B North American three-prong plug

Type A with an extra round earth pin – the standard socket in North America.

Standard: NEMA 5-15
Current: 15 A
Voltage: 100–127 V
Earth: yes
Pins: 3

Type B (NEMA 5-15) adds a round earth pin below the two flat blades. Almost every modern socket in the USA and Canada is type B, so it accepts both two-prong and three-prong plugs. In older buildings, and in much of Japan, you will still find two-slot sockets with no earth hole – a type B plug will not go in there. The earth pin is longer than the blades, so it connects first when the plug goes in.

What it looks like

Two flat parallel blades plus a round (or U-shaped) earth pin, all in a triangle.

The drawings are schematic – they show the pin layout, not the exact dimensions of the standard.

Plugs that fit a type B socket

A type B plug also fits

Only sockets of its own type – elsewhere you need an adapter.

Where it is used 49

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the most common type in the country (40)
one of the types in use (9)