Merrill Lightning Arrestors - 120V or 240V

Merrill Lightning Arrestors are surge protection devices installed on 120 volt or 240 volt power systems, designed to help protect motors and controls from a voltage surge caused by lightning strike events, switching loads, and other sources. Heavy-duty models include threads and a nut for attachment to an electrical panel or enclosed motor controls, including well pump controls, and can be applied as main protection for water well equipment and similar electrical system equipment to provide protection for both residential and agricultural electrical systems. Surges of 500 volts or more are directed to ground; a surge arrester does not absorb lightning, but diverts transient energy and surge current so electricity moves through the air-gap protection path to earth rather than into connected equipment to limit damage to protected equipment. Lightning strikes occur about 100 times per second worldwide and can reach up to 300,000 amps of current. In most cases, preventing repeated surge damage helps reduce maintenance costs and equipment failures.

If you are a homeowner, agricultural property owner, contractor, or commercial property manager using a well pump system or other motor controls, this page explains which Merrill lightning arresters fit 120/240 volt applications, how the devices are connected and installed for effective protection, how to test them with an ohmmeter, and where they are used to safeguard panels, controls, and water system equipment.

Product Specification for Surge Arresters

SKU# LAHD550

Manufacturer: Merrill

Model #: LAHD550

Shipping Weight: 1 lbs

Checking Your Lightning Arrestor

Check a Lightning Arrestor with an ohmmeter

Lightning arrestors have a unique feature unlike other secondary lightning arrestors in that they can be checked with a conventional ohmmeter. This helps confirm whether the arrester can still protect equipment after surge events of short duration.

With arrestor removed from circuit:

1. Set selector knob on ohmmeter to RX100K.

2. Connect both black "lightning arrestor" leads to one ohmmeter lead.

3. Connect white "lightning arrestor" lead to the other ohmmeter lead.

4. Resistance should read infinity (00). If a resistance reading other than infinity (00) is attained, the "lightning arrestor" should be replaced.

In some cases, readings outside the expected value can also point to broader power-quality issues such as harmonics, though replacement guidance remains the same.

Product Literature on Surge Protection

MERRILL Lightning Arrestors Instructions