Manufacturing Plant – Surge & Earthing Issues

Background:

A 4 decade old leading manufacturer of sheet metal components of electrical machines with sophisticated automatically operated CNC machines and robot machines wanted us to suggest the suitable surge protection devices for their factory and to study the existing earth pits on their factory premises aimed at protecting their assets.

Key Issues:

• Frequent failure of electronic devices leading to downtime of machines affecting manufacturing and cost implications on replacement
• Earthing was not maintained properly and the earthing conductors were found corroded at some places and loose connection was observed at some joints.
• The OEM suggested providing two numbers of dedicated earthing for their machines instead of connecting to the existing earth pits.
•  Their vendor asked them to disconnect the other connections to the earth pit provided for their machine. They even insisted that the two earth pits provided for the same machine should not be interconnected below the ground level to ensure the dedicated earthing.

Addressing the Issues:

• The audit found that protection of electronic equipment against transient surges were not provided and the need for deployment of a solution to minimize such surges entering the factory.
• The earthing needs to be maintained properly and the adequate tightness of all the connections should be ensured.

Solution:

• A simple solution of providing SPDs (Surge Protection Devices) at all three possible “risk areas” was recommended. This includes the Main Panel, Sub-Panel and 3 Phase drive.
• Level 1 protection needs to be provided at the main panel, level 2 protection needs to be provided at the sub panel and the third stage of protection needs to be provided for individual machines.
• All the earth pits shall be interconnected below the ground level for faster discharge of fault current. The references from the standards which insist the interconnection of earth pits are as follows.

1.  IS/IEC62305 part 3 - Physical Damage to Structures and Life Hazard under clause 5.4.1 recommends the use of single integrated earth-termination system for lightning protection, power systems and telecommunication systems. Hence the earth pits of LPS shall be interconnected with the earth pits of other equipment.
2. IS732 - Code of Practice for Electrical Wiring Installations under clause 4.5.4.5.1 also states that “all earth electrodes associated with a building, for example, protective, functional and lightning protection, shall be interconnected“

•  Adequate tightness of all the joints should be ensured.
• All the MS bolts & nuts in the outdoor needs to be replaced with
  SS bolts & nuts.