I understand that red is used to identify ac control circuits within a control panel. I'm looking to discriminate between 110 and 24Vac. Excluding yellow and green, is there a colour commonly used for 24Vac

Generally, I don't think you can go far wrong if you follow EN60204-1 for control wiring. This is the "Machinery" industry standard for electrical safety, and does cover "controls".

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Eur Ing Graham Kenyon CEng MIET

Many thanks

The quoted Spec is a little vague, generally the end user specification dictates wire colours to be consistent with other panels on their site.

24Vdc tends to be red/black, 24Vac could be light blue / dark blue but that can easily confuse 110Vac brown/blue.
Some have 24Vac orange/orange whereas other clients have orange/orange to be voltfree non isolated external supply @ any voltage.

You need to nail down what colours are acceptable before you start.

All panels I have worked on previously had the ac/dc colours opposite to the quote above.
Whilst I agree the spec is vague & BS EN 60204-1:2006 is the standard to work too. See paragraph 13.2.4. Red = ac control circuits at any voltage. Black = ac & dc POWER circuits at any voltage. Blue = dc control circuits at any voltage. Orange = excepted circuits according to para 5.3.5. White tends to be functional earths, taken from BS7671.
There is a few colours that you can use, but as per previous post, get customer specs, or at least written agreement.
You can't use, yellow, green or green/yellow if it may be confused!
I have only seen orange "live with main isolator off" that is fed from another source.
Not seen brown in a control panel except incoming (new colours) and in special multicore cables, signal wiring etc.
There are other relevant standards as well depending on the equipment.
HTH
Paul

A couple of years ago I put together a spread sheet on wire colours. Copying / pasting doesn't work to well in the forum but this should identify what was current 2 years ago (still think it is but not checked)

Hope it helps

Regards

Howard Wheeler

Phase L1
BS 7671:2008 - Brown
BS EN 60446:2000 Brown & Black preferred
BS EN 60204-1:2006 no comment

Phase L2
BS 7671:2008 - Black
BS EN 60446:2000 Brown & Black preferred
BS EN 60204-1:2006 no comment

Phase L3
BS 7671:2008 - Grey
BS EN 60446:2000 Brown & Black preferred
BS EN 60204-1:2006 no comment

Neutral
BS 7671:2008 - Blue
BS EN 60446:2000 Blue
BS EN 60204-1:2006 Light blue

Single Phase live, L1
BS 7671:2008 - Brown
BS EN 60446:2000 & BS EN 60204-1:2006 no specific comment

Single Phase neutral, N1
BS 7671:2008 - Blue
BS EN 60446:2000 & BS EN 60204-1:2006 no specific comment

Protective conductor
BS 7671:2008 - Green/Yellow
BS EN 60446:2000 Geen / Yellow
BS EN 60204-1:2006 Green / Yellow

PEN
BS 7671 Green/Yellow with blue markings at terminations or Blue with green/yellow markings at terminations
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

Colours not to be used
BS 7671 Green
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

Functional Earthing conductor (e.g signal earths?)
BS 7671 Cream
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

D.C. (floating) positive (POWER CCTS)
BS 7671 Brown
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

D.C. (floating) negative (POWER CCTS)
BS 7671 Grey
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

D.C. Positive (neg earth system) (POWER CCTS)
BS 7671 Brown
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

D.C. Negative (neg earth system) (POWER CCTS)
BS 7671 Blue
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

D.C. Positive (positive earth system) (POWER CCTS)
BS 7671 Blue
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

D.C. Negative (positive earth system) (POWER CCTS)
BS 7671 Grey
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

Control Circuit positive
BS 7671 Brown, Black, Red, Orange, Yellow, Violet, Grey, White, Pink or Turquoise
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

Control Circuit neutral or mid wire
BS 7671 Blue
BS EN 60446:2000 & BS EN 60204-1:2006 no comment

Conductors other than protective or neutral
BS EN 60204-1:2006 Brown, Black, Red, Orange, Yellow, Violet, Grey, White, Green, Blue, Pink, Turquoise
BS 7671 & BS EN 60446 No comment

A.C. & D.C. power circuits
BS EN 60204-1:2006 Black
BS 7671 & BS EN 60446 No comment

A.C. control circuits
BS EN 60204-1:2006 Red
BS 7671 & BS EN 60446 No comment

D.C. Control circuits
BS EN 60204-1:2006 Blue
BS 7671 & BS EN 60446 No comment

Excepted ccts (not disconnected by supply isolating
device). Eg external interlock circuits, lighting etc
see p27 of EN60204-1 -orange
BS 7671 & BS EN 60446 No comment