House Rewire: Channeling/Wiring Design

Agreed, I did say better to ask, but the question made me wonder if a re-wire was your best starting point that's all

How would the cable be any less loaded by taking multiple trips back up to the ceiling, topologically it's still a ring ...

Reply to
Andy Burns
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Fair point. If I was chasing up to a socket from floor level I would probably go with the extra chase, however down from a ceiling to socket level might encourage me to re-use the chase.

Except when using cat5 for distribution of telephone signals - the input is not differential, and worse, not even balanced (only requiring one and a half pairs per line)

Hum is not the only issue either - capacitive coupling over long runs adjacent to mains wiring can also cause problems with it driving input voltages out of spec for some applications.

There are a bunch of regs that apply here, again hum is not always the main issue (although BS EN 50081 and 50082 do concern electromagnetic adn electrostatic issues with regard to telecoms circuits). There are also requirements for segregation of high and low voltage circuits (or provision of adequate earthed screening. See 528-01-01, and 02

Reply to
John Rumm

yes. OTOH phone signals travel on untwisted pairs for far greater distances than around the house, and seem quite happy. Maybe 600 ohms is low enough to avoid the problem.

yes, though not any app thats designed for this. Low impedance is all thats needed to vanish the hum.

As an example I sent audio at > For possible as yet unknown future apps, we dont know what is and isnt

its kind of odd this one. Even though you've got 4 layers of insulation between mains and LV ccts, 2 of which withstand over 1kV apiece, and the other 2 of which will withstand mains if pushed to it, its still not accepted. I understand the idea is that if the 2 services are terminated in one box theres plenty of scope for safety problems, but when they use different termination boxes, there really isnt. Triple insulation is more than good enough.

Even in case of massive overload and melting (which again has at least

2 layers of protection to prevent that) the plaster over the wires keep the 2 apart. So no less than 3 layers of protection there as well. You can run mains wires over all the unearthed metalwork you like, but not over LV circuits. I have to question it.

NT

Reply to
meow2222

*shrug* That's why I asked :-) I think I was more concerned about any heat generated. I just want to get it as right as I can.
Reply to
Organoman

To be clear, my original comment was along the lines of "if you have to ask *that* there could be a lot else you don't even realise you need to ask/do/avoid"

Reply to
Andy Burns

I know the old "stiff type" overhead drop wire isn't twisted pair, but a lot of the run is, mine is underground wired which is, and BT's cable from where the underground wire is routed to the master socket is too.

With ADSL this is getting more important within the house, a friend who works for BT (actually OpenReach) often complains about in-house and underground cables installed by builders which use alarm cable instead of phone cable.

Reply to
Andy Burns

He won't have an overloading problem but he *might* have an impedance to high to guarantee tripping times at the MCB problem, with all that cable going in.

Cheers

Tim

Reply to
Tim S

Aah, right. With you now :-)

Reply to
Organoman

Assuming 2.5 mm^2 T&E cable and that overcurrent protection is by means of a 32A Type B MCB, the maximum cable length for a conventional ring circuit is 84 metres, measured as the 'circumference' of the ring. This may need to be reduced if there are any unfused spurs taken off near the middle of the ring.

The above limit is set by voltage drop considerations, not earth fault loop impedance. Max lengths for other circumstances are to be found in Table 7.1 of the OSG (p.42).

Reply to
Andy Wade

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