Hello,

I'm about to start installing a loftbox aerial distribution system.

http://www.tvlink.co.uk/loftbox.htm

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.

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

The electrical installation is PME, with bonds to the gas and water main.

The outlet plates will all be non isolated to at least some of their connectors in order to power and control
the LNBs, and to send remote control commands back to the Sky+ box.

Any advice much appreciated.

Many thanks,

Chris Key

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superseded the former practice of using isolated output plates, which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!).

Any advice much appreciated.

HTH, HNY
--
Andy

Andy Wade wrote:

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).

So if you've got neighbouring homes, with their TV signals coming from
separate aerials, but attached to the same metal mast up on the roof,
then earth bonding would be compulsory? That's never occurred to me...
what sort of bonding would be needed - what, where and how would it be
fitted?

(Sounds like an easier option might be a second mast!)

David

On Thu, 30 Dec 2004 14:46:44 +0000, Andy Wade
strung together this:

HNY

Had to think about that for a minute.
--

SJW
Please reply to group or use 'usenet' in email subject

"Lobster" wrote in message
...
Andy Wade wrote:

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).

So if you've got neighbouring homes, with their TV signals coming from
separate aerials, but attached to the same metal mast up on the roof,
then earth bonding would be compulsory? That's never occurred to me...
what sort of bonding would be needed - what, where and how would it be
fitted?

(Sounds like an easier option might be a second mast!)

English Heritage are "encouraging" groups of listed buildings to have a
single aerial. And no satellite TV.

Lobster wrote:

So if you've got neighbouring homes, with their TV signals coming from
separate aerials, but attached to the same metal mast up on the roof,
then earth bonding would be compulsory?

Ooh, that's one you could debate until the cows come home. What you
describe though is surely an unusual situation. The aerials for
neighbouring homes would normally be on separate masts & bracketry, even
if lashed to opposite sides of the same chimney.

what sort of bonding would be needed - what, where and how would it be
fitted?

Bond the cable outers at the points of entry. You could use US
CATV-style 'grounding blocks' (basically just back-to-back female 'F'
couplers with fixing screw holes and an earth terminal) or one of the
types of screened outlet plate which provide an earth terminal. If the
electrical earthing arrangements in the two properties are known to be
different (i.e. not both PME) then use of the aforementioned galvanic
isolator is advisable.

(Sounds like an easier option might be a second mast!)

That is the usual way :-)

--
Andy

"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

Christopher Key wrote:

snip

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?

I don't see why you'll need these. Just earth the system at the earth
terminal on the loft box.

--
Andy

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

snip

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?

I don't see why you'll need these. Just earth the system at the earth terminal on the loft box.

Sorry, should have been more clear. As we have SKY+, i'll be taking a 2nd feed from the LNB down to the
lounge, which won't be connected directly to the loft box. It seemed a little untidy having this earthed
'via' the SKY box.

Many thanks,


Chris Key

Christopher Key wrote:

Sorry, should have been more clear. As we have SKY+, i'll be taking
a 2nd feed from the LNB down to the lounge, which won't be connected
directly to the loft box. It seemed a little untidy having this
earthed 'via' the SKY box.

Still no need, the 2nd IF feed will be earthed via the body of the LNB
and the 1st IF cable to the loft box.

Moreover inserting low-grade connectors & adaptors (such as a grounding
block or ordinary F back-to-backs) in a digital satellite IF line is not
recommended since some of these devices exhibit very poor impedance
match (poor return loss or high VSWR) toward the top end of the IF band
at ~2 GHz. The reflections caused in the cable lead to signal
degradation (inter-symbol interference) which can sometimes cause
missing channels etc. If you need an in-line F coupler for satellite,
use the Cabelcon F-81HQ type which provides a really good 75 ohm match
from DC to 2 GHz+.

--
Andy