Distribution Transformer Buying Guide: What to Confirm Before Ordering

Updated: August 5, 2026

TL;DR

Ordering a distribution transformer requires more than matching kVA and voltage. Before requesting a quote, collect the approved transformer type, primary and secondary voltage, phase, frequency, connection, enclosure, dimensions, terminal requirements, accessories and project approvals.

This is a purchasing guide. Transformer sizing, system design, protection, installation, grounding, testing and energization must be handled by qualified professionals using approved project documents and manufacturer instructions.

What Is a Distribution Transformer?

A distribution transformer changes electrical voltage so power can be supplied at the level required by a building, panel or piece of equipment. Distribution transformers are available in many constructions, voltage combinations and configurations.

The transformer must match the approved electrical design. A similar-looking unit or a transformer with the same kVA rating may not be an acceptable substitute.

Common Distribution Transformer Types

Dry-type transformers

Dry-type transformers use solid insulation and air rather than insulating liquid around their windings. Available constructions include ventilated, nonventilated, encapsulated and cast-coil designs.

Liquid-filled transformers

Liquid-filled transformers use dielectric fluid for insulation and cooling. The type of fluid, tank construction and environmental approvals can vary considerably between models.

Special-purpose transformers

Buck-boost, control, isolation, lighting, drive and other special-purpose transformers serve different functions. They should not be treated as interchangeable with a general distribution transformer.

The project specification, engineer or equipment manufacturer should establish the required transformer type before a quote is requested.

What to Confirm Before Requesting a Quote

1. Transformer type

Identify whether the approved design calls for a dry-type, liquid-filled or special-purpose transformer. Include any specified construction, cooling or insulation requirements.

2. Required kVA

Provide the kVA stated on the approved transformer schedule, specification or replacement documentation. If the required capacity has not been established, return the question to the project’s qualified designer. Do not estimate transformer capacity from incomplete load information.

3. Primary and secondary voltage

Record both voltage values exactly as shown on the plans or existing nameplate. Small differences in voltage descriptions can identify materially different transformers.

4. Phase and frequency

Confirm whether the transformer is single-phase or three-phase and include the required frequency.

5. Connection and winding information

Include the connection configuration, winding material, electrostatic shielding and other construction details stated in the approved specification. Do not select a configuration based on assumption.

6. Impedance and taps

Record required impedance and tap information exactly as specified. These values affect system performance and must be approved by the responsible designer.

7. Enclosure and environment

Identify whether the transformer will be located indoors, outdoors or in an area exposed to moisture, dust, salt air, chemicals, flooding or physical damage. The complete transformer and enclosure must be approved for the intended environment.

8. Temperature-rise and insulation requirements

Include these values when they appear in the transformer schedule or project specification. Do not substitute a different rating without approval.

9. Efficiency requirements

Confirm that the proposed transformer meets applicable efficiency requirements and any additional project specifications. The U.S. Department of Energy maintains requirements for covered distribution transformers, and future compliance dates can affect long-lead projects.

10. Sound requirements

If the transformer will be near offices, classrooms, apartments or other occupied areas, check the project documents for sound limitations. Required sound performance should be included in the quote request.

11. Dimensions, weight and mounting

Confirm available space, access route, mounting method and any maximum dimensions or weight restrictions. Verify these details using the proposed manufacturer’s current submittal.

12. Terminations and entry locations

Record conductor material, terminal requirements and preferred entry locations identified by the approved design. Confirm lug and terminal provisions before ordering.

13. Accessories

List required shields, sensors, fans, mounting hardware, weather protection, monitoring equipment and other accessories. Confirm whether each accessory is factory-installed, field-installed or ordered separately.

14. Listings and approvals

Identify required listings, labels, approved manufacturers, efficiency documentation and submittal requirements. Obtain written approval before ordering an alternate product.

Information Needed for a Replacement Transformer

For replacement work, provide clear photographs of the complete nameplate and the existing transformer. Include:

• Manufacturer and complete catalog number
• Serial number, if available
• Transformer type
• kVA rating
• Primary and secondary voltage
• Phase and frequency
• Connection, impedance and tap information
• Enclosure or tank information
• Overall dimensions and mounting method
• Terminal and conduit-entry locations
• Required accessories
• Approved replacement specification

Do not order from a partial nameplate or handwritten voltage description. Request clarification when information is unreadable, missing or inconsistent.

Questions to Ask About a Proposed Substitute

• Does the complete model match every approved electrical specification?
• Is its construction approved for the intended environment?
• Does it meet the required efficiency and listing requirements?
• Are the dimensions, weight and connection locations acceptable?
• Are all accessories included in the quoted model?
• Does the substitution require revised plans or engineering approval?
• Has the responsible party approved it in writing?

Lead Time and Delivery Questions

Distribution transformers can have substantial lead times. Before issuing a purchase order, confirm:

• Estimated manufacturing and shipping time
• Whether the quoted date is guaranteed or estimated
• Required submittal-approval date
• Freight and unloading responsibilities
• Delivery-site restrictions
• Inspection procedures for freight damage
• Cancellation and return restrictions
• Warranty start date and claim requirements

Common Ordering Mistakes

• Providing only one voltage instead of both primary and secondary voltage
• Leaving out phase, frequency or connection information
• Estimating kVA without an approved load calculation
• Ignoring impedance, tap or winding requirements
• Assuming an enclosure is suitable based only on appearance
• Ordering before submittals are approved
• Accepting an alternate without written approval
• Overlooking dimensions, weight or terminal locations
• Failing to confirm freight, cancellation and return terms

Frequently Asked Questions

Can Revco determine the required transformer size?

Revco can help source a transformer after the required specifications are established. System design and transformer sizing should come from the engineer, equipment manufacturer or other qualified party responsible for the project.

Can I substitute a different kVA rating?

Do not change the specified kVA without written approval. A larger or smaller transformer can affect system performance, available fault current, space requirements and project compliance.

Is a dry-type transformer always suitable indoors?

No. The complete construction, listing, enclosure and project requirements determine whether a specific transformer is acceptable.

Can the same transformer be used for every type of load?

No. Some loads or systems require specific transformer construction or performance characteristics. Those requirements should be established by the responsible designer.

What if the existing nameplate is unreadable?

Do not guess. Check available drawings, maintenance records and manufacturer documentation, then have the replacement requirements confirmed by a qualified professional.

Ordering Distribution Transformers on Long Island

Browse Revco’s transformers and accessories or review available distribution dry-type transformers.

For help preparing a quote request, call (631) 283-3600 or contact one of Revco’s Long Island locations. Product specifications, approvals, availability and lead times should be confirmed before ordering.

Important Safety and Design Notice

This article provides general purchasing information only. It does not provide transformer sizing, electrical-system design, installation, protection, grounding, testing, energization, troubleshooting or maintenance instructions. Follow the approved plans, applicable requirements, equipment listing and current manufacturer instructions. Consult the engineer of record, qualified electrical professional, equipment manufacturer, utility and Authority Having Jurisdiction when required.

About Revco Lighting + Electrical Supply

Since 1978, Revco Lighting + Electrical Supply has supported contractors, builders and facilities teams across Long Island with electrical products, lighting solutions and dependable local service. With branches in East Hampton, Southold, Southampton, Riverhead, Bohemia and Rocky Point, Revco helps customers source the materials specified for residential, commercial and industrial projects.

Helpful Resources

• Revco Transformers
• Revco Distribution Dry-Type Transformers
• Revco Long Island Locations
• U.S. Department of Energy: Distribution Transformers