Guidance
Balancing Mechanism Units (BM Units)
This guidance note describes BM Units, how they are used in the BSC, and how to register them.
What is a BM Unit?
BM Units are units of trade in the Balancing Mechanism. They are used in the BSC to account for all
energy that flows on or off the Total System, which is the Transmission System and the Distribution
System combined. A BM Unit is the smallest grouping of equipment that can be independently
metered for Settlement. Most BM Units consist of a generating unit or a collection of consumption
meters, and the energy produced or consumed by the contents of a BM Unit is accredited to that Unit.
BSCP15: BM Unit Registration tells you how to register BM Units.
Types of BM Units
There are several types of BM Unit, each representing different aspects of the system. Each type is
marked with prefixes in their IDs, as given below. Each type is described separately in the following
sections, along with an overview of the registration process and what you need to do.
If you are only interested in a particular type of BM Unit, refer to the relevant section. The list below
describes each type:
BM Unit Type
Prefix
Overview
Directly Connected
T_
BM Units directly connected to the Transmission
System. These are typically Generation Units.
Embedded
E_
BM Units embedded into a Distribution System.
Interconnector
I_
BM Units related to an Interconnector.
Supplier
2_
BM Units covering Supply. These contain all of a
particular Supplier’s meters for a given GSP Group.
C_
These Additional Supplier BM Units are registered
solely for the purpose of allocating CfD Assets to
them.
M_
Other types of BM Units that don’t fit the above
categories. This prefix does not apply to newly
registered BM Units.
Miscellaneous
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Non-Standard BM Units
The BSC requires that a BM Unit must satisfy the following conditions;
a)
only one Party is responsible for the Exports and/or Imports from the prospective BM
Unit;
b)
the Exports and/or Imports of electricity from and to the BM Unit are capable of being
controlled (and metered) independently of the Exports or Imports of electricity from or to
any Plant or Apparatus which is not comprised in the BM Unit;
c)
the BM Unit does not comprise Plant and Apparatus whose Imports and Exports are
measured by both CVA Metering System(s) and SVA Metering System(s); and
d)
there are no smaller aggregations of the Plant and Apparatus comprised in the BM Unit,
for each of which the above conditions would be satisfied.
The BSC states that the following shall be a single BM Unit;

A single Generating Unit

A CCGT (Combined Cycle Gas Turbine) Module

A Power Park Module (PPM)

A Combined Offshore BM Unit

Power Station Transformers (Station Transformers)

Directly Connected Demand
Any configuration not in line with the above would be a non-standard BM Unit. Non-standard BM
Units need to be approved by the Panel and so a 60 Working Day lead time is required for the
registration of non-standard BM Units.
In addition, the following are also covered in this Guidance Note:
Area
Overview
Exempt Export BM Units
Some Generating BM Units can also apply to be Exemptable and
gain Exempt Export status from DECC.
Changing BM Unit Ownership
Sometimes the ownership of a BM Units needs to change from one
Party to another.
Offshore BM Units
Additional information about offshore BM Units.
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Directly Connected BM Units
What is a Directly
Connected BM Unit?
Directly Connected BM Units are metered equipment directly connected to
the Transmission Network. They are usually Generation Units, relating to
Power Plants or other Generating sites but can also be a large demand site.
The equipment within each BM Unit is independent of other Units, and is
metered separately.
Do I need to do
anything before
registering one?
You need to Qualify as a Generator to register Directly Connected BM Units.
Visit the Market Entry page or BSCP65: Registration of Parties and Exit
Procedures for more details.
Before you submit the BM Unit registration form, you must contact National
Grid, to discuss any obligations and sign the necessary contractual
agreements. National Grid will give you National Grid BMU names.
What forms do I need
to fill in?
BSCP15/4.1 gives general details of the BM Unit(s) you’re registering and
must be sent to the Central Registration Agent (CRA) 30 Working Days
(standard BM Unit) or 60 Working Days (non-standard BM Unit) before the
Effective From Date (EFD).
BSCP20/4.1 registers the Metering Systems related to your BM Unit(s).
