Please note the setup I'm describing is a temporary one and a new cable is being installed within few weeks. However for the time being I have to use a wire close to its max rated current carrying capacity so I'm a bit worried about said cable meting down.
Therefore I'm looking into a possibility of using something to switch off the power if this happens(in addition to a normal overcurrent protection).
Essentially I have one 5 conductor wire that carries all the current on 3 single phase supplies one way(2+2+1) - each wire is 2.5mm2 and it carries 20A at most. And a much thicker common neutral wire carrying the return current. The neutral is adequately oversized so I don't worry about it.
No doubt someone will say 20A is far too much for 2.5mm2 (awg14) and 5 conductors under load in a 5 wire cable, but I checked our "national guidelines" and for a 5 wire cable with 3 wires under load the max is 26A. For a 7 wire cable with all 7 at full load it is 19A. So I assume a 5 wire cable with 5 conductors loaded 20A is probably very close to a max rating.
But I do worry about possibility of shorting these individual single phases between eachother which will trip the breakers eventually, but before it does it may smoke inverters or start a fire (although this particular wire goes only through non flammable cement based masonry the pvc insulation itself is flammable).
All these two-parallel wires are the same thickness, the same length. So the current should distribute equally over them. However as I might be on occasion at 99% of max current capacity of each wire and one wire breaks the other likely will melt down. So in addition I wonder if it's useful to fit a circuit breaker for each individual wire. I'm leaning towards doing that.
Now using a 3 phase rcd will protect from this cable melting down and the current "escaping" to ground. But it will do nothing to protect from shorts between these "phases".
Does any other solution exists to protect phases from shorting to eachother? (other than an overcurrent protection). Also, am I right in thinking this will cause inverters to break as if it shorts at worse posible(180deg) phase difference there will be a total of 630V between the wires (315V peak in 240V AC system). There is no way in hell these inverters can handle this. Would fitting 315V surge protection devices help with such situation? (I'm fitting one type 2 +3 anyway).
In a way it would be somewhat similar to having a short between L1 and L2 on an American style split phase solar system(albeit at far lower voltage). Perhaps some of the members in the US have experienced such shorts and can say if circuit breakers saved their inverters or not?
Therefore I'm looking into a possibility of using something to switch off the power if this happens(in addition to a normal overcurrent protection).
Essentially I have one 5 conductor wire that carries all the current on 3 single phase supplies one way(2+2+1) - each wire is 2.5mm2 and it carries 20A at most. And a much thicker common neutral wire carrying the return current. The neutral is adequately oversized so I don't worry about it.
No doubt someone will say 20A is far too much for 2.5mm2 (awg14) and 5 conductors under load in a 5 wire cable, but I checked our "national guidelines" and for a 5 wire cable with 3 wires under load the max is 26A. For a 7 wire cable with all 7 at full load it is 19A. So I assume a 5 wire cable with 5 conductors loaded 20A is probably very close to a max rating.
But I do worry about possibility of shorting these individual single phases between eachother which will trip the breakers eventually, but before it does it may smoke inverters or start a fire (although this particular wire goes only through non flammable cement based masonry the pvc insulation itself is flammable).
All these two-parallel wires are the same thickness, the same length. So the current should distribute equally over them. However as I might be on occasion at 99% of max current capacity of each wire and one wire breaks the other likely will melt down. So in addition I wonder if it's useful to fit a circuit breaker for each individual wire. I'm leaning towards doing that.
Now using a 3 phase rcd will protect from this cable melting down and the current "escaping" to ground. But it will do nothing to protect from shorts between these "phases".
Does any other solution exists to protect phases from shorting to eachother? (other than an overcurrent protection). Also, am I right in thinking this will cause inverters to break as if it shorts at worse posible(180deg) phase difference there will be a total of 630V between the wires (315V peak in 240V AC system). There is no way in hell these inverters can handle this. Would fitting 315V surge protection devices help with such situation? (I'm fitting one type 2 +3 anyway).
In a way it would be somewhat similar to having a short between L1 and L2 on an American style split phase solar system(albeit at far lower voltage). Perhaps some of the members in the US have experienced such shorts and can say if circuit breakers saved their inverters or not?
