What is a grid connection, and why is 400A a practical rule of thumb for BESS?

When an industrial company considers investing in a battery energy storage system, the technical assessment rarely starts with the battery itself. It starts with the building's existing electrical installation and the agreement the company has with the local distribution system operator (the netselskab that owns and operates the local grid). The capacity in this connection largely determines which technical options are available for an industrial BESS installation, because both offtake and any export of electricity must fit within the agreed limits. Radius Elnet, a Danish distribution system operator, describes the grid connection agreement as the document that defines the customer's access to the collective electricity grid.

This article uses a grid connection of around 400 amperes as a local rule of thumb for industrial BESS projects. It is not an official technical or commercial threshold, but a level at which a battery system can often be assessed on a more solid technical basis. As described below, 400 amperes in a standard 400V three-phase system corresponds to roughly 277 kW. That is an order of magnitude, not a precise cut-off. This article explains the underlying mechanisms, and how the grid connection defines the constraints for a project's potential.

What is a grid connection, and what does the ampere rating tell you?

A grid connection is the physical and legal link between a company's internal electrical installation and the collective electricity grid. It is not merely a cable in the ground, but a formal agreement that defines how much capacity the company is entitled to draw from the grid.

In a professional context, the grid connection agreement is the document that describes the customer's access to the collective electricity grid. The agreement contains specific rights and limitations that are decisive for the operation of a battery system.

Delivery capacity (leveringsomfang): This term covers how much electricity the company has purchased the right to draw from the electricity grid. For business customers, this delivery capacity is often calculated and stated in amperes. The ampere rating is therefore a direct expression of the maximum load the installation may place on the grid at any given time.

Export capacity (indfødningsomfang): While a typical manufacturing company primarily draws power, a battery system works differently. Batteries both consume and export electricity, which means they can also send power back to the grid. A BESS installation therefore also requires that an export capacity has been agreed with the distribution system operator.

The ampere rating on the company's main distribution board thus indicates how much technical capacity has been established between the company and the electricity grid. The higher the number, the more power can typically be moved back and forth, which can be relevant when assessing whether a BESS project has sufficient technical headroom.

Why 400A+ is often a practical reference point for industrial BESS

400 amperes is often used as a reference point because of a combination of physics, Danish grid tariffs, and plant economics. It is a practical rule of thumb and not a general technical minimum threshold. To understand this, amperes must be converted into the power the installation can deliver, measured in kilowatts. It remains a guiding reference point, because the specific value depends on how the installation is built and on local conditions.

In the Danish electricity grid, delivery capacity can be converted from amperes to kilowatts using a fixed formula for a standard 400V three-phase system (as set out in guidance from Forsyningstilsynet, Denmark's utility regulator). A connection of 400 amperes corresponds in this conversion to a power of approximately 277 kW. That makes 400A a guiding reference point, not a formal threshold.

This power size places the project in a category that Radius Elnet designates as medium-sized connections, where small connections typically go up to 125 kW, while medium-sized connections cover the range from 125 kW to 3 MW. This is Radius practice and not necessarily a shared classification across all Danish distribution system operators. A capacity of 277 kW therefore sits at a level where BESS projects are often assessed as industrial rather than small commercial solutions, which here is a practical assessment and not an official category.

Around 400 amperes is therefore often used as a practical reference point when assessing whether there is enough technical headroom for an industrial BESS project. It is a starting point and not a signal that a project is automatically suitable.

What happens at a lower grid connection?

It is technically possible to install a battery system at lower grid connections, but it still requires that the distribution system operator can accept both offtake and any export within the specific agreement terms. The primary question is whether the project has sufficient capacity for the intended operation.

At lower connections, the maximum power at which the battery can charge or discharge is limited. A smaller system can still make sense in specific scenarios if the company's goal is to handle short-duration peak loads within the capacity that has actually been agreed with the distribution system operator.

Unused grid capacity and the difference between agreement and consumption

One of the most important factors in assessing BESS potential is the difference between the company's agreed capacity and its actual consumption. Many industrial facilities are sized for a future expansion or for machines that rarely run at full load at the same time, but spare capacity cannot be assumed from consumption alone. It is a case-by-case project assessment.

When there is a difference between the agreed capacity and actual consumption, there can in some cases be headroom for a battery system without a major upgrade of the connection. That must always be assessed in each project together with the distribution system operator's requirements for both offtake and export.

It is important to note, however, that an existing delivery capacity is not automatically the same as spare capacity for a battery. The distribution system operator must always approve that the battery may also export power to the grid. Any terms on interruptibility or limited export are as set out in the agreement, so we cannot read them directly from consumption alone.

ZynexGroup's approach to site assessment

When we assess an industrial BESS installation, we start from the company's grid connection and historical consumption data. That typically includes the size of the main distribution board, the agreed delivery capacity, and the actual load profile hour by hour.

A data-driven assessment can be used to clarify whether there is technical headroom to reduce peak load consumption and possibly export power to the grid. By knowing the bounds of the installation, we can calculate a realistic business model. Any guarantee or payback arrangements should only be mentioned if they are documented and clearly tied to the specific project assumptions.

How to find the company's ampere rating

To assess whether a facility is a relevant candidate for a battery system, it is necessary to know the current capacity. This figure can be found in several ways.

Physical reading: The main distribution board in the company's electrical room can often give an indication of the installation's size, but it is not always where the formally agreed capacity appears most clearly. In some cases there is a marking on the main breaker, for example with the text "400A", "630A", or "1000A".

Electrical documentation: The company's electrical contractor or the person technically responsible will have access to the building's electrical diagrams, where the rated size of the connection point is shown.

The distribution system operator: The most precise source for the formally agreed delivery capacity is the company's electricity bill or a direct enquiry to the local distribution system operator. Here it is also possible to learn whether there are particular local conditions that affect the possibility of having an export capacity approved.

Once the ampere rating is known, and data for actual consumption is available, the foundation is in place to assess whether a battery system is a technically and economically relevant solution.

Have your facility assessed

If your company wants to explore the options for industrial battery storage, an initial assessment can start from your actual consumption data, electrical documentation, and the local grid conditions.

For a closer dialogue about the project's scope, you can contact us via ZynexGroup's contact form.