What to do with extra wire when connecting Tesla charger

Question

Using Teck90 cable to install Tesla charger. I only need the red, black, and blue wires. Should I just cut the bare copper short and leave it unconnected at both ends? I’m in British Columbia, Canada.

Answer 1

TL;DR Skip the blue wire

Most consumer EVSE (a.k.a., "chargers") in the US/Canada have three wires:

• Hot 1
• Hot 2
• Ground

The two hot wires can be black, white (more below), red, blue, yellow, etc. Any color except green, yellow/green or bare. White is normally the neutral color, so it can only be used with a 2-wire (not counting ground) cable, and then it must be marked with black (or red, blue, yellow, etc.) tape on both ends to indicate it is a hot wire.

Which means this particular cable makes no sense at all. That being said, it happens to be OK. According to the TECK90 cable specifications, this type of cable is armored (that's good), allowed for wet or dry locations (that's good) and available in various sizes (also good). But the combinations are interesting:

• 2-wire plus ground - black, white, bare ground

This is perfect for EVSE - use black as one hot, white marked with another color as the second hot, and bare ground.

• 3-wire plus ground - black, red, blue, bare ground

This is what you've got. It makes no sense in almost any residential applications. What are the residential applications that require 3 wires (plus ground)?

• 3-way switches for lighting - usually need white for neutral
• dryer, oven, similar - need white for neutral

It isn't impossible to find a use for black/red/blue/bare cable in a residential usage, but relatively unlikely.

• 4-wire plus ground - black, red, blue, white, bare ground

This would be unusual as well. But at least could be used in certain situations such as some 3-way switch circuits (but usually don't need 8 AWG or larger wires, and also usually don't need armored cable) to carry, hot, two travelers and neutral.

In fact, the entire TECK90 line seems to be designed much more for industrial uses than for residential uses.

Which really gets back to Harper's Law: Buy the wire last. Before buying any wire or cable, you need to figure out:

• How large the wires need to be (AWG), based on required minimum for a given usage (how much you need) and maximum based on Load Calculation (how much you can get).
• Type of wire or cable depending on: wet vs. dry, indoor vs. outdoor vs. underground, armored vs. unprotected (and protect with wood or conduit or metal) vs. wires in conduit, etc.
• Ease of installation
• Cost (in particular, aluminum is usually significantly cheaper at sizes larger than 10 AWG, but certain applications (especially EVSE) and/or local rules often require copper instead of aluminum).

So in this case, use the TECK90 black/red/blue/bare - it is paid for and will work just fine. But if you had to do this all over again, using requirements of:

• Armored or similar protection required
• Wet location (often, but not always, for EV charging)
• AWG based on circuit requirements (I'll assume this is correct, it is really a separate issue)
• 2 hot wires, no neutral, ground

then, if the price is right, you could easily end up with a 2-wire (plus ground) TECK90 cable. Nothing wrong with the 3-wire, but it includes an extra wire you will never use. Why do I say never? If you decided to take out the EVSE and put in a subpanel so that you could power multiple EVSE (and possibly other things as well), you would find that the blue wire can't be used as neutral. Which means it didn't even get you "future proofing" the way a white wire in a typical black/red/white/bare cable would do.

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By request in comments, a little more explanation on:

Neutral is Always White, but White is NOT Always Neutral

TL;DR Code says so. And if that is good enough for you, you can ignore the rest of this essay.

Note: This is ignoring HUGE wires, where the possibly apocryphal Model T quote, "Any color, as long as it's black" applies and any wire can be remarked as needed. It is also specific to US/Canada as other regions have different color schemes and different rules. Also ignoring certain rules for 3-phase power and other industrial stuff.

There are 3 basic color rules in the NEC for typical residential wiring:

• Green, Yellow/Green and bare wires are ALWAYS ground.
• Black, red, blue, yellow, orange, etc. are ALWAYS some form of hot. Meaning that when in full use they will carry current that is nominally 120V relative to ground and neutral. This includes: always hot, switched hot, 3-way switch travelers (arguably a form of switched hot).
• Neutral is always white (well, also can be gray in conduit, but as you'll see conduit is not the issue here). In conduit, white is always neutral. In cable, white is NOT always neutral.

Note that the first two rules are "color is stuff" and the last is "stuff is color". Also note that the last rule is more specific in conduit. Why? Because in conduit it should never be too hard to replace a white wire with a black/red/blue/etc. wire. The goal is to make things as simple as practical. Replacing wires in conduit, when needed to make circuit wires color-coded by function, is practical to do.

All of which means that the "white is not always neutral" ONLY applies in cables. This is for very practical reasons. If you want to wire up a typical house, nearly everything in a branch circuit (i.e., excluding the feed from the meter to the main panel) can be done with 2-wire or 3-wire cable. (The count of wires does not include ground. Ground is implied, always there, always green or yellow/green or bare, always all connected together. And therefore ignored in this discussion.) Which means that if you want to wire up a house then you can do just about everything except for occasional very large appliances (some ovens, some EV charging, tankless hot water (but please don't!), etc.) and subpanel feeds with the following types of cable, where cable is allowed (excludes Chicago, New York City, etc. where you must use wires in conduit):

• 14 AWG 2-wire for 15A circuits (e.g., most lighting, receptacles, 120V appliances, small 240V appliances)
• 14 AWG 3-wire for 15A circuits (e.g., 3-way switch circuits, new switch loops, multi-wire branch circuits)
• 12 AWG 2-wire for 20A circuits (e.g., most lighting, receptacles, 120V appliances, small 240V appliances)
• 12 AWG 3-wire for 20A circuits (e.g., 3-way switch circuits, new switch loops, multi-wire branch circuits)
• 10 AWG 2-wire for 30A circuits (e.g., water heater)
• 10 AWG 3-wire for 30A circuits (e.g., clothes dryer)

And if you don't mind somewhat higher wire costs then you can use 12 AWG wherever you would use 14 AWG. (Technically even 10 AWG anywhere you would use 12 AWG or 14 AWG, but that is really too much extra cost to justify for most people, most of the time.)

