EFFECTIVE DATE: 3/11/2011 EXPIRATION DATE: 3/31/2013

(Reissue of P09-V-10)

PROGRAM POLICY LETTER NO. P11-V-4

FROM: KEVIN G. STRICKLIN 

 Administrator for 

 Coal Mine Safety and Health 

SUBJECT: 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
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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: 

- 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 startup, 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. 
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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. 

Filing Instructions

This PPL should be filed behind the tab marked "Program Policy Letters" at the back of 

Volume V in the Program Policy Manual. 

Internet Availability

This PPL may be viewed on the Internet by accessing MSHA home page 

(http://www.msha.gov) and then choosing "Compliance Assistance," "Compliance 

Info" and "Program Policy Letter." 

Issuing Office and Contact Persons

Coal Mine Safety and Health, Safety Division

John Arrington, (202) 693-9549

E-mail: arrington.john@dol.gov

Distribution

MSHA Program Policy Manual Holders

MSHA Special Interest Groups

Underground Coal Mine Operators