Defining the Terms
Before getting into the practical handling, it is worth being precise about what these terms mean — because they are used inconsistently across contracts, and the difference between them matters when it comes to adjusting costs and claiming variations.
Provisional Sum (PS)
A provisional sum is an allowance for work that is known to be required but cannot be sufficiently defined at the time of tender. The work will happen — the question is exactly what form it will take. Common examples in electrical contracts:
- Allowance for electrical connection to tenant fitout areas where the fitout scope is not yet confirmed
- Provisional sum for switchgear upgrades in existing buildings where the existing installation condition is not fully known
- Allowance for temporary power supplies during construction where the exact requirements are undefined
- Provisional sum for special systems (data, security, AV) whose specification depends on a specialist consultant not yet engaged
The PS amount is included in the contract sum. When the work is instructed, the actual cost replaces the provisional amount — the difference (whether more or less than the PS) is adjusted through a variation.
Prime Cost (PC) Item
A prime cost item is a nominated supply allowance for a specific product whose exact selection has not yet been made. The PC amount represents the anticipated supply cost of the item; the contractor prices their installation work around this assumed supply value. When the actual product is selected, the PC amount is adjusted to the real supply cost, and the installation pricing may also be adjusted if the product change materially affects the installation scope.
PC items are extremely common in panelboard and switchgear contracts — particularly where:
- The engineer has specified performance requirements but not yet nominated a specific manufacturer or model
- The client wants to maintain flexibility to select a preferred supplier after contract award
- The specification allows alternatives, and the final product selection will be made post-tender through a value engineering or substitution process
Why Provisional Sums Get Estimators Into Trouble
The most common mistakes estimators make with provisional sums are not in the PS amount itself — they are in the associated work pricing and the contract mechanism for adjustment.
Pricing Installation Based on an Underdefined Scope
When a provisional sum is included for a panelboard or switchboard, the estimator still needs to price the installation: conduit, cable, cable tray, terminations, labelling, commissioning, testing. If the scope is genuinely undefined, what do you price installation against?
The answer is to state an explicit assumption in your bid. For example: "Installation pricing is based on a main switchboard of approximately the size and configuration described in the attached sketches. If the actual switchboard delivered under the provisional sum differs materially in physical dimensions, breaker count, cable entry configuration, or termination requirements, the installation pricing will be subject to variation." This single sentence protects you from being held to an installation price that no longer fits the actual equipment.
Not Escalating the PS Adjustment as a Formal Variation
When the provisional sum is instructed and the actual cost is known, the adjustment needs to be processed as a formal variation — not informally absorbed or assumed. Many electrical contractors let PS adjustments drift through without formal variation notices, then find themselves in a dispute at the end of the project about what was agreed.
When a PS is instructed, issue a formal RFI or variation notice immediately, provide a detailed breakdown of the actual cost (supply and installation), and get written approval before proceeding. Treat the PS instruction exactly as you would treat any other variation instruction.
Forgetting Overhead and Profit on PS Adjustments
Check your contract carefully for how PS adjustments are calculated. Some contracts only allow the actual cost of supply and installation — no overhead, no profit margin on the adjustment above the original PS amount. This is particularly common in AS4000 and AS2124 based contracts in Australia, where the default mechanism for PS adjustment is cost-plus-margin-as-specified rather than a full variation rate.
If your contract does not explicitly allow overhead and profit on PS adjustment amounts, negotiate this at tender stage. A PS that comes in at twice the nominated amount and does not allow overhead and profit recovery on the additional cost is a direct margin hit.
Handling PC Items for Panelboards and Switchgear
PC items for major switchgear carry specific risks that are worth understanding before you price around them.
Ensure the PC Amount Reflects Current Market Pricing
The PC amount nominated in the contract documents is often set by the engineer or quantity surveyor months before tender. In a market where switchgear prices are moving rapidly — as they are in 2026, with lead time pressures and tariff impacts — the nominated PC amount may already be out of date by the time you receive the tender documents.
If the PC amount is materially below current market value for the described equipment, flag this in your tender submission. State that based on current OEM pricing, the described item is likely to cost more than the nominated PC amount, and recommend the PC be revised before contract award. This protects both you and the client from a surprise at equipment procurement stage.
