The 100 kW rule: when a half-hourly meter becomes mandatory

Ask around and you will hear that a business needs a half-hourly meter once it uses 100,000 kWh a year. That is a myth. The rule is about peak power demand in kilowatts, not annual consumption in kilowatt-hours, and the difference matters when you plan new equipment, review your metering or check a bill.

Key points

• Sites with maximum demand over 100 kW in any half-hour must be half-hourly metered and settled under the Balancing and Settlement Code.
• It is a kW demand threshold, not a 100,000 kWh a year rule.
• Half-hourly sites are profile class 00. Classes 01 to 08 were used for non-half-hourly meters.
• P272 moved profile classes 05 to 08 to half-hourly settlement from April 2017, and MHHS is now moving every meter.

What the 100 kW rule says

The Balancing and Settlement Code (BSC) is the set of rules that governs how electricity is bought, sold and settled in Great Britain. Under it, a site whose maximum demand is over 100 kW in any half-hour must have a half-hourly meter and be settled half-hourly. These sites are recorded as profile class 00. If you are new to the subject, start with our guide to what half-hourly metering is.

Maximum demand means the highest rate at which the site draws power, averaged over a half-hour. It is not how much electricity you use over a month or a year. A site can use a modest amount of energy overall and still cross the threshold if heavy equipment runs at the same time.

If your demand sits close to 100 kW, ask your supplier how your site is classified, as they apply the detailed definitions in the code.

Why "100,000 kWh a year" is wrong

The confusion is understandable. Both figures contain "100" and both sound like large-site thresholds. But kW and kWh measure different things:

• kW (kilowatts) is power: how hard the site is drawing at a moment in time.
• kWh (kilowatt-hours) is energy: power multiplied by time. A 10 kW load running for 10 hours uses 100 kWh.

A simple calculation shows how far apart the two ideas are. A site using 100,000 kWh evenly across the 8,760 hours in a year would draw an average of around 11.4 kW, nowhere near 100 kW. On the other hand, a workshop that runs several large machines together for a few hours a day can go over 100 kW while its annual consumption looks small.

How to work out your maximum demand

If you already have half-hourly data, finding your maximum demand is straightforward. Each reading is the kWh used in 30 minutes, so doubling it gives the average kW over that period. A half-hour reading of 55 kWh means the site averaged 110 kW. Use this checklist:

• Get at least 12 months of data so seasonal peaks are included.
• Find the highest half-hour readings and double them to convert to kW.
• Look at when the peaks happen: start-up, shift changes, cold mornings.
• Check whether your bill shows a maximum demand figure, and whether it is in kW or kVA.
• Compare your peak with your Agreed Supply Capacity, which is set in kVA.

The difference between kW and kVA matters for capacity charges. Our guide to agreed supply capacity explains how power factor links the two.

Profile classes in plain English

Profile classes were how the settlement system estimated when non-half-hourly customers used their electricity. Each class had a standard shape. The class is shown in the first two digits of the top line of your MPAN.

• 00: half-hourly metered and settled.
• 01: domestic unrestricted.
• 02: domestic Economy 7 (two rate).
• 03: non-domestic unrestricted.
• 04: non-domestic Economy 7 (two rate).
• 05 to 08: non-domestic maximum demand meters, grouped by load factor, which is how evenly the site uses power compared with its peak. Class 05 covers the lowest load factors (under 20%) and class 08 the highest (over 40%).

As MHHS moves every meter to half-hourly settlement, these estimated profiles are being phased out, but you will still see profile classes on bills and contracts.

P272: the move for maximum demand sites

Before 2017, many medium-sized businesses sat in profile classes 05 to 08. They had maximum demand meters, but they were still settled using estimated profiles. BSC modification P272, fully in force from April 2017, moved these sites to half-hourly settlement.

For the businesses affected, that meant half-hourly data collection, metering and data service contracts, and network charges split into time bands. They are now in a similar position to sites over 100 kW: their contract prices and bills reflect when they actually use power.

MHHS: where the rule fits now

Market-wide Half-Hourly Settlement extends half-hourly settlement to every meter in Great Britain, around 33 million of them. Suppliers began migrating meters on 22 October 2025, and the full migration deadline is May 2027. Our MHHS guide covers the timeline and what to check, and Elexon keeps its MHHS programme pages up to date.

Size still matters after MHHS. Larger sites continue to use advanced metering, which is managed by a Metering Service Advanced (MSA) and an Advanced Data Service (ADS). Sites with smart meters are settled half-hourly through the Smart Data Service instead.

Approaching 100 kW? What to check

• Check the profile class on your MPAN and confirm it with your supplier.
• Review a year of demand data, not a single bill.
• If you plan to add EV chargers, heat pumps, ovens, compressors or a new production line, estimate the extra kW and when it will run.
• Check that your Agreed Supply Capacity has room for the change.
• If a meter change is needed, plan it well ahead of the work.
• Make sure your next contract is priced on your new profile, not your old one.

We can arrange half-hourly meter upgrades and make sure the metering and data contracts that go with them are in place before the new load arrives.

Get help with the 100 kW rule and your metering

If you are unsure whether your site should be half-hourly, or you want to know how a change in demand will affect your metering and costs, we can review your data and bills. We'll show you whether you can pay less, and if we can't find a better option, we'll tell you.

Ask for a free quote and bill check or call 07565 147 170.

Frequently asked questions

Do I need a half-hourly meter if I use more than 100,000 kWh a year?

Not because of that figure alone. The mandatory threshold is a maximum demand over 100 kW in any half-hour, which is a measure of power, not annual energy. A site using 100,000 kWh evenly through the year averages only around 11.4 kW. Check your peak demand in kW instead.

What is profile class 00?

Profile class 00 means a site is half-hourly metered and settled, using its actual consumption in every 30-minute period rather than an estimated profile. You can find the profile class in the first two digits of the top line of the MPAN printed on your electricity bill.

What was P272?

P272 was a modification to the Balancing and Settlement Code, fully in force from April 2017. It moved non-domestic sites in profile classes 05 to 08, which have maximum demand meters, onto half-hourly settlement. Those sites now have half-hourly data services and time-banded network charges.