What we buy
Ranges we buy on this page
This guide explains K-4, K-13 and K-20 transformer ratings, the harmonic heating they address, and what each rating does and does not tell you about the neutral.
Before removing a 480-to-208Y/120-volt transformer, separate its K rating from its neutral terminal capacity, winding condition and documented service history.
| Phase | kVA | Voltage | Fluid |
|---|---|---|---|
| 1-phase | 10 - 333 kVA | up to 25 kV | Liquid or dry |
| 3-phase | 75 - 20,000 kVA | 46 kV | Liquid or dry |
Who we buy from
Six kinds of seller
- Recyclers
- Electrical contractors
- Equipment dealers
- End users
- Demo contractors
- Distributors
Fast offers
A written offer the same business day, based on your photographs.
Dedicated logistics
Our own crew, trailer and crane, not a brokered haul.
No broker fees
One buyer from first call to cleared pad, with nothing skimmed.
How it works
Six steps from photograph to payment
- 01
Take pictures
Photograph the nameplate, the inside of the cabinet and the tank from both ends. Four frames on a phone are enough to price most units.
- 02
Send them to us
Email or text the photographs with the site address and whether the unit is still energised. We reply the same business day with questions or a number.
- 03
Review the offer
The offer names the unit, the site, the price and the pickup window. It is written, dated and good for thirty days unless the unit changes hands.
- 04
We schedule freight
A crew, a trailer and a crane if the pad needs one. You get the date and the arrival window, and the site does not have to close for it.
- 05
Testing on arrival
Winding resistance, insulation resistance and a turns ratio check, plus oil analysis where the unit is liquid-filled. Results travel with the unit.
- 06
Get paid
Payment is released against the signed bill of sale and the scale ticket, by check or ACH, with the paperwork copy left on site.
What we handle
The parts sellers dread
Rigging
Crane, skates and a route survey for anything that will not roll onto a trailer.
Oil containment
Pans, absorbent and a spill plan before a drain plug is touched.
Bill of sale
A document that clears a lien, a lease or a bankruptcy file, not a handwritten note.
PCB paperwork
Testing and manifesting for pre-1979 oil, handled before the unit moves.
On the ground
What it is
K-factor describes the heating effect of harmonic current relative to a sinusoidal current of the same RMS magnitude. Its calculation weights each harmonic current component by the square of its harmonic order.
Higher-frequency components therefore contribute disproportionately to the calculated burden on winding eddy-current losses.
A K-rated transformer is designed to handle a specified harmonic heating burden within its rating and stated operating conditions. K-4, K-13 and K-20 identify different capabilities, not different secondary voltages.
A 208Y/120-volt nameplate still needs its own kVA, temperature-rise and connection information read separately.
Local reality
Why it matters when you sell
When a Raleigh hospital removes a transformer from an electrical room, the K rating helps identify what equipment is being evaluated. A legible K-13 marking distinguishes it from an otherwise similar general-purpose dry-type unit.
Photographs should include the complete nameplate, enclosure and accessible terminal markings.
Service history gives that marking context. A transformer feeding computer power supplies can carry substantial harmonic current even without an obvious phase overload.
Keep load measurements, overheating reports and maintenance records with the asset file; darkened insulation near a winding lead deserves attention regardless of the K rating.
Around the site
The numbers
K-4 addresses a lower harmonic heating burden than K-13 or K-20 under comparable conditions. These numbers are not multipliers for allowable kVA or overload duration.
A K-13 nameplate does not authorize thirteen times rated current, and K-20 does not establish a particular harmonic distortion limit.
Neutral loading is a separate check on a four-wire wye secondary. Triplen harmonics, including the third and ninth, can add in the neutral rather than cancel.
Many K-rated designs provide a neutral connection rated for 200 percent of phase current, but verify that provision in manufacturer documentation.
Where it sits
Common mistakes
Treating K-factor as a harmonic filter leads to the wrong conclusion about power quality. A K-20 transformer accommodates the specified heating burden; it does not remove harmonic current from the circuit.
Capacitor problems, voltage distortion and upstream heating still require evaluation of the actual electrical system.
Another mistake is assuming an enlarged neutral terminal makes the entire neutral path adequate. The secondary neutral conductor, lug, panel termination and any intervening bus must be evaluated separately.
Do not infer their capacity from a K-13 label or mistake a bonding connection for a load-carrying neutral.
On the ground
How it affects value
For a buyer's technical evaluation, a documented K rating makes the transformer easier to classify for potential reuse. That designation alone cannot overcome cracked insulation, winding damage or an unreadable nameplate.
A complete K-4 unit with clear records can be more straightforward to evaluate than an undocumented K-20 unit.
Transformer Buyers NC buys used, surplus, failed and obsolete transformers across North Carolina. For K-rated dry-type units, evaluation considers kVA, voltage, enclosure, winding material and condition alongside the harmonic rating.
Manufacturer drawings that establish neutral capacity resolve a detail that a front-door photograph often cannot show.
Local reality
What to do next
Record the manufacturer, serial number, kVA, primary voltage, secondary voltage and K rating before the transformer leaves its pad or room. Capture the connection diagram and neutral terminal designation.
Obtain photographs inside the enclosure only after qualified personnel establish an electrically safe work condition for access.
Keep any harmonic measurements with their dates and load conditions; one current reading does not describe a changing nonlinear load. Note missing panels, damaged lugs and evidence of overheating.
For removal planning, document dimensions, lifting provisions and the route from the electrical room to the loading area.
Get started
Get an offer in minutes
Five fields is all it takes. Photographs help, but a nameplate and a town are enough to start.
No fee, no obligation. We reply the same business day.
Tell us what you have
We reply the same business day.
Questions
Straight answers
Equipment types
Does K-13 require a double-capacity neutral connection?
Do not use the K-13 marking alone to establish neutral capacity. Many K-rated transformers have a neutral connection rated for 200 percent of phase current, but the manufacturer's drawing or terminal data must confirm it. External neutral conductors require their own evaluation.
Service area
Can a K-20 transformer eliminate harmonic current?
No. K-20 identifies a transformer designed for a specified harmonic heating burden, not a filtering function. Third-harmonic current can still flow in a 208Y/120-volt system's neutral. Power-quality measurements are needed to identify distortion and determine whether separate corrective equipment is appropriate.
Payment
What records help identify a used K-rated transformer?
Provide the complete nameplate photograph, manufacturer connection diagram and any documentation specifying neutral terminal capacity. Include test reports and dated load measurements if they exist. For a removed K-4, K-13 or K-20 unit, label the records with its serial number to prevent mismatches.
Logistics
How it affects value: what should a seller know?
For a buyer's technical evaluation, a documented K rating makes the transformer easier to classify for potential reuse. That designation alone cannot overcome cracked insulation, winding damage or an unreadable nameplate.