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Topic Title: DC Cabling
Topic Summary: Colour discussions
Created On: 31 March 2011 11:03 PM
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 31 March 2011 11:03 PM
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johnnymoore

Posts: 10
Joined: 06 December 2010

Hi all,

I'm pretty new to the electrical field & recently received a memo informing me that we have been using incorrect DC cabling colours. Can anyone shed any light on this?

I have been using Red for +, Blue for - & black for any necessary midpoints. Today I was told this has been changed to IEE rules, using brown and grey. Some other's have been using brown & blue for <48VDC (think this is completely wrong though)

I personally find this a bit odd as it then doesn't really help distinguish AC phases & DC when fault finding.

Any comments on this?

Thanks,

Johnny
 01 April 2011 12:01 AM
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Paul1966

Posts: 1538
Joined: 21 December 2004

Unfortunately, the new standard in BS7671 messed about with the coding for d.c. as well as a.c. wiring.

Under the "harmonized" system for d.c., blue is used for the earthed conductor, whether 2-wire or 3-wire, with brown for positive and gray for negative.

So a 2-wire negative-earth circuit will be brown & blue, a 2-wire positive-earth circuit will be gray & blue, and a 2-wire circuit with neither pole earthed will be brown & gray.

For 3-wire, it's brown positive, gray negative, and blue for middle wire (whether earthed or not).

It's a horrible mess, isn't it?

Edited for slip of fingers last night!

Edited: 01 April 2011 at 09:49 AM by Paul1966
 01 April 2011 05:58 AM
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broadgage

Posts: 3170
Joined: 07 August 2007

The new colours for DC are indeed silly, perhaps even more so than the new 3 phase colours.
Not certain what colour is meant to be used for a non earthed center tap on a DC supply. AFAIK blue is only permitted for the earthed neutral of a DC supply, whether this be positive, negative, or a center tap.

In the real world the old colours are still used within equipment, and sometimes elswhere.
Many small batteries come with leads attached, these are invariably black/red I have never seen one with brown/grey leads.
Multi meters for electronics use (not installation testing) invariably come with red and black test leads.
DC circuits on trains still use red/black.
PV modules with attached cables still use red/black.
Battery leads with UPS equipment, and the battery terminals themselves are still red/black.
The traction current on London underground is a three wire DC system and they still use blue for negative and red for positive.

I might , if pressed admit to wiring a house for DC useing the old colours ! I might also admit to not useing an RCD for everything on 12/24 volts DC.
 01 April 2011 09:57 AM
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Paul1966

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Joined: 21 December 2004

Originally posted by: broadgage
Not certain what colour is meant to be used for a non earthed center tap on a DC supply. AFAIK blue is only permitted for the earthed neutral of a DC supply, whether this be positive, negative, or a center tap.


According to Table 51, it's blue for the middle wire of a 3-wire d.c. circuit whether earthed or not:

http://electrical.theiet.org/w...rmonised.cfm?type=pdf

The entry for mid-wire of 3-wire d.c. power circuit is shown as blue, with a reference to notes 2 & 3:

(2) M identifies either the mid-wire of a three-wire d.c. circuit, or the earthed conductor of a two-wire earthed d.c. circuit.

(3) Only the middle wire of three-wire circuits may be earthed.


So the middle wire may be earthed, but is still supposed to be blue even if it isn't.


Originally posted by: g3xoi
And will the system break down where there are multiple, separate, d.c. voltages on a panel? 5v, 12v, 24v and so on.....


See the last section of the table - It gives alternate colors for all "non power" circuits, although still with blue for neutral or mid-wire.
 01 April 2011 06:26 PM
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alancapon

Posts: 7492
Joined: 27 December 2005

The trouble with dc systems is that there have been far too many changes over the past few years, particularly in the telecoms area where the positive pole of the battery is solidly earthed. We started with red/black (red positive & earthed), moved to blue/black (black positve and earthed) and now moved to grey/blue (blue positive and earthed). In the middle somewhere, we also had black/grey for a while, but it did not catch on.

I think most companies have put their marker in the ground, and either stuck with red/black, or moved on to numbering of conductors, or use a combination of the two. Within the electricity supply industry, we already had a standard for alphanumeric coding wires - made from one letter and one or more numbers. For dc, the odd numbers are positive (whether earthed or not), for ac, the phases are odd numbers. We would tend to use "J" for a dc supply and "H" or "M" for a mains supply. We also use A, B, C, D, E, G, K, L, N, P, S, T, V and W as well for control / indications. In terms of colours in panels, we often wire entirely in black or grey, but may use colours to denote other voltages in some cases. We also sometimes run CT and VT wiring in red/yellow/blue, as it stands out more.

Regards,

Alan.
 01 April 2011 08:10 PM
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ArthurHall

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Joined: 25 July 2008

Most new substations I have worked in recently use the new colours. It is no problem for negative earthed control circuits as two core brown and blue can be used. For SCAD systems the brown can be sleaved or taped grey, some companies use 4 core cables and tie back the brown and black cores. Often you have both systems on the same site which is OK as long as you remember blue is connected to earth.

