EFFECTIVE DATE: 06/24/13

PROGRAM POLICY LETTER NO. P13-V-07

FROM: KEVIN G. STRICKLIN

Administrator for

Coal Mine Safety and Health

SUBJECT: Reissue of P11-V-04 - Remote Restarting of Conveyor Belts when a Slip Switch

Stops the Belt

Scope

This Program Policy Letter (PPL) applies to underground coal mine operators, Mine Safety and 

Health Administration (MSHA) enforcement personnel, and other interested parties.

Purpose

The purpose of this PPL is to provide guidance to the mining industry and enforcement 

personnel on the purpose of slippage switches required on belt conveyors under 30 C.F.R. § 

75.1102.

Policy

The function of the slippage switch required under 30 C.F.R. § 75.1102 is to stop the belt when 

the speed of the drive roller is different from the speed of the belt which may cause the belt to 

slip causing friction and overheating and creating a fire hazard to personnel. The American 

Geological Institute and the U.S. Bureau of Mines define a belt slip as "the difference in speed 

between the driving drum and the belt conveyor." A Dictionary of Mining, Mineral, and Related 

Terms 47 (2d ed. 1968). When that action takes place, the slippage switch is designed to 

automatically stop the belt to prevent overheating and ignition of the belt.

Belt slippage can be temporary and may not be excessive. This condition can be caused by a fall 

of material on the belt which would slow down the belt and cause a slight slippage. Some mines 

are restarting the belt remotely from the surface using a Programmable Logic Controller (PLC). 

The safest method of addressing a belt slippage condition is to physically go to the location 

where the slippage occurred, examine the belt and restart the belt at that location. However, 

MSHA believes that remote restarting of conveyor belts can be safely accomplished under 

controlled conditions. For States that permit usage of PLCs to start the conveyor belt from the 

surface, and to ensure that this practice is not taking place when an actual slippage condition 

occurs, remote starting of conveyor belts should be used only under controlled conditions. The 

following are examples of controlled conditions: 
2

- Install an audible and visible alarm circuit along the belt entries to warn miners 

underground that the belt is restarting. 

- Install a locking device in the PLC circuit to allow only one attempt to restart the belt 

from the surface. If the belt does not start the condition should be checked and the belt 

should be restarted locally. 

- Incorporate additional safety circuits in series with the belt slip switch timer to ensure 

that the conveyor belt is not in an actual slip condition. These additional safety circuits 

consist of a revolution per minute (RPM) switch on the main drive pulley which will shut 

the belt down in a few seconds (4 to 7 seconds) if it senses a high rpm on start-up. 

- Install a safety device on the motor circuit to monitor the rate of current increase. If the 

motor current does not indicate an inrush high current for motor start-up, it will shut 

down the conveyor belt in a few seconds versus the 2 to 3 minutes usually allowed by the 

belt slip timer. 

- Provide a lockout circuit to prevent restarting of the belt by the PLC if the RPM switch 

activates indicating high RPM or inrush high current is detected on start-up, so that the 

circuit could not be restarted without someone going to the drive. 

- Install live cameras at locations that will assist the person operating the remote start-up. 

- Train miners on safeguards that should be in place to remotely start a belt under 

controlled conditions.

Background

MSHA is aware that some mines are using a PLC to remotely restart conveyor belts from the 

surface or other remote locations after they detect a belt slippage condition without viewing the 

belt to determine the problem and correcting it if necessary. Running a conveyor belt when a 

slippage condition exists could cause friction and overheating, posing a fire hazard to miners.

Authority

The Federal Mine Safety and Health Act of 1977, as amended, 30 U.S.C. § 801 et seq.; 30 C.F.R. 

§ 75.1102.

Internet Availability

This PPL may be viewed on the Internet by accessing MSHA home page (www.msha.gov) under 

MSHA’s Major Laws, Regulations and Policies choose “Compliance Information (PIBs, PILs, 

the PPM, and More” and select “Program Policy Letters.”

Issuing Office and Contact Persons

Coal Mine Safety and Health, Safety Division

Rodney Adamson, (202) 693-9549

E-mail: adamson.rodney@dol.gov

Distribution

MSHA Program Policy Manual Holders

MSHA Special Interest Groups

Underground Coal Mine Operators