Lightning and Surge in Crusher and Stone-Crushing Motors: Field Protection with Arresters

Crusher and stone-crushing plants are among the toughest sites for electric motors. Alongside dust, vibration and shock loading, the most sudden and destructive threat, often overlooked, is the surge (overvoltage) pulse. A plant installed in the open, on a construction site or in a quarry is exposed both to direct and indirect lightning discharges and to transient overvoltages from grid switching events. These pulses can puncture the motor winding insulation in a few microseconds and take an expensive motor out of service in an instant; moreover, on a critical drive like a crusher this means the whole production stops. At HEM Motor, this article examines the on-site overvoltage sources, surge arrester selection, correct grounding, the effect of overvoltage on motor insulation and the correct motor + protection combination from an engineering perspective.

Overvoltage Sources on Site

On a crusher site, overvoltage does not come from a single source. To design protection correctly, you need to recognize these sources:

• Direct lightning: A lightning strike on the plant or a nearby point creates a very high current and voltage pulse; it is the most destructive scenario.
• Indirect (induced) lightning: A nearby strike induces voltage in overhead lines and cables; it reaches the motor without a direct hit.
• Grid switching overvoltage: Opening and closing of large loads, capacitor banks or lines creates transient voltage surges.
• Starting and breaking pulses: The transients at the switch-on/off of a high-power motor can cause a voltage spike in the system.

What these pulses share is that they are very short but have a very high peak value. Because the motor winding is designed for the continuous rated voltage, these sudden spikes stress the insulation and, with repeated exposure, wear it out and lead to early failure.

Why Is Overvoltage Riskier on a Crusher Site?

While the same motor runs without trouble inside a factory, on an open-area crusher site it becomes far more exposed to overvoltage. There are several reasons. First, location: quarries and construction sites are usually set up on open, elevated, lightning-exposed terrain. Second, supply: these sites are often fed by long overhead lines that easily pick up induced pulses. Third, the ground: dry, rocky, resistive soil makes good grounding difficult. And fourth, the nature of the plant: crusher motors are high-power and start/stop frequently, which increases switching pulses.

When these factors combine, a threat rarely seen in a factory environment becomes a daily risk on a crusher site. So site protection must be approached not by merely adding a standard arrester but with a design that accounts for the extra risks brought by the location, the supply and the ground. A correctly designed protection runs the motor safely even on this demanding site.

The Effect of Overvoltage on Motor Insulation

When an overvoltage pulse reaches the motor terminal, it falls disproportionately on the first winding turns. Because the pulse rise rate is high, the voltage does not distribute evenly between turns; this overstresses the insulation of the first turns. A single large pulse can puncture the insulation instantly (sudden failure), while repeated small pulses age the insulation gradually (cumulative damage). The result is a turn-to-turn short circuit or a phase-to-ground fault. In the dusty and humid crusher environment, where the insulation is already stressed, when overvoltage is added to this process the motor life shortens markedly.

Surge Arrester Selection and Protection Classes

The basic line of defense against overvoltage is the surge arrester (SPD). The arrester shows high impedance and passes no current in normal operation; when the voltage exceeds the threshold value, it becomes conductive, diverts the surge current to earth and limits the voltage at the motor terminal to a safe level. For effective protection, arresters must be placed in stages (coordinated): coarse protection at the main incoming panel, fine protection at the motor panel. The table below summarizes the protection stages.

On open-area, high-lightning-risk sites such as a crusher, coordinated Type 1 + Type 2 protection is essential; if sensitive electronics or a drive are present, it is completed with Type 3. When selecting an arrester, the nominal discharge current (In), maximum discharge current (Imax) and protection level (Up) are determined according to the plant's risk profile.

Grounding: The Foundation of Protection

No matter how good the arrester is, it is useless without a low-resistance, correctly designed grounding, because the surge current the arrester diverts must flow safely to earth. High grounding resistance raises the earth potential during the pulse and makes the protection ineffective. Grounding is especially important on a crusher site because the ground can be dry and rocky, which increases the grounding resistance.

• Keep the grounding resistance low; extend the grounding grid if needed.
• Bond all metal bodies, the motor, panel and structural steel to the equipotential bar.
• The arrester grounding must be short and low-impedance; a long grounding conductor degrades the protection level.
• The motor grounding must be of correct cross-section for touch-voltage safety and protection.

Lightning Protection and Line-Side Measures

The arrester limits the pulse that gets in; but the first link of protection is reducing the pulse from reaching the plant in the first place. On an open-area crusher plant, the lightning protection system (air terminal, down conductor and grounding grid) must be designed correctly. Because the induced-pulse risk is higher on plants fed by an overhead line, where possible it is recommended to route the supply cable underground or to use a strong Type 1 arrester at the line entry.

• The air-termination system and down conductors must cover the protection volume according to the plant geometry.
• The induced-pulse risk is high with an overhead-line supply; the entry arrester must be chosen strong.
• An underground supply cable reduces the direct-strike risk.
• On mobile and portable plants, the grounding must be re-verified at every new setup.