BSCP20/4.3 registers the Meter Technical Details (MTDs) related to your BM
Unit(s), and is submitted by the Meter Operator Agent (MOA).
BSCP75/4.2 details the Aggregation Rules for the BM Unit(s).
BSCP02 details the Proving Test that your MOA must carry out on the
Metering Equipment
You must also provide a single electrical line diagram of the site showing the
metering points and commercial interface.
What information do I
provide on the
BSCP15/4.1 form?
The NG BM Unit ID is the ID provided by National Grid.
The BM Unit ID has a prefix of ‘T_’ followed by the NG BM Unit ID.
The BM Unit Type is ‘T’ for Directly Connected and the BM Unit Configuration
depends on what type of Unit it is – please check the list at the bottom of
the form.
You need to enter the Generation Capacity (GC) and Demand Capacity (DC)
of each BM Unit, as well as the Final Physical Notification (FPN) Flag.
If the BM Unit will be Exempt Export (see below for more details), you must
put ‘Y’ in the relevant column, and enter a P/C Flag.
Finally, you need to state the date on which the BM Unit will become
effective.
What other information If you register the BM Unit(s) as Exempt Export, refer to the Exempt Export
is needed?
section which covers additional processes that you need to follow.
When do I need to
You must submit your forms and the relevant information within the allotted
submit these forms by? timescales in the BSCP.
The lead time of 30 Working Days is a condition of the process.
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Generating Units connected to a 275kV busbar or higher in England and Wales are
Transmission Connected sites.
In Scotland, connections to a 132kV busbar or higher are Transmission Connected.
A Boundary Point is the point where Plant and Apparatus forming BM Units join the Total
System.
BM Units submit Physical Notifications (PNs) to National Grid if their Generation or Demand
Capacity is at or above 50MW in England and Wales, 30MW in South Scotland or 10MW in
North Scotland.
It is optional below these limits.
Interconnector BM Units always submit PNs.
A Metering System ID (MSID) can be reserved by contacting the CRA.
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Embedded BM Units
What is an Embedded
BM Unit?
Embedded BM Units represent metered equipment that is connected to a
Distribution System. They are Generation Units relating to Power Plants or
other generating sites. They can include the imports relating to these sites,
but large embedded demand sites without any generation cannot be
registered as a BM Unit. The equipment within each BM Unit is independent
of other Units, and is metered separately.
Do I need to do
anything before
registering one?
You need to Qualify as a Generator to register Embedded BM Units. Visit the
Market Entry page or BSCP65: Registration of Parties and Exit Procedures for
more details.
Before you submit the BM Unit registration form, you must contact National
Grid, to discuss any obligations and sign the necessary contractual
agreements. National Grid will give you National Grid BMU Names.
What forms do I need
to fill in?
BSCP15/4.1 gives general details of the BM Unit(s) you’re registering. This
must be sent to the Central Registration Agent (CRA) 30 Working Days
(standard BM Unit) or 60 Working Days (non-standard BM Unit) before the
Effective From Date.
BSCP20/4.1 registers the Metering Systems related to your BM Unit(s).
BSCP20/4.3 registers the Meter Technical Details (MTDs) related to your BM
Unit(s), and is submitted by the Meter Operator Agent (MOA).
BSCP75/4.2 details the Aggregation Rules for the BM Unit(s) which must
include Line Loss Factors.
BSCP02 details the Proving Test that your MOA must carry out on the
Metering Equipment
You must also provide a single electrical line diagram of the site showing the
metering points and commercial interface.
What information do I
provide on the
BSCP15/4.1 form?
The NG BM Unit ID is provided by National Grid.
The BM Unit ID has a prefix of ‘E_’ followed by the NG BM Unit ID.
The BM Unit Type is ‘E’ for Embedded. The BM Unit Configuration depends
on what type of Unit it is - please check the list at the bottom of the form.
You need to enter the Generation Capacity (GC) and Demand Capacity (DC)
of each BM Unit, as well as the Final Physical Notification (FPN) Flag.
If the BM Unit will be Exempt Export (see below for more details), you must
put ‘Y’ in the relevant column, and enter a P/C Flag.
