Load at end of long cable

[megloff11x]

Please refresh my decaying memory.

What is the calculation for a long, long run of wire/cable to a load, motor or otherwise, and when will the Voltage drop for a barely thick enough wire be enough to cause problems?

Something is nagging me saying Vdrop=I*R(of wire) isn't the whole picture - there was something else. Or I've confused it with another issue which wouldn't be the first time.

Thanks,

Matt

 

[zbang]

Nothing wrong with starting with I*R, it'll give you a nice number to work with. There is a frequency factor for skin effect, and you could treat the whole thing as a transmission line... As for when the drop will cause problems, that kinda up to the load. A computer or incandescent lamp might not care as much as a heavily-loaded motor. Is there more to this than you're telling us?

Can't help with the memory part

 

[ptonsparky]

Try here: http://www.mikeholt.com/technical.php?id=calculations/technicalcalculationformulas towards the bottom of the page.

Different items are going to have different voltage tolerances. I believe for motors it is 10%, but operating temperature starts going up as the voltage decreases.

 

[dbuckley]

and when will the Voltage drop for a barely thick enough wire be enough to cause problems?

When the current consumption goes up, for any reason, say a slightly increased load on the motor, which means more volt drop, so less power available, so the motor slows and stalls.

If the distance is large, do the calculation for a higher voltage with thinner conductors versus lower voltage with thicker conductors; with enough wire length you can save money, even after buying transformers.

 

[S'mise]

Will this help? formula to find wire size. Name your alowable VD

single phase: 2*12.9*L*I /VD permitted=Circular mil (Copper)

Three phase: substitute 1.732 for the 2