INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

230 single phase A\C running on 460 3 phase circuit- OK?

230 single phase A\C running on 460 3 phase circuit- OK?

(OP)
Is there any reason I should not use 1 leg of the 460 three phase circuit and ground to run a single phase 220 Air condition unit.

Employees at the School maintenance report they do this all the time. If this is true then I connect nothing to the ground on the unit or the same ground I am using with the hot for the 220.

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

In the U.S., using the ground as a neutral is a HUGE code violation. If you have a neutral from your 3 phase instead of the ground, then you're going to supply your 240 a/c with 277 volts. 15% over sounds like trouble to me, but maybe the a/c units you're talking about are rated for that voltage.

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

First, ground is not the same as a neutral. No current should ever be intentionally run through ground.

Second, the voltage to ground is 277 (at minimum) not 230.

Many more reasons, wait to read them.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

(OP)
thank you John2025 and DRWeig. I should have said neutral and not ground, my big mistake, also can not wait to hear more reasons not to do this. The fact that I do not understand how 1 hot and neutral works the same as two hots shows my limited knowledge of electricity, and I actually until now thought I was more knowledgeable. It is true I have never worked with 460 before. thank you both,

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

If this is a 480 Volt, four wire delta system then you can connect from a phase to neutral to get 240 Volts, as long as you don't get the wild phase.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

In addition to DRWeig's reasons, potentially defeating the earthing protection is another one - the earth leakage device may be triggered on core balance (sum of all the phase currents), or it might be triggered on neutral current. In either case, adding a load from phase to neutral might make the protection more or less sensitive giving spurious trips or less protection respectively.

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

(OP)
waross, Thank you for your response.
Please explain a little more. From four wire delta system i can get 240. but with another system I would get 277 with one phase a neutral. So I just meter it and if it is 240, I can connect it to the unit 1 phase and a neutral where I would normally connect two hot wires in my single phase system, yes?

Secondly, again not being familiar with the 460 system.(and by the way, now I am just wanting to know. I have turned the project over to someone else.) The idea of neutral vs. ground in my panels they are both connected to ground, so how are they different.

Liteyear, thank you for response. I know of no earth leakage device in the system.

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Ground is for safety, the ground conductor does not carry current in normal circumstances. Neutral is a current-carrying conductor in normal circumstances.

They're connected together in the panel only.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Years ago large air conditioners were only available with three phase motors. The basic single phase service is a transformer with a 240 Volt secondary winding that is center tapped to give 120 Volts as well as 240 Volts. Hence two hots and a neutral. The neutral is grounded so that a short from hot to ground will have the current return through the neutral and trip the breaker or blow the fuse.
Now the owner of the mansion wants a large air conditioner and requires three phase,- or the farmer or shop owner wants to run a large pump or other machine which requires a three phase motor. A second transformer would be added in an open delta configuration to supply three phase power at 240 Volts.
The third wire was called the wild leg or high leg. The voltage from the two original lines to the neutral will still be 120 Volts but the voltage from the third leg to the neutral will be 208 Volts.
This may be scaled up to 240:480 Volts. I have seen this often in Central America but it is a rare connection in North America.
In this case the wild leg will be 416 Volts to neutral.
Note some old texts give the wild leg voltage as 190 Volts or 198 volts. Those figures date from the days when the standard voltages were 110:220 Volts or 115:230 Volts (with rounding errors).

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

These types of posts should simple end with "You should contact a licensed electrician as you are clearly not qualified to be doing such work"

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

(OP)
thanks to all of you for this information.

Mr. mcgyvr
Perhaps my desire to learn a bit more about the subject was an abuse of the system and in some way inconvenienced you or others. For this I offer an apology.
Or perhaps you missed the entry where I stated I had already turned this project over to someone else but just wanted to follow up with the final questions.

Either way, I have enjoyed being able to come here from time to time and seek advise as I am charged with responsibilities in my job beyond my ability. I recognize this, seek help where reasonable and get help when I find, as in this case, it is needed.

This may be one of those instances the rules instruct that we use emoticons instead of words, if so, sorry for that to, but the comment seemed a bit peremptory.

thank you,
J Rick.

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Hello Gentleman

Is an air conditioner designed for a single phase system which is looking to see current at 180 degree phase angle
negatively affected when hooked up to a three phase system now seeing current at 120 degree phase angle?

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Quote (flexoprinting)

Is an air conditioner designed for a single phase system which is looking to see current at 180 degree phase angle
negatively affected when hooked up to a three phase system now seeing current at 120 degree phase angle?

No. Not at all.

Keith Cress
kcress - http://www.flaminsystems.com

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Ok, Thank's Keith.

