Calibration and MID: calibrated current transformers and MID meters for billing
Anyone billing electrical energy to third parties – tenants, sub-tenants, charging points or other companies – needs approved measuring instruments. In CT-operated metering these are two parts: the energy meter and the current transformers in front of it. Different rules apply to each.
The meter falls under the European Measuring Instruments Directive MID (2014/32/EU, annex MI-003 for active energy meters). Current transformers are not covered by the MID; in Germany the Measurement and Calibration Act (MessEG) and Ordinance (MessEV) apply to them. Billing therefore requires an MID meter and calibrated, i.e. conformity-assessed, current transformers.
CELSA’s calibrated ALO-E plug-on current transformers are suitable for billing; their type is approved by the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig. They are available for 50 A to 5000 A, 1 A or 5 A secondary, in classes 0.2S, 0.2, 0.5S and 0.5 – with a rotatable, sealable secondary terminal cover.
What applies to meters and transformers (Germany)
| Energy meter | Current transformer for billing | Current transformer without calibration | |
|---|---|---|---|
| Rules | MID 2014/32/EU, annex MI-003; EN 50470-3 | MessEG/MessEV; IEC 61869-2 | IEC 61869-2 |
| Evidence | EU conformity assessment, e.g. modules B+D | Conformity assessment, PTB type approval | Manufacturer data |
| Accuracy | Class A, B or C | 0.2S, 0.2, 0.5S, 0.5 | 0.5, 1, 3 |
| Verification period (MessEV) | 8 years (electronic meters) | unlimited | – |
| Billing third parties | yes (with calibrated CTs) | yes | no |
| CELSA examples | DMC6 MID, ECM6 MID (CT-operated); DMC100 MID, ECM80 MID (direct) | ALO-E, WALO-E | ALO, KALO, TQ, IAP |
Which class and which meter version a metering point requires is set by the grid or metering point operator in their technical connection conditions.
Calculators and related pages
Typical Applications
- Re-billing to tenants and sub-tenants
- Billing of charging points and site networks
- CT-operated sub-meters in commerce and industry
Recommended Products
FAQ
Does a current transformer need MID approval?
No. The MID covers energy meters; current transformers are not included. For billing, current transformers must be calibrated or conformity-assessed under national legal metrology – in Germany under MessEG and MessEV.
When does a current transformer have to be calibrated?
When the readings are used to bill energy to third parties, for example tenants, sub-tenants or other companies. For internal evaluation, energy monitoring or cost centres within your own company, legal metrology does not require calibrated transformers.
What does MID B+D mean for an energy meter?
B and D are modules of the EU conformity assessment: module B is the EU type examination by a notified body, module D the quality assurance of production. A meter assessed this way carries the CE and metrology marking and may be used for billing from the factory.
How long is the calibration valid?
Under annex 7 of the German MessEV the verification period for electronic electricity meters is 8 years; after that the meter must be re-verified or replaced. For instrument transformers the period is unlimited.
Can I have a standard current transformer calibrated afterwards?
Only a transformer whose type is approved for it can be calibrated. That is why there are dedicated calibrated series – at CELSA the ALO-E plug-on and WALO-E wound current transformers. Cable and busbar split-core transformers in the CELSA range are not calibrated.
Which accuracy class do calibrated transformers need?
This is set by the grid or metering point operator; 0.5, 0.5S, 0.2 or 0.2S are common. The S classes are specified down to 1 % of rated current and suit metering points with a lot of partial load.
Which meter goes with a calibrated current transformer?
An MID CT-operated meter for 1 A or 5 A secondary, for example DMC6 MID or ECM6 MID. The transformer ratio is set on the meter so that it displays the primary energy.