Lightning conductor for ametuer radio antenna mast - electrician says regular PVC sheated yellow green wire is ok from mast to earth rod

mapj1:

you do not say how your antenna connects to the radio - many designs of ATU are in effect double wound RF transformers.

There are 2 very distinct issues here -

1) earthing PME/TT, and in your shoes I'd look to island as you propose if it is practiacl to keep TT earth and mains earth things apart (but beware of random items like radiators bringing  the PME earth into the shack room). But at install time you need to know the earth impedance, and it may be worth making provision to be able to monitor the voltage between the 2 earths.

The other thing you can do to reduce risk, is simply to unplug the rig from mains, when not in use, breaking the earth as well as L and N, and especially when working on the antennas, and if you are not a heavy user, and do not operate when the mains voltage is misbehaving, that may well be all that is required really, and just use the PME earth for operation in a non-lightning state and when no-one is near the antennas - I'd like to think you'd not be transmitting then anyway.


2) Lightning.

Nothing you can do will protect against a direct strike, just insure and minimise the risk as best possible.

Even a 10 ohm electrode will come up to 100kV plus during a modest 10kA strike - that will sideflash about 4 inches to any easier path, a megavolt will jump perhaps a metre or so.

I tend to just drive the end of the mast into the ground - or a length of scaff pole beside it, but less than 10 ohms is a hard target to achieve.

Induced voltages from strikes in the vicinity are more likely, but the voltages induced vary from nothing up to kV. Gas discharge devices accross the feeder or in a delat between feeder and ground help clip some of that. You need to select the voltage rating to suit the transmitter power.

The only truly safe radio in the thunderstorm is one that is not connected to an  antenna, so make provision to interrupt the antenna feeds by a large air gap and short them to the external ground when not in use - a removable coax link is often the easiest.

If you wish, carry a rod from the grounded mast onwards above the antennas, so that (hopefully) the mast tip is the attractor, rather than your prized rig. However, lightning is fickle stuff.


Others will offer varying opinions - there are as many answers as circumstances.


73 de G7VZY

There is no sperate room per say but it is a corner of the room with the closest socket to the house mains PME will be around 4-5 feet away.

The radio will be unplugged when not in the property but like you said rightly I need to be careful of the two coming near to each other.


There is a gas discharge surge protection device in line with the antenna coax and that device is also earthed through the common earth bar in the IP65 enclosure outdoors. So essentially the following are grounded through a common earth bar - Antenna mast, Coax gas surge protection device and the TT power supply.


During a storm the radio will be disconnected and I am also looking at fixing a 40A isolator between the mains power supply and the TT power supply which I will be turning off when the radio is not in use.


Any thoughts on this setup? Realistically do I need to do all of this stuff or could I just use PME for radio power supply and earth the antenna and coax?

mapj1:

you do not say how your antenna connects to the radio - many designs of ATU are in effect double wound RF transformers.

There are 2 very distinct issues here -

1) earthing PME/TT, and in your shoes I'd look to island as you propose if it is practiacl to keep TT earth and mains earth things apart (but beware of random items like radiators bringing  the PME earth into the shack room). But at install time you need to know the earth impedance, and it may be worth making provision to be able to monitor the voltage between the 2 earths.

The other thing you can do to reduce risk, is simply to unplug the rig from mains, when not in use, breaking the earth as well as L and N, and especially when working on the antennas, and if you are not a heavy user, and do not operate when the mains voltage is misbehaving, that may well be all that is required really, and just use the PME earth for operation in a non-lightning state and when no-one is near the antennas - I'd like to think you'd not be transmitting then anyway.


2) Lightning.

Nothing you can do will protect against a direct strike, just insure and minimise the risk as best possible.

Even a 10 ohm electrode will come up to 100kV plus during a modest 10kA strike - that will sideflash about 4 inches to any easier path, a megavolt will jump perhaps a metre or so.

I tend to just drive the end of the mast into the ground - or a length of scaff pole beside it, but less than 10 ohms is a hard target to achieve.

Induced voltages from strikes in the vicinity are more likely, but the voltages induced vary from nothing up to kV. Gas discharge devices accross the feeder or in a delat between feeder and ground help clip some of that. You need to select the voltage rating to suit the transmitter power.

The only truly safe radio in the thunderstorm is one that is not connected to an  antenna, so make provision to interrupt the antenna feeds by a large air gap and short them to the external ground when not in use - a removable coax link is often the easiest.

If you wish, carry a rod from the grounded mast onwards above the antennas, so that (hopefully) the mast tip is the attractor, rather than your prized rig. However, lightning is fickle stuff.


Others will offer varying opinions - there are as many answers as circumstances.


73 de G7VZY

There is no sperate room per say but it is a corner of the room with the closest socket to the house mains PME will be around 4-5 feet away.

The radio will be unplugged when not in the property but like you said rightly I need to be careful of the two coming near to each other.


There is a gas discharge surge protection device in line with the antenna coax and that device is also earthed through the common earth bar in the IP65 enclosure outdoors. So essentially the following are grounded through a common earth bar - Antenna mast, Coax gas surge protection device and the TT power supply.


During a storm the radio will be disconnected and I am also looking at fixing a 40A isolator between the mains power supply and the TT power supply which I will be turning off when the radio is not in use.


Any thoughts on this setup? Realistically do I need to do all of this stuff or could I just use PME for radio power supply and earth the antenna and coax?