Clean and Impacted estimates

What is the difference between these two estimates on the checker. There is a little note about Bridge Taps on an impacted line, first of all what is a bridge tap?

Secondly how do know if your line should be clean or impacted, surely openreach should know by maps of the line?

I am currently chasing my ISP to chase Openreach to replace my underground feed which I think they accept is sub standard and not twisted pair. But what about the rest of the line can you get a pair swap if the line is within the impacted range?

The normal cause of a bridge tap is where one or more of your extensions is fed from a junction box at your premises, before the line reaches your master socket. So your master socket is at the end of a branch of a star-wired setup rather than the centre of it or the start of a daisy-chain.

That makes all the stuff about testing using the test socket useless, as it doesn't eliminate all the extensions. Which is why when advising people to see what happens using the test socket that we also tell them to make sure no extension sockets works when the faceplate has been removed. (Whether in normal use or not).

Edited by RobertoS (Mon 03-Apr-17 23:20:47)

Well if that is the case there are no bridge taps so I should get the clean estimate which is 66.2 to 80. Surely impacted isn't that simple?

I answered "first of all what is a bridge tap?" . It isn't the only thing that causes a line to be impacted, but is certainly a common one.

Sections of aluminium is another. Rubbish wiring from the PCP to the premises another - such as yours. Extension wiring fitted by builders using cheap burglar alarm cable instead of CW1308 yet another. Unfiltered ring wires. Unfiltered Sky boxes.

No doubt many other possibles.

I'm pretty sure that the extensions are all BT Kits, so should have the correct wiring and only on Saturday I made sure the 2 extensions are after the filter so the only thing I can think of is the rubbish DW3 feed and possibly the rest of the loop back to the cabinet.

In reply to a post by RobertoS:

The normal cause of a bridge tap is where one or more of your extensions is fed from a junction box at your premises, before the line reaches your master socket. So your master socket is at the end of a branch of a star-wired setup rather than the centre of it or the start of a daisy-chain.

I thought that arrangement was more commonly referred to as Star Wired.

I thought bridge taps occur where there is a T before the line reaches the property, perhaps a hangover for a party line, or to make life easier where the original cables were layed before th final destinations were known.

In reply to a post by Michael_Chare:

I thought bridge taps occur where there is a T before the line reaches the property, perhaps a hangover for a party line, or to make life easier where the original cables were layed before th final destinations were known.

I think that is the origin of the term too - because your drop-wire is tapped into a pair that continues on past your house.

The root cause is the signal reflections that come back from the far end of the "spare" piece of cable.

But the problem, and the reflection, is generic to all cases where there is an extra piece of wire involved, including star wiring, or an odd junction box that used to service a standalone bell, or (with VDSL at least) even wiring the modem into the middle of a daisy-chain.

I'll add that we've even seen one case where BT had wired the drop-wire incorrectly in the DP...

The drop-wire had two pairs, and both pairs were wired at the DP end, but not at the NTE.

It stood out because the calculations that work out how long the bridged tap is (from the Hlog graph) gave the same distance that the house was from the pole.

In reply to a post by RobertoS:

No doubt many other possibles.

Plus any of the problem caused by aging infrastructure: moisture in joints; corrosion in joints; weak joints moved by weather (ice or wind); worn insulation; stretched cables.

Plus man-made issues, like picking wires from separate pairs (so the circuit no longer has a "twisted pair"), or dodgy joints.