BT Overhead Telephone Cable.

[Paul35]

Hello All,

Shortly, I am going to replace my guttering. As you can see in the photo, there is a overhead telephone cable near where I want to work.

The question is, IS THIS CABLE LIVE?

If I accidently touched it, will in be live or will I be protected?

Thank you.

 

[stem]

I can't see your photo, but assuming it is a telephone cable usually it wont reach 100 volts even when ringing and will be insulated anyway, so shouldn't pose any more danger to you than the cable in your home that goes to your telephone.

 

[Chri5]

Do you use BT? Because if you use Virgin then the cable is redundant and wouldn't have a live line on it.

BT live lines are 50v alternating dc, which should you mess with it during a ringing in call goes to about 75v. Perfectly harmless other than a tiny tingle.

 

[Paul35]

OK, Thank you.

I did post a photo, not sure why it doesn't show it!?

This is my first post ever! - Maybe I posted the photo wrong?
View media item 50241
I got it now!!! (you have to click on the photo to show it!!) LOL!

 

[Paul35]

The cable belongs to my neighbour not my side. if that helps?

Does anyone know what those cylinder shaped things are? They are resting on my old guttering!

Thanks

 

[Chri5]

I don't see the problem, just work round it. It wouldn't be fair to remove his active BT line, and if you did disturb it and cause fault he would be well within his rights to get you to pick up the £150+ BT mtce call out.

The position of your guttering, the ver hang and the BT wire are all on the party wall, so it's half and half regarding who "owns" the space.

 

[Monkeh]

BT live lines are 50v alternating dc

Which is it, AC or DC?

 

[danechip]

Oh, It's 50 VDC and around 75 VAC when ringing.

Dan.

 

[FDJ]

BT live lines are 50v alternating dc

Which is it, AC or DC?

Its both
50v DC but the ringing is AC.

 

[Monkeh]

BT live lines are 50v alternating dc

Which is it, AC or DC?

Its both
50v DC but the ringing is AC.

I'm aware of that. That doesn't make it '50v alternating dc'.

It's -48VDC with a 60-90VAC (not sure there's actually a consistent voltage across the country) 25Hz ringing voltage. The fact that it's -48VDC, not 48VDC, is actually important.

 

[stem]

Does anyone know what those cylinder shaped things are? They are resting on my old guttering!

I believe they are from time past (pre-1940's) when telephone wires weren't insulated and were connected to the "cylinder shaped" insulators to keep them separate. They are not used now, as the cable is connected to the bracket.

 

[JohnW2]

The fact that it's -48VDC, not 48VDC, is actually important.

Hmmm - I wonder if you might be able to expand on that!

Kind Regards, John.

 

[plugwash]

My understanding is that being negative with respect to earth reduces the incidence of corrosion when a damaged cable comes into contact with earthed water.

 

[Monkeh]

The fact that it's -48VDC, not 48VDC, is actually important.

Hmmm - I wonder if you might be able to expand on that!

Kind Regards, John.

Leg A is 0V. Leg B is -48V. The positive terminal of the battery, leg A, is tied to earth. This prevents leg B from losing material via electrolysis.

 

[JohnW2]

My understanding is that being negative with respect to earth reduces the incidence of corrosion when a damaged cable comes into contact with earthed water.

That sounds credible. The statement obviously makes sense when, as you've done, one states what the polarity of the voltage is being measured relative to (which was really my point)

Kind Regards, John