"Andy Wade" wrote in message ...
Christopher Key wrote:

[Loftbox]
This comes with a fairly heavy duty earth bonding terminal; should this be connected back to the main
equipotential bonding connector? Instinctively, I would have assumed yes, in order to provide some
protection in the event of a lightning strike, and to keep any large
potentials from developing between exposed metalwork, e.g. radiators
and the aerial system.

If all the outlet points are serving a single household then the bonding is optional. The main purpose of
earth bonding an aerial system is to ensure safety in a distribution system serving more than one
household - e.g. in case your neighbour decides to connect the coax to the mains (this used to happen
frequently in the days of live-chassis TV sets with faulty aerial isolators). It is not a lightning
protection measure - that needs to be done outside the house, bonding the antenna system and mast using much
larger conductors. System earth bonding has superseded the former practice of using isolated output plates,
which are a disaster EMC-wise, and don't pass LNB power/control, etc.

The earth bonding terminal should be connected to the main earth terminal of your electrical installation
with a min. conductor size of 4mm^2 (or 4mm^2 copper equivalent, if not copper). (The relevant standard is
BS EN 50083-1.)

However, I understand that some AV equipment is designed to leak to
earth slightly, and am concerned about this causing ground loops and hum.

That can happen, although doesn't seem to cause problems too often. Most A/V equipment is Class 2 and
doesn't have its own earth connection to create a loop. Even if you don't earth-bond you'll still be
connecting the 'grounds' of various bits of equipment together via the coax, into one floating mass, so to
speak. If you do have a hum loop problem the best solution is to fit a 'galvanic isolator' (aka
braid-breaker filter) on the antenna input of the affected equipment. The isolator is available from
companies like Teldis (but sit comfortably when you ask the price!).


Thanks for that. The aerial / mast etc is only serving one property, but I think it is probably worth going
ahead and earthing it. The equipment is all double insulated, and their chassis are all at 75V relative to
the house earth (which is pretty close to local earth), and able to supply around 2ma or so. Enough to tingle
quite a bit, and certainly not the sort of surprise one wants when 25ft up a ladder fixing an aerial.

Elsewhere, you mentioned US Style grounding blocks. I've only been able to find them in the UK from CPC
(CN04175, CN04176), but would rather not pay £5 handling charge on a £1 order! Can you recommend anywhere
else what might carry them?

Once again, many thanks,

Chris Key