Finally, you need to state the date on which the BM Unit will become
effective.
What other information Embedded BM Units need Line Loss Factors (LLFs) for use in their
is needed?
Aggregation Rules. The relevant Licensed Distribution System Operator
(LDSO) is responsible for submitting them within the LLF timescales in
BSCP128: Production, Submission, Audit and Approval of Line Loss Factors.
If you register the BM Unit(s) as Exempt Export, refer to the Exempt Export
section, which covers additional processes that you need to follow.
When do I need to
You must submit your forms and the relevant information within the allotted
submit these forms by? timescales in the BSCP.
The lead time of 30 Working Days is a condition of the process.
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Interconnector BM Units
What is an
Interconnector BM
Unit?
Interconnector BM Units allow Parties to trade over a particular
Interconnector, and always come in pairs. One of the Units is for electricity
entering the System over the Interconnector (Production), and the other is for
electricity being taken off the System (Consumption). Each Interconnector has
many pairs of these Units, one for each Party who has registered to use it.
Interconnector BM Units work differently to other BM Units because the
electricity is not metered for each Party’s BM Units. The Interconnector BM
Unit Metered Volume is assigned by the Interconnector Error Administrator.
Do I need to do
anything before
registering one?
You need to Qualify as an Interconnector User to register Interconnector BM
Units. Visit the Market Entry page or BSCP65: Registration of Parties and Exit
Procedures for more details.
Before submitting the BM Unit registration form, you must contact National
Grid, to discuss any obligations and sign the necessary contractual
agreements. National Grid will give you National Grid BMU names.
What forms do I need
to fill in?
BSCP15/4.1 gives general details of the BM Unit(s) you’re registering. This
What information do I
provide on the
BSCP15/4.1 form?
The NG BM Unit ID is the ID provided by National Grid.
must be sent to the Central Registration Agent (CRA) 30 Working Days before
the Effective From Date.
The BM Unit ID has a prefix of ‘I_’ followed by the NG BM Unit ID.
The BM Unit Type is ‘I’ for Interconnector, and the BM Unit Configuration will
be ‘IC’ for Interconnector Unit.
For the importing BM Unit, enter a positive GC, a zero DC and a ‘P’ for P/C
Flag. For the exporting BM Unit, enter a zero GC, a negative DC and a ‘C’ for
the Flag. In both cases, the FPN Flag is ‘Y’.
Finally, enter the Interconnector ID for the Interconnector these Units are for
(i.e. FRANCE, MOYLE, BRITNED, EWIC), and the date that the BM Units will be
effective from.
What other information We don’t need any other information for Interconnector BM Units.
is needed?
When do I need to
You must submit your forms and the relevant information within the allotted
submit these forms by? timescales in the BSCP.
The lead time of 30 Working Days is a condition of the process.
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Supplier BM Units
What is a Supplier BM
Unit?
Supplier BM Units measure the amount of electricity supplied by Suppliers.
Due to the high number of Supplier meters that exist, individually identifying
them all is unfeasible. Instead, all the meters for a particular Supplier ID in a
specific Grid Supply Point (GSP) Group are grouped into one Supplier BM Unit.
When a Party signs up as a Supplier, they must register 14 ‘Base’ Supply BM
Units, one for each GSP Group. All their supply and SVA registered embedded
generation in a particular GSP Group will be allocated to the relevant BM Unit.
A Party can register ‘Additional’ BM Units for particular sites within a GSP
Group.
Do I need to do anything
before registering one?
You need to Qualify as a Supplier to register Supplier BM Units. Visit the
Market Entry page or BSCP65: Registration of Parties and Exit Procedures for
more details.
You register Base BM Units automatically when you become a Supplier.
Additional Units can be registered at any time after that. In either case, the
Effective Dates must be on or after the next eligible Market Domain Data
(MDD) Go-Live Date. MDD Go-Live dates are published on the MDD Release
Schedule. If you register Supplier BM Units, you need to complete the MDD
process at the same time.
