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Material Substitution on Site: What to Document
A project priced in March starts installation in July. By then the specified LED fixture has been discontinued. The importer holds a nearly identical unit: 5% higher lumen output, same beam angle, different model number. The site engineer says it looks the same. Whether this material substitution causes a handover dispute, a rejected grid application, or a failed warranty claim depends on what gets written down before the crew starts.
Why do material substitutions happen on factory installations?
Thai factory electrical projects carry long lead times, and product availability shifts between quoting and installation day.
Product discontinuation. LED fixture and solar panel models have shorter commercial lifespans than most contractors expect. A manufacturer updates a product line, the old model number is discontinued, and the importer stops stocking it quietly. If the project was quoted off a spec sheet that is now six months old, the model in the contract may no longer exist.
Importer stock limits. Thai importers of solar equipment and commercial lighting hold limited inventory of any specific model. A surge in demand driven by factory decarbonization programmes or BOI-linked projects can clear out a model that had reliable stock a month before. The distributor then offers the nearest equivalent in their current catalogue.
Fixed shutdown windows. A factory shutdown window for electrical work is set months in advance. If the original product needs eight weeks to arrive and the shutdown is six weeks out, the choice is substitute or miss the window entirely.
None of these situations are unusual. The risk is not the substitution. The risk is treating it as an installation detail rather than a document that needs to exist.
What goes wrong when the substitution is not documented?
Three problems arise at different points in the project.
At handover. The customer’s engineer compares what was installed against the specification in the contract. The model numbers differ. The engineer has no context for why, and is not in a position to certify that the substituted product meets the original spec without a comparison. Handover stalls while the contractor searches for documentation that should have been prepared before the crew installed a single unit.
At the grid interconnection application. For solar installations, the PEA or MEA grid application references the specific inverter and protection equipment. If the model number in the application differs from what is on the wall, the application may be rejected as incomplete. Resubmission restarts the review clock, extending the commissioning-to-billing timeline by a month or more.
At the warranty claim. Two years in, an inverter fails. The site register shows the originally specified model. The maintenance team contacts the warranty department with the wrong model number, and the warranty team has no record of the claim. A correct substitution record would have prevented this entirely.
What does a complete substitution record contain?
A substitution record does not need to be a formal document. It needs to be findable, attributable, and complete enough to close a dispute.
At minimum, the record contains:
- Original specification: model number, manufacturer, and the key performance parameters the contract references (wattage, lumen output, string voltage range, efficiency)
- Substituted product: the same fields for the replacement unit
- Statement of equivalence: a short factual comparison showing the substitute meets or exceeds the original specification, supported by datasheets for both products
- Customer approval: written confirmation from the person who has authority to accept the change, with their name and position at the factory
- Date of approval: before installation starts, not after
- Job reference: the job order this substitution applies to
A LINE message thread with the above information, screenshotted and attached to the job record, satisfies this. An email exchange satisfies it. A signed note satisfies it. A verbal conversation does not.
How does the substitution flow into the technical file and site register?
The technical file that travels with the site carries equipment documentation including datasheets and serial numbers. If the installed model differs from the contracted spec, the file should document the installed model, not the original. The substitution record explains the discrepancy for anyone who reviews it later.
The site register also needs to reflect what was actually installed. The job record must contain the substituted product details, not the originally specified ones, so the register is accurate from the moment the job closes. A register showing the wrong inverter model means inaccurate data for every maintenance visit, every warranty call, and every spare-part order that follows. For panel warranties specifically: a ten-year warranty runs against the serial numbers of the panels on the roof, not the ones that were supposed to be there.
When should you stop and wait rather than substitute?
Not all substitution situations call for a fast decision. Stop and wait when:
- The substitute product has lower performance than the contracted specification. A fixture with lower lumen output, a panel with lower wattage, or an inverter with a narrower input voltage range is not an equivalent substitution. It requires a contract variation, not a substitution record.
- The customer contract specifies brand or model without an equivalence clause. Some factory procurement systems require a formal variation order for any change to contracted specifications, regardless of technical equivalence.
- The substituted inverter or protection equipment is not on the list the grid authority will accept. Certain models are required for PEA or MEA interconnection. Substituting outside that list creates a grid application problem that outweighs any scheduling pressure.
- The person who can approve the substitution is not reachable before the installation window opens. A short delay to get the right signature is a manageable cost. A handover dispute over an undocumented substitution is not.
FAQ
Can I substitute a different brand if the specifications are equivalent?
If the technical equivalence is clear and the customer approves in writing, brand substitution is usually acceptable. The standard to meet is the specification in the contract, not the specific brand name. The record needs to show the comparison explicitly and carry approval from someone with authority to accept a brand deviation, which may not be the day-to-day site engineer.
What if the customer cannot be reached for approval before the crew starts?
Escalate to the customer’s project manager or facility manager, not the site contact only. If you still cannot get written approval, do not install the substituted product. The scheduling pressure does not transfer approval authority to your crew or foreman. An incomplete installation is recoverable. A completed installation with an undocumented substitution may not be.
Does a substitution always need a formal contract amendment?
For most field substitutions of equivalent products, written approval from the customer’s authorized engineer is sufficient. A full amendment is needed only when the substitution changes the price or when the customer’s procurement rules require one. When in doubt, ask the factory’s engineering or procurement contact what their process requires before opening any boxes.
If your job records have no place to attach a substitution document, the TRACE 30 program page covers how job documentation flows into the site register. To talk through how this applies to your current load, schedule a call.