electric shock from solar panels

[Steve Firth]

They also have to assume that even if the system is shut down that there will be lethal voltage at roof level.

[Tim Watts]

On Thursday 04 July 2013 02:17 Bill Wright wrote in uk.d-i-y:

Non slates shouldn't be nailed every row. My roofers (who proved they knew what they were doing) opted for every 4th row. That does depend on the tile type and roof slope. You'd love my roof - the reccomended way to walk up it is to slide up a tile (interlocking) on every 3rd row (missing the nailed rows) and expose the 2x1 batten and step on that. I tried it under their direction and it works!

[charles]

There is a difference between titles and slates. Slates are flat and need to be nailed in while tiles, generally, have 'nibs' which support the tile on the battens. They only need the occasional nail.

[John Williamson]

When I had the slate roof on my then home re-timbered, the roofer not only re-used over 90% of the slates, he renailed them. He also put all the new slates on the back, so the front view was identical to the way it was before.

When I looked on Streetview recently, the roof still looked perfect.

If you remove a single slate,then they are impossible to re-nail, though. My roof had a dozen or more hangers showing before I looked at the woodwork.

[Dave Liquorice]

windy or

Nice shift there from tiles to slates. B-)

Unnailed tiles will push up enough across a course or two to gain access to the laths to hook/fix the brackets that then stick out below the bottom edge of the tiles for the panels.

Even properly removed with the use for ripper and decent clips(*) the removed slate is still not as firm as it was before being buggered about with it.

The slidey up brackety things don't work well on slates as you can't get at the laths well enough to get a decent fixing for the bracket. The only lath you can get at all is only accessable in the gap between slates. So you can't hook the bracket onto the lath or get more than a single screw/nail in.

Drilling into rafters and dowel screws with "nutted down" sealing gromits is not a nice solution but is pretty much the only one. Otherwise you are into lifting a lot of slates, cutting around the bracket, putting in flashing around the bracket, sealing flashing to bracket or having some other good overlap cover from exposed bracket over the flashing. The slates that have been removed to get access won't be as well fixed as they where and so on...

(*) Lead or copper strips are traditional but aren't very good, wire clips probably not much better as they work in the same way. I use the plastic ones:

The lower T section is slid up the gap between the two underneath slates and the strap is nailed to the middle lath between them. The the loose slate pushed up under the upper two slates and the top edge onto the upper lath (that's the hard bit) to the correct position and the T/slopey bit pushed up the strap to hold it in place. The slidey bit is on a ratchet so it doesn't slide back down.

[Dave Liquorice]

And the installers probably won't religiously work from roof ladders but walk about on the slates or tiles which will crack or break them. Cracked ones won't show until they break (frost action) after a while...

[tony sayer]

Harry that assumption is rather shall.. we say suspect?. So here we have a possible potential of several hundred volts DC which may, or may not be connected to anything or everything.

That potential and where it rises and what its across is unlike the mains incomer it's a very suspect power source. We can only assume that its going to behave the way it should. The problem is that the power source is up there on the roof with cables coming down into the building and even if the inverter does shut down or go t*ts up whatever, there is still that power "source" up there and thats the real problem. In a fire situation theres no way of knowing where it is or what its doing or where its connected to or to what its connected either.

It may well be safe it may well do what its supposed to do but its analogous to having say large structures all over the roof and a cable coming from next door and connected to that wherever you wish and under fire conditions what has melted thru, what has accidentally connected to whatever?...

The more you think about it the more awkward this one gets for the safety of anyone up there on the roof, or squirting water up there.

Perhaps we shall see apparatus like what they use on high voltage power line working where they bond the cables together and put a big earthing stake in!..

[Mike Clarke]

Now that's making me wonder what would be the situation with our bungalow. We don't have solar panels but the meter and CU are in the eaves space because the supply was originally via overhead cables. At some time in the distant past it was changed to an underground supply with a cable running up the outside of the house into the roof. There's no way a firefighter could get to this without going right through the burning house, assuming that he even knew where it was. The thick cable running up the wall would give a clue but for most of the year it's well hidden behind the dense foliage of a wisteria which grows up the wall.

[tony sayer]

Dennis .. I rather think that over his time as an aerial rigger Bill has spent more time and been on more roofs that you've even seen!....

