Current through wires of different diameter & different material

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Does current remain constant through series-connected wires made of different materials and diameters?

Yes—the current is the same through the entire series path; what changes from section to section is the voltage drop because each wire segment has its own resistance [#21666725][#21666731] Treat each segment as a resistor in series, so the total resistance is R1 + R2 + ... and the current is I = V/(R1+R2+...), while each section drops V = I·R according to its resistivity, length, and diameter [#21666726][#21666727][#21666734] A perfectly joined junction has no voltage across it by itself; the total drop from end to end is just the sum of the drops across the sections [#21666731] The smaller-diameter section has higher current density, but not a different series current [#21666731] Wire resistance is usually very small, so the voltage drop may be tiny, but it is still present [#21666725][#21666727]

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#1 21666724 22 Feb 2013 13:43

Daniel Kinney Daniel Kinney

Anonymous

Post #1
21666724 22 Feb 2013 13:43

Hello!
I just wanted to know if a current running through a wire in series remains constant even if the wires are made of different material (therefore different resistivity) & different diameters?

I just thought the current would have a potential V drop when going from 1,2 to 2,3
(attached picture)!

I just would like to understand a little more. I'm not used to dealing with wires that aren't separated by a resistor or a capacitor!

Thank you!
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#2 21666725 22 Feb 2013 13:54

Richard Comerford Richard Comerford

Anonymous

Post #2
21666725 22 Feb 2013 13:54

The current remains constant; the voltage drop changes depending on resistivity, which varies by material and diameter. Even though the wires may not have as much resistance as a resistor, they do have resistance (unless cooled to absolute zero, but that is a special case). It is possible to have wires of different diameter made of different materials having the same resistivity per unit length. The resistance of most wires is extremely low per unit length, so differences may be minuscule.
#3 21666726 22 Feb 2013 13:59

Richard Comerford Richard Comerford

Anonymous

Post #3
21666726 22 Feb 2013 13:59

Ohm's Law is a law, and can not be violated. Hence, always:

V = IR
V = I (R1 +R2) for series.
V1 = IR1
V2 = IR2
V1 + V2 = V
#4 21666727 22 Feb 2013 14:59

Steve Lawson Steve Lawson

Anonymous

Post #4
21666727 22 Feb 2013 14:59

Think of it this way. A wire is really just a resistor -- a really low value resistor (i.e. a #22 copper wire has .0529Ω/M, so a 1 meter length of #22 copper wire is a 52.9 mΩ resistor. An 18 gauge copper wire is 0.0209Ω/M so a meter of #18 wire is a 20.9mΩ resistor. If the two are butted together, like in your diagram, then you have a series circuit with two resistors, one at 52.9mΩ and one at 20.9mΩ for a total resistance of 73.8mΩ. If 1 volt is applied across this series circuit, then the current will be: 1V/73.8mΩ = 13.6 Amps -- at least for a short while. The current carrying capacity of these two wires is a bit lower than that current, so one or both of them will probably melt!

The reason why wires are typically _not_ considered resistors is because the components that those wires are commonly connected to have resistances (or impatiences) that are vastly greater than the resistance of the wire, and thus the resistance of the wire becomes negligent. BUT, in circuits like the charging system in a car, the resistance of the wire becomes quite significant!
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#5 21666728 22 Feb 2013 15:00

Steve Spence Steve Spence

Anonymous

Post #5
21666728 22 Feb 2013 15:00

Current is decided by the load. If the wires are too small, it will pull that load right up until heat related mechanical failure.
#6 21666729 22 Feb 2013 15:11

Richard Comerford Richard Comerford

Anonymous

Post #6
21666729 22 Feb 2013 15:11

Yes, I've always found my resistors to be impatient (Of course, you meant "impedances".)
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#7 21666730 22 Feb 2013 15:21

Steve Lawson Steve Lawson

Anonymous

Post #7
21666730 22 Feb 2013 15:21

D'oh! Stupid spell-check!
#8 21666731 22 Feb 2013 16:07

Frank Bushnell Frank Bushnell

Anonymous

Post #8
21666731 22 Feb 2013 16:07

The volt drop from point 1 to point 3 will be equal to the sum of the volt drops along section C and section D.

