Twisted pair colours

[Rob the Spark]

Hi everyone. I have a quick question about twisted pair installation microphone cable.

 

When terminating a single FST type cable as a balanced line on XLR connectors, with a white and a blue conductor, what if any is the conventional connection?

 

What I mean is would it be normal to use blue as hot (pin 2) and white as cold (pin 3) or vice versa?

 

Thanks very much to anyone who can help!

 

Rob.

[timsabre]

I don't think there is a convention - I have always used blue as cold as it is a "colder" colour in my mind... and the Canford HST colours used to be red+blue and red is obviously "hot" - but as long as you do both ends the same...

[cedd]

White first then blue also ties in with the telephone twisted pair scheme - at least as far as BT's standard goes.

[sandall]

I don't think there is a convention - I have always used blue as cold as it is a "colder" colour in my mind... and the Canford HST colours used to be red+blue and red is obviously "hot" - but as long as you do both ends the same...

That would be my thinking...

[Stuart91]

I don't think there is a convention - I have always used blue as cold as it is a "colder" colour in my mind...

 

There is apparently an IEC standard for colour coding. VDC make reference to it here (you'll need to scroll down a bit to get to the relevant bit). However the IEC code only covers 36 channels so they have extended it.

 

Obviously for a single pair mic cable it is much simpler, but "white=hot" seems to be the convention.

[Richard P-W]

Just be careful when you say "pin 2 = hot" as this is convention for audio but when you start wiring up DMX connectors, pin 2 is now cold and pin 3 hot!

 

A "Hotter" colour works nicely with white and blue but what about when you strip back a cable to find you have white and red??

 

As an aside, mains wiring in the USA uses white as neutral and black as live...

 

At the end of the day the electrons don't mind so pick what seems sensible to you, stick to it and if it's an installation for someone else - write it down in the notes :)

[Biskit]

When making up XLR extension cables (either 3 or 5 pin), ie. with a trailing connector on each end, I usually put the boots and strain reliefs onto the cable both ends, then mate the connector bits together, then after stripping the cable back I solder pin 1 (screen obviously), then just see how the twist of the pair causes the two leads to lie, and I solder them to pins 2 and 3 whichever way they 'want to go' rather than fighting them. Leaving the connectors mated means that I can easily replicate this when doing the other end, then assemble both connectors last of all. The twist of the cable means that 99% of the time the leads in the other end tend to align with the correct pins anyway (as they are the other way round). Makes things very quick, and having the connectors mated while soldering acts as a heat sink too, so less chance of melting the plastic and ending up with misaligned or loose contacts if you heat for too long.

 

I'm sure this breaks all sorts of conventions for sticking to a consistent wiring... however I'd argue that if ever repairing a cable, you should (and I would) always check both ends for consistency anyway, and never assume a particular convention has been followed.

[TomHoward]

For me, things are blue cold and white hot.

With 5-pin DMX I'll wire earth, cold, hot, but for 3-pin I always wire it to the audio standard and accept that that DMX fixture is using audio standard cabling, rather than changing convention within batches of XLRs.

[Stuart91]

for 3-pin I always wire it to the audio standard and accept that that DMX fixture is using audio standard cabling, rather than changing convention within batches of XLRs.

 

I always do the same too - I think in general it is less likely to cause confusion.

[Rob_Beech]

I've always followed the lighter colour as being hot, although this makes red and white tricky.

 

The most important part is to try and follow the convention that is already in place, if there are already 100 connectors done a certain way, then even though you are making a complete new cable it makes sense to follow their convention even if it makes no sense in your head. Same is good.

[Rob the Spark]

I've managed to get hold of one of the technical gurus at our firm and they agree that the convention is white hot and blue cold as mentioned here by several people.

 

I know it wouldn't really matter if making up an extension cable, but I'm terminating facility panels in a new theatre and may not be the person who terminates the other end at the rack end.

[Brian]

...new theatre and may not be the person who terminates the other end at the rack end.

 

Surely that sort of detail is carried on the drawings for the installation?

[adam2]

...new theatre and may not be the person who terminates the other end at the rack end.

 

Surely that sort of detail is carried on the drawings for the installation?

 

Often not in drawings IME. I think that the reasoning is that anyone competent knows how to terminate electrical power cables, I have never seen blue for neutral and brown for phase for example in drawings, and it is then presumed that the same logic applies to data or signal cables were the position is less clear cut. There is usually a clause somewhere in the specification that requires "all electric cables and cores therein to colour coded in accordance with IET regulations"

 

I agree that blue for cold is sensible as blue is a cold colour, the only drawback of so doing is when cable with red and white cores is encountered. Should one then use white for hot on the grounds that white is hot in the more common blue/white cable ? or should one use red for hot as red is a hot colour ?

 

BTW, I suspect that red/white may replace blue/white in time. There seems to be a move to discourage the use of blue conductors for anything except mains neutral.

 

 

 

[boatman]

Sadly, the old BBC (inherited from the GPO where most BBC engineers in the 50's & 60's started out) wire colour scheme was completely different:

 

Primary colours - Blue, Orange, Green, Brown, Slate

Secondary colours - White, Red, Black, Yellow, Violet

 

So pairs would be Blue/White, Blue/Red, Blue/Black etc up to a 25-pair cable. Oh happy days!

[Brian]

So pairs would be Blue/White, Blue/Red, Blue/Black etc up to a 25-pair cable. Oh happy days!

 

I'll bet, given the huge amount of that 25-pair cable installed for phones, that colour code is the most widely used multipair code.