NTN MEGAOHM Insulated Bearing Series Guide

NTN MEGAOHM insulated bearings are a family of current-insulated bearings developed to reduce electrical pitting in motors, generators and other electrical equipment. MEGAOHM is not one universal construction: NTN documentation includes ceramic-insulated and resin-insulated configurations identified by prefixes such as 7MC, 7MC2, 7MC3, 7MP and 7MP2. A replacement therefore has to be reviewed from the complete designation, not from the MEGAOHM name alone.

What Is the NTN MEGAOHM Series?

MEGAOHM is NTN’s insulated-bearing family for preventing electrical pitting caused by current leakage through a bearing. NTN’s official catalogue describes ceramic and resin types for different application requirements, while a 2021 NTN technical release states that the insulating layer is applied to the width surfaces and outside surface of the outer ring to block the current path.

The catalogue introduction states a general bore-diameter range of 50 to 160 mm. However, individual dimension tables include additional sizes, so the exact available range should be confirmed by bearing number rather than treated as a fixed family limit.

Buyers comparing MEGAOHM products with TFL insulated motor bearings should request insulated bearing cross-reference support. The review should identify confirmed matches, confirmed differences, open technical fields and the person responsible for final approval.

Key Takeaways

• MEGAOHM is a product-family name, not a complete bearing specification.
• 7MC, 7MC2 and 7MC3 identify ceramic-insulated routes; 7MP and 7MP2 identify resin-insulated routes.
• The catalogue’s 3 kV and 5 kV classifications should not be read as continuous motor operating voltage.
• The complete designation must preserve bearing type, size, cage, clearance, tolerance and every suffix.
• Housing shoulder geometry and handling can affect whether the insulation works as intended.
• Current regional availability should be checked before promising stock or lead time.

NTN MEGAOHM Prefix Guide: 7MC, 7MC2, 7MC3, 7MP and 7MP2

The following meanings and voltage-resistance classes are taken from NTN’s MEGAOHM Series catalogue. They should remain tied to the relevant NTN product and test specification.

A prefix match alone still does not establish interchangeability. Two bearings can share the same MEGAOHM prefix but differ in bearing type, boundary dimensions, internal clearance, cage, tolerance, stabilization, lubrication or application approval.

Ceramic vs Resin MEGAOHM Performance

NTN’s catalogue provides a qualitative comparison of ceramic-insulated, resin-insulated and ceramic-rolling-element bearings. For the two MEGAOHM insulation routes, NTN rates both ceramic and resin as excellent for insulation performance. Ceramic is rated better for creep resistance and heat dissipation, while resin receives the more favorable price rating.

These are NTN’s qualitative catalogue ratings, not universal rules for every brand or bearing size. Review the application and TFL’s resin vs ceramic insulated bearing comparison before choosing a replacement route.

Which MEGAOHM Route Is Better?

There is no single best MEGAOHM prefix for all applications. Ceramic routes may be preferred where heat dissipation, dimensional stability and creep resistance are important. Resin routes can offer a commercially attractive insulated solution, while 7MP2 specifically addresses heat dissipation and creep resistance more directly than the standard 7MP route.

The correct decision depends on the original NTN number, bearing position, housing and shaft fits, operating temperature, load, speed, vibration, electrical system, maintenance history and OEM requirements. A buyer should not convert 7MC to 7MP—or 7MP to 7MC—only because both catalogue entries show a 5 kV class.

How to Read 7MC3-6330M2C3

NTN uses 7MC3-6330M2C3 as a ceramic-insulated designation example:

• 7MC3: standard ceramic-insulated MEGAOHM type, listed in the 3 kV catalogue class.
• 6330: the base deep-groove ball-bearing designation, including bearing series and bore code.
• M2: the cage code shown in NTN’s designation example.
• C3: radial internal clearance greater than the normal clearance group.

A request written only as “6330 MEGAOHM” is incomplete because it removes the ceramic construction, cage and clearance fields. Copy the number exactly from the bearing, package label, OEM BOM or previous purchase record rather than rebuilding it from memory.