At the point where two sections join, a certain voltage can be measured with respect to another point along the wire, but the junction itself (assuming a perfect join) is a effectively a single point with no voltage across it.

The current going in at point 1 must be equal to the current coming out at point 3.
The current will be constant all the way along the wire, regardless of its resistivity or diameter.
(Exactly as if it were water flowing through a pipe of varying diameter.)

But each different section will have a certain volt drop along it according to (1) its resistivity, diameter and length ( R ) and (2) the current flowing through it ( I ).
V = I x R

The current density will be greater in the smaller diameter section. That is the only thing that will specifically change at the intersection of the two parts, regardless of the material they are made of.
#9 21666732 22 Feb 2013 17:54

Daniel Kinney Daniel Kinney

Anonymous

Post #9
21666732 22 Feb 2013 17:54

Thank you! Seriously made my day better. I'm new to EE, but I have years to learn. Every little piece of knowledge helps me progress so thank you!
#10 21666733 22 Feb 2013 17:56

Daniel Kinney Daniel Kinney

Anonymous

Post #10
21666733 22 Feb 2013 17:56

*I just wanted to thank all of you guys for taking time out of your day to help me understand a simple concept, but now I understand! Thank you all once again.*
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#11 21666734 22 Feb 2013 23:06

Rodney Green Rodney Green

Anonymous

Post #11
21666734 22 Feb 2013 23:06

Hi. It looks like your question has been well answered, but you can also consider that what you are talking about is resistors in series so according OHMS La each piece of wire are summed R1 +R2 +R3 etc. The total current flow will be I=E/(R1+R2+R3 etc)
#12 21666735 12 Jan 2019 17:28

Richard772 Susan Richard772 Susan

Anonymous

Post #12
21666735 12 Jan 2019 17:28

You can easily measure resistance with an ohm meter… But a basic comparison could be done by put an ammeter in series with each wire and run a current through each to compare.
#13 21666736 16 Jan 2019 11:14

Richard772 Susan Richard772 Susan

Anonymous

Post #13
21666736 16 Jan 2019 11:14

Any suggestion?myprepaidcenter
#14 21666737 28 Feb 2019 12:26

Andrew Piana Andrew Piana

Anonymous

Post #14
21666737 28 Feb 2019 12:26

yes i got manyprepaidgiftbalance dgcustomerfirst
#15 21666738 29 Jul 2020 02:12

khamma love khamma love

Anonymous

Post #15
21666738 29 Jul 2020 02:12

As for for this question, there are various amounts of conductivity but they are not all the same. Three best off the top my head are gold, copper, and aluminum. And I know that granite has more conductivity than limestone.. So as for ratios you’ll have to know which materials you’re talking about. The thicker wire will have less resistance but not because the wire itself is larger. Only because the surface area is larger. Electrons travel best when they’re at or very near the surface of any conductor. You can easily measure resistance with an ohmmeter… But a basic comparison could be done by put an ammeter in series with each wire and run a current through each to compare… The larger diameter wire will read higher current…
#16 21666739 08 Aug 2020 12:53

Jackson Lilious Jackson Lilious

Anonymous

Post #16
21666739 08 Aug 2020 12:53

I am reading these blogs daily basis and it's provides more useful and valuable infromation thanks for sharing.LMpeople
#17 21666740 20 Aug 2020 14:26

Olino Nogut Olino Nogut

Anonymous

Post #17
21666740 20 Aug 2020 14:26

I am reading these blogs daily basis and it's provides more useful and valuable infromation thanks for sharing.
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Topic summary

✨ In a series circuit composed of wires with different diameters and materials, the current remains constant throughout the circuit regardless of variations in resistivity or cross-sectional area. Each wire segment acts as a resistor with resistance determined by its resistivity, length, and diameter. The total voltage drop across the series is the sum of the voltage drops across each wire segment, following Ohm's Law (V = IR). Smaller diameter wires have higher current density, but the current magnitude does not change at junctions between different wires. Wire resistance is typically very low compared to connected components, so voltage drops along wires are usually minimal but measurable. Practical considerations include the current carrying capacity of wires, as excessive current can cause overheating and mechanical failure. Resistance and current can be measured using ohmmeters and ammeters respectively. Common conductive materials mentioned include copper, aluminum, and gold, with resistivity differences influencing voltage drops but not current continuity.
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Current through wires of different diameter & different material

