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Is this wrong

Discussion in 'Solar PV Forum' started by Megavolt, Feb 24, 2012.

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  1. Megavolt

    Megavolt Electrician's Arms

    Was on a job today Which had a pv install done a few weeks ago the panels are on 4 separate roof elevations with the DC cables thrown over the roofs ridges and the DC cables then run down the side of house under some slate tiles of the garage roof to a sunny boy invertor fitted above the consumer unit which is properly 30 meters away from the panels on the back of the house. I was there doing a job in the house. The problem is when I mentioned the PV they said it was done by a frends son and that what a good job they had done now I never said much at the time as I wanted to get all my facts right first. As she will defently be defending her friends son.

    What would you guys do.
  2. whinmoor

    whinmoor Electrician's Arms

    Wakefield/Leeds, West Yorkshire
    Business Name:
    Medoria Solar
    Cables left in the open to rub against the tiles and ridge? Will that survive 25 years?
  3. moggy1968

    moggy1968 Electrician's Arms

    agreed, should have gone into roof space and across the loft.
    cables can be left exposed as they are UV resistant but, inaccordance with regs, must be protected from rubbing and chaffing which it sounds like these aren't. not the biggest crime in the world but I still don't think it's really good enough if the cables can move about as they cross the ridge
  4. FB.

    FB. Electrician's Arms

    I don't like the sound of it, but I suspect that you'll lose a customer if you criticise people close to her.

    But having said that - why did they have you doing a job in the house if they might have been able to use the son-of-a-friend to do whatever electrical work you were doing?

    There are a few arrays near to me with protruding rails, cables running across the tiles or other undesirable things which didn't really need to be that way.

    When the lads clambered up onto my roof to mount the panels and run the cables, I would have kicked their @$$ if the cables or rail-ends were exposed (well, actually I would have cut off their supply line of tea, coffee, biscuits, crisps and pot noodles, which would have hurt them far more).
    The rail ends sticking out further than necessary merely being about the looks, rather than weather and friction which would affect and wear away exposed cables.
  5. moggy1968

    moggy1968 Electrician's Arms

    unfortunately sometimes exposed rail endings is unavoidable. our last 2 jobs we have had this because of the spacing on the joists and manouvering around soil stacks to get a symetrical set of panels. To have trimmed off to our usual 35mm or so would have left an unacceptable overhang so about 100mm of rail had to be left sticking out to fix to a bracket beyond the panel edge. not ideal but unavoidable.
    we have, however, all seen some examples on here which are just plain sloppy!!
    Last edited: Feb 24, 2012
  6. SolarCity

    SolarCity Electrician's Arms

    We have done two jobs with exposed rails.

    On both occasions it has meant that either extra timbers would have been needed or manufacturers guidelines would have been breached.

    On both occasions the customer has been happy (ish) to have slightly exposed rails instead of paying extra.
  7. babba

    babba Regular EF Member

    hear no speak no see no....
  8. Megavolt

    Megavolt Electrician's Arms

    Is it correct to have the invertor so far away from the panels as I thought they normally go in the loft. Close to the panels
  9. GaryM

    GaryM Guest

    No problem with correctly sized DC cables to limit potential volt drop.
  10. mdovey

    mdovey Regular EF Member

    There's a general rule of thumb that it is better or safer to have a long 240v AC run in preference to a long 500v DC run. Hence the preference to mount inverters close to the panels.

    There are differing views as to the suitability of lofts - they can get hot in summer causing inverters to overheat (not dangerous, but it will reduce their output). On the other hand the solar panels will act as a good heat shield reducing the maximum temperature of the loft.

    The solar pv guides all state you should keep the voltage drop of the DC run to below 1% and the voltage drop of the AC run to below 1%. You can reduce the voltage drop by either reducing the length of the run or the thickness of the cable. Thick cable costs more, so a long run of thick cable can prove expensive.

    In practice a drop of more than 1% in the DC cable is unlikely to cause any major problems as long as the voltage at the inverter is still within its operating range - the customer may not be impressed with the performance however, and it may not pass MCS/REAL inspections etc., and it is definitely not good or recommended practice.

