# help required regarding resistors connections

Discussion in 'General Electronics Chat' started by rizi_85, Dec 26, 2005.

1. ### rizi_85 Thread Starter New Member

Dec 26, 2005
6
0
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

2. ### kubeek AAC Fanatic!

Sep 20, 2005
4,670
804
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

Dec 26, 2005
6
0

4. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,373
1,159
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.

5. ### rizi_85 Thread Starter New Member

Dec 26, 2005
6
0
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

6. ### kubeek AAC Fanatic!

Sep 20, 2005
4,670
804
You could try it in similar way, but with a load resistor conected to the third node. Maybe now there will be som difference.

7. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,373
1,159
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.

8. ### rizi_85 Thread Starter New Member

Dec 26, 2005
6
0
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.

9. ### rizi_85 Thread Starter New Member

Dec 26, 2005
6
0
sorry one thing i forgot,

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

10. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,373
1,159
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.

11. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,373
1,159
Don't get me wrong, if you knew on thing about the resistors, you'd solve it easily. Refer to the diagram below:

12. ### rizi_85 Thread Starter New Member

Dec 26, 2005
6
0
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?

13. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,373
1,159
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.