What forms do I need to fill BSCP15/4.1 gives general details of the BM Unit(s) you’re registering. This
in?
must be sent to the Central Registration Agent (CRA) 30 Working Days before
the Effective From Date.
What information do I
provide on the BSCP15/4.1
form?
The Base BM Unit ID is 2__XPPPP000, where X is the relevant GSP Group
letter and PPPP is your four-letter Supplier Market Participant Identifier
(MPID). Additional BM Units are numbered sequentially, i.e. 001, 002 etc,
within each GSP Group.
If you are submitting FPNs, National Grid will provide you with the NG BM
Unit ID.
The BM Unit Type is ‘G’ if these are your Base BM Units, and ‘S’ if you are
registering Additional BM Units. The BM Unit Configuration is either ‘BB’ for a
Base Unit or ‘AB’ for an Additional Unit.
You need to enter the Generation and Demand Capacities (GC and DC) of
each BM Unit as well as the FPN Flag.
Finally, you need to state the date on which the BM Unit will be effective from
(this must be on or after the next eligible MDD Go-Live Date).
What other information is
needed?
As part of the Supplier Registration process, you need to submit BSCP15/4.1
form when setting up Base BM Units. The Effective From Date must match
the date from when you become a Supplier, which is determined by which
version of MDD you are included in.
For an Additional BM Unit, submit the BSCP15/4.1 form at least 30 Working
Days before the Effective From Date, which should be on or after the next
eligible MDD Go-Live Date.
In either case, you must also complete the MDD process at the same time, as
Supplier BM Units must also be registered in MDD. Visit the MDD page or
BSCP509: Changes to Market Domain Data for more details.
When do I need to submit
these forms by?
You must submit your forms and the relevant information within the allotted
timescales in the BSCP.
The lead time of 30 Working Days is a condition of the process.
You must register all 14 Base BM Units, one for each GSP Group, even if you do not plan to use
them all.
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Exempt Export BM Units
What is an Exempt
Export BM Unit?
Some Generating Plants are ‘Exemptable’, which means that the Lead Party
doesn’t need a Generation Licence. This benefits the responsible Party which
is why we ensure that the Plant qualifies as Exemptable.
What is the benefit of
being Exempt Export?
Depending on the size of the Plant, the benefits of being Exemptable apply
to some or all of:
 Transmission Network Use of System (TNUoS) Charges;
 Balancing Services Use of System (BSUoS) Charges; and
 Transmission Losses.
For Exempt Export BM Units, you declare your own P/C Flag.
How can I nominate a
BM Unit as
Exemptable?
BM Units are classed as Exempt under the Electricity Act, where small and
medium generators do not require a generation licence. A BM Unit eligible
to be Exemptable must apply for this status. You can do this with the initial
BM Unit Registration, or separately at a later date.
Note that an SVA Exempt Export BM Unit can only contain the Exemptable
Generating Plant for which it is being registered, it cannot contain additional
generation or demand. A Base BM Unit can be registered as Exemptable, if
it contains a single Exemptable Generating Plant. Alternatively an Additional
Supplier BM Unit can be registered for the Exemptable Generating Plant.
What forms do I need
to fill in?
For CVA BM Units:
For SVA BM Units:
You must submit BSCP15/4.5A to
apply for the Exempt Export status
for a CVA-registered BM Unit and to
choose the P/C Flag.
You must submit BSCP15/4.9A to
apply for the Exempt Export status
for an SVA-registered BM Unit and to
choose the P/C Flag.
What other information For CVA BM Units:
is needed?
We need to check whether the BM
Unit is eligible to be Exemptable.
Once we’ve verified this, we will
confirm or reject your application.
For SVA BM Units:
All you need to do is submit a
BSCP15/4.9A form to us, and we will
confirm the status.
How do I change the
P/C Flag?
Exempt Export BM Units elect their own P/C Flag when they are first
registered as exemptable using the BSCP15/4.5A (CVA) or BSCP15/4.9A
(SVA) form. If the Lead Party wishes to change the P/C Flag of an Exempt
Export BM Unit, the Lead Party must send us BSCP15/4.8 stating whether
they will have a Production or Consumption Flag.
