Hi there . I've read quite a bit on this topic but often the answers aren't crystal clear.
The main supply comes into the house ( UK ) with a TNCS Earth . The mains will be coming out of the house into the inverter shed which is about 5m away . Mains will then come back into the house through AC1 of the inverter ( ESS system with Pylontec Batteries ) with hot water power supply coming in separately from AC2 using ac assistant .
From what i read in the IET rules the house must have its own ground rod . I'm assuming the best place for this is as close to the house board and supply as possible . So since a new ground rod must be used will it be linked to the existing TNCS Earth or should the existing TNCS earth be isolated and everything should be earthed with just the new rod effectively making it a new single TT system.
The AC wiring will be done by a qualified electrician but i want this clear in my head rather than someone coming along and making a mistake as this topic doesn't seem clearcut from all the different forum responses and notes that I've read online.
IET :
The consumer earth electrode
A consumer earth electrode is required for island mode operation, because, as Regulation 551.4.3.2.1 of BS 7671 states, the distributor’s earthing arrangement cannot be relied upon.
Existing consumer earth electrodes, such as those used in TT systems, may be used where they meet the design requirements for the EESS. The selected earth electrode system should meet the requirements of BS 7671, and as much as possible should be installed to reduce the risk of freezing or drying out.
The maximum acceptable earth electrode resistance for installations operating TN-S, or in TT systems where earth fault loop impedance is not restricted to a lower value, is 200 Ω. Above this value, the earth electrode system may not present a stable resistance. This is a major change in the 2nd Edition of the IET Code of Practice for Electrical Energy Storage Systems, which previously recommended a maximum of 200 Ω only for systems below 10 kVA.
In some cases, better earthing needs to be provided. Some consumers have parts of the installation with different earthing arrangements to the main installation. Examples include installations with a PME earthing arrangement for the grid connection, but separate TT earthing arrangements for outbuildings, or electric vehicle charging equipment. An example is shown in Figure 5.
In these systems, the designer should ensure the values of both the consumer earth electrode for the island mode earthing arrangement, and the TT earth electrodes, are low enough to ensure operation of protective devices in the event of a fault to earth in the TT part of the installation. Usually, this will involve the operation of RCDs, and the maximum earth fault loop impedance must meet Table 41.5 of BS 7671.
