The plot thickens.
Installer has responded to my query with a comment that a mains breaker might need to be upgraded from a 3-pole to a 4-pole... But hasn't mentioned anything about my concerns that the system might trip if we use too many high-draw items at once (ie. more than one!).
I've read a bit about 3 vs. 4, and frankly I'm a bit off my kibble so I'm not absorbing all this techno mumble jumble to know whether or not he did answer my question and I just don't get it.
Rito, here we go again.....
Usually, on single phase, 240 v, the circuit breaker is only 1 pole, especially on downstream side of the load. Sometimes, a double pole is used, and all earth leakage (Safety switches), RCD's are double pole, switching both the active 240 volts and the neutral.
A triple pole is used, usually, on 3 phase, and a 4 pole adds the neutral to be switched on 3 phases. Usually, in 'olden days' the neutral wasn't switched at all, even on the mains incomer from the grid, but modern regulations state it must be switched. A lot of 3 phase loads, motors etc, dont have a neutral anyway, so don't need a 4 pole circuit breaker.
Everyone following so far
Now, the tricky bit. Australian standards for off grid states that unless one battery terminal is earthed, say the negative by convention, only the positive needs to be protected by a circuit breaker, but.......above 50 volts dc, ie a nominal 48 volt system, both battery terminals need to be protected, even if one is earthed.
OK so far
The solar input needs to also be protected by a circuit breaker, but, here is a flaw in the regulations. The nominal current of an solar panel is say 10 amps, the short circuit current is only a little more, say 11 amps. That's not enough discrimination for a circuit breaker to give protection from a short circuit. This assumes a conventional regulator, one panel string.
Things get complicated when we start to use a Max power point tracker regulators, as they work by converting a higher voltage input, into a lower voltage output at greater current, just what we need to charge a battery. Its the current that charges it, the voltage is relatively immaterial, as long as its high enough to force current through the battery.
Conventionally, a say 12 volt system would use a solar panel rated at say 18 volts open circuit at say 10 amps, total of 180 watts output. All is good, the battery will charge at 10 amps, the panel has enough head room to make the battery reach float charge of 13.8 volts, all is good with the world. Add extra panels in parallel to increase the current into the battery and it works well. A short circuit on the solar panel will only allow a little more than 180 watts to flow per panel, not enough to cause a fire, certainly enough to damage the panel though, and look pretty cool with fireworks and smoke.
Modern MPPT regulators work differently. Take a Victron 150/100, max input voltage is 150 volts dc, max output is 100 amps. Whilst they will work using a conventionally wired panel at 18 volts, they work better and more efficiently when the solar panels are wired for a higher input voltage, up to 150 volts open circuit. This is say 8 of our 18 volt panels. Now we have over 1.5 kw of solar in a single string, and if a short occurs, 8 times more energy to cause mischeaf. Now we can have a fire, but because of the energy involved, a 10 amp breaker will trip, quite quickly. Be aware that as its above 50 volts dc, the breaker must be double pole, but that's another story.
All grid systems use a MPPT regulator for maximum efficiency.
This brings us to the isolation of a battery system. We need to break the positive and negative, as well as the solar array. How do we do it? In a conventional say 48 volt system, we use a triple pole off load isolator, so pulling it out automatically isolates the dc and solar at the same time. The path length is long enough to break the DC arc.
In a grid system, we have considerably more energy available, the grid at 32 amps, 240 volts, not just 150 volts at 10 amps. How do we isolate this, given that the solar array may well be at 240 volts as well ?
A 4 pole isolator, 2 poles for the 240 v, 2 more poles for the solar. The only issue is the breaker has to be able to cope with DC, and breaking DC is 10 X more difficult than AC as the arc created doesn't automatically go through zero volts 50 times a second, it keeps flowing, so there must be arc shields, magnetic blow out coils large air gaps, etc on a DC breaker. Expensive bit of kit.
The above explanation is necessarily simplified, its not meant to be an Electric Engineering Degree course, but to give an idea as to why Electricians do things the way we do. Some details are of necessity simplified, so not quite kosher, but the concept is there.
High voltage DC is dangerous stuff, arcs formed under fault conditions are not easy to extinguish.
Modern grid inverters have electronic protection that can discriminate between 10 and 10.5 amps, and react in ms, as opposed to conventional circuit breakers that need time to operate.
However, the regulations still require mechanical isolation from the grid, and so it should, as a semiconductor can go short circuit (and that is the usual failure mode of a transistor etc), and allow the uncontrolled grid onto the solar array, or even the roof. Bang, someone gets hurt.
Getting cold now and I must finish locking away the chickens, so hope the above helps.
The option to override the self destruct expire@)>{5f$!!lks*;s?/.....