CT metering and the multiplying factor
Short answer. On larger connections, current transformers scale the current down before it reaches the meter, so the register accumulates a proportionally smaller number and a multiplying factor restores the true figure. Verify the factor against the CT nameplate and the meter change certificate — a wrong factor multiplies the bill with nothing else on the page looking unusual.
Who this is for: Commercial and industrial consumers on CT-metered connections, and anyone whose bill shows a multiplying factor other than 1.
Why the meter does not see the whole current
A meter cannot carry hundreds of amperes through its internals. Current transformers reduce the current by a fixed ratio — 100/5, 200/5, 400/5 — and the meter measures the reduced version.
A 100/5 CT gives a ratio of twenty, so the register advances one unit for every twenty consumed. The multiplying factor of 20 restores the true energy.
Verifying your own factor
Three sources should agree: the CT nameplate at the metering panel, the meter change certificate in your file, and the MF printed on your bill.
Where they disagree, the bill is the one that is wrong, and the other two are your evidence. This is a straightforward correction once demonstrated, and it can be applied retrospectively.
Where it goes wrong
Almost always at a meter or CT change, when a replacement with a different ratio is installed and the billing record is not updated to match.
It is also the reason CT-metered consumers cannot check their bill by reading the meter alone — the displayed register will never equal the billed units, and expecting it to is the usual source of confusion.
A domestic bill should show MF of 1
An ordinary single-phase domestic meter is directly connected and has no current transformers. If a domestic bill shows any other multiplying factor, query it immediately.
It is rare, and it is catastrophic when it happens — a factor of 10 applied in error means paying ten times for every unit.
Frequently asked questions
Can a wrong multiplying factor be corrected for past bills?
Yes. Once the correct factor is established from the CT nameplate and the meter records, the affected cycles are recomputed and the difference appears as an adjustment — a credit where you were overbilled.
How do I read my consumption on a CT-metered connection?
Take the register difference and multiply by the factor. The meter's own display will never show the billed figure, and that is by design rather than a fault.
Related meter guides
Go further
All 10 guides are listed in the meter guides index. To check the reading against your actual bill, open the official duplicate.