DC cable run outside house?

[DomB]

Aye, must admit I'm advising customers to put the inverter downstairs if possible - more accessible and less hot n dusty. If not possible then the same argument leads nicely to an upsell of a nice SunnyBeam or the like.

What are the concerns of DC in SWA?

 

[gr7]

The concern over using SWA on the DC side is that it not double insulated, as far as I'm aware the general opinion is to overlook this minor detail.

 

[edexlab]

Swa is ok but as far as I'm aware it is usually only done as a DC main cable ie from a junction/combiner box (not the norm for smaller systems)
or where a buried or exposed run is required , the double insulated issue is given over to the better mechanical protection of swa.
we're involved in a job where we might have to do this because the arrays are on buildings separate from the supply/plant blocks where the inverters will be sited.

 

[SolarCity]

Out of interest, why do DC cables require double insulation?

 

[malcolmsanford]

As protection. Because you are wiring the panels in series, if you had a sheathed cable it would make it awkward to connect up. The use of double Insulated cables are purely for mechanical protection as often as not your cliping singles around the loft.

SWA is reality is quadruple sheathed and is perfect for any situation. You have the outer PVC , the Armour itself, you then have the inner PVC sheath and finally the conductors PVC.

 

[gr7]

Sheath and insulation are two different things, the DC cables are double insulated and unsheathed (or should be).

 

[gr7]

BiggsSolar, reg 712.412: Protection by the use of Class II or equivalent insulation shall preferably be adopted on the DC side. This includes the cabling, although it is interesting to see the word 'preferably' used.

 

[malcolmsanford]

Dosen't a sheath provide a suitable non conductive material enclosing, surrounding or supporting a cable ?

Agree that singles are un-sheathed and therefore are double insulated to provide that protection, where as SWA is a sheath cable affording better protection that double insulated cables.

I have edited my OP where I in advertantly said double sheated rather than double insulated ,thank you for that piece of editing for me.

 

[gr7]

You would have thought that this is the case Malcolm, the insulation of a cable is tested to xx volts whereas a sheath is designed for mechanical protection only, hence not tested for insulation.

 

[malcolmsanford]

I have to say the more you point this out the more I tend to agree with you. I know that you have to be careful with the switching distances on DC switches and isolators, and yes insulation on DC would have to be rated at a higher capacity.

Thanks always learning as they say.

 

[edexlab]

Also DC >120v double insulation must be used, so I assume below it's not necessarily required.

 

[DomB]

The Reg's, good point! So the definition of "Double Insulation" says "Insulation comprising both basic and supplementary insulation". And the def. of "Basic Insulation" says it is to provide "Basic protection". And I'm thinking SWA does provide basic protection. Maybe I'm getting comfortable about running DC through SWA.

There was mention of interference between the conductors because it's DC - any thoughts there?

 

[SolarCity]

Is it actually possible for a cable to be 'double insulated'? I assumed that the outer cover of the solar cables was for mechanical protection.

 

[SolarCity]

BiggsSolar, reg 712.412: Protection by the use of Class II or equivalent insulation shall preferably be adopted on the DC side. This includes the cabling, although it is interesting to see the word 'preferably' used.

I suppose this is where the issue with earthing comes in. Use of class II equipment is all very well until you consider the huge metal mounting system. I assumed this is what they meant by 'preferably'. Of course, with TL inverters the array must be earthed and the use of Class II equipment is not an issue.