What to Expect When Buying a Used Dry-Type Transformer

When you’re buying a dry-type transformer, one of the big decisions you’ll face is condition. 

Should you buy new, used, or unused surplus? 

The answer depends on your budget, your timeline, and where the unit is going.

At Maddox, we sell both new, used, and unused surplus dry-type transformers. This gives our customers multiple buying options. More importantly, we test and warranty these transformers (no matter the condition) to the same high standard. Even our used units are backed by an industry-leading five-year warranty.

How do we do this? By putting every unit we purchase through a proven inspection and testing process before it ever ships.

Keep reading to learn what that really means.

New vs. Used Dry-Type Transformers

At Maddox, dry-type transformers are sold in three categories:

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Let’s define each more clearly.

New Dry-Type Transformers

A new dry-type transformer is a unit that’s never been energized. These are straight from the factory, and are cosmetically perfect. 

If appearances are critical for your project, such as in a public-facing installation, new may be the best fit. Sometimes engineering, specs, or funding will also require a brand new unit.

Used Dry-Type Transformers

A used dry-type transformer is a unit that has been previously energized at a project. At Maddox, we purchase used units regularly and put every one through a comprehensive inspection and testing process before approving it for resale. The exterior may show some signs of use: scratches, faded paint, or replaced knockouts. But electrically, they're held to the same standards as a new unit in terms of testing.

For many customers, used transformers provide maximum value, on average costing 35% less than new transformers.

Unused Surplus Dry-Type Transformers

“Unused surplus” units fall between new and used. They are transformers that were purchased for a project, but never energized. These could have minor wear and tear from shipping and storage, or other minor cosmetic defects. But electrically, they have never been placed in service.

If you’re looking for near-perfect condition at a lower price, unused surplus can be an excellent option.

How Maddox Tests Dry-Type Transformers

Whether you’re purchasing brand new or used units, quality is key. 

Every used and unused surplus low-voltage dry-type transformer at Maddox goes through three key tests before it’s approved for sale. Two of the tests are IEEE-recognized standards. The third is a widely accepted field diagnostic test.

Let’s look at all three. 

Transformer Turns Ratio (TTR)

For every transformer, IEEE has published an acceptable range for the ratio of input to output voltage. The Transformer Turns Ratio test confirms the actual ratio lines up with what is stated on the transformer’s nameplate. This confirms that the transformer can convert the input voltage to the correct output voltage.

Winding Resistance

The winding resistance test measures the resistance from the start of a coil to the end of a coil as well as resistance across phases. This test helps identify if there are any loose internal connections, faulty taps, open circuits, and broken conductor strands or crimp connections.

Insulation Resistance (Megger) Testing

The final test is insulation resistance testing, commonly called a Megger test. This test determines the quality of the transformer’s insulation system.

A direct current voltage is applied, and the resulting leakage current is measured. Some leakage is normal—but excessive leakage can indicate insulation breakdown. That breakdown could be caused by a number of things including age, heat, moisture, or mechanical stress.

What condition of dry-type transformer should you buy? 

The right dry-type condition comes down to what you need for your specific project. 

Choose a New Transformer if:

• The installation is visible to the public
• Aesthetics matter
• You want or need factory-fresh equipment

Choose a Unused Surplus Transformer if:

• You want near-new condition
• You’re looking for moderate savings
• Availability is important

Choose a Used Transformer if:

• Budget is a key concern
• Cosmetics are not critical
• You want maximum value

On average, used dry-type transformers cost 35% less than new units.

And at Maddox, you still receive:

• Proven testing
• Verified performance
• The same Maddox warranty

The Bottom Line

At Maddox, condition does not determine reliability.

New, unused surplus, and used dry-type transformers are all held to the same electrical performance standards before they leave our facility.

Need a dry-type transformer? Fill out the form below. We have thousands of dry-type transformers in stock in all conditions. And we can deliver them in 3-5 business days. 

We’ll get you what you need, when you need it.