Commercial boiler instumentation cable termination?

[FrankE]

I've wired in several temperature transducers into a commercial heating system. They integrate into the heating system by way of the BMS.

The engineer has specified 4 core screeend twisted pair for all the temperature instuments. There is only one pair being used.
I've no data on the temperature transducers in use and the transducers themselves don't have any dataplate .. or even a brand name or model number on them..
Would the transducers be a PT100, perhaps?
I'm hesitant to chop off the unused pair at the instrument in case the engineer has specified the unused pair for spare use or some other reason (he's on holiday)
Should the drain on individual pairs as well as the collective screen be terminated to earth, the individual drains only or the collective drain only?

Edit: typo in title.

 

[fitz1]

you lost me after the first sentence. sorry i cant help.

 

[Biggles..]

WDIK is your man for this

 

[Agile]

I suspect he has specified four wire cable because thats traditionally used for telephone circuits and more easily available.

Virtually all home telephone circuits are wired with four core. The spare pair should be used to connect the bells in series but thats rarely done.

Tony

 

[Biggles..]

Thought home phone was 6,2 spare cores

orange,green,blue,White orange,White blue,white green

 

[casius66]

Traditionally BT and cable companies used 2 pair to supply the house, then 3 pair internally. Only 1 pair is needed to supply the line to the master socket then 1 wire is needed to extend the bell circuit.
But Agiles' point that it is easily available still stands.
I wouldn't cut back spare pairs you never know when you may need them

 

[FrankE]

It seems the engineer specified single pair but 2 pair was bought in error, though is specified in another part of the project.
It's BS5308/1 BTW.
If I ask the engineer, it may drop the company in it. We'll just chop rhem off at the transducer end and connect the collective drain and used pair drain to earth.

 

[Biggles..]

PT100's would be pretty norm for the course.

I've always been taught and still teach our graduates that any unused cores should be left in place and not cut out,have the end at the sensor capped with a heatshrink termination cap and the panel end be tied down to whatever your ref is whether that be GND or 0v.

I teach this because if one of the pairs shorts to another unused core it'll go high,nothing worse that a shock off of an unused core.

 

[FrankE]

PT100's would be pretty norm for the course.

I've always been taught and still teach our graduates that any unused cores should be left in place and not cut out,have the end at the sensor capped with a heatshrink termination cap and the panel end be tied down to whatever your ref is whether that be GND or 0v.

I teach this because if one of the pairs shorts to another unused core it'll go high,nothing worse that a shock off of an unused core.

Hahaha, thought of that, however can't get crimps off them (went through 2 bags of my own ferrule crimps), let alone Critchleys (and they've asked me to mod the panel twice) so I'm guessing heatshrink is out of the question. They've even nicked my white insulating tape being used as substitute for proper cable IDs. the lovely new panels are looking gash for the sake of a few pounds. I don't get paid enough to supply my own materials.
"it doesn't matter about that just get it connected"

Feh, sparkies!