Control Voltage - 120 V ac vs. 24 V ac/dc Question
Advertise Here
Trending Topics:
Sunday, June 14, 2015

Ship Equipment
Ship Maintenance
Ship Systems
Worldwide Metric
Freeman Marine
Neptune Group

Home Page
About MarineTalk
Buyer's Guide
World InfoDesk
Discussion Forums
Advisory Board
Advertising Information
Submit Company Listing
Edit Company Listing
Site Map
MarineTalk Site Search:
Featured Companies

IMCA - The International Marine Contractors Association
IMCA is the international trade association representing offshore, marine and underwater engineering companies.
    United Kingdom

International Underwriting Association - IUA
The IUA is a worldwide body representing the interests of the marine insurance industry globally.
    United Kingdom

Westermans International Ltd
Westermans International, suppliers and buyers of used and refurbished welding equipment, cnc plasma profile cutters and positioning machines ideal for the marine and shipbuilding industry around the world.
    United Kingdom

Neptune Group Pte Ltd
Neptune Group provides a 60 foot charter yacht for intimate sundowner cruises and larger events within the marina. They are also exclusive agents for Bondway Motor Cruisers and Luxury Live-Aboards / Houseboats in Singapore, Malaysia and Indonesia

Control Voltage - 120 V ac vs. 24 V ac/dc Question


One of the first decisions control system designers must make at the onset of any design process is to decide on a system voltage their project will need. Often use of 120 V ac for control system power is based on traditional usage, simply because it has always been done that way. However, there are viable alternatives to 120-volt control systems that have evolved over the history of the control system.

Modern control systems are often very complex. Troubleshooting control systems frequently requires that they be powered up while the system is checked. The use of 24 V reduces the likelihood of injury caused by shock. A typical control system uses 24 V ac for panel and field I/O devices. This system would also use 24 V dc for analog instrumentation. And, alternately, 24 V dc could be used for panel, field I/O and analog devices. The flexibility in the choice of ac and dc or all dc or all ac covers most control situations.

Deciding what voltage level is most appropriate depends on several factors. For small systems, all the controls can be implemented using 24 V dc. For systems with motor starters, 24 V ac is available by providing a step down transformer connected to the power feeders at the starter. Systems with analog instruments and starters probably are best served by having both 24 V ac and dc available. Where 120 V ac is needed for specific applications, interposing relaying can be provided. Today, many factors are combining to help propel the adoption of 24 volts for control purposes.

By John F. Heneage, P.E.
Control Engineering Online  

You may also like:
Trending Technology, World Shipping & Maritime News

Latest Marine News and Technology Articles | Maritime 2015 Buyer's Guide


E-mail:  Contact Us

Copyright 1998 - 2015 MarineTalk
Division of Link Internet Business Solutions
All rights reserved.

The reproduction, retrieval, copying or transmission of this Web site content,
in whole or in part, is not permitted without the express permission of
MarineTalk .