Price Installation to Match the PC Scope, Not a Minimum
Installation pricing for a PC item should reflect the likely actual scope of the equipment being supplied — not a minimal interpretation that looks competitive. If the PC is for a 1600A switchboard with 24 outgoing circuits, price the installation for a switchboard of that size and configuration. Pricing for a smaller switchboard to appear more competitive, then claiming a variation when the actual board arrives, is a practice that damages client relationships and creates unnecessary disputes.
Track PC Adjustments Through the Contract Period
On a project with multiple PC items — which is common on medium-to-large commercial electrical contracts — maintain a running PC schedule throughout the project. For each PC item, track the original nominated amount, the actual supply cost when procured, the adjustment amount, and the approval status. This is basic project cost management but it is frequently not done systematically, leading to end-of-project surprises when the cumulative PS and PC adjustments are reconciled against the contract sum.
Contract Clause Checklist for Provisional Sums and PC Items
Before signing a contract that contains significant PS or PC items, check that the contract clearly addresses:
- Adjustment mechanism: How exactly is the PS or PC adjusted when the actual cost is known? Is it cost only, cost plus a percentage for overhead and profit, or a full variation rate?
- Instruction process: How must the PS or PC be formally instructed before the contractor proceeds? A verbal instruction is not sufficient — you need a written instruction before committing to procurement or installation.
- Installation variation rights: If the actual equipment under a PC item is materially different from what was assumed when pricing installation, does the contract allow an installation variation? Make sure it does and document your installation assumption clearly at tender.
- Timing of adjustment: When in the contract programme is the PS or PC expected to be instructed? If it is instructed late, does this affect the programme, and is there provision for programme extension?
- Lead time obligation: Who is responsible for procurement timing on PC items? If the client controls product selection and delays it, your lead time clock does not start until the selection is confirmed — ensure the contract recognises this.
A Note on Defined vs Undefined Provisional Sums
Some contract forms distinguish between defined provisional sums — where the work is sufficiently described that the contractor has been able to price all associated preparatory and enabling work — and undefined provisional sums, where the work is so uncertain that even the associated work cannot be reliably priced. The distinction matters because it affects whether the contractor can claim additional associated costs when an undefined PS is instructed.
In Australian standard form contracts (AS4000, AS2124, ABIC), this distinction is explicitly built into the contract mechanism. If you are working under one of these forms, ensure you understand which type of PS each item has been classified as, as this directly affects your entitlements when the work is instructed.
Conclusion
Provisional sums and PC items are a normal and necessary feature of electrical contracts on complex projects — but they require careful management from tender through to final account. The estimator who states clear installation assumptions, monitors the contract mechanism for adjustments, and processes PS and PC changes through formal variation procedures will recover every dollar they are entitled to. The estimator who treats these items informally will consistently lose money on them — often without knowing exactly where it went.
Frequently Asked Questions
What is a provisional sum in an electrical contract?
A provisional sum (PS) is an allowance for work that is required but cannot be fully defined at tender. The PS amount is included in the contract sum. When the work is instructed, the actual cost replaces the PS amount through a formal variation — the difference between the PS and actual cost is adjusted up or down depending on what the work actually entails.
What is a prime cost item in electrical estimation?
A prime cost (PC) item is a nominated allowance for a specific supply item whose exact product has not yet been selected. The contractor prices installation around the PC amount; when the actual product is chosen, the PC amount is adjusted to the real supply cost. PC items are common for panelboards and switchboards where the specification is not finalised at tender.
Can I claim overhead and profit when a provisional sum is adjusted?
It depends on the contract. Many standard form contracts restrict PS adjustment to cost only, or cost plus a specified margin, which may be less than your standard variation rate. Check the contract mechanism explicitly before signing. If the contract does not allow overhead and profit on PS adjustments, negotiate this at tender — particularly if the PS amounts are significant relative to the total contract value.
What should I do if the PC amount is too low for the specified equipment?
Flag it in your tender submission. State that current OEM pricing for the described equipment exceeds the nominated PC amount and recommend the PC be revised before contract award. If the PC amount is not corrected and you install equipment that costs more than the PC, you are only entitled to the actual supply cost — but your installation pricing may not reflect the true scope if you priced against a smaller or simpler item than what is actually supplied.
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