witzl wrote:it would've made more sense if the power that be originally thought to keep string voltages in the ELV range (ie, below 100Vdc)... rather than up around 500Vdc.
DC voltage is far more lethal than AC, as it carries a LOT more energy than an equivalent AC voltage.
Hence why DC breakers are more expensive than AC ones, and using an AC breaker on a DC supply will melt/burn the AC breaker (as another poster mentioned already).
Im not sure how that translates to fire fighting a house with a rooftop solar system.... but i know a couple of NSW fireys who say they are unwilling to work on a house with rooftop solar - be that warranted or not, it's the bloke holding the hose and driving the truck that saves your house! If he's not willing, then your house burns down.
To me it would just make more sense for strings to be kept in extra-low voltage ranges. Much safer for all involved, and would only require a little more cabling. Of course it would be near impossible to get the industry to backflip on its pretty standard 500Vdc string voltages now.
Problem with ELV is the same for a.c. it is impractical because cabling sizing will be so much largerand all inverters will have to be changed out for ELV.
The d.c. does'nt carry more energy than a.c. its incomparable in that respect.
A.C. mains is derived from a low impedance source so can have big amps feeding faults but crosses zero many times a second so switching of normal operating currents do'nt create a problem but an under KA rated a.c. breaker automatically disconnecting a fault can blow too more explosively though, i've seen many in switchboards and this problem is widespread and rarely attended to and is getting worse as the A.C. network is being upgraded causing bigger KA at the switchboards. 3KA was old standard domestic now it's 6KA
D.C. draws a long switching arc , aka welder, so will burn a device that cannot draw out and extinguish it internally. With solar the source has a limited currrent,a higher source impedance as you probably know.
Fireys should carry CO2 or foam for these fires though, but hey how much can you carry for a fire thats spread to the roof timbers too, would think a cable or panel fire would more than likely burn itself out though.
But hey i've long been thinking of putting on my COC's that solar systems i fit,or anyone elses, do not comply with AS standards for automatic disconnection of cable arcs that can cause fires,as there is nothing available to comply with this ruling
it is skirted and hence building codes too.
On a similar note, I think there should be a recall and remove all d.c. polorised breakers and retrofit with rotorary isolators or similar rated to 1kV and then it can cater for any size system and if upgraded there should never be an issue, it's been an over site by the regulatory bodies not being quick enough, playing catch up now though.
