Balancing Mechanism Units

What is a BM Unit?

Balancing Mechanism (BM) Units are used as units of trade within the Balancing Mechanism. Each BM Unit accounts for a collection of plant and/or apparatus, and is considered the smallest grouping that can be independently controlled. As a result, most BM Units contain either a generating unit or a collection of consumption meters. Any energy produced or consumed by the contents of a BM Unit is accredited to that BM Unit.

How are BM Units categorised?

There are several types of BM Unit, each covering different aspects of the system. Each is marked with a particular prefix to its ID, as shown below:

BM Unit Prefix Description
Directly Connected T_ These BM Units are directly connected to the Transmission System.
Embedded E_ These BM Units are embedded into a Distribution System.
Interconnector I_ These BM Units are related to an Interconnector.
Supplier 2_C_ These BM Units cover Supply, and contain all of a particular Supplier’s MPANs in either a Base or Additional Supplier BM Unit for a given Grid Supply Point (GSP) Group.These Additional Supplier BM Units are registered solely for the purpose of allocating CFD Assets to them.
Miscellaneous M_ Other types of BM Units that don’t fit the above categories. This prefix does not apply to newly registered BM Units.

A complete list of all active BM Units can be found on the ELEXON Portal.

How do I register BM Units?

The BM Unit Registration process is described in BSCP15 ‘BM Unit Registration‘, which covers the procedures and timescales for registering BM Units. Registering a BM Unit requires a lead time of 30 Working Days, and you will normally need to speak to National Grid before this process begins, so you should leave plenty of time to complete the whole process. You can register BM Units using form BSCP15/4.1, which must be sent to the Central Registration Agent (CRA). Guidance on the BM Unit registration process, including filling in BSCP15/4.1, along with further information about BM Units, can be found in our BM Unit Guidance.

If you are a new Supplier joining the market, you need to set up 14 Supplier BM Units (your Base BM Units, one for each GSP Group) as part of your registration. You can register all other BM Units on an ad-hoc basis as and when they are required.

If you looking to register BM Units for Electricity Market Reform (EMR) purposes please see the Registration of BM Units for EMR guidance document . There are no material changes to the registration of BM Units for CFD Assets registered for CMRS. However, there are new registration processes for BM Units registered for CFD Assets registered in SMRS.  For naming convention for Additional BM Units registered for CFD Assets please click here.

What are the timescales for registering BM Units?

Registering a T_, E_ or I_ BM Unit requires a lead time of 30 Working Days and 60 Working Days for a non-standard BM Unit,  you will normally need to speak to National Grid before this process begins, so you should leave plenty of time to complete the whole process. Additionally if a Metering Dispensation needs to be sought for the site, refer to the Metering Dispensations page for the timescales associated with this. A standard BM Unit includes the following:

• The Export of a Generating Unit, CCGT Module or Power Park Module registered in CMRS
• A Combined Offshore BM Unit
• The Imports though the station transformers of a generating plant registered in CMRS
• Premises (or a customer supplied by a Party) directly connected to the Transmission System at one Boundary Point
• An Interconnector BM Unit

Other BM Units may be non-standard and their configuration needs to be agreed by the ISG.  Please contact for advice on whether a BM Unit is standard or a non-standard configuration.