 'open delta' which is used with mostly 120/240V single phase loads, with a 'stinger' to provide the 3rd phase for a small amount of 3 phase loading. Another version is a symmetric 240V three phase system tapped for grounding and to provide for a small amount of 120V loading.

-Jon
A huge red flag if you go into a panel and see every 3rd space skipped. I've known guys to terminate a circuit, not realizing it's a high leg. Some people have never seen a high leg panel, may not have heard of it.
 

paulengr

Senior Member
A huge red flag if you go into a panel and see every 3rd space skipped. I've known guys to terminate a circuit, not realizing it's a high leg. Some people have never seen a high leg panel, may not have heard of it.

About a year ago city engineer said panel is 480. Pump says 460/230 so no reason to question it. I get handed a 50 HP 480 V VFD and ticket that says put it in. So I open panel and see red, orange, blue…hmm, very odd color scheme. Which of course turns out to be high leg delta. So job is done before I even get started,

My own screw up about a month before is I’m at a machine shop with an ancient 50 HP DC motor running on an MG set (Ward Leonard). The shop is 480 based on previous experience and there’s almost no telling what this antique uses easily. So I do all the conversion work, energize the breaker, test with my meter and…oh crap, 230. Turns out one side of shop is 230 the other 480. I had to think real hard but there was such much else on this big lathe I would have to modify we just ate the drive.
 

jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
About a year ago city engineer said panel is 480. Pump says 460/230 so no reason to question it. I get handed a 50 HP 480 V VFD and ticket that says put it in. So I open panel and see red, orange, blue…hmm, very odd color scheme. Which of course turns out to be high leg delta. So job is done before I even get started,

My own screw up about a month before is I’m at a machine shop with an ancient 50 HP DC motor running on an MG set (Ward Leonard). The shop is 480 based on previous experience and there’s almost no telling what this antique uses easily. So I do all the conversion work, energize the breaker, test with my meter and…oh crap, 230. Turns out one side of shop is 230 the other 480. I had to think real hard but there was such much else on this big lathe I would have to modify we just ate the drive.
So much stuff we don't see until we're in the middle of it. Too much out there to teach and warn about; something will be overlooked.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Engineer
... Turns out one side of shop is 230 the other 480. ...
My apologies for the duplication, but
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Yes, it's quite common to see something like this in older facilities that have had additions & upgrades over the years. Any time it's not new construction, troubleshooters need to contemplate the history of the building.

My first encounter with something unconventional was corner-grounded 480. I was called in to troubleshoot a recently-installed big VFD which refused to start. It said "phase loss", but the bewildered tech had measured ~480 L-L on all three phases. I later learned that the building was built during World War II and that CGD was a wartime-expediency materials-conserving measure -- motor starters had two contacts and two fuses each, plus a grounded (white) wire. Of course, by the time we worked on it, it was almost impossible to distinguish any colors of the old cloth-covered wire.

My all-time favorite has to be an airplane that had a 14-volt electrical system on the left engine and a 28-volt system on the right. Also a 190Y110-volt generator that provided about 50-60-70 Hz, depending on how fast the engine was turning, and another one that provided ~400 Hz. It wasn't a kludge or a partial upgrade; it was the test-bed airplane for an avionics firm; the intent was to provide the capability to hook up and test absolutely anything that came along, including oscilloscopes and spectrum analyzers that were designed for indoor laboratory use.
 

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
Great post, this standard at one point was going to be used by almost all the Americas but now its shrank back to just the US.
and all of our neighbors to the south pretty much follow something similar except one thing
they use 220Y/127 instead of 208Y/120.
It would be cool to see the equivalent chart/ standards that they use south of us say in Mexico or Brazil.
I did a lot of remote cellular telephone equipment shelters in Argentina. Some of those shelters has to be located at the local telephone exchanges. I found that they used all 220 volt tools and appliances, their neutral conductors were blue, and they didn't see the need for equipment bonding conductors in feeder circuits to other buildings. Nor did they see any need for a grounding electrode system at the second building.
 

