Should DC Negative be BLACK or YELLOW

[FilterGuy]

Folks,
We are so used to DC negative being black that it almost feels like a law of physics. However, since AC wiring always has the hot wire as black (In the US), there is a growing trend in the marine world to make the DC negative yellow. This helps avoid any confusion between the two. At first I scoffed at the idea, but I am coming around to see the logic of it.

What do y'all think? Good idea? Bad? Why?

Table A: Marine Color Code

Color Item Use Red DC Positive Conductor Positive Mains Black or Yellow DC Negative Conductor Return, Negative Mains Green or Green w/ Yellow Stripe DC Grounding Conductor Bonding System Bonding Wires (if insulated) Brown Generator Armature Generator Armature to Regulator Alternator Charge Light Generator Terminal/Alternator Auxiliary Terminal to Light to Regulator Pumps Fuse or Switch to Lights Grey Navigation Lights Bonding Wires (if insulated) Tachometer Tachometer Sender to Gauge Orange Accessory Feed Ammeter to Alternator or Generator Output and Accessory Fuses or Switches Common Feed Distribution Panel to Accessory Switch Pink Fuel Gauge Fuel Gauge Sender to Gauge Purple Ignition Ignition Switch to Coil & Electrical Instruments Instrument Feed Distribution Panel Electrical Instruments Brown w/ Yellow Stripe Bilge Blowers Positive Mains (particularly unfused) Yellow w/ Red Stripe Starting Circuit Starting Switch to Solenoid Tan Water Temperature Water Temperature Sender to Gauge Green/Stripe (G/x) (except G/Y) Tilt Down and/or Trim In Tilt and/or Trim Circuits Blue/Stripe (Bl/x) Tilt Up and/or Trim Out Tilt and/or Trim Circuits

 

[John Frum]

Jeff Cote makes a case for red(positive) and yellow(negative) for DC and I believe they use black(hot) and white(neutral) for AC.
Actually all of the above is from memory and my memory sucks.

I wish we had a simple unambiguous standard.
Europe uses brown(hot) and blue(neutral).

One problem is 3 conductor AC cable in North america uses red and black for the hot wires.

 

[nosys70]

green and yellow should be used only for hearth.
blue only for neutral.
other colors for phase.
in DC, usually black is negative , red is positive.
in computer , red is 5V, yellow is 12V, orange is 3.3V

 

[offgriddle]

If it's DC in USA, be it by land or by sea, the main voltage supply wire colors shall forever remain RED for positive and BLACK for negative. Of course, in order to identify the positive, (and any isolated ground), negative supply wires in a bundle that lead to multiple devices, for identification purposes I will allow the RED positive and the BLACK negative to have stripes of different colors that correspond to the wiring diagram. Urp and Asia and so on can do what they want like using brown to indicate hot instead of red to indicate hot, Bob forbid we apply some common sense and convention with wiring, right? Anyway, the great Oz has spoken. Have a nice day.

 

[Delmar]

In my industrial control days I created lots of SCR motor panels having both AC and DC wiring. Panels were accepted by UL and CSA without question.


edit: Since DC negative both carries current and is grounded I prefer white, or blue/purple if available. Actually prefer whatever spare wire is within arms reach.

 

[FilterGuy]

I poked around the wild-wild-web a bit and found so many DC color code 'standards' that it makes your head spin. It comes down to what is the primary regulating body for what you are doing and where you are at. Then add to that things like boats that move from place to place. With so many standards it is almost like there is no standard.

On boats, unless it is fresh from the factory, you must assume there is no standard. The mess that owners create with boat wiring is amazing. The only thing you can use the color for is to build a starting premise. Having a starting premise can usually speed up the verification of what it actually is.

 

[JoeHam]

For a while now US boat manufacturers have used the yellow negative standard. I believe the ABYC standards apply here. My 2016 boat came that way.

 

[kernel]

Yes, red and white for grounded pv source circuits. I will usually mark negative white except for battery connections; for continuity as most inverters use this code, and ungrounded pv. The negative is ungrounded, current carrying and should not be marked white. Its always considered hot to a visiting electrician and it should be.

