Potential Transformer (PT) Protection Fuses
DENCO PT fuses are high-interrupting, current-limiting fuses designed to protect the primary windings of potential transformers. They are compact ferrule-type fuses that fit standard mounting clips, are non-venting for quiet operation, and carry a blown-fuse indicator on the 9F60 series.
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Specifications
| Parameter | Value |
|---|---|
| AC voltages | 0.625kV, 2.4kV, 2.75kV, 4.8kV, 5.0kV, 5.5kV, 7.2kV, 8.25kV and 15.5kV (AC) |
| Extended voltage range | 0.625kV to 38kV (AC) |
| Ampere range | 0.25A to 5A |
| E-rating range | 0.5E to 200E |
| Interrupting ratings | 50kA, 52kA, 63kA, 80kA, 100kA and 120kA RMS symmetrical |
| Type references | 9F60 Series, EJ-1; types DAAA, DBBB, D24T, D48T, D50T, D72T, DBDE, DBHH |
| Mounting | Cylindrical clip-on, compatible with standard clips; clip-mounted and clip-lock variants |
| Indicator options | Blown-fuse indicator on the 9F60 series; open fuse trip indicator, trip length 0.25 in |
| Construction | Compact ferrule type, non-venting, with catalog number and manufacturing date on an affixed label |
Catalog numbers
| Catalog no. | Availability | Last reviewed |
|---|---|---|
| EJ-1 | Active | 2026-08-27 |
| DAAA-3 | Active | 2026-08-27 |
| DAAA-5 | Active | 2026-08-27 |
| DAAA-7 | Active | 2026-08-27 |
| DAAA-10 | Active | 2026-08-27 |
| DBBB-1 | Active | 2026-08-27 |
| DBBB-2 | Active | 2026-08-27 |
| DBBB-3 | Active | 2026-08-27 |
| DBDB-1 | Active | 2026-08-27 |
| DBDB-2 | Active | 2026-08-27 |
| DBDB-3 | Active | 2026-08-27 |
| DAAB-1 | Active | 2026-08-27 |
| DAAB-2 | Active | 2026-08-27 |
| DBBD-1 | Active | 2026-08-27 |
| DBBD-2 | Active | 2026-08-27 |
| DBBD-3 | Active | 2026-08-27 |
| DBBN-1 | Active | 2026-08-27 |
| DBBN-2 | Active | 2026-08-27 |
| DBBN-3 | Active | 2026-08-27 |
| DBDE-1 | Active | 2026-08-27 |
| DBDE-2 | Active | 2026-08-27 |
| DBDE-3 | Active | 2026-08-27 |
| DBHH-1 | Active | 2026-08-27 |
| DBHH-2 | Active | 2026-08-27 |
| DBHH-3 | Active | 2026-08-27 |
Applications
- Potential transformer primary winding protection
- Protection for 0.625kV to 15.5kV transformers or distribution systems
- Indoor or enclosure-mounted switchgear
Limits and boundaries
- Standards evidence is not stated on the PT catalog pages and is outstanding (Q3)
- G.E. 9F60 equivalence is a cross-reference claim and requires DENCO confirmation before publication
Technical documents
Data sheets, dimensional drawings and time-current curves for this family are available on request. Ask for the documents you need.
What we need to quote
Voltage and whether the system is AC or DC, continuous current, required interrupting rating, physical dimensions and mounting, any indicator requirement, and the standard or approval you must meet. A photograph or drawing of the existing part is usually the fastest route.
Common questions
Are PT fuses E-rated?
A PT fuse that conforms to the requirements for an E rating meets the performance characteristics of ANSI/IEEE C37.46 — the same 300-second and 600-second melting criteria that apply to any E-rated fuse. Not every PT fuse is E-rated, though: fast-acting PT fuses are specified instead by their own opening-time tests, and the two are not substitutes for each other.
Why are PT fuse ampere ratings so small?
A potential transformer is an instrument transformer. It is there to present a voltage to metering or relaying, not to carry load, so its primary draws a fraction of an ampere. The fuse is sized to that, and its job is to protect the primary winding and clear a fault in the transformer without damaging the switchgear around it.
What do you need to quote a PT fuse?
The system voltage and whether it is AC or DC, the ampere or E rating, the required interrupting rating, the overall length and diameter, the clip or bolt centres it has to mount in, and whether an indicator is required. A photograph of the existing fuse in its clips is usually faster than a written description, and it lets us check the mounting as well as the fuse.
Technical review
Specifications on this page are quoted from DENCO’s product catalog. Confirm any rating against DENCO engineering before specifying.
Related
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