# help required regarding resistors connections

#### rizi_85

Joined Dec 26, 2005
6
Hey everyone!
i m new in this field and need some help.

my question is:

if u have a black box containing three resistances, how can u determine that whether these resistors have a ∆ - connection (delta connection) or a Y - connection (wye connection)

thanks

#### kubeek

Joined Sep 20, 2005
5,791
1) mesure resistances between A, B and C ( resistance a is on the other side of triangle than A, like in geometry)
2) If it is delta, then when you apply voltage from C to B, the voltage on A against B should be V*( c/(b+c) )
If it is Y connected, the voltage should be V*(c-b+a)/2a

#### rizi_85

Joined Dec 26, 2005
6

#### JoeJester

Joined Apr 26, 2005
4,390
Rizi,

Are you leaving something out of your question?

Are the resistor values in the delta box and wye box equal? I mean you can put three equal resistors in a wye and three resistors, each equalling to 3X the resistor value used in the wye configuration, connected in the delta fashion that would have the same readings.

Assume the resistors are 1k and do the analysis.

Let us know what you come up with when you do the analysis.

A short treatise is found here.

Be aware of the loading effects if your using very high resistors and the meter is a low ohms per volt.

#### rizi_85

Joined Dec 26, 2005
6
well, i was given this problem in a lab test and unfortunately i couldn't do it.

i was given a black box with three wires coming out of it. nothing more than that was given. resistances were of moderet values.

but the main thing was that i couldn't assume that resistors were of same value as specified by the instructor.

hope now u can understand the problem
thanks

#### kubeek

Joined Sep 20, 2005
5,791
Originally posted by rizi_85@Dec 27 2005, 05:18 AM
well, i was given this problem in a lab test and unfortunately i couldn't do it.

i was given a black box with three wires coming out of it. nothing more than that was given. resistances were of moderet values.

but the main thing was that i couldn't assume that resistors were of same value as specified by the instructor.

hope now u can understand the problem
thanks
[post=12698]Quoted post[/post]​
You could try it in similar way, but with a load resistor conected to the third node. Maybe now there will be som difference.

#### JoeJester

Joined Apr 26, 2005
4,390
Let me see if I got this correct ...

You were given: A black box with three wires and a DMM.

You were asked if the black box was wired delta or wye. Nothing else.

#### rizi_85

Joined Dec 26, 2005
6
yea u r rite!

i was given a black box and a DMM and i had to tell that whether box is wired delta or wye.

#### rizi_85

Joined Dec 26, 2005
6
sorry one thing i forgot,

i was also given a DC power supply along with black box and DMM

#### JoeJester

Joined Apr 26, 2005
4,390
Well, I'm sure your lab assistants could answer the question in the following diagram.

One of those boxes is wired delta and one is wired wye. Let them choose, giving them the box, a DMM, and a power source.

They got a fifty-fifty chance. You can even tell them the delta connections have resistors that are 3x the value of the resistors used in the wye connected box.

#### JoeJester

Joined Apr 26, 2005
4,390
Don't get me wrong, if you knew on thing about the resistors, you'd solve it easily. Refer to the diagram below:

#### rizi_85

Joined Dec 26, 2005
6
Originally posted by JoeJester@Dec 28 2005, 12:03 AM
Don't get me wrong, if you knew on thing about the resistors, you'd solve it easily. Refer to the diagram below:
[post=12720]Quoted post[/post]​
thanks very much

i'll analyse these diagrams but still i have one question.

how can we analyse the box if the resistors are NOT of same values?

#### JoeJester

Joined Apr 26, 2005
4,390
how can we analyse the box if the resistors are NOT of same values?
I would say ... visually.

The other way would be to have published knowns of what to expect under the normal operating conditions and troublehoot a faulty circuit ... or we would be working with a schematic with known values.

You should be able to show your analysis work ... so someone could grasp your anaylitical process.