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Forum Index : Solar : earthing
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Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Thanks Yahoo2. Yes i did know the answer to the earthed solar panels problem and wondered if anyone else did. The link was a good read, and always good to have a fresh look at regulations and problem areas. Sometimes it just works |
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| Privatteer Newbie  Joined: 09/06/2012 Location: AustraliaPosts: 39 |
Well if you go by that document pretty much every solar install in Aust just became non-compliant. |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Hi Crew ,, Read that new AS 5033 --What a can of worms it's going to be for new installations, considering what has been installed at my place .. I'm wondering if this new AS 5033 will be retrospective ??? . anyone know???. That would be a mammoth task ??. better go find myself a mechanical engineer to certify my tracker -- that will cost more than the system ,betcha. Think I'll move into the jungle with Allan and hide from the "feel-good regulators" Bruce. Bushboy |
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Don B Senior Member  Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Without having read the latest revision of AS 3000, or AS5033, there are a few first principles that might shed some light on how to earth things effectively. The neutral is a current carrying conductor. If it is connected to some form of earth in more than one location on your installation, then the earth system may share some of the neutral current. Should the neutral conductor have a high resistance join or, worse still, an open circuit, then significant currents have no alternative but to flow via any earth paths that the current can find. This could well mean a voltage of up to 240V AC across poorly connected earthed metal. The "earth" itself is an inherently high resistance conductor - even in the best wet organic material. If this is the only path for electrical current to flow, then significant voltages will be seen between where current enters the "earth", and where it reappears (via a second earth rod/pipe/structure). For things that merely need a reference earth, the safest thing is to have one common connection point only. This is best described as "christmas tree" earthing, because the connection diagram would look exactly like that. Even so, the safest installation is one where all metallic items have a reliable low resistance metallic bond. As Warpspeed has commented, some inverters may not have galvanic isolation, so directly earthing a DC supply source may introduce significant corrosion problems. The manufacturer's recommendations should be followed exactly here. Dissimilar metals connected together in a wet (even occasionally damp) environment will probably be subject to galvanic corrosion. This can be greatly exacerbated if there are stray DC currents flowing. If you keep these principles in mind, then the often confusing requirements of earthing regulations might make a little more sense. Regards Don B |
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Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
Here is a pdf. on grounding Solar and Various Generators, battery storage, inverters. Some of this may be useful for safety. Note; The use of grounding electrodes embedded in a concrete post to prevent corrosion. Cheers---------Roe US National Electrical code 690.00 Time has proven that I am blind to the Obvious, some of the above may be True? |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
I set out yesterday to respond to Glenn's thread re steel conduit, but my computer froze before I could complete the post. Now I can't find it again, however, this thread seems to be picking up some of the points. Glenn's concern appeared to be how best to protect his installation from the effects of a lightning strike. Because of the huge amounts of energy in a lightning strike, it is very difficult (and expensive) to reduce the risk to a small level, however, it helps to understand what happens during a lightning strike so that the damage can be minimised by the intelligent use of earthing. A lightning strike is one or several DC pulses involving huge voltages and currents. While the lightning current is trying to conduct itself into the ground, it can develop large voltages along the earthing conductors, even where these are very low resistance. As an example, if the earthing system resistance is one ohm, then a thousand volts will develop for every one thousand amps of lightning current (and there will be several). Even with a very good earth rod system, getting down to one ohm earth resistance (the resistance between the rod and the general earth mass) is a difficult exercise. What this means is that, in the event of a lightning strike, all of the metal connected to that earth system will rise up by hundreds or thousands of volts relative to the general earth mass. As you move further away from the earth rod, the voltage rise diminishes, but, in the near proximity to the rod, it is possible to get a shock between the soles of your feet, with the effect being worse the further apart your feet are (step potential). If you now have another part of your installation separately grounded, this ground will tend to be at the potential of the general earth mass, and a significant voltage drop can exist between the two systems. This voltage drop can be enough to exceed the insulation level of your interconnecting conductors If the two earthing systems are interconnected, then there will still be a voltage difference due to the voltage drop of the lightning current flowing through the interconnecting earth conductor, but it will be vastly less than if there was no bonding at all. It is also obvious that the larger the bonding conductor, the lower will be the voltage drop. This is definitely not a job for a length of fencing wire, and I would suggest that a bit of 10mm sq copper would be a good start. The unavoidable voltage rise due to lightning current flow in the earthing system can most sensibly be handled by only earthing the neutral at one point (as the regulations require), and also paying attention to earthing all equipment to ground at one point only (preferably the same earth bar where the MEN point is), using appropriate sized insulated earthing conductors for this. Having a sensible earthing system will not eliminate the possibility of damage due to inductive and/or capacitvely coupled energy causing some components to fail, but you will have done your best, and kept yourself as safe as possible. Regards Don B |
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