Hi guys

So I did a bit of a search here on the site, and saw a few conversations about the speccing of cables for both the AC and DC side. Thought I'd start this thread to see if we can consolidate some of the info a bit more.

So first off, AC "House wire" as I see it being referred to at electrical suppliers is AC only, and not recommended for the DC side of things, so other than the supplier being open and obvious on which is which, as below examples:

"House" 6mm --> https://www.arb.co.za/6-0mm-housewire-red-coil-100m.html
"Solar" 6mm --> https://www.sonopsolar.co.za/product/solar-cable-6mm/

How does one know which is which, and what to use where from a layman's perspective? I have seen that the amount of wire cores inside the cable is a consideration? I tried to look at current and voltage ratings, and these seem in order upon first glance.

Also, as to colour standards, we know that AC side is red, white or yellow, blue = LIVE (PHASES), black = NEUTRAL, green/yellow or bare copper = EARTH, are there standards for DC as well, and where can one find specs on this? I've only seen Black and Red being mentioned thus far.

Lastly, this I believe is part of wiring standards, and one is not to mix AC and DC cables in the same conduits. Understandably so, but some other standards might be obscure to the layman aswell again. I am sure that some of these standards should be known by your installer/sparkie, but I like to know myself, so is there a decent place where one can browse through to ensure one is compliant?

Please enlighten me?

 

1 hour ago, Minerva10210 said:

"House" 6mm --> https://www.arb.co.za/6-0mm-housewire-red-coil-100m.html
"Solar" 6mm --> https://www.sonopsolar.co.za/product/solar-cable-6mm/

How does one know which is which, and what to use where from a layman's perspective?

Solar cabling is double insulated with extra UV protection.

The copper cross section inside will be the same, they will both work, with one lasting longer than the other in harsh conditions due to the covering over the copper.

Finer copper strands make cabling more manageable ( floppy), but sometimes rigidity is preferred for neatness.

1 hour ago, Minerva10210 said:

How does one know which is which, and what to use where from a layman's perspective?

When it comes to cable, the tables are reversed. Normally there are extra requirements for DC breakers, switches, fuses, because DC arcs are harder to extinguish, and breakers need a bit more current before they trip. But when it comes to cable, it is the AC side that adds requirements, though only in rare occasions. There is something called Skin-Effect that happens only with AC, which means you have to make the cables thicker. BUT... at 50Hz this effect is so small that for all practical purposes you don't have to worry about it.

So long story short: any AC-rated cable can also handle DC, given that you stick to the voltage and current ratings.

But as @phil.g00 said, the environment that the cable will be in plays a role. Solar cable is generally UV-rated because it's going to go in a harsh environment. So the requirement has nothing to do with the DC, it has to do with where the cable will be used.

Solar cable is often also rated for higher voltages, because PV arrays can go up to 1000VDC or even 1500VDC. If you have a measly 150V array, then the AC cable again is fine when used in the right environment.

Continuing the theme on environment: Even AC cable might have requirements. GP wire must go in conduits. Surfix on the other hand is considered armoured and need not be in conduit.

Current ratings play a role too. General purpose "house wire" (GP wire) generally goes up to 25A. That's a lousy 1.2KW.

Multi-stranded or not: Also as Phil said, that's about making them flexible enough, eg when you have to pull it into conduit or trunking. DC cable is generally lots of very thin strands for this reason (and still rather inflexible).

So if you need a <20A DC connection in a shaded area, and you properly fuse the wire and enclose it in separate conduit... by all means use GP wire for your DC 🙂

 

Oh I forgot another one. Continuing my theme on why AC is more problematic when it comes to cable. With AC you have eddy currents. The fluctuating magnetic field around the cable (Physics 101, or for me it was 144, right hand rule) induces an eddy current in any metal raceway/conduit and induces a voltage in that metal, sometimes causing unpleasant shock when you touch it. This is much reduced with DC. You still get that effect on solar cabling (because the MPPT creates a 40Khz+ ripple), but it is much less of a problem than with AC.

This is why, with AC, both live and neutral must run in the same raceway.