How many voice channels does an E1 Primary Rate Interface (PRI) have?

E1 connections have 32 channels in total.

Typically, for E1 CCS and CAS protocols, 30 channels are used as B-channels and 2 channels are used as D-channels. For this reason, the frame structure of an E1 PRI connection is said to be 30B+2D where the 2 D-channels are located on timeslots 0 and 16 and the remaining channels are used as B-channels. Hence;

Channel 0 D-channel (Used mainly for clocking and synchronisation)
Channel 1-15 B-channel (Voice)
Channel 16 D-channel (Signalling)
Channel 17-31 B-channel (Voice)

The word 'typically' is used above because there are certain protocols that allow for a different D-channel configuration, for instance, SS7.

For information on T1 connections please look at the knowledgebase entry 'How many voice channels does a T1 Primary Rate Interface have'?