AI for Electrical Estimating: Set Fitting Allowances and Provisional Sums

Put every item the customer will choose into a fitting allowance, a stated sum per item type, priced to supply the item, and settled against the real price once chosen. Put every part you cannot scope yet into a provisional sum, replaced by the actual cost. AI can draft the wording and the selection sheet, but you set the amounts.

The amounts have to come from your trade price list and your own labour rates. An assistant will happily write plausible-looking figures that match nothing you can buy, so every number in the worked example below is a round placeholder, there to show the arithmetic and nothing else.

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Four kinds of line on a domestic quote

Every line on a quote is one of four things, and the arguments start when two of them get blurred together. The test is a question you ask of each line. For the whole domestic quote around these lines, see the electrician quote template with scope and exclusions.

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In formal building contracts the names are tighter. A prime cost (PC) sum is an allowance for items from a supplier or subcontractor the client chooses, adjusted up or down to the actual cost. A provisional sum is an allowance for work not yet defined well enough to price, replaced by a valuation of what is actually done. The contractor's own handling and profit are treated separately. A domestic quote borrows both ideas, and the label matters less than three statements the customer can read: what the sum covers, what happens when the real cost differs, and who decides.

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A three-bedroom rewire quote, block by block

The worked example is the rewire of a three-bedroom semi-detached house, quoted in three blocks. Block A is the fixed price for everything specified: cabling, containment (trunking or conduit), the new consumer unit, standard white accessories, smoke and heat alarms, testing and certificate. Your cost book sets that figure, so none is invented here. Blocks B and C are the subject, and the right numbers for them are on your supplier's trade list and in your own day rate.

Block B holds the fitting allowances. Each is supply only, because the fitting labour is already in Block A.

Block C holds the provisional sums, each tied to a named unknown and a basis of charge.

After selections and first fix (cables and back boxes), the final account looks like this. The customer chose a $14 downlight, which is above the $10 allowance, so the order waited for a signature on the selection sheet.

The sum is +64 +15 -15 +16 -16 -80 -450 +60 = -406. The customer ends up with a credit of $406 because the supply move was never needed, and every allowance that went over was approved in writing before anything was ordered. Nobody was surprised by the final account, which is the real goal. Look at your own quotes and ask what share of the total sits in open-ended lines, and whether the customer would still call it a price.

Setting the amount: price the choice the customer will actually make

An allowance is a forecast of a purchase somebody else will make, so the forecast has to be honest. The method has five steps.

1. List every item the customer will choose, from the plans and the walk-round, with quantities. Quantity is what gets disputed later, so it goes on the quote. How electricians use AI to count fittings from drawings covers checking those counts.
2. Show the customer three price levels for each type from your trade list: standard, mid-range and premium. Ask which they lean towards.
3. Set the allowance at the level they lean towards. If they cannot say, use mid-range, not the cheapest.
4. Work the figure out from your list. In the example, a fire-rated downlight costs $8 on the trade list, a 25% handling charge adds $2, and the allowance is $10 each.
5. State the basis in one line: supply only, at the price the customer pays including your handling charge, fitting included in the fixed price, and whether any sales tax is included.

The temptation is to shave the allowance to win the job. If the customer ends up choosing a $14 downlight and your allowance was $6, then across 16 fittings that is a $128 gap, against $64 if you had allowed $10. The cheaper quote bought you an awkward conversation at second fix (accessories and fittings), when the customer has already moved the furniture back.

If your trade price list sits in a spreadsheet, you can load it into a ChatGPT or Claude project so the assistant totals the differences for you. Check three lines against the list by hand, because a misread column is the likeliest error.

Provisional sums: three bases of charge and when each fits

A provisional sum without a basis of charge is a guess the customer cannot check. Pick one of three bases for each sum and write it next to the figure. The same logic, applied to a different trade and a larger job, appears in the loft conversion quote template with stages and provisional sums.

