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Mercury Relay - 35 AMP - 2 Pole - 24 VAC Coil - Normally Open

SKU: 235NO-24A-18

Mercury Displacement Relays are all designed and built to meet the most exacting demands of industry. They have won their high place in the electrical field by doing the tough and tricky jobs that ordinary equipment could at best do in an uncertain manner. They have proved their ability to stand up under the most adverse conditions of temperature, dust and moisture, in all types of applications.

The 35-AMP normally open contactors are designed and manufactured to high quality specifications and the contactors are commonly used in various heating, lighting, and many other industrial applications including high voltage ultraviolet type loads. The contacts are encased in hermetically sealed stainless steel tubes to provide reliable switching for millions of operations. MDI has manufactured this contactor since 1975. It is available in the single, two, three & four pole models.

235NO-24A-18 (Resistive) SpecSheet

235NO-24AH-18 (Gen Purpose) SpecSheet

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This product contains mercury.
Please click to check if you are in IMERC compliance.

  • Coil Data
    • 25 Ω
    • 484 mA
    • 11.6 VA
    • 5.8 Watts
    Coil: 24V 50/60 Hz
  • Contacts:
    • 35 AMP @ 600 VAC Resistive
      • -or-
    • 35 AMP @ 480 VAC General Purpose
  • Longevity: Millions of Cycles
    Torque Specifications
    • Coil Screws: 7 in-lb
    • Terminal Screws: 31.5 in-lb
  • Coil Terminals: #6 Binding Head Screws
  • Load Terminals: 4-14 AWG Compression Type
  • Operate Time: 50 milliseconds
  • Release Time: 80 milliseconds
  • Contact Resistance: .003 ohm
    • After Cycling Under Load
  • Dielectric Withstand: 2500 VAC RMS
  • Temperature Range: -35°C to 85°C
  • 35NOH
  • AC Resistive
    • 240 VAC @ 35 AMPS
    • 480 VAC @ 35 AMPS
  • AC Inductive
    (P.F. 0.4 or Greater)
    • 120 VAC @ 25 AMPS
    • 240 VAC @ 15 AMPS
  • General Purpose
    (P.F. 0.7 or greater)
    • 240 VAC @ 35 AMPS
    • 480 VAC @ 35 AMPS
  • DC Resistive Heating
    • 48 VDC @ 60 AMPS
    • 125 VDC @ 16 AMPS
    • 250 VDC @ 12 AMPS
  • Tungsten Lamp
    • 120 VAC @ 35 AMPS
  • Motor Loads
    • Single Phase
      • 120 VAC @ 2 H.P.
      • 240 VAC @ 3 H.P.
    • Three Phase
      • 240 VAC @ 5 H.P.
      • 480 VAC @ 7.5 H.P.
  • 35NO Only
  • AC Resistive
    • 240 VAC @ 35 AMPS
    • 480 VAC @ 35 AMPS
    • 600 VAC @ 35 AMPS
  • Tungsten Lamp
    • 120 VAC @ 35 AMPS
  • Motor Loads
    • Single Phase
      • 120 VAC @ 1 H.P.
      • 240 VAC @ 1 H.P.

Made in the USA

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Since 1975, MDI
Quality - Durability - Reliability

Call Us Toll Free: (800) 634-4077

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Non-Mercury Alternatives

All the care required for the manufacture of high-grade instruments is used in the manufacture of the switches. All switch parts are specially cleaned, and contamination is avoided by use of tweezers, gloves, etc., when making assemblies.
Contactors are hermetically sealed with high quality glass to metal seals.
The stainless steel tube is totally encapsulated in high grade UL approved epoxy to prevent moisture damage and voltage breakdown through the protective coating.
The coils are wound on compact nylon bobbins and molded onto the metal tube to provide minimum power loss. This allows for low coil power required to actuate the contactor. This also enables the units to handle high loads with minimum derating due to higher ambient temperatures.
Inert gases internally prevent excessive arcing between the mercury and the electrodes which enables the unit to function for millions of cycles with very low contact resistance, and minimum deterioration of the internal parts.
Available in all standard coil voltages, in single, two and three pole arrangements. Other coil voltages available upon request.
In multiple pole units each tube is actuated by its own coil. This eliminates pull-in variation between contact tubes, assuring consistent switching.

The load terminals are isolated from each other by the glass in the hermetic seal. "The plunger assembly", which includes the ceramic insulator, the magnetic sleeve and related parts, floats on the mercury pool. When the coil is powered causing a magnetic field, the plunger assembly is pulled down into the mercury pool which is in turn displaced and moved up to make contact with the electrode, closing the circuit between the top and bottom load terminal, which is connected to the stainless steel can. For constant duty applications, a return spring is used in place of the buffer spring.

Mercury to Metal Contactor Illustration

Click to Enlarge

While MDIs contactors handle high inrush, such as lamp loads, very well, mercury contactors are susceptible to damage by short circuit currents, and should be fused to minimize short circuit fault currents. Fast acting UL class RK-1 and class J fuses and semiconductor I²t fuses more effectively protect relays than other fuses. These are low-peak fuses designed to limit short circuit currents. Regardless, when there is a short circuit, relay operations should be closely monitored afterward because of the possibility of concealed damage that could cause the relays to behave inconsistently.

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