Ice Bridge Ground

[aaronvan]

Cell and microwave towers often have an "ice bridge ground." Does that simply protect the coax/wave guides from falling ice while serving as a ground or is there some other theory behind it?

[Mads Barnkob]

Cell and microwave towers often have an "ice bridge ground." Does that simply protect the coax/wave guides from falling ice while serving as a ground or is there some other theory behind it?

It is there for electrical safety alone. From the US electrical code we have:

Grounding of electrical equipment. Conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials [Sec. 250-2(b)].

There is however slight differences to EU electrical code on machines, EN60204-1:

Currently the NEC in Article 100 defines the terms "ground" or "grounded" as "connected to the earth or to some conducting body that serves in place of the earth." Yet, the NEC often uses the term "ground" when it really means "bond" (connected to an effective ground-fault path to clear a fault) [250.2 and 250.4(A)(5)]. The two concepts have quite different meaning.

Grounding - Grounding metal parts to the earth in premises wiring is only useful to provide a path for lightning, shunting high-frequency noise, or reducing static discharge.

Bonding - Bonding all metal parts together and then to the system winding is done to provide a low-impedance path to the source (system) to facilitate the opening of the circuit-protection device to remove dangerous voltage on metal parts. In addition, bonding the system to metal parts (typically to the X0 terminal of a transformer) stabilizes the system voltage to the metal parts and it provides a zero system reference (to the metal parts).

So far it is all clear, those are the definitions. The question is now is what to connect to Ground and what pieces of equipment should be bonded together.
The approach of the Noth American Techical norms (mainly NEC and NFPA 79) is unfortunately a bit different from the IEC (IEC EN 60204-1) and that makes the subject more complex since at the end the risk of electric shock is the same for a worker in UK or in USA.
So why two different approaches? That probably goes back to the cultural difference between the two people: the Anglosaxon Pragmatism vs the Greek and Roman Dialectics.... but we are going too far now...

Both approaches recognise the need for a ground fault path, and that is the main reason for bonding. The real difference is the concept of Class II electrical devices or apparatus that is in the EN 60204-1 but that cannot be found the National Electrical code or in the NFPA 79.

[aaronvan]

I understand the grounding function; however, what has me curious is the cable tray-looking competent. The cables always seem to run under, which made me wonder if they are just for falling-ice protection while serving as a ground path.

[Mads Barnkob]

Modern antenna towers are not floating, isolated from ground, as old ones are.

It properly just is cable protection from falling ice from the tower itself and the grounding on it is just a result of the rules for machine building and grounding all metal objects. A galvanized iron cable tray / walkway does not make any fantastic ground anyway, so that would not primarily be used for that.