Light, Medium and Heavy Duty Power Cords
Often, there are labels on power cords1 that you may see at your local hardware store such as “Light-Duty”, “Consumer Grade”, “Medium-Duty”, “Commercial Grade”, “Heavy-Duty”, and “Industrial Grade”. But what makes a cord this grade or that? Elements such as the jacket material, the thickness of the cord, and the environment in which it is used play a large role in determining the real durability of the cord. Let’s break this down for both North American, and Harmonized Power Cords. And be forewarned, we do our best to avoid the depths of power cord minutiae, but no promises are made.
For cords born in the USA
In the American Wire Gauge (AWG) standard the higher the number, the thinner the cord. Generally speaking, they step down by twos. 18 AWG cords are thinner than 16 AWG cords are thinner than 14 AWG cords, and so on. The thicker the cord, the more power it can deliver.
It may then be a fair assumption that the durability of the cord might be light, medium, and heavy duty according to gauge. While this is a reasonable simplification that will generally be correct, context matters.
For example, in household wiring, 14 AWG might be light duty (15A circuits) with 12 AWG preferred for heavier loads (20A circuits).
Likewise, in industrial environments, 14 AWG may be medium duty, with bigger 12, 10 and even 8 AWG cords for heavier loads.
However, as a generalization, the following table breaks out use cases for gauges 18-10 AWG.
| AWG | Max Amps | Common Duty Label | Typical Use Cases |
|---|---|---|---|
| 18 | 10 A | Light Duty | Lamps, chargers, radios, small electronics |
| 16 | 13 A | Medium Duty | Fans, computers, printers, AV gear, vacuums |
| 14 | 15 A | Heavy Duty (consumer) | Power tools, space heaters, microwaves |
| 12 | 20 A | Extra Heavy Duty | Air conditioners, large appliances, shop tools |
| 10 | 30 A | Industrial/High Load | Welders, dryers, high-capacity equipment |
In addition to the thickness of the cord, the characteristics of the cord jacket also play a large role in the durability of the cord - and again - context matters, such as the environment in which a given cord is deployed.
Some of the typical cord types in North America are: SVT, SJT, and SJTOW. Without digressing into history of the origins of these abbreviations, here is what they stand for:
SVT
S = Service cord (300V)
V = Vacuum cleaner/light-duty (lightweight construction)
T = Thermoplastic insulation and jacket
SJT
S = Service cord
J = Junior (300V rating instead of 600V)
T = Thermoplastic insulation and jacket
SJTOW
S = Service cord
J = Junior (300V)
T = Thermoplastic
O = Oil-resistant jacket
O = Oil-resistant insulation
W = Weather-resistant (outdoor-rated)
While SJT is thicker and sturdier than SVT, SVT is more flexible than SJT. The environment in which they are deployed makes a big difference in the longevity of the cord. SVT will handle environments demanding frequent movement (such as vacuuming) better than SJT. However, both will fail in oily environments (like a mechanic’s shop floor) or in wet conditions where SJTOOW is required..
International Harmonized Cords
For harmonized cords2, the physics are the same but the units of measurement differ. Instead of descending numbers for thicker wires, the cord is encoded with an identifier that includes the conductor nominal cross section in mm² in the last position indicating the thickness of the wire.
E.g. in the harmonized code for a common international jacket, H05VV5-F 3G1.0, the final 1.0 is the nominal cross section of the conductors.
The comparison between harmonized and North American wire nomenclature is nuanced. While some international standard wire sizes map to common AWG cord measurements, others fall on odd numbers. See the following table for a cross reference3.
| Harmonized Size (mm²) | Approx. AWG | Max Amps (at 60°C) | Typical Use Cases |
|---|---|---|---|
| 0.75 mm² | 18 AWG | ~6–8 A | Small appliances, lamps, chargers |
| 1.0 mm² | 17 AWG | ~8–10 A | Light loads, extension leads |
| 1.5 mm² | 15 AWG | ~13–15 A | Power tools, general circuits |
| 2.5 mm² | 13 AWG | ~20–23 A | Wall sockets, HVAC units |
| 4.0 mm² | 11 AWG | ~25–30 A | Electric cooktops, high-demand equipment |
| 5.0 mm² | 10 AWG | ~30–35 A | Welders, ovens, commercial gear |
Harmonized Material Codes
We’ve already reviewed the seemingly-straight-forward encoding of nominal cross sections in mm² at the final position of the harmonized code, and crossed them with their North American counterparts, but the similarities end there. While the North American system uses alpha designations to indicate safe operating environments, the harmonized code opts for tokens that represent the material (the actual chemicals) the jacket is made out of and leaves knowledge of the adequacy of the material for a given environment up to the engineers who spec in the power lead.
For example, here are the lists for insulating materials (3rd position) and jacket (sheath) materials (4th position).
Insulation
| Insulating Material | Code |
|---|---|
| (EPR) Ethylene Propylene Rubber | B |
| (EVA) Ethylene Vinyl Acetate Copolymer | G |
| (CR) Chloroprene rubber for welding cables | N2 |
| (NR a./o. SR) Natural a./o. Synthetic Rubber | R |
| (SiR) Silicone Rubber | S |
| (PVC) Polyvinyl Chloride | V |
| (PVC) Polyvinyl Chloride Heat-resistant | V2 |
| (PVC) Polyvinyl Chloride Low-temperature | V3 |
| (PVC) Polyvinyl Chloride Cross-linked | V4 |
| (PE) Polyethylene Cross-linked | Z |
| Halogen-free Thermoplastic Compound of Polyolefine | Z1 |
Jacket/Sheath
| Sheath/Jacket Material | Code |
|---|---|
| (EPR) Ethylene Propylene Rubber | B |
| Glass Fiber Braid | J |
| (CR) Chloroprene Rubber | N |
| (CR) Chloroprene rubber for welding cables | N2 |
| (CR) Chloroprene Rubber Heat-resistant | N4 |
| (PUR) Polyurethane | Q |
| (NR a./o. SR) Natural a./o. Synthetic Rubber | R |
| Textile Braid | T |
| Textile Braid with Flame Retardant Compound | T2 |
| (PVC) Polyvinyl Chloride | V |
| (PVC) Polyvinyl Chloride Heat-resistant | V2 |
| (PVC) Polyvinyl Chloride Low-temperature | V3 |
| (PVC) Polyvinyl Chloride Cross-linked | V4 |
| (PVC) Polyvinyl Chloride Oil-resistant | V5 |
To illustrate how the systems align, a common counterpart to SJTOOW is H05RN. The R is for “(NR a./o. SR) Natural a./o. Synthetic Rubber” and the N is for “(CR) Chloroprene Rubber” which are suitable for oily and wet locations.
Conclusion
What started as a simple question, “So what makes a cord light, medium, or heavy duty?” ended up revealing that there is much more to it than a simple answer. There is mystery buried in the numbers and letters of power cords, but for all intents and purposes, it comes down to three things: wire gauge (or cross-section), jacket construction, and the environment it’s built to survive in. While labels like “light-duty” or “industrial grade” offer a helpful shorthand, the real story is written in the specs - AWG or mm², SJT or H07RN, PVC or chloroprene.
