AC Distribution

DIY off grid systems must address the bunch of code compliance issues surrounding safe installation of AC sub-circuits and AC switchboards /distribution boards.

Bear in mind that it is not allowed in this country, and most others that people wire their own switch or distribution boards. The purpose of that law is to try to prevent people killing themselves and others. Energy from an inverter is no less or more dangerous then energy from the grid. It is likely that in the event of a death, people who have wired their own AC distribution boards could be held responsible in fairly serious ways.

The following description assumes a NZ based MEN (multiple earthed neutral) system. Under MENm the AC neutral current carrying condutor is bonded to ground at various points in the distribution network, including at the genrator, substation, street transformer, and at the house. However in each house the bond should occur at one place only.

The point of the earth-neutral bond is to reduce electric shock risk, should an appliance become faulty. Having only one live wire means that should that live wire short to a metal outer case of an appliance then ac breaker/fuse will blow and the danger removed. RCDs are now also compulsory since 2003. The point of them is to detect an imbalance in current flowing out through the phase, and not returning via the neutral. See wiring diagram below. Hence the bond must go before the RCD not after. Thats important.

One of the purposes of rules, is to make sure you understand the point of them. As people seem determined to wire their own boards, the diagram below may help. Also attached is a typcial NZ DB baord. Metal boards have largely been phased out. You can see the neutral bond highlighted.

Note the seperate neutral buses for each RCD. I recomend you get name brand german made breakers and RCDs. Dont be tempted by cheap chinese trademe stuff. You only live once.

Lastly, you need to be sure that your inverter and/or generator doesnt have its own internal bond. Those can be found in some gear that isnt really intended for permanent household wiring.

Remember, it will only cost you a couple of hours plus travel to get an electrician to sign off your work. Not only is that a good second opinion on your work, but peice of mind for you and your family. Most provinces will contain at least one solar friendly sparky, who will be able to help you out there.

For our humble abode, 3 circuits is all we need. Heres the result, covers off.

www.zoneblue.nz

AC Distribution