Connector for cut telephone cable?

[dennis]

They are one of the few bits required to have the 230V warning stickers on them, along with the rectifiers.

[Frank Erskine]

On Tue, 28 Jul 2009 12:59:52 +0100, "dennis@home" had this to say:

That's because they're connected to a mains supply (well some are, others work off 50V).

The output of a ringing generator is nominally 75V.

[Dave Plowman (News)]

They might be, but the output certainly isn't. Do you really think it would be allowed to pump mains voltage down such poorly insulated circuits in the home? The figure which sticks in my mind is approx 80 volts.

[Pete Zahut]

The BT66B and block insert were used when terminating a UG feed cable to internal wiring or at the top of a pole to terminate the feed cable to the dropwire. The boxes I linked to were used mainly under the eaves of a house (or at least that's where I've seen most of them) for piecing out dropwire. I suggested them because they're a bit more unobtrusive than the grey BT66B and blend into the background better.

I've got two of them on the back wall of our house so that when we have a BBQ I can temporarily hang speakers out there and make temporary connections in the boxes, then disconnect and take the speakers back in afterwards.

[Dave Liquorice]

Might be supplied from 230v mains but ringing is as I quoted from the BT SIN 352 v4.5 earlier.

20mA loop at +/-80v?.

There is no ringing on ISDN only data. The line voltage is higher than POTS though something around 100v IIRC.

[Bob Eager]

Wriggling when caught out, once again. So predictable.

[dennis]

None of the ones we made were mains powered.

[dennis]

Who is wriggling?

I am quite willing to accept it is less than 230V, after all it is a long line with reactive loading.

[Andy Dingley]

There's no such thing (pedantically) as a "230V warning sticker". It's a "low voltage warning sticker" with 230V added to it as an annotation. The regulations categorise voltages into groups, but the requirements for warnings are based on the group and not the precise voltage. Although the sticker might well carry the voltage as a number, the set of stickers required, their placement and their wording is standardised on the broader basis of the voltage group.

230V is "low voltage". As is anything, "up to 1000V AC or 1500V DC between conductors, and up to 600V AC or 900V DC between conductors and earth."

"Extra-low voltage" is the next category down, and that's defined as, "not exceeding 50V AC or 120V DC between conductors or from conductors to earth. "

You might note an important cost-saving factor here. Not that it has much to do with safety (electricity doesn't get safer by putting a different label on it), but it saved a vast amount of money for a public body by categorizing their system as ELV rather than LV. Telephone switchgear is 50V DC (48V in the US), so it's ELV.

However ringing current exceeds the ELV category and is LV, thus needs to be treated as LV, the same as 240V or 230V mains supply. There is (AFAIR) some get-out clause for line wiring, where the ringing current is applied intermittently and (most importantly) it is only in short pulses with breaks between (this allows the electrocutee to disengage) phone local loops don't need to be treated as LV. Ringing generators though supply 75V AC and generate it continuously, such that they are then treated as 230V and require placarding and protection as if they're LV. You can have a 50V battery busbar that's made of 12" wide inch-thick solid copper and has the current behind it to justify it left bare at the top of a rack, but the ringing generator brushgear needs a cover over it and a warning label.

[Andy Dingley]

No, 20mA current loop was short-haul used for teleprinters (same hardware, but no phone dials and no routing) (and mostly a US standard, DEC CRT terminals supported it for _years_ afterwards).

Old Telex began as a current loop of about 60-65mA. This was such a high current that I recall there was actually a problem with electrolytic corrosion in UG plant from it. This current was used for local lines to Telex exchanges, but long-haul lines (mostly leased lines) went to +/- 35mA (i.e. same current, but non-polarised overall relative to earth, so as to reduce electrolysis).

The last years of Telex it used specialised modems to carry it over standard phone lines. There was still a good business for a decade or two in running "obsolete" Telex hardware in 1st world offices over POTS lines, just as the easiest way to talk to Telex machines "in country" in the 3rd world - mostly by oil and mining companies.

[dennis]

That sounds quite convincing. Its a shame I can't get at the design drawings anymore, then I could see what was actually in the box. I have thought of a better reason why I must be wrong though.. there are voltage limiters on the lines and they would trip if it were 230V on the line. I don't recall what voltage they trip at but it was well below 230V.

Ah well everybody makes mistakes (except TMH).

[Andrew Gabriel]

No, you only need a pair of pliers -- no special tools. They aren't really crimps, they're IDC's, but no punch-down tool is used -- it's built inside the jelly filled thing, and is operated just by squeezing it with pliers.