Earth Testing Flashcards
Reasons why we earth test
•Unwanted earth faults cause problems.
•Detection at an early stage is necessary.
•Earth fault testing of 450V ac system is automatic.
•Presence of earth faults is indicated in two ways:
-indicator light in PCP and SCP switchboards.
-Audible alarm.
115V System
- Automatic system for 450V ax system does not work on 115V ac system.
- No physical connection between primary and secondary transformer windings.
- Done at first fuse panel after transformer.
- Usually done by insulation resistance test using the MIT 420.
Control and Communications Switch
- Control and communications switchboard provides 24 volts DC emergency supplies.
- An Earth fault test panel on the switchboard provides for testing the positive and negative side of the DC supply.
- A push button with intergral lamp is fitted to the switchboard.
Electrical Distribution Panels
- Each electrical distribution panel has an earth fault indication.
- This will illuminate if there is an earth fault on any circuit powered from the EDC up to and including the primary winding of a transformer.
Earth Bonding
All equipment generating or operating at greater than 35V AC or 50V DC must be earth bonded.
Earth bonding
- All equipment generating or operating at greater than 35V AC or 50V DC must be earth bonded.
- The term enclosure means any:
- Metal box
- Cabinet
- Console
- Cubicle
- Frame
- starter… that is metal which personnel may come into contact with.
Portable Electrical Equipment
•Portable electrical equipment has two classifications
-class 1
-class 2
•Portable equipment voltage is limited to 115V AC
•Portable equipment fuse rating is limited to 20 amps.
•The following items are exempt from this
-equipment operating at 440V AC, 3 Phase.
-locally approved 240V AC private equipment.
Private electrical equipment
- Mains voltage powered private electrical equipment is to be registered in the ship’s private Electrical Equipment log.
- The equipment should be PAT tested.