Electricians who wind up servicing these likely appreciate it, even though i could care less what color the wires are, its the polite thing to do and standardization is a good thing.
(North america)

 

[offgriddle]

For a while now US boat manufacturers have used the yellow negative standard. I believe the ABYC standards apply here. My 2016 boat came that way.

Hmmm my most recent real boat was a 1995 fiberglass Stingray bowrider with 75hp Force outboard, power tilt/trim yada. I don't remember the wiring convention specifically but I always followed the red+ black- theme and identified different colors and striped wires denoting individual sub circuits and devices. I certainly will be mindful of yellow negative and as always move cautiously, observantly and use a volt meter! Thank U.

 

[offgriddle]

Yes, red and white for grounded pv source circuits. I will usually mark negative white except for battery connections; for continuity as most inverters use this code, and ungrounded pv. The negative is ungrounded, current carrying and should not be marked white. Its always considered hot to a visiting electrician and it should be.

Electricians who wind up servicing these likely appreciate it, even though i could care less what color the wires are, its the polite thing to do and standardization is a good thing.
(North america)

OK battery negative cables = black.

Negative cables coming in from solar panels, even though they are DC and DC wiring has typically used black to denote negative, are marked white BECAUSE they are not earth grounded and serve the function like an AC neutral wire, which means they can carry some returning current just like in an AC circuit?

If one earth grounds the metal mounting parts of a DC solar panel, does that also earth ground the black negative wire on the panel or is the negative wire isolated from the panel's aluminum frame parts etc?

 

[kernel]

OK battery negative cables = black.

Negative cables coming in from solar panels, even though they are DC and DC wiring has typically used black to denote negative, are marked white BECAUSE they are not earth grounded and serve the function like an AC neutral wire, which means they can carry some returning current just like in an AC circuit?

If one earth grounds the metal mounting parts of a DC solar panel, does that also earth ground the black negative wire on the panel or is the negative wire isolated from the panel's aluminum frame parts etc?

They can be white, because they are bonded to ground at one (one) point in the building electric.

Module frames are isolated from pv negative until or unless bonded to the ground network.

It is why ungrounded pv inverters note;
'Warning in case of ground fault normally de-energized conductors may be energized"

And so, ungrounded pv source circuits use black and red. And the frames are conductive and bonded, so..... watch out!

 

[offgriddle]

They can be white, because they are bonded to ground at one (one) point in the building electric.

Module frames are isolated from pv negative until or unless bonded to the ground network.

It is why ungrounded pv inverters note;
'Warning in case of ground fault normally de-energized conductors may be energized"

And so, ungrounded pv source circuits use black and red. And the frames are conductive and bonded, so..... watch out!

~ OK, i think im picking up what your laying down, thank you.
~ So far, all iv'e done is bond but NOT earth ground all DC negatives together, which include things like the battery negative terminal, SCC negative terminals, PV negative and inverter negative terminal. While the DC side of the house is not intentionally connected to earth ground, if the solar panel frames for example which connect to earth ground are not isolated from the negative DC wiring, they would provide a negative path to earth ground in that manner. Not sure what would happen in that case, do you?
~ The AC side of the house is a horse of a different color and the AC neutral is combined with earth ground in my standard household breaker panel which is supplied by either the inverter AC output or the gas generator AC output.
~ I Intend on keeping the DC negative and AC earth ground isolated from one another just like the DC and AC hots are isolated from one another, sound good? OG

 

[SolarRat]

For a while now US boat manufacturers have used the yellow negative standard. I believe the ABYC standards apply here. My 2016 boat came that way.

Yes, and for the past 10 years I keep thinking I should switch to the ABYC standards for all my new wiring. BUT...

My boat is a 2003. Black is negative. Yellow is usually some sort of switched B+, the old "standard".

I figured installing new wires with the the new yellow standard, while still having all the old OEM wires on the old standard would be a nightmare!

So...If the boat/rv came with yellow negative wires, I'd use yellow. If it came with black, use black. Someday we will all be using yellow...

 

[John Frum]

So...If the boat/rv came with yellow negative wires, I'd use yellow. If it came with black, use black. Someday we will all be using yellow...

Yep, If the existing stuff is consistent just stay with the program.
If its not then cursing is approved.

