Blue Terminal - 24V or 0V???

Timeismoney08

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So we've run into an inconsistency between a few engineers that feel the blue terminals should be used for 24V or 0V distribution.

I know we don't have to use colors at all and there probably is no standard for this, but what do you do at your place?



Thank you!
 
We used to do blue = +24VDC OR 0VDC, grey=AC (hot), white= AC(neutral), green=ground. Now we use grey for everything except ground (still using green=ground).
 
nothing wrong with blue terminal for your 24V (I assume you mean DC).
We use grey for all voltages.
Ground are green/yellow with the metal din rail clamping.


If the DC wiring is blue I do not see a reason to use different terminal color. Also Now you have to stock 2 different terminal types.

But that is just me
 
jimtech67 said:
Also Now you have to stock 2 different terminal types.
Click to expand...

That is pretty much why we started using all grey terminal blocks, to avoid issues where we ran out of blue terminal blocks but had too many grey or vice versa. Also to avoid confusion when a spare blue terminal block was used for AC because there were no grey ones left etc which happened pretty often in the field.
 
as a SI, I used:


Black - 480VAC
Red - 120VAC (controls)
Blue - all 24VDC & analog
Green - ground


but that's been about 15 years ago.... now I use grey for everything
 
We use:

480v black
120v+ red
120v common white
24v+ blue OR brown
24v common blue w/ white stripe
Earth green or green w/ yellow stripe
 
Last edited:
I generally use the 'Whatever Is Left On The Shelf From The Last Build' color scheme.

Most of the time that is all grey, grounds are green/yellow. It differs if a customer has a specific requirement and I have enough left over for the next job.
 
JesperMP said:
Aren't blue terminals for designating intrinsically safe circuits in EX areas ?
Click to expand...

Pretty much that is the only place I've seen blue terminal blocks used.

12.2 Marking of connection facilities

Connection facilities, terminal boxes, plugs and sockets of intrinsically safe apparatus and associated apparatus shall be clearly marked and shall be clearly identifiable. Where a colour is used for this purpose, it shall be light blue for the intrinsically safe connections.

Where parts of an apparatus or different pieces of apparatus are interconnected using plugs and sockets, these plugs and sockets shall be identified as containing only intrinsically safe circuits. Where a colour is used for this purpose, it shall be light blue.
Click to expand...

As I understand it you can also identify them in another way other than colours, otherwise it shall be light blue.
 
Everyone,

this post is off topic but brings up a good safety point.

While it is accepted and its in the code book that green is supposed to be ground, DON'T accept this as being correct !!

I worked on one system that used green wire for 120 volt outputs and no I am not kidding!
I assumed ground and got lit up real fast, triac outputs.
I was not happy, I brought in the safety managers and pointed out this problem and wanted to replace the wiring. they replied, I would have to do the wiring on over a dozen panels ! keep it the way it was!

WHY would you use green for power wiring?
it was the weekend and that's all we had!

So DON'T assume green is ground on any panel, verify first.
I never made that mistake again at that facility.

james
 

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