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Originally Posted by Homeownerinburb
The high leg will be the square root of the voltage from phase A to C squared minus A to N squared
240 squared minus 120 squared then find the square root of this
57600 – 14400 = 43200 squared root = 207.846 volts on the high leg
The only color code required by the NEC is that the high leg be orange.
The engineer tells me this is delta.
When I walked the job last week, I did not get to see any 240v work, but there were some 120v faceplates not installed, and I saw red and black.
I think I will go with black, orange and red. It seems to be the standard that the building is wired to and seems common enough that any electrician with an active brain should understand it.
This is a small shop system. One ground, one neutral. There is a 'stinger' wire that is only used with the other 240 volt to ground wires to feed three phase appliances. Its perhaps 270v to ground. You get 240 volts between the other 2 wires and 120 volts from either of those 2 wires to ground. Its sort of a 'fake' three phase because it uses just 2 transformers. One must be careful on placing breakers to balance the loads. We had one set of transformers blow up already and cause quite a fire. This is why they advise you to try and stay inside 15 HP motors, we can run 30 HP+ but not start them at the same time.
There is NO 208v available in the panel. Its a great system.
And again, why not downside feed wire size to the panel considering one has 3 hot wires? Especially one at 270 volts?
Last edited by ballvalve; 07-16-2012 at 01:45 PM.
You have three phase OPEN delta (two transformers), which never when used correctly delivers 208 or 270.
Yes, balancing is difficult and you will probably never achieve it completely. The wild leg will always get less use than the other two phases, because the other two phases are the only source of 120v to the neutral. Even if you do not use the two low legs to produce 240v, they will always be working harder than the wild leg, if you have any 120v loads.
You cannot use the wild leg to neutral to achieve 208v because then you would be running thru one winding on one of the transformers and half way thru another winding on the other transformer. It is very untidy.....
It's called an Open Delta. It is real three phase power; nothing fake about it. At one time it was a very common system and is still used today.
You don't have 270V anywhere. That is impossible. Depending on your supply voltage you could have 214V high leg to ground.
I suppose the stinger leg could be smaller. I don't know if it is allowed by code or not. JW are you out there?
There is required by code, and then there is custom and practice, which, I grant you, is an amorphous thing.
Where the 3 phase is being used to mostly deliver 120/240, in what is essentially the equivalent of single phase practice except that we have a third leg to give us some more options on the 240 and the potential to deliver 3 legs at 240 (there is a water heater going in), then black and red for the two low phases and orange for the high phase would not mix up even a home remodeller like me.
And it seems to be what the rest of the building was wired to, and it seems to me that is very important, assuming it is not stupid in some way.
As I have posted many times.....I work in the backup generator field in the NY-NJ area. We service and repair units from 5-10 KW all the way up to very large units over 500 KW
We have 120/240 3 phase in our building.....It is Delta and one leg to neutral is about 210V while the others are 120.
Any 2 will be 240
We supply generators when needed to buildings thruout the area.
Most buildings are 120/208 Low Wye or 277/480 High Wye....
The color code usually used is black, red and blue for the lower voltage (120/208) and brown, yellow and orange for the higher voltage( 277/480).
I can reconnect most any 12 lead reconnectable generator for either voltage and have many times. I can also do one for the 120/240 Delta configuration and did that on a 400 KW unit that we use for our own building.....
We have rarely serviced or worked on or seen pretty much anything other than the 3 voltages I mentioned and we cover a lot of area......
Orange is strongly suggested by code, but not required. Best to follow what is common in your area.
110.15 High-Leg Marking
On a 4-wire, delta-connected system where the midpoint of
one phase winding is grounded, only the conductor or bus-
bar having the higher phase voltage to ground shall be dura-
bly and permanently marked by an outer finish that is orange
in color or by other effective means. Such identification
shall be placed at each point on the system where a connec-
tion is made if the grounded conductor is also present.
The only time the high leg will see current will be on a three phase appliance or a single phase appliance that does not utilize the neutral. It must be able to carry the same current as the other line that is supplying one of these loads in the event of a short circuit. This is the reason that it must be sized the same as all the other ungrounded conductors.
RED LEG Delta is what I call it and thats how I ID it.....with red tape....
"It"?
Sorry, what is the it? The phase that is 208v to the neutral between the other two phases?
I'd certainly not use red. It is very traditionally the opposite end of the phase in single phase from the black.
Which is why I like having the two low phases in open delta red and black. They make sense with 120v for me.
Seems like sometime back in the 70's the high leg was labelled red. I'm not sure. I was not pulling wire in the 70's. I was playing with army men and doing anything I could to got out of going to school.
I was trying to get smoochy with girls.
Series High Delta 120/240 60 Hz 3 Phase power. My voltage reconnection chart tells me I could make that 139/277. I assume it too would have a "high" leg to neutral since it is the same wire configuration and that is a voltage that must be used somewhere but not around here. All one would need to do is adjust the voltage regulator to get to that output voltage on a generator assuming it (the regulator) was capable of running at that odd voltage. As I said.....Black, Red, Blue are the colors used on 120/208 or 120/240 voltage power being supplied in buildings in this area.
We use red to ID the higher phase to neutral. Red stands out and I like it that way....Unless your colorblind you should be able to quickly recognize this is a good way to ID a phase that should not be used with a neutral to create a circuit.
You do whatever you like or is required in your area......
The internal parts of a generator are outside the scope of the NEC but once it leaves the generator it must comply with the NEC.
As Dave has pointed out with his post of 110.15 of the NEC if a color is used to identify the high leg it MUST be orange or if one wanted they could put a tag on it that shows that it is the high leg.
The only other colors that are mandated by the NEC is white or gray for the grounded neutral and green or green with yellow strips for the equipment grounding conductor.marked by an outer finish that is orange in color or by other effective means.
The ungrounded (hot) conductors can be any color that the installer chooses. It has been a standard of practice (SOP) throughout the country to use Brown Orange and Yellow for 480/277 but then if there is a transformer that steps this system down to a 240/120 delta system then the orange color cannot be used for the 480/277 as the high leg of the 240/120 will be required to have this orange color. If the high leg of the 240/120 is identified with a tag the 480/277 still can’t be orange as this color is set aside to identify the high leg. If the building does not have a system with a high leg and is supplied with only a 480/277 wye system then the use of the “BOY” is allowed although I strongly object to this SOP (standard of practice).
I have installed many of a system using the standard black color that the conductors of size 4 and larger comes in and identify the phases using marking stickers as Phase “A”, Phase “B”, and Phase “C” looking at the panel from the front from top to bottom, left to right, or front to back.
In the premises wiring system electricians are not allow to just choose which color they want to use to identify the high leg, neutral, or the equipment grounding conductors. These conductors are mandated as to what color is to be used by 110.15 for the high leg, 200.6 for the neutral, and 250.119 for the equipment grounding conductor.
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