 

[Delmar]

~ So far, all iv'e done is bond but NOT earth ground all DC negatives together, which include things like the battery negative terminal, SCC negative terminals, PV negative and inverter negative terminal. While the DC side of the house is not intentionally connected to earth ground...I Intend on keeping the DC negative and AC earth ground isolated from one another...

Check the inverter battery negative terminal to see if it's connected to case ground. It is on my APC UPS. And the UPS output ground & neutral is bonded in my breaker panel, effectively bonding battery negative.

 

[jasonhc73]

Meh...

DC color codes for mains have no standard on purpose. I think because such low voltage systems the colors denote a circuit so you can identify it at the end where the power is needed.

DC
Black - -
Red - +
Orange - high voltage

AC (USA)
Black - L1
Red - L2
White - N
Blue - L3 (3phase)
Bare/Green/Green /yellow - ground
Brown - L1
Orange - L2
Yellow - L3

How can the USA have 2 colors for 3P? Like 240v split phase, a 3 phase alternator can be tapped twice for essentially 6 phases.

 

[offgriddle]

Check the inverter battery negative terminal to see if it's connected to case ground. It is on my APC UPS. And the UPS output ground & neutral is bonded in my breaker panel, effectively bonding battery negative.

Yes I will check but my invertor is a mobile, off the shelf unit from an auto parts store so it may not be case/chassis grounded to the neutral of the AC output. HOWEVER, when I upgrade to a real, stationary, (my dream is a 24VDC in 5000 watt/240 VAC), invertor I would expect there would be terminal provided for case/chassis earth ground for AC protection.

 

[offgriddle]

Meh...

DC color codes for mains have no standard on purpose. I think because such low voltage systems the colors denote a circuit so you can identify it at the end where the power is needed.

DC
Black - -
Red - +
Orange - high voltage

AC (USA)
Black - L1
Red - L2
White - N
Blue - L3 (3phase)
Bare/Green/Green /yellow - ground
Brown - L1
Orange - L2
Yellow - L3

How can the USA have 2 colors for 3P? Like 240v split phase, a 3 phase alternator can be tapped twice for essentially 6 phases.

Hmm Maybe below is a bit more clear Xplanation ..
NEC Color Code for US

The United States National Electrical Code (US NEC) has made mandatory color code for neutral power conductors and protective ground conductor. Apart from these mandatory colors, any color can be used for line or hot power conductors. The common color code for three phase in, on or behind the wall electrical wiring is shown below.





In three phase power supply, the combination of Black, Red and Blue wires for power conductors are used for 120/240V AC whereas the combination of Brown, Orange and Yellow wires for power conductors are used for 277/480 V AC.


In case of single phase power supply, Black wire is used as the line wire and in case of 220V supply, Red wire is used as the secondary line conductor.

 

[offgriddle]

I thought red and black were the standard for DC. I've never seen anything else. You learn something new every day.

I believe that red and black still is the standard for DC main power cables in US automotive and general DC applications. With that being said, multi wire cables in vehicles and boats etc. that power up multiple devices can use other colors to indicate hot and ground to identify power wires that run to specific devices. In such case refer to the wiring diagram and/or use your volt meter. Black is the most common hot color for AC single phase in the USA followed by Red. One can use colored tape, (not white or green), to identify other hot wires in an AC single phase situations too if multiple hot wires need to be individually identified.

 

[tictag]

Meh...

Good to "UK" separate from "Europe" in the colour coding picture! ... a prediction of things to come ;-)

Bit disappointing to see such drab colours, though ... Brown, Black, Grey...


I reckon we should restrict solid colours to DC circuits with AC circuits carrying a spiraling coloured stripe e.g.

Type	DC	AC (Low Voltage)	AC (High Voltage)
L1 / Positive	RED	RED / PURPLE	RED / ORANGE
L2	-	RED / BLUE	RED / YELLOW
L3	-	RED / CYAN	RED / GREEN
Neutral / Negative	BLACK	BLACK / WHITE	BLACK / GREY
Earth	GREEN / YELLOW	GREEN / YELLOW	GREEN / YELLOW

DC is always a solid colour, AC is always a 'varying' colour.
Red is always live, Black is always return
Low Voltage AC has 'colder' spirals
High Voltage AC has 'hotter' spirals