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

I thought that motors only saw current at 180 degrees when they were forced over-speed and went into regeneration. If we can do that with an A/C unit we may have broken the over unity barrier some new and challenging effects here.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Give me a break Bill, I'm a machine Tech. not as clever as you folks. You know what I meant. blush

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Point taken flexoprinting.
I probably should have answered:
The voltage phase angle between three phases is 120 degrees. It is derived by combining three single phase sources that are displaced 120 degrees from each other.
A single phase voltage has no reference voltage to be displaced from. Sort of like asking "What's the difference between a bicycle?"
Now as to the phase angle between the voltage and the current: That depends on the load for either single phase or three phase circuits and loads.
For most loads the angle of the current may be between minus 90 degrees and plus 90 degrees depending on if the load is inductive or capacitive.
Some motor applications may be an exception. Loaded down-hill conveyors, electric cranes lowering heavier loads and induction generators come to mind. When an overhauling load drives an induction motor much above synchronous speed the current angle relative to the voltage may exceed 90 degrees. At that point the motor is regenerating and returning energy to the source. To make it more fun, there may be magnetizing current at 90 degrees lagging flowing into an induction generator while real current at 180 degrees flows out of the induction generator or motor.
Not going to happen with an AC unit.
From time to time we get OPs with over-unity (perpetual motion) schemes. My previous comment was more aimed at those posters. grin
Keith said it best:

Quote (itsmoked)

No. Not at all.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Well.. Perhaps I was a bit wordy. LOL

Keith Cress
kcress - http://www.flaminsystems.com

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Hey there Bill [et al],

Re the wild legs / open delta thing you mentioned earlier: my old books talk about Scott connections, T connections, 'teaser transformers' and so on being used to 'kluge' / fudge / cheat / cajole three-phase power supplies from a single-phase source.

I've never claimed to score 100% in comprehension, so I'm wondering if what you're referring to is the same sort of thing...

Thanks!

Carl

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Hello crshears [et al];
No relation to the Scott, or Fortesque connections. These were used primarily to convert between two phase (at 90 degrees angle) and three phase (at 120 degrees angle).
Delta connections at the load side have fallen out of use for utilization. There are still legacy installations and the odd new installation. There is a niche filled by the open delta which is still in use.
You are familiar with the common (in North America) 120:240 Volt center tapped transformer used for residential and small commercial installations.
You are familiar with the delta connection.
Now consider a 240 Volt delta (full delta or open delta) transformer secondary, With phases labelled "A", "B", "C".
A 120:240 V distribution transformer is used from "A" to "C".
The center point is grounded and the transformer will supply a normal single phase load.
However a three phase panel is used. When single phase loads are connected, every third breaker position is unused.
Three phase loads use three consecutive breaker positions.
This arrangement allows us to service 120:240 Volt single phase loads and 240 Volt three phase loads from the same transformer bank and the same panel.
It may help to draw a vector sketch.
With this arrangement the single phase voltage from ground and/or neutral to "B" phase is 208 volts and is called the "Wild" leg.
Single phase loads are generally NOT connected to the wild leg.
An installation may be a combined single phase and three phase panel, a single phase panel (with the wild leg not brought to the panel), and a three phase panel with a wild leg with a higher voltage to ground on one phase or a mix of single, combined and three phase panels.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Gotcha, Bill, and thanks; in the past I've thrown together concepts using that scheme. It might even be of use on board...?

CR

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

For awhile twenty some years ago, three phase lighting transformers at 480:120/208 Volt and in the 25 KVA or 37.5 KVAs range were supplied with two transformers in "T" configuration. I was never able to find out what the advantages were of this connection. I haven't seen a new one for years.
The connection was similar to, but not identical to a Scott connection. The neutral was supplied from a tap on one of the transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Can't say I recall seeing a beast like that ever...not that I was thinking of doing anything like that; my reference was to if we transition to an actual three-phase supply being brought on board, of which there suddenly is a slight possibility due to an unexpected but positive change in local circumstances...

CR

RE: 230 single phase A\C running on 460 3 phase circuit- OK?

Availability depends on the policies of the local utility. The old school solution to the need for a small amount of three phase power in addition to a large amount of single phase power is an open delta connection. The open delta avoids the issues found with a wye:delta bank when the delta is closed.
In jurisdictions where the open delta is used, you may see a 50 KVA or 100 KVA distribution transformer feeding a number of single phase loads at 120:240 Volts. Next to it on the pole will be a 5 KVA transformer in open delta to feed a small three phase service at 240 Volts delta.
One installation that I used to see often was a small machine shop with three phase motors situated in a predominantly residential area.

Bill
--------------------
"Why not the best?"
Jimmy Carter

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close