Whichever basis you use, the order of events is the same. You find the unknown or receive the request, tell the customer in writing with the basis and a photo where there is something to see, wait for a yes (an emailed reply is enough for your records), then do the work. A provisional sum is neither a cap nor a promise. It is a starting figure that the actual cost replaces. If you want to promise not to exceed it without agreement, write that sentence into the clause. If you do not, say that the actual cost may be higher or lower.

Who chooses, and by when

Name the chooser on the schedule. Usually it is the customer. On a refurbishment it may be a designer or a builder, and then the schedule must also say who can sign off an overspend. Without that line, you can end up with a designer's choice and a customer who never agreed to pay for it.

The deadlines come from the work, not from convenience. The type of fitting decides back-box depth, ceiling cut-outs and cable positions, which is why "recessed or surface?" has to be settled before first fix. Models and finishes only matter at second fix, but lead times mean the order goes in well before. A schedule for a two-week rewire might read like this:

A selection sheet turns those deadlines into something a customer signs. If you want to see the same discipline applied to a whole house, the home builder selection sheet with allowances and deadlines is a useful neighbour.

Overspend and underspend: wording that settles it before it starts

Four rules settle nearly every argument. Nothing above its allowance is ordered without a signature. Underspend is credited and overspend is added, on the same basis, so the customer sees the same arithmetic both ways. The supplier invoice is shown on request. And a provisional sum is announced before work is charged against it, with the basis stated.

The weak version of all this is one sentence, and every electrician has seen it: "Allowances are estimates and subject to change." It tells the customer nothing about direction, size or who decides. Here is the version that does:

Fitting allowances. The price includes the allowances listed in Schedule 2.
Each allowance is a sum for supplying the item, at the price you pay us
including our handling charge. Fitting is included in the fixed price unless
Schedule 2 says otherwise. You choose each item by the date shown in Schedule
2. We will not order any item that costs more than its allowance without your
signature on the selection sheet. If an item costs less than its allowance,
the difference is taken off the final account. If it costs more, the
difference is added. We will show you the supplier's invoice on request. If
you have not chosen by the date shown, we will fit the standard item named in
Schedule 2.

Provisional sums. A provisional sum is our estimate for work we cannot define
until [named event]. We will tell you before doing any work charged against a
provisional sum and give you the basis of charge. We will invoice the actual
amount. If the work is not needed, the sum is taken off the final account.

This is illustrative wording, not legal advice. Rules for consumers usually expect prices and open-ended items to be clear and fair, so have your standard terms reviewed by a qualified adviser before you rely on them. Can AI write your electrician terms and conditions? explains what a legal review should cover. When an overspend becomes a real change to the job rather than a choice within the schedule, the right document is a variation, and electrical change orders written with AI covers it.

For items over the standard fitting time, add one more line to Schedule 2: "Feature fittings over 5 kg, or needing ceiling reinforcement, are fitted at our day rate." Otherwise the allowance covers the supply of a chandelier and your Block A labour quietly covers three hours of hanging it.

Where AI fits: clauses, gap checks, selection sheets and notices

Drafting the clauses from your own policy

Give the assistant your policy as bullet points and tell it not to add rules. This is the prompt I would start from:

Turn these points into two short clauses for a domestic electrical quote,
"Fitting allowances" and "Provisional sums". Plain English, short sentences,
no legal Latin. Use only my points. Do not add any rule I have not listed.
- Allowance = supply price of the item including our handling charge;
  fitting is in the fixed price.
- Customer chooses by the date in the schedule; if not, we fit the standard
  item named there.
- Nothing over its allowance is ordered without a signature on the selection
  sheet.
- Under: credit. Over: added. Supplier invoice shown on request.
- Provisional sum = our estimate for work we cannot define yet; we tell the
  customer before doing it and charge the actual cost on the stated basis;
  unused sums are deducted.

The assistant returns clean paragraphs, and then two sentences that were not in the points: "Any unused allowance will be retained as a handling fee" and "Allowances are final once the quote is signed". The first contradicts the credit rule. The second removes the customer's right to a reduction. Both go. This is the typical failure of a drafting assistant. It writes what quotes usually say, not what your policy says, so the check is a line-by-line comparison of the draft against your bullets.

