Connection to the utility network

From Electrical Installation Guide

The possible solutions for the connection of an installation to the utility network are the following:

  • Connection to the LV network for small and medium size installations requiring less than 400 kVA. Fixing this limit is always under the responsibility of the local utility managing the LV network
  • Above this previous limit, connection to the MV network with either LV or MV metering. LV metering is generally authorized for installation including a single MV/LV transformer not exceeding the rated power limit fixed by the utility, generally around 1250 kVA.
The possible connections to a MV utility network are the following, (see Figure D8, D9 and D10):
  • MV single-line service,
  • MV ring-main service,
  • MV duplicate supply service, including two load break switches equipped with an automatic change over,
  • MV dual supply service with two independent connections to the utility and two bus bars connected with a bus tie. The two utility incomers and the bus tie are equipped with an automatic change over.

Comparison of this four modes of connection are summarized in Fig. D7

Fig. D7 – Comparison of the modes of connection
Characteristic to consider Configuration
Single-line Ring-main Duplicate supply Dual supply
Activity Any Any Any High tech, sensitive office, health-care Very sensitive installations
Site topology Single building Single building Single or several buildings Single or several buildings Single or several buildings
Service reliability Minimal Minimal Standard Enhanced Very high
Power demand < 400 kVA ≤ 1250kVA Any Any Any
Other connection constraints Any Isolated site Low density urban area High density urban area Dedicated measures taken by the utility
Fig. D8 – MV connection with LV metering
Fig. D9 – MV connection with MV metering
Fig. D10 – Dual MV connection with MV metering