Transformer primary winding series connection wire colour - Page 1
Forum section: electronics / projects

author: Ionforbes
author_rank: Contributor
timestamp: July 29, 2021, 11:14:22 am
content: Hi all,Quite a trivial question but I couldn't find an answer elsewhere. I'm using a transformer in a project and its primary is 2x115V windings which I'll connect in series for 240V. Internally I'm using brown wire for live connections, blue wire for the neutral and green/yellow for the earth but is there a standard on what colour to use for the little bit of wire connecting the two 115V primaries? It's only a one-off personal project but since it's mains wiring I want to do it properly for the safety of future me who may poke around inside a few years later.Thanks,Ion

author: Berni
author_rank: Super Contributor
timestamp: July 29, 2021, 11:42:36 am
content: Black since that's what the Americans use for there 120V liveBut for real. It doesn't really matter. Internally equipment can use any color code they like since there are so many different wires that its impossible to have a standard color code for every single thing. But it is good practice to avoid the standard color codes to avoid confusion. So if you are using the EU color code for mains wires, then use those colors only on mains to make it clear it is mains. For anythyng else that is not live, neutral or earth, just use any other color. There are plenty of weird colors that don't have a standard use.

author: Ionforbes
author_rank: Contributor
timestamp: July 29, 2021, 11:50:09 am
content: I didn't realise that colour codes don't have to be followedinsidethe equipment. I guess I'm just overthinking it!

author: Berni
author_rank: Super Contributor
timestamp: July 29, 2021, 12:09:58 pm
content: The standard mains color codes are there to help electricians wire things up correctly. They commonly open up a junction box and just find a mess of wires inside coming in from all directions. Not having a standard would make that a living hell to sort out what is what. Dangerous mistakes could also occur.But when it comes to the inside of equipment, they are much more complex than an electrical cabinet. Some wires might carry AC power, some DC power, some might be switched power for some sort of load, some might be digital signal lines, some might be 24V signal lines, some might be analog lines, some might be digital communication buses. So we just don't have nearly enough colors to color code all of that. Also typically the inside of equipment is serviced by someone who is specifically familiar with that type of equipment. So its impossible to make a certain color code be required by law.But for some things color coding standards do exist so its best to follow them to make things easier to understand for people. For example DC power uses red and black, or USB has specific wire colors by standard. Power supplies in PCs have standard wire colors (as per ATX spec)

author: ajb
author_rank: Super Contributor
timestamp: July 29, 2021, 04:15:11 pm
content: Yes, it doesn't really matter all that much inside of equipment unless you have particular standards to meet that tell you otherwise, but NEC (US), IEC, and other standards define additional colors to support three phase wiring. In the US, Black/Red/Blue are used for each of the three phase lines in 120V/208 systems, and in IEC Brown/Black/Gray are used. It wouldn't be unreasonable to use those colors for additional lines carrying mains voltage inside of an appliance where needed. In single phase systems in the US, red is used for the second line conductor in 240V circuits and is also sometimes used for switched mains conductors, so there's some parallel there for using it for a similar purpose inside of equipment.Another thing to consider is that serviceable wiring, whether inside of equipment or facility wiring, should not rely on easily confused colors for differentiating conductors that do or do not carry hazardous voltages. Well, really, you shouldn't rely on color alone at all, but comprehensively marking wiring is a level of effort typically only justifiable in things like industrial cabinets. This is a problem with the US system using Green for PE and Red for phase, given how common red-green color blindness is. That's one of the reasons why we use IEC colors for mains inside of our equipment, even though we're building it in the US and largely for the US market and it mostly gets serviced by us rather than end users or third party technicians. (In residential wiring in the US this is less of a problem because the predominant wiring material is "NM" cable, which has an uninsulated ground conductor along with the Black line, White neutral, and optional Red second line/switched leg wires. All conductors are solid copper until you get to very large gauges since as a rule residential wiring is not installed in conduit here except in specific circumstances. But commercial/industrial wiring in conduit/raceways does use green insulated wire for PE conductors, and it usually doesn't even have a yellow stripe to distinguish it.)

author: TimFox
author_rank: Super Contributor
timestamp: July 29, 2021, 04:29:22 pm
content: It is relatively easy to find the standard color codes (for different regulatory regimes) for house wiring and power cord wiring (black/white/green or brown/blue/green-yellow).See, for example,https://community.fs.com/blog/necessity-and-standards-of-electrical-wiring-color-codes.htmlThere are also codes for "appliance wiring" inside an appliance, where there are both high-voltage (120 or 240 V) and low-voltage wires, but they are harder to locate.I remember one US code that specified the same color for wires inside an appliance with numerical labels at each end to distinguish them.