real world a/c resistance

[rambojoe]

ok. I really tried to find my answer but web searches only brings up formulas that involve "on paper" properties if you will- as in conductor length, cross section area and temp and such. bear with me because I genuinely want to elevate my status from a mere pipe bending "mechanic.
the question is resistance of conductors and how to measure it on the job from load center to, say, light pole base 185' away (with ballast leads disconnected). on the job im sure I could play around with my meter and find my answer but if I spent a few hours educating myself it would be followed with the foreman asking "what the heck are you doing?!"
I can use my ammeter and figure out total power and amps easily but id like to know the ohms of 2 wires w/o all the length and diam. formulas.
so...using ohs law, I should be able to measure E & I at the loadcenter and compare at the light pole base (except with the ballast isolated I cant get I) and find resistance. right? or is simply using the multi meter between the conductors what I want?
Im sorry if im over thinking this...thank you for reading. Again,just looking for a quick way to find resistance of two conductors on the job....

 

[kwired]

ok. I really tried to find my answer but web searches only brings up formulas that involve "on paper" properties if you will- as in conductor length, cross section area and temp and such. bear with me because I genuinely want to elevate my status from a mere pipe bending "mechanic.
the question is resistance of conductors and how to measure it on the job from load center to, say, light pole base 185' away (with ballast leads disconnected). on the job im sure I could play around with my meter and find my answer but if I spent a few hours educating myself it would be followed with the foreman asking "what the heck are you doing?!"
I can use my ammeter and figure out total power and amps easily but id like to know the ohms of 2 wires w/o all the length and diam. formulas.
so...using ohs law, I should be able to measure E & I at the loadcenter and compare at the light pole base (except with the ballast isolated I cant get I) and find resistance. right? or is simply using the multi meter between the conductors what I want?
Im sorry if im over thinking this...thank you for reading. Again,just looking for a quick way to find resistance of two conductors on the job....

You can measure resistance that way - but that is DC resistance. AC has a thing called reactance that will effect the overall impedance as well.

 

[Carultch]

You can measure resistance that way - but that is DC resistance. AC has a thing called reactance that will effect the overall impedance as well.

So if I use an oscilloscope to measure voltage across the source, voltage across the load, and the current in the circuit, how can I look at the respective graphs, and calculate the effective "AC resistance"?

 

[rambojoe]

ok thankyou. I just hope I can be able to find the answer w/o needing a tool I've never heard of! that's the point- to be able to use my trusty fluke and not crazy formulas....I assume voltage drop will come into play here some how.
on another note- I have found my ohm meter useful for finding broken strands on service calls. and thanks for accepting my question, again it is genuine. I was afraid to ask...once I figure things out im happy. hell, I still cant stand the whole "garden hose " analogies and "the eagle flies over rhode island and pie" stuff. although the latter isn't too bad...

 

[luckylerado]

ok. I really tried to find my answer but web searches only brings up formulas that involve "on paper" properties if you will- as in conductor length, cross section area and temp and such. bear with me because I genuinely want to elevate my status from a mere pipe bending "mechanic.
the question is resistance of conductors and how to measure it on the job from load center to, say, light pole base 185' away (with ballast leads disconnected). on the job im sure I could play around with my meter and find my answer but if I spent a few hours educating myself it would be followed with the foreman asking "what the heck are you doing?!"
I can use my ammeter and figure out total power and amps easily but id like to know the ohms of 2 wires w/o all the length and diam. formulas.
so...using ohs law, I should be able to measure E & I at the loadcenter and compare at the light pole base (except with the ballast isolated I cant get I) and find resistance. right? or is simply using the multi meter between the conductors what I want?
Im sorry if im over thinking this...thank you for reading. Again,just looking for a quick way to find resistance of two conductors on the job....

