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Topic Title: Red and White OK for DC ?
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Created On: 20 March 2013 10:50 AM
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 20 March 2013 10:50 AM
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broadgage

Posts: 1298
Joined: 07 August 2007

Wiring an off grid home for both 12 volts DC from a battery bank, and 230 volts AC from a generator.

Would it be acceptable to use red for the DC positive and white for the DC negative, so as to avoid confusion with the 230 volts AC which will be in the conventional blue and brown.

The regs would appear to require that both voltages use blue and brown, which does not seem very sensible.

Most of the installation will be at 12 volts DC with only limited 230 volts AC power circuits.

Or what about red and black for DC with the new colours for 230 volts AC ? In the real world, red and black still seems to be the norm for DC.
 20 March 2013 12:13 PM
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AJJewsbury

Posts: 11492
Joined: 13 August 2003

As the 12V is ELV then you seem to be able to use any of Brown, Black, Red, Orange, Yellow, Violet, Grey, White, Pink or Turquoise for L according to table 51.

So if neither of the distributed 12V wires is earthed (i.e. the 12V system is unearthed or earthed to say a mid-point that isn't distributed), then you've got two non-neutral conductors, so it seems to me you can use any of that long list - including red/white or red/black.
- Andy.
 20 March 2013 01:31 PM
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dickllewellyn

Posts: 1150
Joined: 19 March 2010

Out of curiosity, how would you go about wiring such a system? What size cables will you be using? What effect does volt drop have etc...

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Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 20 March 2013 03:56 PM
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broadgage

Posts: 1298
Joined: 07 August 2007

Whilst in theory voltage drop may be calculated from published data, in the real world the exact load and the actual circuit length are not allways known.

I usually proceed as follows.

General purpose lighting 2.5mm cable, 10 amp fuse.
Small power 4.0mm cable, 16 amp fuse.
For short runs within a normal size dwelling, if in doubt, one size larger.

A 10 amp lighting circuit would be designed so as not to be regularly loaded to more than 5 amps, say 5 lamps each 11 watt CFL or 20 lamps each 3 watt LED.
If the lamp wattage to be used is unknown or likely to be altered then I allow only 4 lamps per circuit.

Small power sockets would normally be USA type mains sockets, readily available but not normally used for mains voltage in the UK.

For larger loads or long cable runs then I would calculate the voltage drop and size the cable accordingly, allowing between 3% and 10% voltage drop according to the type of load, and likely hours of use.

In view of the preference for non standard colours and the need for relatively large cables by domestic standards, I would normally use PVC singles in insulating conduit.

Any mains voltage circuits in the area would normally be FP200.
 21 March 2013 09:50 AM
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BigRed

Posts: 558
Joined: 10 November 2006

Can I suggest that the cable you use is proper ELV as in car/boat stuff? 6mm elv cable is about the same diameter as 2.5mm 500V stuff
Just finished wiring a boat and was surprised how small the overall diameter was. Obviously, usual rules apply on compartments etc.
 21 March 2013 10:28 AM
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broadgage

Posts: 1298
Joined: 07 August 2007

I would normally use standard mains rated wire or cable for ELV installations.
IME the ELV stuff is less well made and often as expensive.

Whilst I would prefer to keep mains voltage and ELV in different conduits etc, this is sometimes not convieient, and if everything is insulated for the highest voltage present then that simplifies matters.

Mains rated PVC singles are also available in a wide range of colours which can be handy.
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