Lightning Protection Best Practices

[Josh]

A few months ago I lost my TV due to lightning. Last night I lost my DVD due to lightning as well. I am about to install CBUS and I want to find out what are best practices regarding lightning protection. I know there are no sure guarantees, but the must be ways to reduce the 100% change of being hit or rather reduce the number of hit units.

[Richo]

A few months ago I lost my TV due to lightning. Last night I lost my DVD due to lightning as well. I am about to install CBUS and I want to find out what are best practices regarding lightning protection. I know there are no sure guarantees, but the must be ways to reduce the 100% change of being hit or rather reduce the number of hit units.

Here are some links to discussions containing this subject:

http://www.cbusforums.com/forums/showthread.php?t=607
http://www.cbusforums.com/forums/showthread.php?t=452

[Don]

C-Bus units all incorporate overvoltage protection diodes across the C-Bus lines. These are quite robust, and generally limit the damage due to lightning strikes to the units near the entry point of the surge. I have been told of cases in Cairns where lightning strikes are fairly common (in cyclone season), and the affected networks lost only a few of the units; never the whole network. This might be some relief.

Surges on the mains side of units of sufficient voltage could jump across the isolation to the C-Bus lines. There's nothing stopping you running the C-bus differential pair through almost any Varistor or gas-disharge based surge protector, but avoid impalanced types and types that incorporate any filtering function, as this could affect the C-Bus data. Protection of this type should be able to reduce damage due to indirect discharge.

At my home, cyclone season also brings lots of lightning, and in the past 8 years, I have not had any C-Bus losses due to surges. I have protected my installation with surge arrestors at the main switchboard, and also with an earth 'mat' bonded at approximately 10 places into the ground below the house to reduce potential differences through the building(it was easy as the house is on steel stilts).

Ideally, you could run all C-Bus wiring in metal conduit, and ensure that the conduit is earthed at many points to a ground plane, but in practice, it should be sufficient to avoid obvious things like long runs outdoors (elevated or underground). A bridge is a good idea, but it would not be very effective against a direct strike as it provides an extra 10mm or so of clearance between the networks, and the opto-couplers are rated to less than 10kV. A bridge is good for limiting the number of units affected by intermittent shorts or water damaged cables, etc.

Don

[Josh]

Thanks for your response guys.

This really puts my mind at ease.