Capacity Mode


This capacity heatmap provides an indication of the available transformer capacity at substations. The map indicates transformer capacity only. It does not guarantee the same capacity is available in the upstream networks. The heatmap is a snapshot, representing a moment in time, of a continually changing network system. It cannot be relied upon in isolation to assess the viability of a connection to a premises. Whilst we use reasonable endeavours to ensure that the capacity map and related information is accurate, we do not warrant, and do not accept any responsibility or liability for, the accuracy or completeness of the content or for any consequence or loss which may arise from reliance on the capacity heatmap or related information. The data provided must be considered in conjunction with explanations in ‘Important details about the Heatmap’ section. The available capacity figures will be periodically updated, and you should check the webpage routinely for the latest version. The legal disclaimer terms and conditions for use of our website apply to the capacity heatmap and related information.

At ESB Networks we are committed to improving the experience of our customers. As part of this commitment, we have developed our interactive Available Capacity Heatmap interface. It contains capacity information on all our 3-phase LV, MV and HV DSO substations. It provides an interface that enables the easy identification of potential transformer capacity in the vicinity of your site. An excel file is available to download from the download section on this page.

We envisage that the map will be used to inform initial discussion between ourselves and our customers. Although we have taken steps to ensure the accuracy of the map, it cannot replicate the level of accuracy provided by the detailed assessment carried out as part of the formal application process.  Please read the accompanying notes and important details section to understand what the map does and does not provide.


If the Available Capacity Heatmap indicates that there is insufficient capacity to accommodate your development, please contact us to discuss the next steps. We will always work with customers to find solutions. Generation customer queries should be directed to Demand customer queries should be directed to

  1. Map Preparation Date: 23 Nov 2020
  2. What can I learn from the map?
    1. The map indicates transformer capacity available at each distribution High Voltage (HV) substation. The HV data is intended to guide industrial/large commercial scale users to HV substations where a connection is more likely to be achieved without significant reinforcement. This is relevant as substation and transformer installations are the longest lead time component of connections if they must be built or reinforced.
    2. In the map HV substations are classified into two categories corresponding to the supply voltage i.e., 38kV or Medium Voltage (MV). 
    3. The map also gives the location and available demand capacity for all 3 phase Medium Voltage to Low Voltage (MV/LV) substations.The LV data capacity is in the range of customers looking to connect demand less than 500kVA. This scale would be of most interest to small businesses, farming, and small community projects. If the indicated capacity meets your needs, then you can be reasonably assured no new substation development is required. However, site specific detail such as proximity and physical access could still be an overarching limiting factor.
    4. Available capacity for LV generation is not specified because of additional considerations that are mainly site specific, see point No 5 below.
    5. The pins on the map are colour coded by ranges of available capacity which can be separately filtered. Filtering can also be independently applied by voltage level.

  3. How do I know which substation to review for my site? 
    1. For LV substations, use the map to locate your own site and then find the nearest LV substation to it. Typically, a substation must be within 300m or less to be suitable for connecting at LV otherwise a new substation must be provided nearer to you.The pop-up box also shows the parent HV substation that supplies the LV substation. Also check this for available capacity. 
    2. For HV substations, the best indication of which one supplies your site is to find the nearest LV substation and identify its parent HV substation. Review the HV substation for available capacity and the parent of that station if one is listed in the pop-up panel.

  4. Does the Capacity Available value mean I can connect the amount shown?
    Not necessarily. There are many site-specific issues and detailed technical checks that must be completed to give that assurance and they can only be completed as part of an application. Below are some of the factors that influence the answer: 
    1. Am I the first to apply? All connection offers are provided on a first come first served basis so other customers may have applied ahead and used a proportion of the available capacity.
    2. Proximity to the substation: typically for LV, you must be a maximum of 300m from the substation and much closer for the higher level of LV capacity. For 38kV and MV circuits, capacity is not assured, and new lines may need to be constructed or existing one upgraded. 
    3. HV substations are sometimes a parent supply to other downstream substations. In cases where the parent substation has limited capacity then all child substations will be curtailed by that limit. Furthermore, if just one child substation absorbs all the available capacity then that will result in no spare capacity for the other child stations. This form of interaction requires continual re-assessment to ensure no system overload occur.
    4. A similar interaction can occur on circuits where apparently available capacity cannot be contracted because of customer increases on other circuits which share a common source with a capacity limit.
    5. Generation, at all voltages, is particularly onerous due to the limited latitude to accommodate the associated voltage rise. This has an acute effect on the necessary proximity to a substation.
    6. Capacity available is also influenced by disturbing load such as flicker and harmonic emissions.
    7. The stated available capacity may exceed the maximum rating for an individual network component such as transformer capacity or standard circuit connection capacity. In such cases, a single customer/connection will be constrained by the network component and therefore will not be able to avail of the full value indicated.