How to Read 7MP-NU214L1BC4P6

NTN uses 7MP-NU214L1BC4P6 as a resin-insulated cylindrical roller-bearing example:

• 7MP: standard resin-insulated MEGAOHM type, listed in the 5 kV catalogue class.
• NU214: the base NU-design cylindrical roller-bearing designation.
• L1B: the cage code shown in the catalogue example.
• C4: radial internal clearance greater than C3.
• P6: a bearing tolerance/precision class.

This example shows why the insulation prefix cannot be reviewed separately from the mechanical suffixes. Substituting a C3 or normal-clearance bearing for C4, changing the cage, or omitting P6 can make an otherwise dimensionally similar candidate unsuitable.

Understanding 3 kV, 5 kV and 100 MΩ at 500 VDC

NTN’s catalogue uses more than one electrical field. The series introduction states insulation resistance of at least 100 MΩ at 500 VDC. The designation table separately assigns 3 kV or 5 kV high-voltage-resistance classes to the MEGAOHM prefixes.

For cross-brand comparison, request the test method, voltage waveform, duration, leakage or resistance limit, temperature, humidity, electrode/contact arrangement, sample scope and report format. TFL’s guide to insulation test evidence can help structure this request.

Global Catalogue vs the Current European MEGAOHM Range

NTN’s global MEGAOHM catalogue documents the broader family architecture, including ceramic 7MC variants and resin 7MP variants. NTN Europe’s current MEGAOHM product page focuses on a ceramic-coated outer-ring solution with resistance up to 3,000 VDC, standard-bearing dimensional compatibility and steel- or brass-cage ranges.

In July 2026, NTN Europe announced an expansion adding sheet-metal-cage bearings for smaller motors to complement its brass-cage offering for larger motors. That announcement describes an expanded ceramic-coated European commercial range; it should not be used as proof that every historical 7MC, 7MP or 7MP2 designation is stocked in every country.

For quotation, separate three questions: what the NTN designation means, whether NTN currently supplies the exact item in the buyer’s region, and whether TFL can offer a technically reviewed replacement. These are related but not identical questions.

Why Housing Shoulder Height Matters

NTN describes the insulation layer as covering the outside and width surfaces of the outer ring. The MEGAOHM catalogue warns that the specified housing shoulder height must be observed to prevent current from passing through the bearing side faces. This creates an important replacement boundary: matching bore, outside diameter and width does not by itself prove that the installed current path remains blocked.

Check the candidate drawing against the housing shoulder, fillet, relief and contact surfaces. NTN’s installation figure shows an approximately 10° to 15° entrance relief with a 0.5 mm minimum feature to facilitate assembly, but the actual housing design should follow the applicable NTN drawing and machine requirements rather than a generic rule.

NTN MEGAOHM Handling and Installation Precautions

• Do not drop the insulated bearing or strike it directly with a hammer during installation.
• Do not install a bearing that has visible coating defects or an unusual surface appearance.
• Do not attach a conductor across insulated surfaces; this can reduce the effective insulation resistance.
• Observe the required housing shoulder height so the side faces do not create a bypass current path.
• Use the specified housing-entry relief and suitable mounting tools to avoid damaging the insulating layer.
• For DC motors such as railway traction applications, NTN instructs users to earth-ground the shaft during a voltage-resistance test.

These precautions matter because mechanical shock can damage the insulating layer even when the bearing still appears dimensionally usable. Insulation damage can allow electrical pitting, abnormal noise, vibration and premature failure.

When a MEGAOHM Cross-Reference Should Be Put on Hold

• The buyer provides only “MEGAOHM” or a base number without the 7MC/7MP prefix.
• The bearing marking, package label, drawing and purchase record show different numbers.
• The 3 kV or 5 kV value is supplied without the test method or required acceptance criteria.
• The original clearance, cage, tolerance, lubrication or stabilization suffix is missing.
• The proposed change switches between ceramic and resin insulation without reviewing temperature, fit and approval requirements.
• The housing shoulder or side-face contact geometry has not been checked.
• The OEM or end user requires the exact NTN part or written approval for alternatives.
• The application, position, VFD/drive system or grounding arrangement has changed since the original bearing was selected.