How do I opt in or out
of the Base Trading
Unit?
Embedded Exempt Export CVA BM Units can choose whether they will be
part of the relevant Base Trading Unit or not. To do this, the Lead Party
must send us BSCP31/4.8 stating whether they will be part of the Base
Trading Unit or whether they will be a ‘Sole’ Trading Unit.
If you do not say otherwise, the BM Unit will be added into the Base Trading
Unit.
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Changing BM Unit Ownership
Parties who own a BM Unit may want to transfer the ownership to another Party. There is a different
procedure for transferring CVA and SVA BM Units.
For more information on this process, refer to the Change of CVA BM Unit Lead Party (CoBLP) and
Supplier ID Transfer guidance.
Change of BM Unit Lead Party
(CoBLP)
Transfer of Supplier ID
How do I transfer BM
Units?
To transfer CVA BM Units (such as
Directly Connected or Embedded BM
Units), the existing and the new Lead
Party need to confirm the BM Units
being transferred and the transfer
date. This can only happen once
both Parties have agreed.
Supplier BM Units must be
transferred as a set belonging to a
particular Supplier ID. In this case, it
is the Supplier ID that is being
transferred, and the related BM Units
move along with that. Each Party
must confirm the details.
What forms do I need
to fill in?
The existing Lead Party must submit
BSCP15/4.11A with the BM Unit(s)
that they are handing over, and the
Effective To Date (ETD) of their
ownership.
The existing Lead Party must submit
BSCP15/4.6A with the Supplier ID(s)
that they are handing over, and the
ETD of their ownership.
The new Lead Party must submit
BSCP15/4.11B with the BM Unit(s)
they are taking on, and the Effective
From Date of their ownership. This is
the following calendar day from the
existing Lead Party’s ETD.
The new Lead Party must submit
BSCP15/4.6B with the Supplier ID(s)
that they are taking on, and the EFD
of their ownership. This is the
following calendar day from the
existing Lead Party’s ETD.
When do I need to
submit these forms
by?
Both Parties need to send their forms
with enough lead time to process the
transfer. We need to receive the
forms at least five Working Days
ahead of the transfer taking place. If
any of the BM Units being
transferred submit FPNs, we will
inform National Grid of the proposed
transfer and a lead time of up to 30
Working Days may be required.
The lead time for this is within two
Working Days after both forms have
been submitted. As long as the forms
are correct, and the new Lead Party
has fully Acceded and Qualified as a
Supplier, the ID and related BM Units
can be transferred.
What else should I
note?
If the Change of Balancing
Mechanism Unit Lead Party (CoBLP)
involves BM Units in a Trading Unit,
this generally won’t affect the
configuration unless one of the
Parties (usually the new Lead Party)
wants to make a change. In this case
the new Lead Party may wish to be
excluded from the Trading Unit, and
you need to complete BSCP31/4.6.
If the existing Lead Party is
transferring their last Supplier ID,
they must also complete a
BSCP65/01 form to deregister their
Supplier Role.
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Offshore BM Units
Registering an offshore BM Unit is no different to registering an onshore BM Unit. All offshore BM
Units are Transmission Connected, so they are registered as Directly Connected (T_) BM Units. You
still need to fill out the same forms within the same timescales.
There is the option of combining multiple offshore Power Park Modules into a single BM Unit, a
Combined Offshore Power Park Module (COBMU). National Grid must approve this configuration in
each case - we will confirm this with them before progressing applications.
Switching Groups
Offshore and onshore Power Park strings can be moved between BM Units. You can set the relevant
BM Units up in a Switching Group, and opt to run the relevant strings in any of the BM Units within
that Group. To set this up, you must enter the relevant details in the table at the end of the
BSCP15/4.1 form as well as submitting the applicable Aggregation Rules (BSCP75) for all setups when
you are registering.
Need more information?
For more information please contact the BSC Service Desk at [email protected] or call 0870
010 6950.
You can find out more here:
Change of CVA BM Unit Lead Party (CoBLP) and Supplier ID Transfer Process
Trading Units
Embedded Generation and Embedded Benefits
Production/Consumption Flag
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