Mounting and protecting external DC cable runs

[cookiemonster]

i have a potential customer who wants a PV system but is concerned about the disruption of running cabling down from loft. She is adamant that she doesn't want carpets/ floorboards disturbing and definately doesn't want cable chases because of her expensive wallpaper and trunking is also a no-no. She thinks she isn't going to have an issue with inverter being sited downstairs. So the question is do folks run DC cable down the outside of house and besides PV Cable being double insulated how else do you mount / protect external DC cable runs? TIA

 

[andyemms]

If it is a side of the house not being used I just clip direct to the wall. If however it is regularly used and at risk of damage then you need to provide mechanical protection as you feel suitable. I tend to use high impact resistant conduit where this is the case. Interested to hear other views on this....

 

[Worcester]

Always high impact conduit it black / white to suit property and try to locate it so that it is not highly visible. We also label the conduit with PV Cable stickers.

 

[andyemms]

Indeed, labels are a must! Thanks Worcester.

 

[SolarCity]

It depends on circumstances. Some of our external runs have been at high level and extra protection has not been required. No danger of them being banged by anything (ladders etc.) We make tags for the cables to identify what they are. Looks neat and professional.

If the cable run is a little longer and reaches down to damagable heights then we install in conduit. It's easy to do a nice neat job out of conduit and on the side of most buildings it certainly doesn't have too much of an impact on the aesthetics. Again, we label the conduit.

 

[cookiemonster]

Thanks very much for your advise guys - just one more question though - do you have two lines of conduit - one for DC+Ve and one for DC-Ve or are they safe next to each other in the same piece of conduit?

 

[edexlab]

Always high impact conduit it black / white to suit property and try to locate it so that it is not highly visible. We also label the conduit with PV Cable stickers.

same again but i do use galv for exposed damage prone areas where I can i also run them separately +/_-
in two conduits

 

[BruceB]

521.8.1 would suggest they shoould be in the same conduit
Regards
Bruce

 

[SolarCity]

I don't think 521.8.1 would apply as it's DC. Just don't think it is necessary. In think I'd have thought it was a good idea to keep them in the same conduit (if using galv) in case of lightning strikes.

 

[BruceB]

There is nothing in 521.8 limiting it to ac circuits.

 

[SolarCity]

Haven't got the regs to hand but I'll take your word for it.

 

[Worcester]

The SMA guide on capacitance etc recommends bundling +ve and -ve together.

 

[edexlab]

same again but i do use galv for exposed damage prone areas where I can i also run them separately +/_-
in two conduits

when i use galv i do use a single conduit for both+/- when i've used two conduits always plastic and spaced slightly apart

Worcester
where does it say bundling together +/- in the capacitance info ? can you post the title as i don't remember seeing this in any lit I've read , I'm concious of the risk of short circuits etc caused by any damage and can't see a problem with using two separate plastic conduits to reduce the risk of shocks, i also clip cables separately in runs spaced a couple of inches apart or on opposite sides of the purlins etc for this same reason,

 

[Worcester]

Correction:

It wasn't the SMA guide (been reading too many guides recently!) it is the DTi's Guide - the one we all work to and know so well

2.2.4.2 Surge Protection measures
All d.c. cables should be installed to provide as short runs as possible, and positive and negative cables of the same string or main d.c. supply should be bundled together, avoiding the creation of loops in the system.
This requirement for short runs and bundling includes any associated earth/bonding conductors.

 

[edexlab]

My view is that when separated in two conduits a few inches apart is not going to form a loop anywhere near the loops you inevitably get when connecting panels up on an array I always try to keep them as close together to reduce the effect of lightning but I think you have to reduce the risk of short circuit as much as you can
as it happens recently a house in my area had a direct hit from lightning with two of our installed systems in the vicinity one was about 45 metres away the other about 150 metres and as far as i know there have been no reports of any equipment damaged in neighbouring properties which i have to say surprised me