Incoming BT Cable and proximity to other services

[ban-all-sheds]

Looking for answers to two questions:

1) What voltage is the insulation on the incoming BT cable rated at (it's the relatively recent round cable, black sheath, quite stiff)?

2) If it is 250V+ will I get EMI problems if I route it in conduit (0.5m or so in length) with an electrical cable?

 

[blondini]

1) BT lines operate on 50v DC, but ringing current is delivered at 80v(rms) AC.

2) It's not safe for people working on the BT network, and I'm sure it's not permited, to route phone wiring alongside mains wiring.

 

[ban-all-sheds]

1) BT lines operate on 50v DC, but ringing current is delivered at 80v(rms) AC.

But that doesn't mean that the insulation isn't rated for a higher voltage - the electricity cables in your house, for example, are rated at 450/750V...

2) It's not safe for people working on the BT network, and I'm sure it's not permited, to route phone wiring alongside mains wiring.

It's both, as long as the insulation is rated to the highest voltage present, i.e. 230...

 

[blondini]

1) BT lines operate on 50v DC, but ringing current is delivered at 80v(rms) AC.

But that doesn't mean that the insulation isn't rated for a higher voltage - the electricity cables in your house, for example, are rated at 450/750V...

2) It's not safe for people working on the BT network, and I'm sure it's not permited, to route phone wiring alongside mains wiring.

It's both, as long as the insulation is rated to the highest voltage present, i.e. 230...

I didn't read question 1) properly and now I don't understand your reply on 2).

 

[Spark123]

2) is what BS7671 says about proximity of LV cables to ELV cables, though I don't know if this is taking into account any interference induced from the mains cable into the telephone cable.

 

[JOHNBOY42]

NO,NO,NO,NO,NO.......... besides the safety aspect if it is run alongside a 240v cable it will affect your adsl signal

 

[ban-all-sheds]

NO,NO,NO,NO,NO.......... besides the safety aspect if it is run alongside a 240v cable it will affect your adsl signal

I wasn't thinking about ADSL, more a 50Hz hum.

ADSL operates at kHz frequencies - will it be affected by a 50Hz signal?

 

[Spark123]

From an interference POV, I'm wondering if it would as telecoms cable is normally twisted pair hence any interference induced into one core of the pair should also be induced into the other, the ballance of the cable being taken should cancel it out. Not sure if broadband uses the pairs like this?

How the theory works in practice is another matter - I have seen normal telephone white stuff run in trunking with conduit singles before and they worked OK for voice without interference, not that I'm condoning such practice!

 

[drgl]

Run a phone cable next to mains for any length and you can get a nasty hum. Christmas tree lights can knock out ADSL so best to seperate from mains cable!!

 

[ban-all-sheds]

Fair enough - second hole through the wall it is...

 

[dazfast]

Looking for answers to two questions:

1) What voltage is the insulation on the incoming BT cable rated at (it's the relatively recent round cable, black sheath, quite stiff)?

2) If it is 250V+ will I get EMI problems if I route it in conduit (0.5m or so in length) with an electrical cable?

Mmmm lots of experts
For .5 of a metre it will be fine... obviously don't wrap it around the cable, but for that distance it WILL NOT affect the voice cable... I remember doing a test in my lab years ago for CAT5 data cable for mains induced RFI and it hardly measurable for a metre... Don't forget in in compartemtalised trunking they run along side each other for many metres! only 3mm apart! Can't be bothered to quote numbers and get all technical but, it the end it won't affect the voice cable!!!