DC cable run outside house?

[DomB]

Hi all,

Just wondering about preferred methods for running DC cables down the outside of the house: two-core SWA? Or do you tend to install the inverter in the attic, as close as poss to the arrays?

Cheers

 

[i=p/u]

ive heard attic

 

[DomB]

I figure the problem with the attic is the ease of checking the inverter is running OK (other than standing and watching the Generation Meter) - I guess a monitoring system can then be sold to people who really want it in there. Plus there the additional cost of another AC isolator by the main CU. Hm.

I'm favouring the inverter being near the CU at the mo, with the right cables to avoid DC losses.

 

[i=p/u]

some good diagrams on this site somewhere, ive seen them, but dont know where they be, try a search.looks straoight forward to me and i aint a spark yet

 

[goodwilld]

Inverter in the attic to prevent losses. The gen meter near the conusmer unit.

 

[DomB]

I'm thinking DC losses are about the only disadvantage of the inverter being next to the Consumer unit, but they can be overcome with the right cable. I guess safety with DC is something too, but again that comes down to cable and routing choices.

Having the inverter in the loft has a few drawbacks - it could be down for weeks before being checked, the loft may not be boarded or lit etc and it involves installing two AC isolators (no biggy, but hey). I guess lofts are dusty too which is not ideal. And they make me itch. I hate lofts.

 

[goodwilld]

Some Inverters do make a noise which is a factor you need to think about, the Gen meter will tell you if it's not working.
You just don't like lofts, do ya.

 

[DomB]

You know that. Itchy coughy lofts.

Noise is a good point. Space restrictions too.

I spose the Gen Meter would be red all the time if there was a problem, but then that could be for a number of reasons, cloudy day etc. At least with the inverter's green LED glowing nicely they know all is well.

At an install we have coming up we could place the inverter at either location - the loft or by the CU. I'm landing on the side of the CU at the moment. Guess that's where this has all come from

 

[JulianC]

Is it gold plated?

 

[DomB]

lol, you're right, 23.99 (+ labour! ;-)) aint gonna swing it but every little helps eh. I'm thinking more about being able to monitor the inverter really.

 

[Markc]

Depending on system size I don't know many who would want a ruddy great inverter next to their consumer unit. There hardy small. No issue with it being in the loft. Generation meter will show what it's doing and the client is just as likely to look at that as they will a remote monitor. I find most clients are happy with that and unless they ask for it (and it's only been one so far) the additional cost of a monitor is hardly deal breaking on a installation cost.

I would question DC voltage in a SWA. I don't know if this is OK or not.

 

[edexlab]

Everyone goes on about losses in DC cables, do a cable calculation for 4.0mm 2 % VD which is acceptable (2% on DC 1% is reccommended for AC)
I think if you do it correctly you'll be surprised ,you can also do this on sunny design , I try to avoid putting the inverters in the loft for lots of reasons .We went to Germany earlier on this year and found that some of the general ideas taught in this country were frowned upon over there!

 

[mmccx]

SWA is fine to use as dc cable

 

[mmccx]

Everyone goes on about losses in DC cables, do a cable calculation for 4.0mm 2 % VD which is acceptable (2% on DC 1% is reccommended for AC)
I think if you do it correctly you'll be surprised ,you can also do this on sunny design , I try to avoid putting the inverters in the loft for lots of reasons .We went to Germany earlier on this year and found that some of the general ideas taught in this country were frowned upon over there!

I wouldn't go on whether the Germans frown upon our practises or not we are a different country! For example i spoke to a guy from belgium trying to sell A frames saying they didn't worry about mounting all modules on the short side regardless of whether they had been tested to be allowed to be clamped in this way

 

[edexlab]

I know what you are saying but are you going to ignore 10+ years of vast experience of grid connected systems small and 300kw plus versus this country's limited experience
thats not the point of the original post anyway the idea is to show the actual length of run allowable on pv ,which will show that you are not limited to just putting the inverter in attics which will actually shorten the operational life of the inverter and have an effect on output during the most productive months (this is not my own opinion this is what the 300 odd engineers at Sma have found in the last 30 years)
As for the Belgian he's a salesman need i say anymore