MEGAOHM Replacement Evidence Checklist

1. Photograph the full bearing marking and package label from clear angles.
2. Copy the complete NTN designation, including 7MC/7MP prefix, cage, clearance, tolerance and other suffixes.
3. Attach the OEM drawing, BOM line, old purchase record or repair report when available.
4. State the equipment, bearing position, motor/generator type, VFD context and grounding arrangement.
5. Provide load, speed, fit, operating temperature, lubrication, vibration and contamination conditions.
6. Define the required electrical class and the test/report format needed for approval.
7. State quantity, delivery country, required date, urgency and whether a sample or partial shipment is useful.
8. List required documents such as drawing, dimensional inspection, electrical test report, certificate or traceability record.
9. Ask TFL to separate verified matches, verified differences, assumptions and unresolved fields.
10. Confirm stock, MOQ, lead time, quote validity and final approval responsibility before ordering.

Organize the request with TFL’s insulated bearing RFQ checklist. Complete evidence allows a faster review of stock, low-MOQ or sample options, production lead time, required documents and ceramic or resin replacement candidates.

Technical References

• NTN Catalogue 3030/E: Insulated Bearings MEGAOHM Series — supports the 7MC/7MP prefix definitions, 3 kV and 5 kV classes, 100 MΩ at 500 VDC statement, designation examples, qualitative performance comparison, dimension tables and installation precautions.
• NTN Global: Expansion of the MEGAOHM Series — supports electrical-pitting prevention, ceramic/resin insulating layers on the outer-ring width and outside surfaces, series applications and insulation-resistance context.
• NTN Europe: MEGAOHM Product Overview — supports the current European ceramic-coated outer-ring offer, up-to-3,000-VDC statement, standard-bearing compatibility and steel/brass cage positioning.
• NTN Europe: 2026 MEGAOHM Range Expansion — supports the July 2026 addition of sheet-metal-cage bearings for smaller motors and the distinction from the brass-cage range for larger motors.

NTN, MEGAOHM and the listed NTN designations are used nominatively for neutral source identification and buyer decoding. Their use does not imply affiliation, authorization, certification, automatic TFL equivalence, identical performance or drop-in approval.

FAQ

What does NTN MEGAOHM mean?

MEGAOHM is NTN’s family name for insulated bearings designed to block current through the bearing and reduce electrical pitting. The family includes different ceramic and resin constructions, so the complete designation is still required.

What is the difference between 7MC, 7MC2 and 7MC3?

NTN describes 7MC as a protected ceramic-layer type with high voltage resistance, 7MC2 as a protected ceramic-layer type and 7MC3 as the standard ceramic type. The catalogue lists 7MC at 5 kV and 7MC2/7MC3 at 3 kV.

What is the difference between 7MP and 7MP2?

7MP is NTN’s standard resin-insulated type. 7MP2 is the heat-dissipating and creep-resistant resin type. Both are listed in the 5 kV catalogue class, but their resin construction and application positioning are not identical.

Are all NTN MEGAOHM bearings ceramic coated?

No. NTN’s global MEGAOHM catalogue includes ceramic 7MC routes and resin 7MP routes. Current regional marketing may emphasize a narrower ceramic-coated range, so always check the exact prefix and current source.

What do the 3 kV and 5 kV MEGAOHM ratings mean?

They are NTN catalogue voltage-resistance classes assigned to specific MEGAOHM constructions. They should not be treated as continuous operating voltage or as directly equivalent to another manufacturer’s voltage claim without comparing test methods.

Can a 7MP resin bearing replace a 7MC ceramic bearing?

Not automatically. Even when both are listed in a 5 kV class, the insulation material, heat dissipation, creep behavior, housing conditions, bearing suffixes and approval basis can differ.

What does 7MC3-6330M2C3 mean?

It identifies a standard ceramic-insulated 7MC3 MEGAOHM bearing based on a 6330 deep-groove ball bearing, with the M2 cage code and C3 radial internal clearance.

Can TFL quote an NTN MEGAOHM replacement?

Yes. Send the complete NTN number, bearing and label photos, application, electrical requirement, quantity, destination, required date and document needs. TFL can check stock, MOQ, lead time and replacement candidates for field-by-field review.