Protection coordination is probably the Grid Code study that generates the most penalties when done poorly — and the one that stays most invisible until a fault occurs. A plant can operate for years with uncoordinated protections, but the day a short circuit happens in a specific zone, instead of isolating the fault, the system trips upstream and de-energizes the entire facility. In many industries, the operational loss from a single hour of downtime exceeds the total cost of the study.
This guide explains what CRE requires in terms of protection coordination in 2026, how an acceptable study is carried out, and what errors delay or invalidate the deliverable.
What does coordinating protections mean?
Coordinating protections means ensuring that, in the event of an electrical fault, only the device closest to the fault operates — not those upstream. This is called selectivity: the system isolates the problem without sacrificing healthy areas.
In practice, this translates into adjusting the operating times and currents of each relay, breaker, and fuse so that their operating curves are staggered. The relay farthest from the fault must wait long enough for the closest one to operate first.
If there is no coordination, the typical outcome is that the main breaker trips for any minor fault on any branch. Result: complete shutdown of the facility from a fault that should have been local.
The 4 typical protection zones in industry
An industrial load center typically has 4 zones that require coordination with one another:
Zone 1 · Service entrance and main substation
Where you receive supply from CFE or from the Qualified Supplier. The protections here are the slowest (most time-tolerant) because they must allow the downstream ones to operate first.
Zone 2 · Main transformers
The transformers that step voltage down from medium voltage to low voltage. Differential, backup overcurrent, and temperature protections.
Zone 3 · Distribution switchboards
Where energy is distributed to the various internal load centers. Overcurrent and short-circuit protections, coordinated with the following levels.
Zone 4 · Final loads and motors
The end-consuming equipment: process motors, furnaces, production lines. Fast protections, frequently with fuses or thermal-magnetic breakers.
Correct coordination means the time-current curves of the 4 zones are staggered with intervals of 0.2 to 0.4 seconds between consecutive levels.
What an acceptable coordination study delivers
A protection coordination study that CRE accepts must contain at least:
- Updated single-line diagram of the entire facility
- Complete list of protection equipment: brand, model, current settings, interrupting capacity
- Time-current curves (TCC) of each protection, plotted in standard logarithmic format
- Selectivity analysis for three-phase and single-phase faults at each node
- Recommended settings for each relay, with technical justification
- Coordination verification table showing the intervals between each level
- Signature of a certified expert in good standing before CRE
The typical deliverable runs between 80 and 200 pages depending on the complexity of the facility.
Standard software accepted by CRE
The authority does not require a specific tool, but the most widely accepted studies are run in:
- ETAP (Electrical Transient Analyzer Program) — the most used by professional firms
- PowerWorld Simulator — a robust alternative, common in large projects
- DigSilent PowerFactory — used in stability studies and more complex systems
- EasyPower or SKM PowerTools — more compact alternatives
If your current firm uses low-profile software or Excel-based calculations, CRE may require the study to be re-run in a recognized industrial tool.
Common errors that invalidate the study
1. TCC curves not checked against the real short circuit
The coordination study depends on the prior short-circuit study. If the calculated fault currents are not realistic (for example, an incorrect transformer model), the entire coordination falls apart. That is why both studies are run together. See electrical studies of the Grid Code.
2. Lack of coordination in single-phase faults
Many studies coordinate well for three-phase faults but forget the single-phase case. Ground protections require their own separate analysis.
3. Undocumented "factory" settings
If relays leave the factory with default settings and no one changed or documented them, no theoretical study has real usefulness. A CRE audit may require verifying that the physical settings match those in the study. Periodic injection testing, included in the substation preventive maintenance checklist, is the way to confirm that the physical relay operates on the curve you designed.
4. Not considering N-1 contingencies
If your facility is critical (continuous-process industry, hospitals, telecommunications), coordination must hold even if a transformer or a line is out of service. Studies that only coordinate under normal conditions are incomplete.
5. Old studies not updated
Any modification to the facility (new load, new relay, transformer change) invalidates the prior coordination. CRE requires the study to be updated with each significant modification.