Checking a draft quote for gaps

Strip out the customer's details and ask the assistant to read your draft the way an awkward customer would:

Here is a draft domestic rewire quote with customer details removed.
1. List every item type the customer is likely to choose that has no
   allowance.
2. List every unknown that could change the price that has no provisional
   sum or exclusion.
3. For each, say which line of the quote made you think so.
Do not suggest items outside the stated scope.

A typical answer (illustrative): extractor fans, because line 14 reads "bathroom fan, supply and fit" without a model; the doorbell and its transformer, line 22; dimmers, because line 9 says "dimmable". On unknowns, it flags loft access for new circuits (line 6 says "via loft" but says nothing about boarding) and the condition of existing cable behind fitted kitchen units (line 11). It also suggests a smart-home hub because the quote mentions a thermostat, which is outside your scope, so that one is dropped. For each real gap you decide between an allowance, a provisional sum and an exclusion line. The assistant finds the holes; it should not choose how to fill them.

Building the selection sheet

From the Block B table, the assistant produces the sheet the customer signs. Give it the deadlines from Schedule 2 and ask for blank columns for the choice. After the customer chooses, paste the prices back and it fills in the differences. A trimmed result:

Recompute the differences with a calculator before anything goes to the customer. Assistants get this arithmetic right most of the time, and the odd miss lands on you.

Writing the overspend notice

When a choice goes over its allowance, the customer needs a short message with a deadline. The assistant drafts it from three facts you supply: the item, the amount over, and the lead time. A version worth sending:

Hello [first name], the three pendants you have chosen come to $255 against the $240 allowance, so $15 more. If that is fine, please sign the selection sheet and we will order them today. They take [number] days to arrive, so we need your reply by [date] to keep second fix on schedule. Kind regards, [your name]

The first draft the assistant produced said "unfortunately" twice and apologised for the overspend, as though you had caused it. The customer chose; you are reporting. Cut the apology and leave the numbers.

Writing the notice when a provisional sum is triggered

The same pattern works when a provisional sum is used. Here the customer has asked for extra points in the kitchen, and the price list is in the project:

Draft a short email. The customer asked for extra points in the kitchen.
Facts: four double sockets at $100 each and one fused spur at $120, from
our price list; charged against the $600 provisional sum for extra points;
the cable must go in at first fix on [date]; we need a yes by [date].
No apology, no sales language.

Hello [first name], you have asked for four extra double sockets and one fused spur in the kitchen. At our price-list rates that is $520, charged against the $600 provisional sum for extra points, so the final account falls by $80 unless you add more. If you are happy, reply yes and we will do the work at first fix on [date]. We need your answer by [date] so the cables go in before the plaster. Kind regards, [your name]

The assistant's first draft said $500, because it priced the spur at the socket rate and multiplied five items by $100. The sum is 4 x $100 + $120 = $520. That is why the price list lives in the project and why every figure in a notice is rechecked by hand.

When the customer buys their own fittings

Customers often find a fitting they love online, and the allowance for that item stops being yours to manage. Before you agree, run six checks.

1. Does the item's protection rating suit the room and position? A bathroom or outdoor position needs more than a bedroom does, and the rating is on the box or the datasheet.
2. Does it work with the circuit and any dimmer? Check whether the lamps are dimmable and what driver type the fitting needs.
3. Is it complete: driver, fixings, instructions, any remote or control unit?
4. Will it be with you by the second-fix deadline? Late delivery is the customer's delay, so the schedule should say so.
5. What happens if it fails? You fit it once. Refitting or replacing is charged, and the guarantee on the product is between the customer and the seller.
6. Has the allowance for that item come off the quote?

The clause that covers all six fits in a paragraph:

Customer-supplied items. We will fit items you supply once we have checked
that they suit the circuit and the location. If an item is incomplete, faulty
or unsuitable and has to be refitted, the extra time is charged at our day
rate. We cannot guarantee the item itself. The allowance for any item you
supply is taken off the final account.

If you judge an item unsuitable, say so in writing, with the reason, rather than fitting something you are unhappy with. A short email with a photo of the box or datasheet is enough, and the assistant can draft it in a minute from the facts.

