Eaton Electric
Eaton Engineering Services & Eaton Engineering Systems
L2 Metering Solutions From Eaton
Energy metering is a small but significant
element in the requirements of the 2006 Edition of the UK Building
Regulations Part L2. The requirements apply to non-domestic premises
with a floor area greater than 500m² and effectively call for
monitoring of the supply to any final distribution board with an
input power greater than 50kW. This would include the vast majority
of MCB distribution boards and calls for a fresh look at the design
and installation of final distribution systems to achieve
cost-effective solutions.
The UK Building Regulations Part L2: Conservation
of fuel and power in buildings other than dwellings is now divided
into two sub-sections – Part L2A applies to new buildings and L2B
applies to existing buildings. The metering requirements are broadly
similar but the focus is inevitably on ensuring that new buildings
are designed to conserve fuel and power.
Requirements
The essential requirement of L2 is to provide
sub-metering so that at least 90% of the estimated annual energy
consumption of each fuel can be identified with various end-use
categories such as heating, lighting, small power, ventilation,
pumps and fans. This must form part of an overall metering strategy
that will help operators understand the patterns of energy use in
their buildings and, if possible, effect energy savings of 5-10% or
more.
The requirements apply to premises with a floor
area greater than 500m² (including separate buildings on
multi-building sites). An additional requirement calls for automatic
meter reading and data collection facilities in buildings with a
total useful floor area greater than 1000m². The requirements apply
to fuels such as gas, LPG and oil as well as to electricity.
Specific recommendations are made for plant and
equipment for which separate metering should be provided as follows:
-
Boiler installations greater than 50kW
-
Chiller installations greater than 20kW
-
Electric humidifiers greater than 10kW
-
Motor control centres feeding pumps & fan
loads greater than 10kW
-
Final electricity distribution boards greater
than 50kW
Final Distribution Boards
This last requirement is significant in that most
Type B (three-phase) distribution boards are rated 100A or more and
therefore exceed 50kW. So metering of supplies to all distribution
boards should be considered.
Another important consideration is the fact that
many final distribution boards supply both small power and lighting
loads. Ideally, in many applications, these should be metered
separately so that patterns of usage can be identified with each end
use.
Where loads such as pumps and fans are fed
directly from a main switchboard or panelboard, metering will
normally be supplied at that point. Supplies to final distribution
boards could be metered at this level also but, if lighting and
small power loads are to be metered separately, this can potentially
double the number of branch circuits on the main board and require
additional cable feeds to more Sub Distribution boards.
However, the design of distribution boards is a
delicate balance between compact dimensions and the provision of
adequate space for wiring. This leaves little or no room to
accommodate meters. Consequently, the installer is faced with two
options:
If loose meters are installed, the contractor
will have to spend time selecting appropriate equipment and
designing a suitable installation. The appearance of the finished
installation may not be particularly satisfactory and, for the
customer, the additional cost may be high.
The second option above normally involves
ordering custom-built distribution boards to accommodate the meters.
This is costly and can result in manufacturing delays, which are
outside the control of the contractor. The answer to this is a new
generation of standard final distribution boards with integral
meters. Consequently, Eaton has developed standard “Meter Packs” as
part of its Memshield 2 distribution system. Eaton’s first offerings
are Type A - single-phase boards with single or dual channel
metering (monitors two independent groups of load e.g. Lighting and
power, separately, with one, two channel meter).
The availability of standard factory-built meter
packs and metered distribution boards, available over the counter,
puts the contractor back in control. At the same time it reduces the
time and effort required to design the metering solution and install
the meters. It enables the contractor to offer a quality,
value-added product and enjoy a better profit margin than would
otherwise be the case.
Meter Types
A number of factors should be considered when
selecting a meter.
Where fiscal billing is involved it may be
necessary to select an Ofgem-approved meter or an MID (Measurement &
Instrumentation Directive) approved instrument. This will give both
parties the assurance of an instrument that should be accepted in
any dispute over billing. For other applications, normal meters will
offer a cost-effective solution, frequently with a wider range of
measurement functions and communication options.