As Alan said traditionaly AC wiring was grey and DC black single cores. However NGC is now going to all white wiring.
Most power companies decided to ignore the colour changes on primary plant and stick with RYB, however this gets complicated for CT and VT wiring as RYB cables are now dificult to source, so they are having to use 'new colour' cables or go with white cores and sleaves and/or ferrules. NGC now sleave all CT wiring red and all VT wiring yellow.
 01 April 2011 08:21 PM
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alancapon

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Originally posted by: ArthurHall
. . . However NGC is now going to all white wiring. . .

That is interesting. We tend to use white cored SWA (obviously with the cores numbered), then not use white for wiring within the cabinets. This means by looking at a connection, it is easy to tell what it is (from its standard ferrule ID) and whether it is wiring to the plant or not (whether it is a white core). A substation we are rebuilding at the moment is wired like this, and it makes it easier to disconnect the plant wiring without having to check for "live ends" all the time.

Regards,

Alan.
 02 April 2011 10:13 PM
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BobJamesCo

Posts: 295
Joined: 26 November 2004

As a critic of harmonised colours, which have made the UK a laughing stock in Europe, ( Try showing a Polish spark how to add a new circuit to a 5 year old 3 phase DB. )
I would like to add to the DC colours debate, I produce around 30 small control panels a year, mainly for plastic extruders, For the 24v DC circuit I use Purple for + and - , and have never had a customers technician not understand it..
To bring the colours for power into the control circuits shows complete stupidity and lack of common sense.
With the Harmonised colours and the producing of an amendment to the New 17th edition so soon, I believe the IET has lost its way..
Back to 24v......use purple
 02 April 2011 10:28 PM
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alancapon

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Originally posted by: BobJamesCo
. . . I would like to add to the DC colours debate, I produce around 30 small control panels a year, mainly for plastic extruders, For the 24v DC circuit I use Purple for + and - , and have never had a customers technician not understand it. . .

If we are not wiring everything in black, we have been known to use purple for 24v and grey for other dc voltages (48 or 110).

Regards,

Alan.
 02 April 2011 10:52 PM
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Paul1966

Posts: 1538
Joined: 21 December 2004

Originally posted by: BobJamesCo
To bring the colours for power into the control circuits shows complete stupidity and lack of common sense.

With the Harmonised colours and the producing of an amendment to the New 17th edition so soon, I believe the IET has lost its way..


Yet still so many people seem to want to follow it. Why don't more people just ignore the joke that it's become and carry on using more sensible methods?
 03 April 2011 03:37 AM
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gkenyon

Posts: 5354
Joined: 06 May 2002

Just to add to the mess, EN60204-1, which is a Harmonized Standard for safety of electrical equipment for "machines", where a "machine" is as defined in the Machinery Directive and the UK Supply of Machinery (Safety) Regulations, and includes control panels if they are for the "machinery", has d.c. power circuits as Black, and a "Neutral" as "Light blue".

Since the standard recommends PELV, then for example the 24 V d.c. may well be Black (+ve) and "Light Blue" (-ve Earthed).

And to make matters worse, d.c. control circuits (e.g. often switched positive d.c.) are recommended to be "Blue".

Excellent. The standard does have these as "recommendations", and does permit other colours that aren't "Light Blue", which is supposed to be reserved for a Neutral conductor, and "Green/Yellow", which is reserved as "Earth".

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 03 April 2011 10:20 AM
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Paul1966

Posts: 1538
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Originally posted by: gkenyon
and a "Neutral" as "Light blue".


Way back when the European scheme was adopted for flexes the original standard specified light blue rather than just "blue."

Gradually over the years, it seems as though many manufacturers of flexes have forgotten about the "light" part.
 03 April 2011 10:42 AM
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broadgage

Posts: 3170
Joined: 07 August 2007

Originally posted by: Paul1966

Originally posted by: gkenyon

and a "Neutral" as "Light blue".




Way back when the European scheme was adopted for flexes the original standard specified light blue rather than just "blue."



Gradually over the years, it seems as though many manufacturers of flexes have forgotten about the "light" part.


Yes, I believe that LIGHT blue was specified in order that persons with defective colour vision, or studying a black white and photograph would know which wire was which.
Dark wire=live
Light wire=neutral
Striped wire=earth.

The drawback of the old colours was that red and green looked similar to many people, and that was dangerous to a colour blind householder fitting a plug to an appliance.
These days very few householders ever need to fit a plug, though if they do, knowing that the stripped wire is the earth is useful.
With a dark blue neutral and a light brown live, a colour blind person might well reverse live and neutral, but should still correctly identify the earth.
In the real world, reversing live and neutral on a portable appliance seldom matters, afterr all in Europe the same appliance is equiped with a plug that can be inserted either way round, and no one worries.
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