Wednesday, January 18, 2012

Safety Grounding

Grounding can be a very complex and confusing topic.  Therefore, many hams ignore it and hope for the best. 

I’ve heard folks say, “My power supply is grounded back through the wall and my radio is grounded to that.  That’s good enough, isn’t it?  The radio works fine.” 

This is a damaged radio waiting to happen.  Nearby lightning, let alone a nearby strike, has the potential to cause damage in this type of an installation.  If you are stuck with this arrangement, like in an apartment or hotel room, then you must disconnect your power supply from the wall and disconnect you radio from the antenna whenever they’re not in use. 

It is also important to make sure that the antenna connection is at least a couple feet from any conductors even the house wiring.  If at all possible connect your antenna to a ground connection that is not part of the house wiring.  I know of a case where an arc jumped about eight inches from a dangling antenna connector to a wire running from a power supply to a radio and destroyed both the radio and the power supply.  The antenna had not even been hit directly.  The hit was on a fence several feet from the antenna mast.  The mast’s base was buried in the ground.  This can be thought of in simple terms as the antenna and its feed line act as receiving antenna very close to a one terawatt[1] transmitter, i.e. the lightning strike.  There are inducted voltages like go on in a transformer too.  The point is, it does not take a direct hit to cause a lot of damage.

So what to do?  Here is a link[2] to a very good discussion on some practical things you can do.  My recommendations are as follows

                First, read “House Ground Layouts” carefully

                Second, see what others have done

                Third, read “House Ground Layouts” carefully again

                Last, put in the best system you possibly can

One thing I should mention here.  Most modern ham radio equipment has a lug of some sort to attach a ground wire.  One should not fail to connect this to ground.  The owner’s manual for the equipment will have recommendations for this connection.  This becomes very important for radio frequency, RF, ground and needs to be done properly.[3] 

I have not gone into equipment safety grounding aspect of safety grounding primarily because if one follows the advice in the references, it will be covered adequately for commercial equipment build after the 1980’s.  However, if you are using home brew (ham speak for home made) equipment or equipment built before 1980 you should assure that metal cases are grounded properly[4].  Failure to do so could result in fatal electrical shock.

[1] - Lightning and Atmospheric Electricity Research at GHCC  This is a very informative but somewhat technical.
[2] - House ground layouts  This reference is recommended by ARRL as a practical approach to the problem.
[3] - See posting “Radio Frequency Ground”
[4] - Grounding for this type of equipment must be handled on a case by case basis so I will make not recommendations along this line.  It is up to the user to become informed on the hazards and how to mitigate such hazards.

No comments: