An important consideration in any system that is remotely located is the possible impact of lightning. A lightning strike can cause damage in two ways:
A direct strike on an electrical conductor can discharge extremely high voltages and currents which can cause considerable damage. Unfortunately nothing can be done to protect equipment from this. However, lightning will always take the path of least resistance, so an elevated conductor connected directly to ground will attract it away from vulnerable equipment. This is the principle of lightning conductors. Furthermore an elevated lightning conductor may be able to attract surges before them build up sufficient charge to cause major damage. A radio mast acts as an effective lightning conductor so should always be electrically bonded to ground.
A far more common cause of damage is induced surges from nearby strikes. A strike on a radio mast will induce a surge on the aerial and its connecting cable. A strike on a reservoir can cause the entire water surface, and any instrumentation in it, to briefly attain a high voltage relative to the surrounding ground. The earth’s surface has a finite resistance, so a strike to ground can elevate the local earth potential, and any cables buried in it, to a significant voltage relative to another ground point.
Induced surges could well achieve levels of of up to 1000 volts at up to 1000 amps.
These surges can be dissipated through lightning protection units. These clamp the potential to a defined voltage relative to their earth terminal. The protector should be chosen so it doesn’t affect the normal signal level but does clamp at a sufficiently low voltage to protect the equipment.
The illustration on the right shows the importance of earthing, and should be understood by anyone installing lightning protection. The ideal earth connection is heavy gauge cable connected to a buried copper mat covering a large area. A more realistic connection is a long spike driven into the ground. The normal mains earth is not ideal since the wire is relatively light gauge and may be excessively long.
We offer a range of lighting protection units as described below:
Zapgap: Aerial Lightning Protection Unit
This can be plugged into the aerial jack on an enclosure to protect equipment from surges induced on the aerial.
ZM06-x: Mains Surge Protection Unit
This is a DIN-rail mounting module that protects equipment from surges on the mains power supply.
The suffix -x defines the mains supply voltage:
ZM06-1 is for use on 110VAC supplies
ZM06-2 is for use on 230VAC supplies
ZDxx: Line Surge Protection Unit
This is a DIN-rail mounting module that protects equipment from surges on analogue instrumentation and communication lines.
ZD06 clamps at 6V and is intended for use on leased lines and private wires that carry audio signals.
ZD33 clamps at 33V and is intended for use on either 4-20mA current loop instrumentation or digital inputs/outputs that may be susceptible to lightning-induced surges. A typical application would be on a level gauge located remotely in the centre of a reservoir.