That's 6 types of cable and you have covered everything on any circuits up to and including 30A, which covers most of most houses. In order to keep things simple, the 2-wire cables almost always (exception, apparently red/black commonly used in Canada for 240V-only) are black and white. 3-wire cables almost always (exception, this TECK90 stuff!) black, red and white. Which means you can use the "natural" colors for:

• Lighting
• 120V receptacles
• 240V/120V receptacles (e.g., clothes dryer)
• 120V appliances (dishwasher, disposal, 120V HVAC equipment, etc.)
• New-style switch loop (if the neutral isn't needed then the white wire is capped but required for future use)

leaving only:

• 240V receptacles (not so common for most people)
• 240V appliances (e.g., air conditioning/heat pump compressor, water heater)
• Some 3-way switches (note: new 3-ways require neutral, which must use the white wire, so either they are wired with /3 cable and use white as neutral (i.e., 2 travelers, no always hot or switched hot) or if that isn't practical then /4 cable (2 travelers, neutral and either always hot or switched hot) and use white as neutral.)
• Old-style switch loops

and probably a few other odd-ball things I haven't thought of. In each of these cases, white is marked as a hot wire with tape (easy and clear but can fall off), marker (sometimes hard to find) or heat-shrink tubing (more work).

The NEC (and other building rules) is a balance between cost and safety. The NFPA (which writes the NEC, with plenty of input from industry and others) at some point made a determination that allowing one direction of changing wire functionality (white from neutral to hot, but not the other way around) provided a reasonable balance. Specifically:

• It keeps the number of cable types to a minimum - i.e., for most purposes a standard set of /2 and /3 can always be used, no matter what the application (instead of having to have 4 types, /2 with white, /2 without white, /3 with white, /3 without white)
• A "hot" color always gets treated as possibly hot unless/until you are sure that power has been removed from the circuit
• White on a 240V circuit (which is usually quite obvious - water heater, etc.) is mostly obvious to people working on the circuit. Exception, where extra care is needed: 240V receptacles - but those are not as common in a typical residence, and when they are present (e.g., cooktop) very often dedicated circuits.
• In order to make it more obvious when white is not neutral, there are some additional rules. For example, in an old-style switch loop, white is used as the "always hot" instead of the "switched hot". That means that a non-contact voltage tester will activate on that white wire if the circuit has power, whether or not the switch is on. Since the black wire is presumed to be "hot", that increases safety because if someone is working near that circuit (obviously if they are working on that switch then they'll be aware of the situation) and their NCVT beeps on a white wire then they know it is not a neutral. If the white wire was the switched hot wire and the switch was off then they could get zapped in a combination of: white wire conductor exposed for some reason + someone flips the switch on.

If you allow the other way around: mark a non-white wire white for use as a neutral then:

• You have increased options on cabling, but not actually gained anything in terms of cost-saving except for the occasional "I've got this cable and would like to use it for xyz" (see Harper's Law: Buy the wire last.).
• There is no fundamental difference between two hot wires, but of course there is a huge difference between them and the neutral wire. Which has some interesting ramifications. For example:

If you have a /2 black/white cable to a hot water heater and you are replacing it, if the tape falls off the white wire it doesn't matter. You hook things up and put on a fresh piece of tape. But if you have a /2 black/red cable to a 120V receptacle and you are replacing it, if the tape falls off one of the wires you MUST figure it out so you know which wire is neutral because hot and neutral have specific locations (and functions) on a 120V receptacle. Just guessing will only be right 50% of the time. Not allowing hot colors to be marked as white/neutral avoids this dangerous situation.

If you have /3 black/red/white cable to a subpanel, the two hots are interchangeable and the white is neutral, so there is absolutely no guesswork required. If you have /3 black/red/blue cable to a subpanel then you must be 100% sure which wire was used as neutral. If it was marked and that came off then double-checking (and the main feed could be 150' away in another building) is a must.

These problems don't happen with white-marked-as-hot because the end result is "all wires the same", whereas hot-color-marked-as-white-neutral results in "wires no longer the same".

Answer 2

This cable is for 3-phase delta!

Teck is cable for mines, where they use a lot of 3-phase delta. Black, red, blue are all "hot" colors and none of them can be used for neutral, fortunately you don't need neutral for an EVSE.

You can use this cable for EVSEs (EV chargers) as long as you use 2 of the wires only, and cap off the 3rd at both ends.

Safety ground must be the bare wire. That's what it is for.

But don't buy this variety of cable anymore. Okay? Hold out for black-white-red. Somebody makes it, because they know Teck is used for more than mines.

Torque all terminals to spec at both ends with a torque wrench or driver. Remember the spec is INCH pounds not foot-pounds!

Answer 3

The bare wire must be used for ground. Wires colored red, black, or blue in this size may not be used for ground (there is an exception for much larger wire gauges that aren't made in arbitrary colors, but you're not at that size).

Since the EVSE doesn't use neutral, use any two of the non-bare wires for the hots. It doesn't matter which you choose.

You can trim back some of the excess of the unused third insulated wire, but it's a good idea to keep 6" or so, in case you want to swap this Tesla EVSE for some other device later that does need the third wire without having to replace the entire cable run.