TW wire was 'the norm' from when to when?

15 years ago

Just doing a little "forensic" analysis on an older building, before pros show up to bid on the big re-wire, re-PANEL, conversion of overhead service drop to buried, etc.

Anyway, it's all EMT, metal boxes, and TW copper conductors... SIX different brands of TW, obviously from different eras, judging by the "age" of the rubber, the style of fonts/graphics printed on the rubber, etc... figured the original builder used only 1 or 2 brands of TW back in the early 1950s, and the other brands came from the increasingly bad "work" since then. At some point the "upgrades" stopped, because there's no 90C wire (e.g. THHN) to be found.

Just curious as to what years TW (60C, rubber insulation) was "standard issue", and when the change to 90C wire (thermoplastic insul.) occurred?

Featured Answer

Ron Natalie

8 years ago

last modified: 8 years ago

Officially, it means nothing as an acronym or abbreviation. It is a designator for a particular type of conductor and its insulation. While they have their origins in real words, its just a code the listing entity uses.

You can intuit T means Thermoplastic (insulation). I suggest that W means Wet no Wiring.

Thermoplastic-insulated wire is rated 600 V and is designated as follows:

TW — Indicates a single conductor having flame-retardant, moisture-resistant thermoplastic insulation. The wire is rated 60°C wet or dry.

THHN — Indicates a single conductor having flame-retardant and heat-resistant thermoplastic insulation with a jacket of extruded nylon or equivalent material. The wire is rated 90°C dry only.

THW — Indicates a single conductor having flame-retardant, moisture- and heat-resistant thermoplastic insulation. The wire is rated 75°C wet or dry.

THW-2 — Same as THW except that the wire is rated 90°C wet or dry.

THHW — Indicates a single conductor having flame-retardant, moisture- and heat-resistant thermoplastic insulation. The wire is rated 90°C dry and 75°C wet.

THWN — Indicates a single conductor having flame-retardant, moisture- and heat-resistant thermoplastic insulation with a jacket of extruded nylon or equivalent material. The wire is rated 75°C wet or dry.

THWN-2 — Same as THWN except that the wire is rated 90°C wet or dry.

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Comments (13)

bus_driver
15 years ago
TW is not rubber. It is thermoplastic.
brickeyee
15 years ago
TW is PVC, poly vinyl chloride.

It showed up after WWII until recently replaced in NM by 90 C THxx type.

It is normally rated at 60C and is visibly thicker than THxx type insulation.

TW in NM appears about 1/16 inch thick, while THxx is closer to 1/32 thick (thickness is over the wire).
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bus_driver
15 years ago
I have not attempted to determine if any manufacturer still makes TW. But the NEC still includes it and if an installer has some, it can be installed in accordance with the NEC and local codes, if any. I still see some that I installed in 1958 that has been, and still is, completely trouble free.
mike_kaiser_gw
15 years ago
Remember that you can't necessarily determine when the upgrades stopped based solely on the absence of 90Ã¯Â¿Â½ wire because there's no way to determine how much TW wire the electrican/owner had in stock. Let's, for sake of discussion, say that TW was phased out in 1970. If the building owner got a good deal on TW wire, he could have been using it in the 1980's. Especially in years past folks weren't too quick to throw stuff out.

I can get you a good deal on some brand new Armstrong vinyl floor tiles from the 1960's.
tombs31
15 years ago
I was still installing tw in the late 70's.
mikezusa
12 years ago
I know this is a dated thread, but today I pigtailed a strand of THHN to TW wire.... TW looked much heartier than the new THHN... both 14g.

Is there any harm in joining the two under a wirenut?
bus_driver
12 years ago
No harm whatsoever.
mikezusa
12 years ago
So I am assuming the issue with TW is the 60C rating. What precautions need to be considered? In regards to light fixtures esp?

I can imagine wrong wattage bulbs are an issue. When a fixture calls for a specific wattage these days, does it take into acount 60C wiring?
Ron Natalie
12 years ago
Wattage doesn't mean anything really for insulation temperature. A higher temperature rating will mean you can have slightly higher ampacity on the wiring but for most branch circuits it's immaterial, you'll use 14 for 15A, 12 for 20A.

Certain fixtures might require 90C wiring for the fixture wiring for heat issues. You can splice in a length of 90 to your 60c branch circuit wiring at some convenient point (next box in the chain). The whole circuit doesn't need to be 90c wiring.
Efren Pinafiel
8 years ago
What is the meaning TW of wire
greg_2015
8 years ago
last modified: 8 years ago
Efren,

What do you mean? Are you asking what TW is? I think that's been explained above.

Or are you asking what TW is an abbreviation of?

If so, google tells me it's "Tracer Wire".

Or it's also telling me "Thermoplastic Wire". That one probably makes more sense.
bob lang
2 years ago
In the early 1960s in the Cleveland, Ohio area I was wiring houses with TW (thermoplastic wire). Because of the 60C rating, ceiling lighting fixtures would have a fiberglass and foil shield to protect the wire from the heat of the light bulbs. we were still wiring houses in knob and tube so the 60C wire was in free air which also prevented overheating.