E&M is a type of signaling using on analog telephone trunks.

E&M connections use an E and M wire in addition to the wires to carry the voice.
Since the voice can use either 2 wires or 4 wires, the total numbers of wires used on an E&M circuit is either 4 or 6.

The E wire was originally called the Ear lead and the M wire was originally called the Mouth lead.

Signals sent on these wire are typlically -48 volts, ground, and open.

See Also

• Understanding and Troubleshooting Analog E&M Start Dial Supervision Signaling - Cisco Document
• Multitech - one of the few makes of ATAs and gateways with E&M support.