Power My Home solar panels in the UK.

What type of cable from an inverter?

    • jules

      I am shortly to move into a new build and would like to have solar panels fitted to the south facing rear. As the walls have yet to be completed I intend to ask the builder to lay a cable from the loft through to the junction box in readiness. What size cable would you recommend and is there anything else I should consider before the house is completed

    • Norman

      The standard cable is 4mm 2 twin and earth.

    • Norman

      Standard practice is to site the inverter in the attic as near to the panels as possible.

      There are two reasons for this:

      1. To keep the DC cable run as short as possible. (it’s high voltage and small amounts of power can be lost in the run to the inverter)
      2. Space. Due to the size of the inverter the attic is best placed rather than within the house.

      Attics get very hot in the summer so your inverter may have a fan which kicks in to stop overheating. As your roof faces South West it will get the sun late in the evening so the noise may affect your child. Maybe check this with your installer.

      If you have an internal garage this could be suitable. The inverter could be wall mounted onto a fire proof MDF board.

    • Stuart

      Volts drop and maximum cable run for a 4 KW solar PV system
      AC side.

      Figures from BS7671 : 2008
      Incoming Voltage single phase 230v
      4 KW Solar PV System.
      4000 watt / 230 v = 17.39 Amps
      Maximum Volts Drop = 1% = 2.3 Volts

      Current Carrying Capacity Table 4D2A reference Method B enclosed in conduit.

      1.5 mm = 16.5 amps (not acceptable as below the 17.39 amps required)
      2.5 mm = 23 amps (maximum length 7.34 meters but not recommended by SMA)
      4.0 mm = 30 amps (maximum length 12 meters)
      6.0mm = 38 amps (maximum length 18.11 meters)
      Volts drop Table
      2.5 mm = 18 mV/A/m
      4.0 mm = 11 mV/A/m
      6.0 mm = 7.3 mV/A/m
      Example if we want to use a 2.5mm Cable this is how we work out the volts drop.
      Amps x Length x Volts Drop /1000 = 2.3 volts (maximum volts drop)
      17.39 x Length x 18 /1000 = 2.3
      17.39 x 18 x Length = 1000 x 2.3
      313.02 x Length = 2300
      2300/313.02 = Length
      Length = 7.34 Maximum Length in Meters

      This is why we use 4.0mm or even 6.0mm cable from the mains to the inverter.

      Using the same working the maximum length for 4.0mm is 12 meters and for 6.0mm is 18.11 meters.

      You need a 6.0mm cable running from the mains DB to the inverter to comply to BS 7671.

    • Linas

      hi ,what cable size from panels to inverter for 8kw system ,and between panels .distance 6m from panels to inverter .thank you .

A better way.

"I've witnessed many fantastic changes, innovations, and installation companies come and go. My fellowship with ethically-minded MCS solar panel installers goes back decades. Today, I offer my experience to ensure you gain real independence from this crazy world."

Stuart Lovatt
Power My Home Solar Panels
Sundial House, 44 Panton Road, Chester CH2 3HX.
01244 722 607

Est. 2004.