Unresolved support ticket open for more than six months - RESOLVED: after 8 mths
Quote from: mal0z believe me - a lifetime in telecomms has taught me that many problems are caused by poor earths.
So are the two conductors in a phone line "floating" or is one tied to to earth?
As 'Anotherone' says - a perfect telephone line is a balanced 600 ohm circuit.
Using twisted pair - therefore any interfering signal induced, would on a perfectly balanced line be equally induced on each of the wires and therefore balance out and so would not interfere with the audio / ADSL signal on the line.
But of course - the cable is not perfect, and more to the point the terminating circuits at the exchange and the customers end on the telephone and ADSL filter are not perfect - so there will be a mismatch in the impedance to earth, so some interfering signals will appear on the circuit.
It is the quality of the ADSL filter, router and exchange equipment therefore that determines how immune to interference the circuit is.
As I said on another thread - railways have a particular problem with their line side telephone circuits because of interference from the electrification, so they specify much tighter specifications for their telephone equipment used in Signal Post telephones etc etc. ( I did try to find the relevant specs but web sites have changed since my day ( a few years ago now !!. )
Now every overhead mast is earthed - obviously - but if one of these earth circuits degrades and becomes a higher impedance - because of or corrosion - then you get additional noise and this can cause interference to telephone and radio. And in wet weather, you've probably seen / heard the crackling as the water allows leakage across the insulators - and this too will cause local interference. Likewise with radio signals - ( and ADSL is at radio frequency don't forget - even though it should be confined to the telephone line ).
OK so how does this apply to the home environment - well just the same - if you have a bad earth on some circuits - this can cause local noise to be radiated - and hence get into the telephone lines, even interfere with broadcast radio and television. We used to call this "rusty bolt effect" as this can interface with any stray noise around and create harmonic signals that spread around and into nearby circuits.
So conclusion is - yes get the house electrical earthing looked at if you get a lot of interference to telephone, ADSL, radio, TV etc etc., and use good quality ADSL filters too of course.
Apologies to any younger qualified electrical / telecomm engineers around here, I haven't been active in this field for a while - I'm digging into memories of about 15 years ago and more- so apologies if I've missed anything or got a detail wrong. please correct me.
Using twisted pair - therefore any interfering signal induced, would on a perfectly balanced line be equally induced on each of the wires and therefore balance out and so would not interfere with the audio / ADSL signal on the line.
But of course - the cable is not perfect, and more to the point the terminating circuits at the exchange and the customers end on the telephone and ADSL filter are not perfect - so there will be a mismatch in the impedance to earth, so some interfering signals will appear on the circuit.
It is the quality of the ADSL filter, router and exchange equipment therefore that determines how immune to interference the circuit is.
As I said on another thread - railways have a particular problem with their line side telephone circuits because of interference from the electrification, so they specify much tighter specifications for their telephone equipment used in Signal Post telephones etc etc. ( I did try to find the relevant specs but web sites have changed since my day ( a few years ago now !!. )
Now every overhead mast is earthed - obviously - but if one of these earth circuits degrades and becomes a higher impedance - because of or corrosion - then you get additional noise and this can cause interference to telephone and radio. And in wet weather, you've probably seen / heard the crackling as the water allows leakage across the insulators - and this too will cause local interference. Likewise with radio signals - ( and ADSL is at radio frequency don't forget - even though it should be confined to the telephone line ).
OK so how does this apply to the home environment - well just the same - if you have a bad earth on some circuits - this can cause local noise to be radiated - and hence get into the telephone lines, even interfere with broadcast radio and television. We used to call this "rusty bolt effect" as this can interface with any stray noise around and create harmonic signals that spread around and into nearby circuits.
So conclusion is - yes get the house electrical earthing looked at if you get a lot of interference to telephone, ADSL, radio, TV etc etc., and use good quality ADSL filters too of course.
Apologies to any younger qualified electrical / telecomm engineers around here, I haven't been active in this field for a while - I'm digging into memories of about 15 years ago and more- so apologies if I've missed anything or got a detail wrong. please correct me.
Quote from: Catweazle OK, just had an electrician check the earthing system. He spotted straight away that there's a PME (Protective Multiple Earth) terminal installed, so that's a good sign i.e. the earth bonding to the water pipes shouldn't be necessary. Here's a Wikipedia link to earthing systems: http://en.wikipedia.org/wiki/Earthing_system (PME is also known as TN-C-S).
Quote It is possible to have both TN-S and TN-C-S supplies from the same transformer. For example, the sheaths on some underground cables corrode and stop providing good earth connections, and so homes where "bad earths" are found get converted to TN-C-S.
(see the Wikipedia article...)
When you get the consumer unit, I would opt for dual RCD's + MCD's whilst you're at it. Apparently RCD's are rather sensitive to earth leakage.
Edit - a bit more...
Quote In TN-S and TT systems, the consumer has a low-noise connection to earth, which does not suffer from the voltage that appears on the N conductor as a result of the return currents and the impedance of that conductor. This is of particular importance with some types of telecommunication and measurement equipment.
Quote from: Catweazle
. I've opted for the electrician to quote me for a new consumer unit as the old fuse box layout is very dated, and somewhat confusing - he can also ensure that all the earthing is routed via the PME terminal.
That's a good idea. Nothing worse than trying to rewire a fused unit in the dark/semi dark
just reset the trip, as most of the time the trip goes when an old tungsten bulb goes on switch on. And at least you know that no body can put ythe wrong value fuse wire in.............
Nothing wrong in that - we thought that the houses electical system may have been the problem - and the OP has wisely got an electrician in to update it. ?
You're sounding a little bit tetchy.
Quote from: Catweazle The latest BT engineer was much better-informed than the last few, but that's probably because he's a trainer from one of the regional centres.
I'll bet you he wasn't an engineer. Most of BT's engineers work at Martlesham. What you had was a technician - and I'm not knocking that - they often know more than engineer's - who sometimes have their heads in the clouds.........