If you know the length just go to Chapter 9 table 8. The resistance per 1000 foot is right there for the taking. Calculating it from measured amps and volts will yield an answer in ohms but as stated earlier this is not all resistance. Some of that opposition to current flow is due to impedance and capacitance resulting in reactance which is measured in ohms and when all tolled (inductive reactance plus capacitive reactance plus resistaance) is expressed in ohms as impedance.

Good info but how do you apply it to the field? Voltage drop calcs do not consider impedance as far as I know.

I think I would leave the oscilloscope on the bench. Might be a good lab though for a power factor and phase angle lesson.

 

[iwire]

ok thankyou. I just hope I can be able to find the answer w/o needing a tool I've never heard of! that's the point- to be able to use my trusty fluke and not crazy formulas....I assume voltage drop will come into play here some how.
on another note- I have found my ohm meter useful for finding broken strands on service calls. and thanks for accepting my question, again it is genuine. I was afraid to ask...once I figure things out im happy. hell, I still cant stand the whole "garden hose " analogies and "the eagle flies over rhode island and pie" stuff. although the latter isn't too bad...

I would be very very surprised if a standard ohmeter could find broken strands. You need a much more sensitive meter for that.

 

[Strathead]

ok. I really tried to find my answer but web searches only brings up formulas that involve "on paper" properties if you will- as in conductor length, cross section area and temp and such. bear with me because I genuinely want to elevate my status from a mere pipe bending "mechanic.
the question is resistance of conductors and how to measure it on the job from load center to, say, light pole base 185' away (with ballast leads disconnected). on the job im sure I could play around with my meter and find my answer but if I spent a few hours educating myself it would be followed with the foreman asking "what the heck are you doing?!"
I can use my ammeter and figure out total power and amps easily but id like to know the ohms of 2 wires w/o all the length and diam. formulas.
so...using ohs law, I should be able to measure E & I at the loadcenter and compare at the light pole base (except with the ballast isolated I cant get I) and find resistance. right? or is simply using the multi meter between the conductors what I want?
Im sorry if im over thinking this...thank you for reading. Again,just looking for a quick way to find resistance of two conductors on the job....

Since you are asking what you consider a serious question, please answer this one.

Why are you asking? Or what are you trying to accomplish that requires this answer? I am a decent electrician and goo troubleshooter. For that, I have never needed more than Ohms law and DC resistance to obtain enough data to find problems on the level that field electricians need.

 

[ActionDave]

ok thankyou. I just hope I can be able to find the answer w/o needing a tool I've never heard of! that's the point- to be able to use my trusty fluke and not crazy formulas....I assume voltage drop will come into play here some how.
on another note- I have found my ohm meter useful for finding broken strands on service calls. and thanks for accepting my question, again it is genuine. I was afraid to ask...once I figure things out im happy. hell, I still cant stand the whole "garden hose " analogies and "the eagle flies over rhode island and pie" stuff. although the latter isn't too bad...

I can't do much math and what I can do I do as little of as I can, but being able to do basic Ohms Law calcs is important.

 

[ggunn]

If you know the length just go to Chapter 9 table 8.

Table 8 is DC resistance. For AC resistance (impedance @ 60Hz) use Table 9.

 

[rambojoe]

Since you are asking what you consider a serious question, please answer this one.

Why are you asking? Or what are you trying to accomplish that requires this answer? I am a decent electrician and goo troubleshooter. For that, I have never needed more than Ohms law and DC resistance to obtain enough data to find problems on the level that field electricians need.

fair enough question. I have odd ways of learning things before I can say "yes, I know this subject with a complete understanding" its just another obstacle in understanding in MY WAY of how P I E and R really works together. again, bear with me! and more in motorcycle trouble shooting, I have found connectors that only had a few strands remaining in the crimp part with my ohm meter. it had very high resistance. im trying to find a way to not use the tables- merely get a actual reading in the field. there has to be instances when the table is different than what is installed- say a backhoe ripping a pipe and pulling the conductors down the hand hole and pulling connections apart. now im not really sure....I just have a desire to better understand and MEASURE resistance in a circuit. its just self education, the hard way

