UL 3172 Furnace Lead Wire for Protected Internal Appliance Wiring
UL AWM Style 3172 is a single conductor with extruded insulation and a non-extruded covering, rated 200°C and 600 Vac with Horizontal Flame, across a 26 AWG through 18 AWG conductor range in solid or stranded form. The insulation is extruded silicone rubber; the covering is one or more glass or aramid braid fibrous coverings.
This page is for buyers sourcing that construction as an internal lead inside a furnace or heated appliance assembly, where the equipment design specifies or is evaluating Style 3172. The official Use for Style 3172 is internal wiring of appliances; furnace internal leads are a practical equipment context within that Use, not a UL-defined application, and the Style record names no appliance type.
Internal Component Wire, Not External Supply Cable
The distinction that causes the most confusion in furnace enquiries is between the wire inside the appliance and the cable that feeds it.
Style 3172 is appliance-internal component wire. It is not building wiring, field wiring, branch-circuit wiring, tray cable, conduit wiring, portable cord, general facility wiring, external furnace supply cable or general power distribution cable, and it is not offered for any of those roles here.
An enquiry that says “furnace wire” without saying which side of that line it sits on cannot be matched to a construction, because the two requirements are answered by different products under different standards. Stating that the lead is internal to the appliance assembly is often the single most useful line in the enquiry.
Verified UL Style 3172 Construction
| Parameter | Style-level information |
|---|---|
| UL AWM Style | 3172 |
| Construction | Single Conductor with Extruded Insulation and Non-Extruded Covering |
| Temperature rating | 200°C |
| Voltage rating | 600 Vac |
| Flame | Horizontal Flame |
| Conductor size range | 26 AWG–18 AWG |
| Conductor form | Solid or Stranded |
| Insulation | Extruded Silicone Rubber |
| Minimum average insulation thickness | 30 mils |
| Minimum thickness at any point | 27 mils |
| Covering | Same as Type SF-2 Fixture Wire; one or more glass or aramid braid fibrous coverings |
| Official Use | Internal wiring of appliances |
| Marking | General |
The construction is three parts in sequence: conductor, extruded silicone rubber insulation, then the non-extruded fibrous covering. The product description states that structure directly, which is why the braid is a covering rather than a second insulation.
The two insulation figures are separate requirements. 30 mils governs the average across the wall; 27 mils sets a floor at every individual point. Quoting only the average leaves half of the requirement unstated.
Specifying a Furnace Lead Beyond the Style Number
“UL3172 furnace lead wire” is not yet a purchase specification. The Style fixes the boundaries in the table above and leaves the rest to the ordered construction.
26–18 AWG is the permitted range, not an indication that sizes within it are interchangeable. The required conductor size comes from the equipment design, and it is specified rather than selected here. No ampacity value appears on this page, no AWG is chosen on the basis of assumed furnace wattage, and no heater current or circuit load is inferred, because none of that is established by the Style record.
Conductor Requirements Are RFQ Fields
The Style conductor requirement establishes the size range and the solid or stranded form. It establishes nothing else about the conductor.
Conductor material, conductor finish or plating, strand count, individual strand diameter, conductor diameter, conductor resistance and ampacity are all outside what the Style defines. Tinned copper is not standard here; neither is bare copper; no strand count is stated. Where the design controls any of these, state it in the enquiry:
- Required AWG
- Solid or stranded requirement
- Conductor material, if controlled
- Conductor finish or plating, if controlled
- Detailed strand construction, if controlled
These are confirmation items against a qualified construction, and they are among the most common reasons a furnace-lead enquiry has to go back to the customer before it can be quoted.
Fibrous Braid Requirements
Style 3172 permits one or more glass or aramid braid fibrous coverings, following the covering construction referenced for Type SF-2 fixture wire. Two variables sit inside that sentence: the fibre and the number of layers.
This page discusses a glass-braid furnace-lead version in commercial terms because glass fibrous braid is a permitted Style 3172 covering. That is not a statement that every Style 3172 wire uses fiberglass — aramid fibrous braid is equally permitted by the Style.
For a furnace-lead enquiry, identify whether the drawing, an existing wire specification or the assembly design controls the covering material. Where it does, the required covering is confirmed for the ordered construction rather than assumed from how the product is described.
Neither fibre is described here as better than the other, and no abrasion percentage, tensile value, heat-life figure or flexibility ranking is offered, because the Style record establishes the covering construction and not those properties. The covering is also not armour and is not described that way.
What the Braid Construction Does Not Establish
The presence of a fibrous covering does not by itself establish a quantified abrasion resistance, cut resistance, tensile strength or mechanical life, and none of those is claimed on this page.
