Why is a –48 V DC a positive ground system?

The short story is that –48 V DC, also known as a positive-ground system, was selected because it provides enough power to support a telecom signal but is safer for the human body while doing telecom activities.

What is a -48 volt DC power system?

Telecommunication networks consist of central offices or exchanges where switching and routing equipment is housed. -48 volt DC power systems offer excellent power efficiency, especially in large-scale deployments. DC power distribution is more efficient compared to AC power due to reduced energy losses during conversion and transmission.

What is a -48V power supply system?

Products basically use -48V power supply system, and the actual measured voltage is generally –53.5V. This is because for reliability reasons, communication equipment is equipped with a backup battery (-48V). In order to ensure reliable charging of the battery, the supply voltage needs to be slightly higher than the battery voltage.

Where did -48 volt DC power come from?

The origin of -48 volt DC power in telecommunications can be traced back to early telegraph systems. In those days, telegraph networks utilized batteries to power their communication lines. A 48 volt DC standard was adopted to provide compatibility and standardization across different systems.

What is the operating voltage range for -48V system equipment?

For -48V system equipment, the required operating voltage range is -38.4V ~ 57.6V, but in fact we generally require the operating range -36V ~ -72V. The main consideration is that -48V system equipment must be compatible with –60V power supply system, which requires –48~-72V.

Why did Bell choose -48VDC?

In the late 1800’s, most homes of were not yet wired for electricity; in fact, communications beat power to the home in much of the United States. The reason Bell selected -48VDC is because it provides enough in power to support a signal, but not enough to be dangerous.