# Solar DC Voltage Drop Calculator

In accordance with industry guidance, the voltage drop for the DC solar PV string should be calculated to ensure it does not exceed the maximum permitted voltage drop % at the stc between the solar array and the inverter.

2.1.4 d.c. Cables – General
2.1.4.1 Cable Sizing
Cables should be sized in accordance with BS 7671. These calculations shall also take into account the multiplication factors in 2.1.2 of this guide. Guidance on a method of cable sizing including any de-rating factor requiring to be applied and typical current carrying capacities for common cable types are provided in Appendix 4 of BS 7671.

The DTI Guide to the installation of PV systems 2nd Edition states,

2.1.4.1 Cable sizing; Cables should be sized such that overall voltage drop at stc between the array and the inverter is <3%.

The MCS, Guide to the Installation of Photovoltaic Systems also states,

2.1.4.1 Cable sizing; Cables should be sized such that the overall voltage drop, at array maximum operating power (stc), between the array and the inverter is <3%.

## DC Voltage Drop Calculation

DC Volt Drop Calculation Parameters:

• DC Voltage (U)
• Length (1 way) (L)
• Cable Type & Size

DC Volt Drop Calculation Results:

• Volt Drop V
• Volt Drop %
• Full Length (Lx2)
• Resistance Per Meter (Ω)

## DC Volt Drop Formula

R is the resistance per meter of the selected cable.
Ib is the load in Amps.

Volts Dropped = (L x 2) x Ib x R
Volt Drop % = Volts Dropped / Voltage(U) x 100

### Solar PV DC Voltage Drop Calculator App

In order to carry out a volt drop calculation of the DC string you will need to know the resistance per meter for the cable type and size.

Within our “Electrical Tools and Reference” app we have created a new DC Volt Drop calculator with the resistance per meter for the cable type Photovoltaic Solar EN 50618 H1Z2Z2-K and sizes ranging from 1.5mm² up to 240mm², we have also included the manufacturers data sheet for the cable type used, you can check out this app here → The Electricians App.

## Solar DC Volt Drop Calculator

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References:
Photovoltaics in Buildings Guide to the installation of PV systems 2nd Edition, source.
Guide to the Installation of Photovoltaic Systems, source.

Disclaimer: Rules, regulations and specifications may change over time, always ensure you are using/referring to the latest version of any guide or document.