Where a furnace assembly genuinely depends on one of those characteristics at the lead’s position, it is a requirement to state and have evaluated against a specific construction with supporting documentation — not something the presence of a braid answers.
The 200°C Rating Is a Wire Rating
Style 3172 is rated 200°C. The Style record does not use the word continuous, and neither does this page.
The rating applies to the wire. It does not establish a permitted furnace chamber temperature, and it does not establish that the wire is suitable at any particular position within the appliance. Proximity to a heating element, radiant exposure and local ambient at the routing position are equipment design questions that the wire rating does not answer, and nothing here recommends routing a lead closer to a heating element on the strength of the 200°C figure.
No furnace temperature, radiant heat level, thermal cycle count, duty cycle, service interval, airflow, heater power, motor power or expected service life is stated on this page.
600 Vac and Flame Classification
The voltage rating is 600 Vac, stated as an AC rating rather than a generic 600V, and not restated as a DC, peak, impulse or dielectric test value without separate documentation.
The Style-level flame designation is Horizontal Flame. VW-1 is a separate classification, is not claimed here, and Horizontal Flame is not converted into it. Vertical flame capability, where a specification requires it, is order-specific and separately confirmed.
Dimensional Requirements
The Style-level insulation wall requirements do not by themselves produce one universal finished outside diameter. The covering construction affects the result and is itself variable within the Style, so no finished OD is published on this page.
Furnace assemblies frequently constrain dimensions nonetheless. Where they do, state the maximum OD, the routing clearance, terminal entry dimensions, ceramic or metal feed-through clearance, clip or channel dimensions, and the required stripping length. These come from the approved construction and the equipment drawing rather than from the Style table.
Termination and Lead Preparation
Whether the requirement is bulk wire or a separately specified finished lead changes the scope of the quotation, and that is worth settling in the first enquiry.
Where the requirement goes beyond bulk wire, supply the cut length, strip length, terminal interface, connector interface and lead-end preparation. Crimped terminals, connectors, cut-to-length service and finished assemblies are not presented here as automatically available; each is confirmed per order.
What UL Style 3172 Does Not Define
- Conductor material and conductor plating
- Strand count and strand diameter
- Finished OD and OD tolerance
- Electrical resistance and ampacity
- Colour
- Cut length, terminal and connector
- Packaging and reel length
- MOQ, stock and lead time
Each is established from the ordered construction, the customer drawing or a verified SKU specification.
Substitution Risk in Furnace Lead Sourcing
A wire that is 200°C, 600V, silicone insulated and braided in appearance is not thereby equivalent to a Style 3172 construction. Those four attributes describe a group of products rather than one specification, and appearance in particular is a weak match criterion for a braided lead.
For a furnace lead replacement or a second-source exercise, compare the required Style, the AWG, the conductor requirements, the insulation construction, the fibrous covering, the dimensions, the termination interface, the marking and the equipment drawing requirements. No other UL Style is treated here as automatically equivalent or interchangeable with Style 3172; any alternative construction is a separate construction requiring independent engineering evaluation against the appliance design.
Common RFQ Mismatches
- “UL3172” requested with no AWG. The Style spans 26–18 AWG.
- Tinned copper assumed for all Style 3172 wire. Conductor material is not set at Style level.
- Fiberglass assumed to be the only permitted covering. Aramid braid is equally permitted.
- One fixed outside diameter assumed for the Style. OD varies with construction and covering.
- “Furnace wire” requested without distinguishing internal component wiring from external supply wiring.
- A temperature requirement given with no Style identified. Several constructions meet a temperature figure.
- Terminal or strip requirements omitted. Bulk wire and finished leads are different scopes.
- 200°C read as a permitted furnace chamber temperature. It is a wire rating.
- MOQ or reel length assumed to be part of the Style. Neither is defined by it.
RFQ Checklist
- UL AWM Style 3172 requirement
- AWG within 26–18 AWG
- Solid or stranded requirement
- Required conductor material
- Required conductor plating or finish
- Detailed stranding, if controlled
- Required glass or aramid fibrous covering
- Finished OD or maximum OD, if controlled
- Colour / identification requirement
- Furnace or appliance type
- Internal routing location
- Customer drawing or existing wire specification
- Cut length, if applicable
- Strip length
- Terminal / connector interface
- Marking requirements
- Quantity
- Packaging requirements
- Destination
- Required compliance documentation
These are request-for-quotation inputs, not options presented as automatically available.
UL Marking and Documentation
Material is supplied as UL-recognized component wire where supplied under qualified manufacturing scope, and UL marking is applied according to the confirmed ordered construction. The Style-level marking designation is General.
CSA AWM, FT1 and dual UL / CSA certification are not claimed here; any additional certification depends on the ordered construction. Applicable RoHS / REACH documentation can be confirmed according to the ordered construction.