[Nightjar]

AIUI, the main concern is cables inside the house that may be exposed by the fire and that fire fighters may come into contact with if they enter the building.

Colin Bignell

[Dave Liquorice]

Hum, in our case there are several CU's dotted about the place, or do you really mean that they find and pull the main cut out? The location of that is not immedately obvious here but could probably be worked out by where the overhead feed runs.

The local ambulance service have a database of actual location and directions to homes so they can find them quickly. In rural areas the post code isn't good enough and the caller may not know it... The information being provided by the home owners. I wonder if the fire service also have such a database, location of the property(*) and location/access to things like mains cut outs?

Seems wise, as far as entry in concerned. But it doesn't stop 'em standing back, breaking windows and squirting loads of water in, won't stop the fire but may contain it.

I wonder what the insurance companies are making of this?

And possibly where you live. Fire cover here is a single pump with retained crew, they can probably get to most most homes around here in 10 to 15 minutes from the brigade receiving the call. If the place has solar PV and they don't enter until a senior officer has arrived (at least 30 to 40 mins) and given the OK, the place will be effectively burnt down.

Having said that in 10-15 minuets the place will be well alight anyway as a couple did more or less burn down in the last few years and that was without solar PV slowing down entry.

(*) The fire service will most likely have a bit of a give away from the great column of smoke from the fire, the ambulance may well not have that.

[Thomas Prufer]

AFAIK, here, the minimum distance for a spray (not stream) of water to be safely directed at an electrical installation carrying up to 1000 Volts is one meter. So I think live mains is not much of a problem, as far as spraying water goes.

Compare that to the dangers of a electric hybrid vehicle in the garage, with a battery storing a significant amount of energy, using lithium which can do odd things in a fire with water added. Or propane/butane tanks, properly or improperly stored, the nasty by-products of burning PVC, a full cistern sitting on rafters that are burning, and PV panels are just one more thing in a long list of caveats.

Thomas Prufer

[docholliday93]

There must be many houses like mine (most of the ones in my street, for exa mple) where the electricity supply comes in from an underground cable direc tly into the cellar. To get to it you have to go down stairs at the back of the main part of the house, then from the bottom of the stairs all the way to the far corner of the cellar. Gas comes in there, too... House next door had a fire some years back, and the fire brigade got it und er control quite quickly, so they must have some procedure worked out.

[news]

You say "some years back" - might that have been before the days of needing a risk assessment to even put their wellies on?

[Nightjar]

As I said in another reply, AIUI, the problem is firemen inside the building walking into exposed live cables, or breaking into them when cutting into walls or ceilings when trying to reach the seat of a fire.

Colin Bignell

[harryagain]

The inverter can't work without mains power any more than an electric motor can.

There are AC and DC isolators adjacent to the inverter

But the DC is always there on the panels in sunlight.

[harryagain]

Well that wouldn't work, HV is de-energised before it is earthed before working on.

The point is that you can't stop the panels from functioning in daylight (other than covering them up.)_

Maybe they could have a spray paint device.

[dennis]

I am friends with a building inspector who is a chartered structural engineer and has been doing buildings for decades. I will believe what he tells me. Why do you think I let someone put a hole in my roof big enough to put a water cylinder through, if he had said it was likely to be a problem it wouldn't have happened. You can't even see where it was done from the outside and its only the new sarking that gives it away inside.

[The Medway Handyman]

London Ambulance use a system called FREDA (Fast Response Electronic Dispatch of Ambulances). As soon as control has the address, the info is sent to a data terminal in the ambulance, the system sets the ambulance's sat nav - and its position is fed back to control.

Very often the crew get the address before they get the details of the job. They also get updated by control on the way.

The system has a database of historic incidents by postcode, so in some areas the data terminal will flash up 'stab vest mandatory' or 'do not leave ambulance until Police are on scene'.

On Cat A calls, control stay on the phone to the caller, they can tell them where the ambo is and when the ambo gets to the street, control tell to caller to send someone outside to wave (if possible).

[Tim Watts]

On Thursday 04 July 2013 19:17 The Medway Handyman wrote in uk.d-i-y:

Christ, it's a shit world...