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Earthing of VSAT dishes
Former Community Member
I am trying to apply the principles of BS 7671 to VSAT installations in Africa. My chief concern is the connection of the VSAT dish to the electrical supply provided by the customer. The standard practice I've adopted is shown in the attached sketch. The metallic parts of the dish are connected with copper conductors and then to an earth spike (or spikes) near the dish foundations. The earth cable is then run (either in a conduit of buried) to the equipment building. At the entry to the building, the earth cable is used by surge arrestors fitted to the RF cables. The earth cable then runs to an earth bar fitted into the equipment cabinet. The mains supply to the equipment is supplied by the customer, the earth of which is also connected to the cabinet's earth bar. The power supplied by the customer may be from a generator 100% of the time, or more like comes from the town's municipal supply, These supplies are often erratic so a back-up generator is often in use, and as a matter of course we always fit an on-line UPS. Is this approach sensible? Thanks for any assistance.
Or at least when the login server problem is fixed.
Well the sites on Genset will be TN-S I presume, as there are more than piece of kit from reach genset and class 1 gear outside, so I'd expect an NE link at the genset, and an earth electrode of some kind.
BS7671 may not be the best standard to be looking at for this, or at least it will not provide an exhaustive list of what needs considering. There are two distinct problems, the ADS and the lightning. On a genset ADS will be funny anyway, as the prospective fault current will be quite limited.
In both genset and TT supply, the use of an RCD is key.
Lighting. To be under the cover of an air terminal some way away is probably the most sensible, but even so those other cables (RF not shown) could become quite significant in terms of importing or exporting a violent change in potential to some other place or equipment you are not expecting, as there will be quite a large and variable voltage slope across the ground in a lighting state.
As drawn there is nothing leaping out as wrong, but what are the surge arrestors doing - all they do is connect two things together if the voltage exceeds some break over limit - I'm not clear what the 2 things are. Perhaps one is a kind of local earth voltage via that long lead, what is are the other(s)
You may also wish to have surge protection that clamps the mains voltage when it comes in, so it is clipped in some known way if it tries to exceed its voltage by a large margin.
I think there is more to know in terms of the rest of the installation to understand the issues involved.
Or at least when the login server problem is fixed.
Well the sites on Genset will be TN-S I presume, as there are more than piece of kit from reach genset and class 1 gear outside, so I'd expect an NE link at the genset, and an earth electrode of some kind.
BS7671 may not be the best standard to be looking at for this, or at least it will not provide an exhaustive list of what needs considering. There are two distinct problems, the ADS and the lightning. On a genset ADS will be funny anyway, as the prospective fault current will be quite limited.
In both genset and TT supply, the use of an RCD is key.
Lighting. To be under the cover of an air terminal some way away is probably the most sensible, but even so those other cables (RF not shown) could become quite significant in terms of importing or exporting a violent change in potential to some other place or equipment you are not expecting, as there will be quite a large and variable voltage slope across the ground in a lighting state.
As drawn there is nothing leaping out as wrong, but what are the surge arrestors doing - all they do is connect two things together if the voltage exceeds some break over limit - I'm not clear what the 2 things are. Perhaps one is a kind of local earth voltage via that long lead, what is are the other(s)
You may also wish to have surge protection that clamps the mains voltage when it comes in, so it is clipped in some known way if it tries to exceed its voltage by a large margin.
I think there is more to know in terms of the rest of the installation to understand the issues involved.
