High-Voltage Longwall Addendum

1. Section 30 CFR 18.53(b) requires each cover of a compartment in the high-voltage motor-starter enclosure containing high-voltage components be equipped with at least two interlock switches arranged to automatically deenergize the high-voltage components within that compartment when the cover is removed. My longwall has control/communication relays installed in the same bay as high-voltage motor contactors. The common bay is divided into two compartments by a removable grounded metal or insulated barrier that can only be removed from inside the bay. This barrier separates the high-voltage components from the control/communication relays to comply with 30 CFR 18.53(a). Will interlocks located on the cover of the common bay satisfy the requirements of 30 CFR 18.53(b)?

Yes. However, testing and troubleshooting can only be performed on the control/communication relays when the high-voltage components in this bay are deenergized.

2. Can protective relays such as the overcurrent, ground-fault and ground-wire monitor relays be located in the high-voltage motor contactor compartment?

No. These relays have only low-voltage inputs and outputs. In order to prevent accidental contact with a high-voltage circuit while troubleshooting low- and medium-voltage circuits, these components must be located in a control/communications compartment(s).

3. I want to use a high-voltage contactor with electronic circuits that provide short-circuit, overload, undervoltage and ground-fault protection and also ground-wire monitoring as an integral part of the contactor. Is this contactor permitted for a high-voltage longwall?

Yes. A high-voltage contactor assembly with integral electronic circuits may be installed provided:

4. 30 CFR Section 18.53(g) requires that "Control circuits for the high-voltage motor starters must be interlocked with the disconnect device." What is the definition of a control circuit?

The control circuit includes all components used to control the operation of the high-voltage motor starters. These include start/stop switches, MMI devices, programmable controllers, and protective relays. In general, the control circuit includes all components located in the control/communications compartment.

5. Low-voltage lighting circuits and low- and medium-voltage PTO circuits are neither high-voltage motor starter circuits nor control/communications circuits. In which compartment should these circuits be located?

The intent is to separate circuits by voltage classification. If connected to the line side of the disconnect device, they must be located in the disconnect device compartment and separated from high-voltage components. If connected to the load side, they cannot be located in the disconnect device compartment.

6. Can insulated high-voltage wiring pass through the control/communication compartment?

Yes, but it must be separated from control/communication circuits by a grounded metal or insulated barrier.

7. Can a reinforced flame-resistant cable guard be used as the insulated barrier described in item 6?

Yes.

8. Does the barrier described in item 6 require interlock switches?

The barrier requires interlocks only if it can be easily removed without removing additional components or wiring.

9. Can low- and medium-voltage wiring be run through the high-voltage motor starter compartment?

Yes, provided it cannot contact high-voltage components and the separation method is documented on approval drawings.

10. Can the main disconnecting device required by 30 CFR 75.815(a) be installed in its own separate enclosure?

No, unless the enclosure is physically attached to the power center as an integral part with a rigid connection.

11. My longwall shield pumps are not included in my Part 18 longwall approval. Are these pumps considered longwall equipment that must be deenergized by the main disconnecting device?

Yes. All equipment that moves with the longwall must be deenergized. Stationary equipment at the section mouth does not need to be deenergized.

12. Are high-voltage cables extending from a combination power center/motor starter required to have additional ground-fault protection?

Yes. These cables must meet 30 CFR 75.814(a)(4). One device may meet multiple requirements, but separate devices are encouraged. Additional devices are required for other subsections.

13. How is the maximum temperature rise of the neutral grounding resistor determined?

It is the increase in temperature with maximum ground-fault current. Protection must be set at 50% of this value.

14. Do the new regulations require any tests or inspections before equipment is placed in service?

Yes. New designs require MSHA inspection. Existing approved designs do not, but are subject to enforcement inspections and compliance checks.