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Flexible cord types SJ SJT SO

Type SJ, SJT and SO flexible cords are multi-conductor cables designed for portable or temporary electrical connections that require high flexibility. Their construction with extra-flexible copper conductors and resistant jackets makes them suitable for hard and extra-hard use conditions. The SJ designations indicate junior hard service with a nominal voltage of 300 V, while the letter T denotes thermoplastic insulation and jacket, and the O indicates oil resistance. S cords correspond to extra-hard service with a 600 V rating.

Service, voltage and temperature

Section titled “Service, voltage and temperature”

The nominal voltage for SJ and SJT series cords is 300 V, while type S and SO cords reach 600 V, allowing their use for powering higher-power industrial equipment. Versions with a thermoplastic PVC jacket (SJT) normally operate between −20 °C and 60 °C (−4 °F and 140 °F). Cords with rubber or neoprene insulation and jacket (SJ, SO) maintain flexibility over a wider range, typically from −40 °C to 90 °C (−40 °F to 194 °F), depending on the specific compound.

Construction

Section titled “Construction”

Each flexible cord is composed of two or more stranded soft copper conductors class K or similar, with a cross-section ranging from 0,82 mm² (18 AWG) up to 33,6 mm² (2 AWG). The individual insulation can be PVC (thermoplastic) in SJT types, or EPDM rubber in SJ and SO types. The outer jacket, likewise of PVC or neoprene, groups the conductors in a round shape and provides mechanical and chemical resistance. Conductors are identified by colors according to the corresponding code (black, white, green for three conductors, adding red or blue for four conductors).

Types of flexible cords

Section titled “Types of flexible cords”
Code Description AWG size No. of conductors Insulation Jacket Max. voltage Typical use
SJ Junior Hard Service 18 – 10 2 to 4 Rubber Rubber 300 V Hard indoor use
SJT Junior Hard Service Thermoplastic 18 – 10 2 to 4 PVC PVC 300 V Hard indoor use
SJTO SJT oil-resistant 18 – 10 2 to 4 PVC Oil-resistant PVC 300 V Hard indoor use with presence of oils
SJTW SJT weather-resistant 18 – 10 2 to 4 PVC Weather-resistant PVC 300 V Hard outdoor use
S Hard Service 18 – 2 2 or more Rubber Rubber 600 V Extra-hard indoor use
SO S oil-resistant 18 – 2 2 or more Rubber Oil-resistant neoprene 600 V Extra-hard indoor use with oils
SOOW S with oil- and weather-resistant insulation and jacket 18 – 2 2 or more Oil-resistant rubber Oil- and weather-resistant neoprene 600 V Extra-hard outdoor use with exposure to oils

Current carrying capacity

Section titled “Current carrying capacity”

The ampacity values shown correspond to cords with copper conductors, maximum ambient temperature of 30 °C (86 °F), and operation at voltages up to 1000 V. For installations with several grouped cables or temperatures above 30 °C, the correction factors indicated at the end of the table must be applied.

AWG size Conductor diameter (mm / in) Cross-section (mm²) 2 – 3 conductors (A) 4 – 6 conductors (A) 7 – 24 conductors (A)
18 1,0 mm / 0.040 in 0,82 mm² 7 A 5,6 A 4,2 A
16 1,3 mm / 0.051 in 1,3 mm² 10 A 8,0 A 6,0 A
14 1,6 mm / 0.064 in 2,1 mm² 15 A 12 A 9,0 A
12 2,1 mm / 0.081 in 3,3 mm² 20 A 16 A 12 A
10 2,6 mm / 0.102 in 5,3 mm² 30 A 24 A 18 A
8 3,3 mm / 0.129 in 8,4 mm² 40 A 32 A 24 A
6 4,1 mm / 0.162 in 13,3 mm² 55 A 44 A 33 A
4 5,2 mm / 0.204 in 21,2 mm² 70 A 56 A 42 A
2 6,5 mm / 0.258 in 33,6 mm² 95 A 76 A 57 A

Correction factors for ambient temperature above 30 °C:

  • 31 °C – 40 °C (88 °F – 104 °F): 0,82
  • 41 °C – 45 °C (106 °F – 113 °F): 0,71
  • 46 °C – 50 °C (115 °F – 122 °F): 0,58

Applications

Section titled “Applications”

SJ cords are used in portable power tools, heavy appliances, and workshop extensions operating at 120/240 V. SJT variants are intended for indoor use with medium mechanical stress, such as industrial vacuum cleaners or mobile lighting fixtures. SO and SOOW cords cover 480 V or 600 V applications in submersible pumps, construction equipment, temporary outdoor lighting systems, and industrial machinery where resistance to oil, moisture, and abrasion is required.

Frequently Asked Questions (FAQ)

Section titled “Frequently Asked Questions (FAQ)”

What is the nominal voltage of a type SJ cord?

Section titled “What is the nominal voltage of a type SJ cord?”

The type SJ cord has a nominal voltage of 300 V, which classifies it as junior hard service, and it can be used in 120 V or 240 V circuits.

Up to what ambient temperature can a standard SJT cord operate?

Section titled “Up to what ambient temperature can a standard SJT cord operate?”

An SJT cord with a PVC jacket operates continuously between −20 °C / −4 °F and 60 °C / 140 °F; at higher temperatures an ampacity correction factor must be applied.

What sizes does the SO series cover?

Section titled “What sizes does the SO series cover?”

SO cords cover from 18 AWG (0,82 mm²) up to 2 AWG (33,6 mm²), with two or more conductors, allowing management of loads up to 95 A in 2- to 3-conductor configurations.

What is the current capacity of a 16 AWG three-conductor SJ cable?

Section titled “What is the current capacity of a 16 AWG three-conductor SJ cable?”

An SJ 16 AWG cord with three conductors has a base ampacity of 10 A at 30 °C / 86 °F, according to reference values for copper cables with PVC insulation.

What does the letter O mean in the SO or SJTO designation?

Section titled “What does the letter O mean in the SO or SJTO designation?”

The letter O indicates that the outer jacket is oil-resistant; if a double O appears, for example in SOOW, both the insulation and the jacket are oil-resistant.

How is the ampacity of an SJT cord derated when installed at 40 °C?

Section titled “How is the ampacity of an SJT cord derated when installed at 40 °C?”

At 40 °C / 104 °F, the correction factor is 0,82; therefore, an SJT 14 AWG cord rated at 15 A is reduced to approximately 12,3 A.

References

Section titled “References”