FAQ

TL;DR: Current in a series path is constant, even across different wires. Example: #22 Cu ≈ 0.0529 Ω/m; “A wire is really just a resistor.” [Elektroda, Steve Lawson, post #21666727]

Why it matters:** This FAQ helps beginners and hobbyists size wires, predict voltage drop, and avoid overheating in real builds.

Quick Facts

Series rule: V = I(R1 + R2 + …); individual drops add, current stays the same. [Elektroda, Richard Comerford, post #21666726]
Typical copper examples: #22 ≈ 0.0529 Ω/m; #18 ≈ 0.0209 Ω/m. [Elektroda, Steve Lawson, post #21666727]
Example load: 1 V across 73.8 mΩ series wire → ≈13.6 A (risk of damage). [Elektroda, Steve Lawson, post #21666727]
The load sets current; undersized wire heats to failure. [Elektroda, Steve Spence, post #21666728]
Perfect junctions add no drop; drops occur along each resistive section. [Elektroda, Frank Bushnell, #21666731

Does current stay the same through wires of different materials and diameters in series?

Yes. In a series path, the same current flows everywhere. Material and diameter change resistance and the voltage drop, not the current. [Elektroda, Frank Bushnell, post #21666731]

Where does the voltage drop happen when the wire changes diameter or material?

Voltage drops along each wire segment according to V = I × R for that segment. At a perfect joint, there is no extra drop. [Elektroda, Frank Bushnell, post #21666731]

How do I calculate total resistance for several wire sections in series?

Add the resistances: R_total = R1 + R2 + …. Then use Ohm’s Law, V = I × R_total, to find current or drop. [Elektroda, Richard Comerford, post #21666726]

Can different wires end up with the same resistance per meter?

Yes. Different materials and diameters can yield the same resistivity per unit length, so their voltage drops can match at a given current. [Elektroda, Richard Comerford, post #21666725]

What’s a real example of current through mixed wire gauges at 1 V?

One meter of #22 Cu (52.9 mΩ) plus one meter of #18 Cu (20.9 mΩ) totals 73.8 mΩ. Current ≈ 1 V / 0.0738 Ω ≈ 13.6 A. [Elektroda, Steve Lawson, post #21666727]

Who decides the current—the source, the load, or the wire size?

The load and source set the current. If the wire is too small, it still tries to carry that current and overheats. [Elektroda, Steve Spence, post #21666728]

What happens if my wire is undersized for the circuit?

It runs hot, the insulation can degrade, and the conductor can melt. That is a heat-related mechanical failure risk. [Elektroda, Steve Spence, post #21666728]

Is a wire basically a resistor?

Yes. “A wire is really just a resistor”—usually a very low-value one—so its resistance still causes voltage drop and heat. [Elektroda, Steve Lawson, post #21666727]

How can I measure and compare wire resistance or current at home?

Use a DMM. 1) Measure resistance with the ohmmeter across a known length. 2) Or put an ammeter in series with a test source. 3) Compare readings between wires. [Elektroda, Richard772 Susan, post #21666735]

Does the junction between two wires add voltage drop?

Assuming a perfect, low-resistance join, treat the junction as a single point. The drop occurs along each segment, not at the ideal joint. [Elektroda, Frank Bushnell, post #21666731]

Why do designers often ignore wire resistance in small-signal circuits?

Connected components usually have much higher impedances than the wire. The wire’s small resistance becomes negligible in those contexts. [Elektroda, Steve Lawson, post #21666727]

How does current density change when wire diameter changes?

Current density increases in the smaller-diameter section. That raises temperature for the same current, increasing drop and heating risk. [Elektroda, Frank Bushnell, post #21666731]