Mobile crusher plants pose a special challenge: every time the plant is moved, the grounding and protection are rebuilt. So at every site change the grounding resistance should be measured and the arrester connections checked; otherwise the protection on the new site may be weaker than expected.

The Motor Itself: A Selection Robust to Site Conditions

If the overvoltage protection is the outer line of defense, the motor itself is the inner line. On a crusher site the motor must withstand not only overvoltage but also dust, moisture, vibration and shock loading. Therefore a reinforced insulation class, a high IP protection class and a mechanically strong frame matter. The right motor selection, combined with overvoltage protection, provides long and reliable operation on site.

• Reinforced/high insulation class (F/H): Withstands voltage spikes and extra heating.
• High IP protection (IP55, IP65/66 on dusty/wet sites): Prevents dust and water ingress.
• Cast-iron frame: Robust against shock, vibration and mechanical stress.
• Thermal protection (PTC/PT100): Detects overload and heating early.
• Anti-condensation heater (space heater): Prevents moisture condensation during standstill.

Periodic Maintenance and Insulation Monitoring

Overvoltage protection is not something to install once and forget; it must be kept alive with regular maintenance. Most arresters have a status indicator and an arrester at the end of its life must be replaced; otherwise it will not protect on the next pulse. Likewise the grounding resistance should be measured periodically and monitored for whether it rises with seasonal drying. When the motor insulation resistance (megger) is measured regularly, the slow wear caused by overvoltage is caught early and a measure is taken before the motor fails completely.

• Check arrester status indicators regularly; replace any at the end of life.
• Measure the grounding resistance periodically; it can rise especially in the dry season.
• Monitor the motor insulation resistance with a megger regularly; a drop is an early warning.
• Check the tightness of terminal and grounding connections against vibration.
• Clean dust buildup; a dusty surface adversely affects both heat dissipation and insulation.

These simple but regular checks prevent the installed protection from weakening over time. On a critical drive like a crusher, a planned maintenance program prevents the long and expensive downtime that a sudden motor failure would cause.

Integrated Site Protection Strategy

Effective protection is provided not by a single device but by a layered approach. The right strategy on a crusher site addresses, together, lightning protection (air-termination system), coordinated surge arresters (Type 1+2+3), low-resistance grounding, equipotential bonding and a motor selection suited to site conditions. Each of these layers engages when the previous one fails, so a single weak link does not put the whole system at risk. In addition, a motor protection relay (thermal, phase loss, unbalance) and correct fuse/breaker coordination provide complementary protection against electrical faults.

Overvoltage and Other Site Threats Together

On a crusher site, overvoltage is not the only thing threatening the motor; dust, vibration, shock loading and moisture act at the same time. What matters is to design the protection by considering these threats together. For example, if the insulation is already worn on a motor with poor dust sealing, an overvoltage pulse damages it far more easily. Similarly, vibration can loosen terminal and grounding connections over time; and a loose grounding fails to protect precisely at the moment of overvoltage. So site protection must be approached holistically:

• Dust: High IP protection and dust sealing keep the insulation clean and durable.
• Vibration: Periodic tightness of connections prevents loosening and contact loss.
• Shock load: Flywheel/inertia and correct starting reduce mechanical shock.
• Moisture: An anti-condensation heater prevents condensation and insulation weakening at standstill.
• Overvoltage: Coordinated arresters and low-resistance grounding prevent sudden and cumulative damage.

Because these threats act not one by one but in combination, the motor and protection selection must cover all the site conditions. In a well-designed site protection, these layers complement each other and the motor life is markedly extended.

Frequently Asked Questions

Does a surge arrester alone protect the motor?

No. The arrester is at the center of protection but is not sufficient on its own. Low-resistance grounding, equipotential bonding, coordinated SPD stages and a robust motor selection must work together. If the grounding is weak, even the best arrester does not provide the expected protection.

Which IP protection class is needed on a crusher site?

IP55 is accepted as the minimum standard; on sites with heavy dust and water (dust-suppression spray, rain), IP65 or IP66 is recommended. Dust sealing directly affects motor life, so the site condition must be evaluated clearly.

How do I recognize overvoltage damage?

In sudden failure the motor goes out of service instantly and a low resistance is seen in the insulation measurement (megger). In cumulative damage, increasing leakage current, heating and repeated protection trips appear over time. Periodic insulation measurement catches overvoltage-related wear early.

Conclusion and Supply

On a crusher and stone-crushing site, overvoltage is a threat as serious as dust and vibration but often overlooked. Surge pulses from lightning and switching are brought under control with coordinated surge arresters, low-resistance grounding and a motor selection robust to site conditions. At HEM Motor we offer motors with reinforced insulation, high IP protection and cast-iron frames for crusher and quarry sites, with fast delivery from manufacturer stock and application-specific technical support. Reach us with your site's power, protection and environment details; let us choose the right motor and protection combination together and prepare a tailored quote for you.

Related guides: Stone Quarry and Mine Motor Protection, Crusher Motor Dust Sealing IP65/66, Crusher Motor Failure and Downtime Cost, Motor Grounding and EMC Connection and Motor Protection with Thermal Relay and Fuse.