  5. Why are there no specific available capacity values for LV generation provided?
    The basic value that can be calculated reliably is related to the transformer size and existing contracts. This could be misleading, for generation at LV, because the exact amount of LV generation permissible is heavily influenced by broader criteria that must be met to make an acceptable connection and are predominantly site and application specific. The upper limit is the size of the transformer or 500kVA, whichever is less, but may be considerably less in order to meet the necessary criteria such has:
    1. Voltage rise limit which is influenced by conductor size and length, single phase or 3 phase connection and connection point of other demand and generating customers.
    2. Harmonic emissions from connected equipment.
    3. Rapidly changing impact of other customers sharing common network, both at connection point and upstream at HV Stations.
    4. Evolving rules of the Enduring Connection Process (ECP).

  6. What do the different markers colours mean? 
    Each substation has been given an overall classification (Red/Amber/Black) based on the calculated available capacity. The colour meanings differ for HV and LV and for Demand and Generation as shown below:  
    DEMAND: 38kV and MV 
    GREEN    Greater than 5MVA   
    AMBER    Between 0 and 5MVA  
    BLACK    No capacity available 

    Generation: 38kV and MV 
    GREEN    Greater than 15MVA 
    AMBER    Between 0 and 15MVA  
    BLACK    No capacity available 

    Demand and Generation: LV 
    GREEN     Greater than 200kVA 
    AMBER     Between 20 and 200kVA  
    BLACK    20kVA or less available 

    Connections to the substations/transformers with an overall BLACK classification are still possible, however there might be a requirement for significant network reinforcement to overcome the impact on the network constraints. 

  7. How has the data been produced? 
    The data has been produced by a basic analysis of the available transformer capacity, existing loads and contractual commitments to new customers. Detailed assessment aspects, necessary for connection offers, such as upstream circuit capacity and service contingency requirement are not included. 

  8. What are the available capacity figures based on? 
    1. HV station capacity in winter 2019/20. 
    2. MV station capacity at the start of May 2020. 
    3. Base load information comes from Special Load Readings 2019/20, which include 2019 Summer Valley load used in the Generation capacity preparation.  
    4. Demand calculation incorporate demand contracts and offers up to 28th September 2020. 
    5. Generation calculations incorporate generation contracts and offers up to 28th September 2020. 

  9. How often is the Network Capacity Map updated? 
    The Generation Map is updated once a quarter. The Demand Map is updated once a year. 

  10. Are the substation locations accurate? 
    HV substation locations are only indicative. The exact locations of MV/LV substation are provided.

  11. How long does a connection take? 
    In general, where HV substation capacity is adequate, MV connections up to a maximum of 10MVA will entail construction of overhead line or new underground cable network, associated civil works and minor station works only and typically do not require planning permission. These would not be expected to take longer than 6-9 months. However, any instances requiring significant station work such as the installation of a new transformer or MV switchgear will require increased time, and possibly planning permission and would typically be expected to take approximately 2-3 years.

    LV connections alone are usually completed within 6 months of application.

  12. What other important points should be kept in mind about the data in the map? 
    1. The map does not replace a full formal application in determining network capacity.  
    2. The map does not provide capacity figures for the final connection from HV substation to customer premises. Such connections will need to tap into the existing MV (10kV or 20kV) network and capacity availability are subject to many variables and bespoke assessment is necessary. 
    3. In some cases, the available capacity shown in the Demand Map may already be contracted to individual customers but is not currently being fully utilised.
    4. The information provided in the Generation and Demand Maps does not guarantee the same capacity is available in the upstream DSO networks.
    5. Any increased load on the Distribution System will impact on the upstream Transmission System and reinforcements may be required on the Transmission System in order to cater for these loads. This will be separately assessed by the TSO. 
    6. An individual connection cannot be greater than the capacity of an individual transformer.  In the case of 38kV and MV, the available capacity shown is the total of all transformers in the substation at the respective voltage.  Therefore, full capacity utilisation may, sometimes, only be possible with more than one connection. (Note, a single premises cannot have more than one connection).

Demand or Generation Application

Select the application form relevant for your connection type.

Application Forms

Demand & Generation Map Data

heatmap-download-version-nov-2020.xlsx 8.25 MB Download

If you have a general query

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