USA Mains Power Cable Specifications

For many design engineers and purchasers the area of US Mains leads can be a minefield as unlike in the UK the American standards are a little more complicated.

This Blog will guide you thought the various different type of cables and what the common abbreviations actually mean.

Let’s start with the basics.   National Electrical Manufacturers Association (NEMA)[is the equivalent to the British BS Standards so many people refer to the leads as NEMA leads but as with all thing that’s quite generic.


The most common connectors are the two pin and the two pin + earth these are:

NEMA 1-15 ungrounded (Type A)


This is the ungrounded 2-Pin Connector plugs are generally polarised and can only be inserted one way because the two blades do not have the same width. The blade connected to neutral is 7.9 mm wide and the hot blade is 6.3 mm wide. This plug is rated at 15 A.


NEMA 5-15 grounded (Type B)


The NEMA 5-15 plug is rated 15 A at 125 volts, and has two flat parallel blades like NEMA 1-15, as well as a (longer) ground pin. Both current-carrying blades on grounding plugs are normally narrow, since the ground (earth) pin enforces polarity. NEMA 1-15 plugs are also compatible with NEMA 5-15 sockets. In the US the National Electrical Installation Standards (NECA 130-2010) specifies that the ground hole should be on top. Sideways installation is also permitted.


Cable Types:

 Common types include Type SJT, SVT, SEOW, SJ, SJOW, SJOOW, SO, and SOW, each designed for specific applications.


S = Severe Service Cord – 600 volts (also 277/480 or 480) – May be utilized in place of SJ or SV in extra-severe service

SJ = Junior Severe Service – 300 volts (also 120 or 120/208 or 120/240 or 240 or 277, but not 277/480)

T = Tinsel Cord (only if first letter of code for a portable cord)

T = Thermoplastic (if not first letter of code)

H = Heat Resistant

HH = High Heat Resistant

N = Nylon Outer Jacket Material

E = Elastomer (flexible thermoplastic that looks and feels like rubber)

O = Oil-Resistant Outer Jacket

OO = Oil-Resistant Outer Jacket and Oil-Resistant Interior Insulation

P = Parallel Cord (conductors are not twisted around each other)

V = Vacuum Cord – 300 volts (typically used with vacuum cleaners and other portable cleaning equipment)

W-A = Weather Resistant (UL approved for indoor and outdoor use)

W = Weather and Water Resistant (CSA approved for indoor and outdoor use)


Typical Conductor Sizes:

The most common wire size for a USA Power lead is 18 AWG which it the most widely adopted however 16 AWG and even 14 AWG can often be found with the standard  NEMA 5-15 plug.

I hope this has helped it’s certainly not easy to get to grips with the various types and if you are designing products for the US market it’s important to get this right.  If you are worried about which cable to use then of course your local cable assembly experts are on hand to assist.

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