LV installation systems: access rules

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In our previous post we saw that an LV Functional Panel doesn’t have just electrical Distribution functions (which are its raison d’être), but also some functions related to its Installation System. And we listed the most important among these functions.

We expressly omitted to talk about one specific function. It is not one of the most complex ones and it does not impact the good performance of the Low Voltage LV Panel. However, it requires a very special attention because it can have a dramatic impact on personal safety.

This function is Access Management. In a few words, it consists of the access rules to the different parts of the LV Panel. The main target is to prevent accidental contact with active parts.

It is our assertion that the best way to define these access rules is to adopt a strategy based on the LV Panel life cycle.

What are the main phases of the panel’s life cycle?

We typically distinguish three phases:

• Operation (setting parameters, recording measurements, locking, padlocking, etc.).
• Maintenance (cleaning, checking, testing, repairing, etc.).
• Evolution (adding, modifying, expanding, etc.).

Functional modularity and life cycle

As we have seen in our previously, one collateral benefit of functional modularity is that it can provide a dedicated area for each person according to his/her responsibilities and skills. The good news is that responsibilities and skills are related to the different phases of the panel’s life cycle, because each one of the three phases mentioned above requires different skills and responsibilities.

An example using doors

A transparent door will allow seeing display screens, devices’ front plates, and the like, while preventing direct contact.

A fully metallic door will prevent, not just direct contact, but also seeing anything installed behind it. We can also install a device on the door itself allowing its operation while the door remains closed.

How many access levels do we need?

At this stage it could be useful to remember that we are talking about Low Voltage Electrical Distribution panels for non-critical small or medium size buildings. This means that the LV panel may not necessarily be installed in a dedicated electrical room with restricted access to authorised professionals, but anywhere in the building. Therefore, the first access level that we have to take care of is the access to the panel itself.

Thus, after having secured the access to the LV panel, we can address the question of the access levels of the LV panel.

What are the tasks related with such a panel that one could reasonably want to execute?

1. We may just want to look at the indicators (energy consumption, alarms, on/off position of the circuit breakers, etc.).
2. We may want to operate the devices (opening or closing a circuit, consigning a circuit, changing a melted fuse, etc.).
3. We may want to modify the installation (expanding the panel with additional functions, equipping a spare space, etc.).

The number of access levels required can be defined according to the LV panel life cycle and to the different types of personnel that would execute the different tasks mentioned above.

Thus, it seems reasonable, in this type of LV panel, to propose three different access levels.

In this example the 1^st layer is a transparent door on the switchgear compartment and a fully metallic on the duct compartment. The doors are meant to allow only looking at the devices, and prevent operation of the devices. This layer is optional for the switchgear compartment, but mandatory for the duct compartment. When the door is fully metallic even looking at the devices is impossible, except for those devices installed on the door (e.g. HMI). In most cases, we need a key in order to open this door, giving access to the 2^nd layer.

The 2^nd layer consists of front plates. It allows not only looking at the devices, but also operating them while being protected from accidental contact with active parts. A special tool is required in order to remove these front plates to access to the 3^rd layer.

The 3^rd layer gives access to the functional units and therefore it allows any possible action on the panel. Access to this layer must be strictly reserved to professional electricians.

It is obvious that both layers 1 and 2 must be removable or opened with a sufficient angle to allow the professional electrician to work on layer 3 comfortably and safely.

Writtent by Frederic Waterlot and Daniel Barstz