 

[Strathead]

fair enough question. I have odd ways of learning things before I can say "yes, I know this subject with a complete understanding" its just another obstacle in understanding in MY WAY of how P I E and R really works together. again, bear with me! and more in motorcycle trouble shooting, I have found connectors that only had a few strands remaining in the crimp part with my ohm meter. it had very high resistance. im trying to find a way to not use the tables- merely get a actual reading in the field. there has to be instances when the table is different than what is installed- say a backhoe ripping a pipe and pulling the conductors down the hand hole and pulling connections apart. now im not really sure....I just have a desire to better understand and MEASURE resistance in a circuit. its just self education, the hard way

OK then...

First and foremost, in an AC circuit, it is impedance that really matters. BTW, the motorcycle you mention is DC so it is a little easier. This is the sum of resistance and reactance. That is important, because unless you have voltage on the circuit, you will be doing head swimming math to determine the affect of alternating current on the circuit. As someone else said, you had more than broken strands if you were able to find the problem on a deenergized circuit with just an ohmmeter. By far the most effective way to determine if you have a problem with your wiring as it relates to your question is to take a voltage reading at the source, and a voltage reading at the load (while under a load) and compare them. Combining this with an amp reading and a quick calculation is also the easiest way to get impedance. Part of the "why" is that a couple strands in a lug has the same resistance as many strands under the lug, unless or until, you start to heat the wire up. An Ohmmeter is not going to put out enough amperage to heat up the wire.

[Edit] This is not meant to discourage your quest. The question is a good one and BTW, when you gain "complete understanding" can you come back and show us the way!:lol:

 

[rambojoe]

I hope this thread doesn't get me in trouble or make people think "jeez, whats this guy smoking". thanks again for the help

 

[iwire]

I hope this thread doesn't get me in trouble or make people think "jeez, whats this guy smoking". thanks again for the help

Heck no, the members here like to help people that are interested in learning.

Ask away.

 

[rambojoe]

thank you strat head. and I prefer teles myself you explained it very well. unfortunately im at home injured from tripping over crap in a walk way so I figured its time to brush up on theory. questions like this don't work too well on the job so im glad this forum is a great resource!

 

[Tony S]

Go to college before you kill someone playing around with you’re meter. The internet is no place to learn electrical theory.

 

[rambojoe]

Heck no, the members here like to help people that are interested in learning.

Ask away.

and I promise im the JW on the job who is happy to show the new guys the tricks. "helping you helps me" a few months back I showed an app. the quick way to run small stick in steel studs w/o a tape measure! lets say the back of the bend is his new friend the other JW's just stand around looking cool.....

 

[rambojoe]

Go to college before you kill someone playing around with you’re meter. The internet is no place to learn electrical theory.

will do. after this job is done. then after the next one. and so on. night school after schlepping 4" rigid sounds no fun. except maybe to meet women. I regard the safety of those around me highly, plus im sure the only way to kill one with a meter is to stab them in the neck with the probes...

 

[ActionDave]

Go to college before you kill someone playing around with you’re meter. The internet is no place to learn electrical theory.

:thumbsdown::thumbsdown::thumbsdown::thumbsdown::rant:

This is the best resource I have ever found for any field electrician to ask and learn.

 

[Strathead]

thank you strat head. and I prefer teles myself you explained it very well. unfortunately im at home injured from tripping over crap in a walk way so I figured its time to brush up on theory. questions like this don't work too well on the job so im glad this forum is a great resource!

I have a Tele.

 

[ggunn]

Go to college before you kill someone playing around with you’re meter. The internet is no place to learn electrical theory.

Feeling crabby today? When I changed engineering fields (and yes, I went to college) from semiconductors to energy, I had a lot of learning to do, for example, the theory pertaining to three phase power. The internet was a valuable resource for me.