The European standard for watt-hour meters,
EN61036, classifies meters into two categories. Class 1 is the
higher accuracy classification and is the type frequently used for
sub-distribution metering. The lower accuracy Class 2 meters are
widely used for the main intake position in an installation.
For lower power applications (normally up to 65A
single phase and 100A three phase) a direct reading meter will be
used (no external ct’s); the incoming supply is taken to the meter
and then an output from the meter feeds the distribution board. For
higher power applications, current transformers (CTs) are used; the
supply is taken directly to the distribution board and current
transfomers on the conductors measure the current flow.
CT measurement also requires a connection to the
phase and neutral conductors to provide a reference voltage at the
Meter; in some cases this requires use of one of the outgoing MCB
ways in the distribution board. With Eaton’s Memshield 2
distribution boards, the reference voltage can be taken from the
busbar. This leaves the full complement of MCB ways available.
The normal requirement of a meter is to measure
energy (kWh). In general this will be provided by a digital display.
However, many instruments will also give a pulsed output, which can
be used to transmit data to a building management system (BMS) or
Automatic Metering System (AMS). This is normally restricted to kWh
measurement.
Where additional information may be required, a
multi-function meter will display data such as line voltage (V),
current (A), power (kW), reactive power (kVAr) and power factor. In
many cases, instruments will be capable of displaying many or all of
these parameters. If remote collection of this data is required,
however, a higher level of communication, such as Ethernet or
RS-485, will be required.
Meter Packs
Eaton’s meter packs form part of the popular
Memshield 2 range of MCB distribution boards and devices. The meter
and associated components are housed in an enclosure with dimensions
and finish to match the Memshield 2 distribution boards.
The first units were designed to be mounted below
Memshield 2 Type B (three-phase) distribution boards. One was a 100A
direct-connected Ofgem approved and certified meter while the second
was a 100-200A Class 1 multi-function meter using current
transformers. Both meters provide visual indication of energy (kWh)
used and a pulsed output for automatic meter reading and data
collection but the second is a multi-function instrument also
providing visual readout of other parameters such as line voltage,
current, kVAr and power factor.
These have recently been joined by a 125A and
160A split load meter pack incorporating two Meters for use with two
Memshield 2 Type B TPN distribution boards. This provides separate
metering of small power and lighting loads. The meter pack, which
sits below the two boards, allows both boards to be fed by a single
cabled main supply. They have a 125A/160A rotary disconnect switch
incomer and incorporates two sets of current transformers and two
multi-function meters.
There is also a meter pack designed to be mounted
alongside Memshield 2 Type A SPN single-phase distribution boards
(but is limited to 65A). The meter is an MID-compliant
multi-function instrument providing visual readout of kWh, kW, A,
kVAr and kVArh together with pulsed output for kWh measurement.
Boards With Integral Meters
Eaton has also introduced a range of Type A
single-phase distribution boards with integral meters. These include
both single meter units and split-metering units for separate
metering of lighting and small power loads. They use multi-function
meters, which provide visual readout and pulsed output for
measurement of kWh and can also provide visual readout of other
parameters such as line voltage and current. Modbus RS485 RTU
communication is offered as an alternative and provides access to
additional electrical parameters.
The single-meter boards are available with 9 or
12 MCB ways (65A max). The split meter boards for independent
metering of small power and lighting circuits are available in a 6 +
6 or 8 + 4 configuration. These split load versions employ a two
channel Meter feeding two separate busbars within the board, each
channel supplying a maximum of 65A. This allows the boards to be
used up to their nominal rating of 100A total.
As mentioned previously, metering for plant and
services such as pumps and fans can be provided on the outgoing side
of switchboards and panelboards. Eaton has introduced outgoing
metering facilities for its Series G panelboards up to 800A with
removable side gland plates. They make use of side cable extension
boxes with hinged doors and DIN 96mm x 96mm cut-outs. The contractor
selects the version of Board with removable side gland plates,
selects the meters and appropriate CT module to achieve the required
solution and, without the need to customise the steel enclosure,
fits the meters. Unused meter ways are simply blanked off with a
clip-in cover.
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