Cable length using r1 and r2

[Integrator741]

Hi. How do I calculate cable length using csa and r1 and r2 reading. (On a dead circuit). Cuz I am trying to calculate voltage drop on elv cable.

So I got a 1.5 cable that will have 24v going through it to 100w device. How do I get voltage drop from this information?

Thanks.

 

[BobK]

Voltage does not go through a cable, current goes through a cable.

So, first calculate the current: If it is 100W at 24V the current is 100 / 24 = 4.16A.

Next calculate the resistance: For the given size of wire, you can find the resistance / length. For example, 22AWG wire has 0.053 Ohms / meter. Multiply that figure by the length of the wire to get resistance.

Finally, use Ohm's law to calculate the voltage drop: V = I * R

Bob

 

[Integrator741]

Voltage does not go through a cable, current goes through a cable.

So, first calculate the current: If it is 100W at 24V the current is 100 / 24 = 4.16A.

Next calculate the resistance: For the given size of wire, you can find the resistance / length. For example, 22AWG wire has 0.053 Ohms / meter. Multiply that figure by the length of the wire to get resistance.

Finally, use Ohm's law to calculate the voltage drop: V = I * R

Bob

Thanks. Is there a formula to calculate cable length?

 

[BobK]

Calculate it from what?

Bob

 

[Minder]

Short circuit the destination end and measure resistance at the source end.
Or use one of the cable charts for your cable.
M.

 

[Integrator741]

Short circuit the destination end and measure resistance at the source end.
Or use one of the cable charts for your cable.
M.

I did that. I got 0.55 ohm. How would I use that to calculate the length? Also quick question. If I got an ELV circuit (24v) and my equipment takes 100w I get current of 4.16A. Does that mean Extra Low Voltage circuit could actually kill me?

 

[BobK]

I thought you were trying to calculate voltage drop. If you already know the resistance and the current, why do you need the length?

Anyway, calculating the length is elenentary scool arithmetic.

Divide the resistace of the cable by the resistance per meter of the cable, which you can get from a chart.

Bob