The base family number for the AC control module in a Ross Hill / NOV SCR drive — and why the dash suffix, not this number, decides whether a board will run on your set.
Independent sourcing, not an authorized distributor. Ross Hill, NOV, and other manufacturer names and part numbers are used for reference only. Supplied as new-surplus, used-tested, or reconditioned, with condition disclosed before sale.
| Part number | 0521-2500 |
|---|---|
| Manufacturer | Ross Hill / NOV |
| EI reference | EI-0521-2500 |
| System | Ross Hill / Hill Hayes / NOV SCR drilling |
| Module type | AC control (RHCC) — base family number |
| Function | SCR gate firing, drive assignment, and system protection |
| Assignable to | Drawworks, mud pumps, and rotary table |
| NOV equivalent | Number carried forward (verify against the label) |
| Condition | New-surplus, used-tested, reconditioned |
0521-2500 · 521250000 · 05212500 · RHCC AC control module · Ross Hill AC control module · Ross Hill AC firing module · EI-0521-2500
It is the AC side of a Ross Hill SCR drive: it generates the SCR gate-firing signals, handles drive assignment, and carries the system protection. Assignment is the part most people mean when they describe the symptom — it is what lets a bay be given to the drawworks, a mud pump, or the rotary table.
It works as a matched pair with a DC control module from the 0522-2400 family. The AC module fires; the DC module regulates. A fault in one is regularly misattributed to the other, which is why the fault finder starts from the behaviour rather than the board.
Because 0521-2500 names the family, not the board. Across this family the dash suffix can carry the supply frequency and, in at least one record, an additional protection feature. Two modules sharing this base number are commonly not substitutes for one another.
This is the single most common way a spare gets bought and cannot be used. The board arrives, it seats in the rack, and it does not behave. Mechanical fit proves nothing on this equipment.
| Number | What our records describe | Relationship |
|---|---|---|
| 0521-2500 | AC control module (RHCC), the base family number. SCR gate firing, drive assignment and protection. | this page |
| 0521-2500-14 | AC control module, recorded as 50 Hz. Runs as a matched pair with the DC regulation module. Also seen as 521250000. | Verify frequency |
| 0521-2500-32 | AC control module. Variant within the AC family; suffix not yet characterised. | Different variant |
| 0521-2500-19 | AC control module with reverse power relay. Number derived from our own records, not yet confirmed against a unit. | Unconfirmed — different feature set |
| 0521-2500-35 | AC control module, 50/60 Hz. Number derived from our own records, not yet confirmed against a unit. | Unconfirmed — verify frequency |
Where a row is marked in red we have an unresolved question about that number. We would rather say so than present a derived number as a confirmed fact.
A 50 Hz-recorded module on a 60 Hz set is not a board you troubleshoot — it is a board you take back out. The -14 is recorded as 50 Hz and the -35 as 50/60 Hz in our records, so the frequency question is live on this family in a way it is not on the DC side.
Tell us the frequency and engine configuration of the set along with the number, and we will match the variant rather than guess at it.
| What you are seeing | What it usually indicates |
|---|---|
| No gate firing pulses, or a gate firing pulse failure alarm on one drive | The AC control module owns SCR gate firing. Verify supply voltages at the card before condemning it. |
| Missing or erratic firing pulses | Either the firing signal path on the AC module or the power section itself — establish the SCR generation before ordering. |
| Drive assignment dropout — mud pump, drawworks, or rotary table will not take or hold assignment | Assignment lives on the AC control module alongside firing and protection. Compare dash suffixes between two otherwise identical sets before swapping boards. |
| Board fits the rack but the drive misbehaves | Wrong variant for the configuration. On this family the suffix can carry the frequency. |
Starting from a symptom — a gate firing pulse failure, a misfire, phase loss, one leg dead? The SCR Drive Fault Finder maps what you are seeing to the suspect module and part number.
Yes — a PLC-based AC control retrofit inside the existing SCR house footprint, when a like-for-like swap is no longer viable. That is a decision about the whole control section rather than one board, and it is worth taking only when the family has genuinely run out of supply.
Most of the time it has not. See SCR house rebuild and retrofit for how the two paths compare, and the Ross Hill / NOV cross-reference for the legacy-to-replacement mapping.
We verify the exact dash number and revision against the physical unit before quoting, and send photos of the label on the unit being offered. If your board carries both a Ross Hill number and an NOV number, send both.
These are the details that let us identify the right unit instead of guessing at it.
Supplied as new-surplus (unused, from the secondary market), used-tested, or reconditioned, with condition disclosed before sale and photos on request. Availability on legacy Ross Hill and NOV equipment changes constantly — send the number and we will tell you what we can actually find.
Condition always disclosed before sale. Photos on request. Same-day response on most requests.
Condition disclosed before sale. Same-day response on most requests.