Most large services are not metered directly. The current is far too high to run through a meter, so instrument transformers step it down: current transformers reduce the current to a manageable secondary value, and where the service is at primary voltage, potential transformers do the same for voltage.
The meter therefore measures a scaled-down replica of what the site actually draws. A constant — the meter multiplier — converts the register reading back to real units before it reaches the bill.
That multiplier is a number in a database. And a number in a database can be wrong.
Why it is worth checking
A wrong multiplier is the most consequential error that can appear on an industrial account, for a reason that has nothing to do with its size and everything to do with its invisibility.
It scales every determinant by the same factor. Energy, demand, power factor adjustment, every demand-based rider, the taxes on top. The bill remains perfectly self-consistent: the numbers add up, the demand looks plausible for the energy, the load factor is unremarkable. Nothing signals an error. The site simply appears to be a larger consumer than it is, or a smaller one, and every subsequent decision — the budget, the efficiency business case, the tariff selection — inherits the distortion.
An error in a demand rate would be spotted in a month. An error in the multiplier can persist for years.
How the arithmetic works
The multiplier is the product of the transformer ratios and any internal meter constant:
Multiplier = CT ratio × PT ratio × register constant
A current transformer marked 800:5 has a ratio of 160. A potential transformer marked 7200:120 has a ratio of 60. Metered at primary voltage with both in circuit, the multiplier before any register constant is 160 × 60 = 9,600.
Checking a bill against the meter register
Take one billing period and reconcile it end to end.
- CT ratio (800 : 5)160
- PT ratio (7200 : 120)60
- (Multiplier: 160 × 60)9,600
- Register reading, start of period41.882
- Register reading, end of period85.632
- (Register difference)43.750
Billed energy: 43.750 × 9,600420,000 kWh
If the figure on the bill is not this figure, the discrepancy is in the multiplier, in the read, or in the transcription of one of them. Values here are illustrative; use your own register readings.
The same multiplier applies to the demand register. If energy reconciles and demand does not, the problem is not the multiplier — look at the demand interval definition and at any ratchet instead.
When multipliers go wrong
The pattern is nearly always the same: something in the physical installation changed and the billing record did not follow.
- A service was upgraded and the current transformers were replaced with a higher-ratio set. The meter was reprogrammed; the billing constant was not updated.
- A meter was replaced with a different model carrying a different internal register constant.
- The account was set up from a work order that transposed two digits.
- A second service point was added and the multiplier from the first was copied across.
The common thread is that none of these is a metering fault. The meter is measuring correctly. The number that converts its output into billable units is the thing that is wrong, which is why calibration tests come back clean and why asking for the meter to be tested is the wrong first request.
It also explains the timing pattern. Multiplier errors tend to originate at a specific, datable event rather than drifting into existence, so they show up as a step in the twelve-month trend rather than as a gradual change. A demand and energy series that jumps by the same proportion in the same month, with no operational explanation, is the signature. If the step coincides with a known service change, that is close to conclusive and it tells you exactly which date the correction should run from.
Checking yours
- Find the multiplier printed on the bill, usually near the meter number.
- Find the CT and PT ratios on the instrument transformer nameplates, or in the utility's meter record for the service point. You are entitled to ask for that record.
- Multiply them out and confirm the product matches the multiplier being billed.
- Take two consecutive bills, difference the register readings, multiply by the multiplier, and confirm the result equals the billed kilowatt-hours.
- Sanity-check the result against connected load: a site whose total connected capacity is 900 kW cannot legitimately be billed a 4,000 kW demand.
- If anything fails to reconcile, write to the utility citing the specific readings and ratios rather than the conclusion. A letter enclosing arithmetic gets a different response from one enclosing a complaint.
That fifth step catches most real cases on its own. A demand determinant that exceeds what the site could physically draw is arithmetically impossible, and it is the one check that requires no documents at all.
If it is wrong
Billing adjustments — how far back a utility may rebill, how far back it must refund, and on what basis — are governed by the state commission's rules, not by negotiation. Those rules are public. Read the ones for your jurisdiction before deciding what to ask for, because the answer to "how many years" is written down and it varies.
Then check whether anything downstream inherited the error. A tariff selection made on inflated demand figures may have been the wrong choice, and switching rate schedules has its own notice periods and minimum stay rules that a correction does not automatically reset.
Where this fits
Verifying the multiplier belongs at the top of any bill review, because it is the assumption every other check rests on. It appears as step one in the 12-point audit for any commercial electricity bill, and it is the reason the section on reconciling a statement in how to read an industrial electricity bill says to check the multiplier before assuming the utility has made a mistake elsewhere.