Flicker Index

Senior Member
Location
Pac NW
Occupation
Lights
Remember old school things that were rated 117 and 118v ?
Oh and there are some third world countries with 127v power, derived from 220Y/127
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
My first brush with real weirdness was when my partner and I moved our integration business into a building in Seattle that had been built as a railroad service foundry in 1899 without electricity, then electricity was run to it sometime in the early 1910s. When we scoped out the building, there was a 480/277 panel, so we assumed that the other panels were subs from that. But we kept getting weird readings on the 480V lines and some of the subs, so I went up on the roof to get a good look at the pole pigs (the power pole was in the middle of the building, likely because they had added onto the original structure and wrapped around the pole). I saw only two transformers, one big and one small, with just two wires coming off the primary lines. I knew about open delta and I knew about 4 wire high leg delta, but only for 240V and we had 480/277. Turned out the original service was 240/120V 3ph 4 wire open delta, something I did not know existed. That then also meant that somewhere buried in the bowels of that building there must be a 480Y transformer. Took us a few hours to find it (wiring was nuts in there), a 75kVA in a dry sump covered with a diamond plate solid top, so the transformer was just cooking away in there. It had turn-to-turn shorts inside and the insulation was basically crumbling off of the line and load cables.

The Landlord refused to pay for anything regarding that, kept thinking it was a “utility problem”, which of course it wasn’t and even though my partner was a registered PE, he refused to accept that he had to pay to fix anything that had to do with electrical power, he said that was our problem. We ended up calling the Fire Marshall, who condemned the building until that was fixed. Because of the pole being in the middle of the building, Seattle City Light wouldn’t give it a new 480V service drop, or even ANYTHING new, so the landlord had to pay to have them put in a new pole on the corner of the street to drop a new service.

We didn’t change anything with the old service drop, we just tied the new 480 service into the existing 480 panel and disconnected the circuit to that burned out 240-480V step up transformer, assuming we would have to put in a little single phase tranny for the lights and plugs. Found out later though that City Light never disconnected the old service (probably because it was too old for their records), but since there was only the one new service drop assigned to our address, there was only the one meter being read and of course only one bill. So we ended up with free power for the 120/240V loads. I just took a look at a satellite map of that building, the pole in the middle is no longer there so someone eventually figured it out but we had that for over 3 years that way.
 

mlnk

Senior Member
What about a 240/120 4-wire transformer that has three 120-volt-to-ground legs with no stinger? Is that called a delta or wye?
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
What about a 240/120 4-wire transformer that has three 120-volt-to-ground legs with no stinger? Is that called a delta or wye?
It is called nonexistent.
It sounds like you are describing a 240V delta transformer with 120Vcenter taps on all three legs. The NEC would require these taps to be grounded, but they are not electrically the same point as a wye neutral so connecting them together would not provide a true common point.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
It is called nonexistent.
It sounds like you are describing a 240V delta transformer with 120Vcenter taps on all three legs. The NEC would require these taps to be grounded, but they are not electrically the same point as a wye neutral so connecting them together would not provide a true common point.

As you note the three centerpoints of the three windings in a Delta secondary are not electrically at the same point.

If you connect them together it would be a bolted fault at half the voltage of the delta. I'd expect rapid dissipation of any magic smoke contained in the transformer.

Jon
 

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
It sounds like you are describing a 240V delta transformer with 120Vcenter taps on all three legs. The NEC would require these taps to be grounded, but they are not electrically the same point as a wye neutral so connecting them together would not provide a true common point.
Those three points would be a dead short between three phase windings which are always at different voltages relative to each other. The results of energizing such an assembly would be fun to watch but only from a safe distance.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
As you note the three centerpoints of the three windings in a Delta secondary are not electrically at the same point.

If you connect them together it would be a bolted fault at half the voltage of the delta. I'd expect rapid dissipation of any magic smoke contained in the transformer.

Jon
Unless it was a “6 wire” system where all of the center points were ungrounded and run with separate conductors. Then of course they would not be grounded conductors, so you couldn’t use white, which means having 6 different colors, also not including green. Black, red, blue, brown, yellow, then what? Purple or pink? Stripes? Whew, what a mess that would be in a residential installation. Can you imagine all the extra confusion that would create in the DIY crowd? Good thing that is non-existent…
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Unless it was a “6 wire” system where all of the center points were ungrounded and run with separate conductors.
Of course, in a 6-wire system like that, one of the center points could be grounded if desired. But there is no requirement to ground it, as 250.20(B)(3) is restricted to 4-wire deltas.

Which means BTW, that if you ever want to have a 120/240V delta system that is ungrounded (for whatever reason), you could do that by using a 5-wire or 6-wire system has has center taps on more than one coil.

Since we're talking about unusual systems, you certainly can create a "240/120 4-wire [system] that has three 120-volt-to-ground legs with no stinger," it just won't be a delta. If the primary is 3-phase, just add another phase to a 120/240V 3-wire secondary system, at some angle to the single phase already present. 60/120 degrees would be easy to do with two transformers. Or you could get 4 wires out of the usual 5 wire 240/120V 2-phase system.

Cheers, Wayne
 
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