Mistakes that cost money, and how each one showed up

These are illustrations of the usual failures, not reports of particular jobs.

• The lump allowance. A line read "Lighting allowance: $600" with no quantity. The customer wanted 30 downlights and the electrician had allowed for 16. The argument was about a count, not a price. The fix: item type times quantity, on the quote.
• The cheapest-item allowance. Allowances were set at the cheapest fitting to keep the headline low. Customers chose mid-range items, and the final account was a surprise on a job that had gone well. See the $128 against $64 sum above.
• The contingency in disguise. A provisional sum of $1,000 "for unforeseen items" read as padding. A provisional sum needs a named unknown and a basis of charge, or it is a contingency under a different label.
• The heavy fitting. The allowance covered supply and the fixed price assumed ordinary fitting time. A large feature light took an afternoon with two people. The extra line in Schedule 2 fixes it.
• The customer's own fittings. A customer bought non-dimmable lamps for a dimmer circuit. The fix is a written check of compatibility before anything is installed, and a fitting charge that does not depend on whether the item works.
• No deadline. Second fix was booked, the pendants had not been chosen, and a day was lost. The fix is the deadline table, and the line that says what is fitted if nobody chooses.

Ten jobs of actuals: how to tell the allowances are right

After ten completed jobs, compare each allowance with the average of what customers actually chose. The gap is the average actual price minus the allowance, divided by the allowance. With the same placeholder prices:

My suggestion, not an industry rule: raise an allowance when the average actual runs more than 10% above it over ten jobs, and look at the reason before changing it. An allowance sitting well above the actual prices is harmless to the customer but makes your headline figure higher than it needs to be, so trim it if the gap persists. If overspend is concentrated in one fitting type, the customers may be choosing something your standard schedule never offered. Count your disputes too, and the time spent writing variation emails. The aim is fewer of both. The assistant can do the sums if you give it the figures. The decision to move an allowance stays with you.

Questions electricians ask about allowances and provisional sums

Should allowances include sales tax?

Say which. State on the quote whether every figure includes any sales tax or similar charge, and use the same basis for the allowance and for the price of the chosen item. If the allowance is tax-inclusive and the supplier price you compare it with is not, you will create a difference that does not exist.

Is a contingency percentage better than provisional sums?

They do different jobs. A contingency is a percentage held against unknowns you have not named, and customers often read it as padding. A provisional sum names the unknown, shows a figure, and is replaced by the actual cost. If you use a contingency, label it, say what it covers and say whether any unused part is credited.

What if the customer wants to supply their own fittings?

Agree it in writing before the quote is accepted. Check that each item suits the circuit, the room and any dimmer you are installing, charge fitting time at your rate, and state that you do not stand behind the product itself. Deduct the allowance for that item, because you are no longer supplying it.

Do the same terms apply to commercial work?

Not necessarily. In commercial contracts the terms prime cost sum and provisional sum are usually defined by the contract itself, and the valuation rules sit there. Domestic quotes rely on your own wording, so it needs to be plain and complete. Read any commercial contract's definitions rather than assuming they match your domestic terms.

Further reads

• AI Electrical Quoting Software: Build Three-Option Upgrade Packages — Offer standard, better and best packages instead of open allowances.
• 10 ChatGPT Prompts for Electricians: Quotes, Emails and T&Cs — More prompts for quotes, emails and terms.
• Simpro Electrical Reviews: Is It Worth It for a Small Firm? — A crew-size rule for Simpro, how to read its reviews as a small electrical firm, and a demo script for job costing, quoting and compliance paperwork.
• Bill of Quantities Template: A Worked Example Checked With AI — A worked bill of quantities with Excel check formulas and AI prompts for codes, descriptions, units and totals, with measurement left to the QS.
• AI Tools and AI Development: The Complete 2026 Guide — the AI hub, including every tutorial in the AI-for-business series.

Sources: Designing Buildings wiki entries on provisional sums and prime cost sums (definitions and adjustment); the author's own quote-structure method. All dollar figures are round placeholders, not market prices.