Automatic Meter Reading (AMR) presents many parallelisms with the fast emerging field of Wireless Sensor Networks (WSN) even if for this purpose they use the power cables as transmission medium. Among these parallelisms it is worthwhile to mention that both systems are essentially multihop and operate in a very noisy environment. For this reason the present paper reviews relevant results in the field of WSN with application to PLC based AMR systems and extracts lessons applicable to AMR and to PLC in general. Based on these lessons, this paper develops a theoretical model called the "Star of chains model" with regularly spaced devices forming chains that connect to a concentrator station, which is useful to derive the capacity of a system and to provide some basic rules of the thumb for creating it. A specific and simple MAC layer protocol based on the WSN protocol known as "Ripple control" is proposed to take the most out of the presented model. This protocol allows for good throughput while coping with the necessary retransmissions in noisy environments and with the necessary creation of periods of contention for the automatic registration of new nodes. The protocol may useful also for other applications in narrow band PLC as well as in Broadband Powerline Communications (BPL). A simulation based on OPNET modeler has been developed to check the capacity calculations. The model and protocol presented are a first step that will be refined and extended in the future.