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Voltage Drop Calculator

We've developed this handy calculator which will show you the approximate voltage drop based on cable size, supply voltage, current draw and cable length.

If your Voltage drop is Orange then the size cable selected will not be suitable. If it is Green then you are within the generally accepted 3-4% for max. voltage drop.

Note: This calculator does not take into account any heating effects of current passing through the cable so for safety, even if the voltage drop is acceptable, you should still ensure that the nominal current carrying capacity of your cable is higher than the current draw of your circuit (under normal operating conditions).

Enter values, hit ENTER/RETURN key to calculate

Select cable cross-sectional area (mm2)
System nominal DC voltage (V)
Current draw (Amps)
One-way circuit length (m)

It is important to note that voltage drop occurs not only along the positive cable to the load but also along the negative return cable. When you enter the cable length as the 'one-way' distance to the load the calculator assumes (for simplification) that the return distance is identical, giving you a total cable length that is twice that of your entered value. In practice, your return cable length might be much shorter as it may be grounded to a nearby point on the chassis (at least in vehicles), so the remainder of the distance back to the battery negative should have an extremely low resistance relative to a cable. In this case, the actual voltage drop would probably be less than calculated, but it provides a 'worst case' figure to work with. 

Voltage drop can also be caused by high temperatures, although to a lesser degree than cable length, because as temperature increases, resistance increases and vice versa. In high voltage systems, voltage drop is not such an issue which is one of the reasons why electrical cables running many miles are operating at hundreds of KV. The other reason is that the same power can be delivered at a higher voltage but with a lower current, meaning that smaller-sized, less expensive cable can be used.

Please note: All calculations are made based on our cable specification and different manufacturers' or retailers' specifications may differ. For further help please contact a member of our sales team. 


Disclaimer - The information contained in these articles is provided in good faith and we do our best to ensure that it is accurate and up to date, however, we cannot be held responsible for any damage or loss arising from the use or mis-use of this information or from any errors or omissions. The installer is ultimately responsible for the safety of the system so if you are in any doubt, please consult a qualified electrician.

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