    A voltage drop of more than 1% in the AC cable can be more problematic. Grid voltages can typically be seen in excess of the nominal 240v and that could result in the voltage at the inverter going beyond the 253 maximum voltage after which it will perform a safety shut down. Again not dangerous per se, but not a good performance if the inverter shuts itself down for 10 minutes multiple times a day.

    The potential danger with the install as described is that not only do the DC runs sound as if they look unsightly, but if they aren't secured properly they may rub against the tiles which would wear the insulation. A spark cause by a worn DC cable could be a fire risk
    Last edited: Feb 25, 2012
  11. FB.

    FB. Electrician's Arms


    I understand that DC loses less over distance but it's more dangerous than AC. As mentioned: a thick enough cable will restore transmission efficiency over longer distances.

    I have 15m DC cables running from the panels (through the tiles behind the panels into the loft, in trunking where necessary), to my inverter, which is in a cool, non-dusty, downstairs utility room. The AC cable from the inverter is about 1.5m. As it happens, the grid voltage in my area is relatively high; in the high 230's to high 240's. Usually just a little over 240.

    My theory is that the inverter stands little chance of overheating, is free from effects of damp and dust and the AC cable is a short as reasonably possible. It is also much easier to get to the inverter for inspection and for monitoring what the inverter is doing. Actually, I wonder whether the noise of the cooling fan at full speed (especially as it ages, like an old computer cooling fan which groans a bit) might be audible if it was sited in the loft above one of the bedrooms, but in the downstairs utility it is well away from the living or sleeping areas.
  12. Earthstore

    Earthstore Guest

    Just a small point to add, even if the fan was noisey above a bedroom, it would not be on at night anyway, and if the inverter has a fan, they do not run all the time, just when the inverter is working hard..
  13. danesol

    danesol Regular EF Member

    North West

    I think if it was me.... I would state to the customer that the installation looks fine apart from the loose cables going over the ridge tiles which if they ever get an official inspection they may be closed down as cables shouldnt be allowed to routed in this manner ( official installation guidelines etc ) explaining that if the cables ever rub and cause a breach a short could occur and could be highly dangerous.

    This way you remain totally professional making a valid comment without leaving a sour taste, just as you would if you saw any other electrical fault which could potentially cause a fire or serious harm to anyone who comes into contact. To go into too much detail would I feel look OTT at this stage.... when all you need to do is plant the seed
  14. FB.

    FB. Electrician's Arms

    Hi Earthstore.

    The facing of my house and panels - and the local weather pattern - mean that it would be a consideration.

    My array faces SouthEast, with an open field out the back. The sun is on the panels from the moment the sun rises above the horizon - and the slightly steep 40-degree angle puts the panels perfectly facing at the sun around 9am from April to August. Long before the angle is perfect, the inverter's cooling fan will need to come on.
    The cooling fan came on between 8am-9am some sunny mornings recently - and that's with still quite low sun (about 10-15 degrees off the horizon).
    Bright sunshine streams into the back rooms of the house at annoyingly early times of the morning in spring and summer when the sun comes up early. We tend to get a lot of bright sunny mornings in this area too (and it tends to get progressively hazier from mid-morning); even with heavy curtains it's difficult to keep the rear bedrooms dark enough to sleep in the summer if we also happen to want the windows open for a bit of air (therefore the breeze moves the curtains).
    Sunrise is about 7am at the moment, but my panels will be catching the sun as early as 4.30am from through the summer.

    I need my beauty sleep and if my profile included a picture, you'd agree that 5am is too early for me to be dragging my lazy carcass out of the sack!
  15. FB.

    FB. Electrician's Arms

    For curiosity's sake, I picked the 21st June (usually the longest day) weather data from the Cambridge Universty data and their records show a good general impression of what I believe is a fair representation of the weather pattern, with its bias towards morning sunshine. This has always seemed to hold true for my location in East Anglia too.

    Digital Technology Group - Cambridge Weather on 21 June 2007

    2008 (no direct sun that day):
    Digital Technology Group - Cambridge Weather on 21 June 2008

    no data available

    Digital Technology Group - Cambridge Weather on 21 June 2010

    Digital Technology Group - Cambridge Weather on 21 June 2011
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