Re-updating protections: when it makes sense
The practical rule:
- Every 5 years even if there are no changes, to verify that the physical settings remain valid
- Every time a relay or power breaker is added or replaced
- When the capacity of a main transformer is modified
- When significant load is added (> 15% of installed capacity)
- After an operational fault that caused a non-selective trip
Typical corrective adjustments in case of non-conformity
If the study reveals deficient coordination, the most common corrective measures:
- Readjustment of curves and time dial on existing relays (the cheapest option, $20,000–$80,000 MXN)
- Replacement of electromechanical relays with digital relays (when the current ones lack the necessary flexibility; $40,000–$150,000 MXN per relay)
- Addition of intermediate protections at levels that lacked them (zone relays, additional differential protections; $200,000–$1,500,000 MXN)
- Reconfiguration of the grounding system if the single-phase fault is not being cleared properly
The typical schedule to implement the corrections is 8 to 16 weeks from approval of the proposal to operational verification.
Total cost of the study + corrections
| Item | Range (MXN) |
|---|---|
| Protection coordination study | $120,000 – $400,000 |
| Readjustment of existing relays | $20,000 – $80,000 |
| Replacement of 2–4 relays (if applicable) | $80,000 – $600,000 |
| Addition of new protections (if applicable) | $200,000 – $1,500,000 |
| Electrical verification testing | $50,000 – $180,000 |
Typical total: $200K – $2.5M MXN depending on the starting point.
The connection with CRE penalties
A deficient or absent study can generate penalties of $300,000 to $2,000,000 MXN for this item alone, not counting the operational cost of a resulting fault. In 2025, a Bajío automotive plant received a $4.7M penalty for failing to update coordination after a substation expansion. More detail in CRE penalties for Grid Code non-compliance.
Do you need a coordination study?
At Enerlogix we coordinate protection studies as part of our Grid Code service, within the 360 Management Plan: we contract the certified expert, oversee technical quality, carry out the operational corrections with your maintenance team, and leave the file ready for the next CRE audit.
If your plant has CRE observations on this item, or if you have gone more than 5 years without re-updating coordination, request a free 360 Management Plan evaluation. We review your current situation and deliver a no-obligation roadmap.
To understand the general framework, read the Grid Code 2026 pillar — Complete Guide.
Frequently asked questions
Coordinating protections means ensuring that, in the event of an electrical fault, only the device closest to the fault operates, not those upstream; that is called selectivity. In practice, the times and currents of each relay, breaker, and fuse are adjusted so that their curves are staggered. If there is no coordination, any minor fault trips the main breaker and de-energizes the entire facility.
It must include at least: an updated single-line diagram of the entire facility; a complete list of protection equipment with brand, model, settings, and interrupting capacity; time-current curves of each protection in logarithmic format; a selectivity analysis for three-phase and single-phase faults at each node; recommended settings with justification; a coordination verification table; and the signature of a certified expert in good standing before CRE. The typical deliverable runs between 80 and 200 pages.
The practical rule: every 5 years even if there are no changes, to verify that the physical settings remain valid; every time a relay or power breaker is added or replaced; when the capacity of a main transformer is modified; when significant load is added, greater than 15% of installed capacity; and after an operational fault that caused a non-selective trip. Any modification to the facility invalidates the prior coordination.
For an industrial plant, the coordination study ranges from 120,000 to 400,000 MXN. If there are non-conformities, readjusting existing relays costs from 20,000 to 80,000; replacing 2 to 4 relays from 80,000 to 600,000; adding new protections from 200,000 to 1.5 million; and verification testing from 50,000 to 180,000. The typical total ranges from 200,000 to 2.5 million depending on the starting point.
The most common are: time-current curves not checked against the real short-circuit study; lack of coordination in single-phase faults, since ground protections require a separate analysis; factory settings that no one changed or documented; not considering N-1 contingencies in critical facilities; and old studies not updated after modifications. CRE may require verifying that the physical settings match those in the study.
