Is TN-C-S (PNB) the new name for PME?

No. PNB and PME are two different TN-C-S arrangements, and A4 lists both. PME has the supply PEN earthed at two or more points (Figure 3.9A). PNB has one point at which consumers' installations connect to a single source, with the PEN earthed at a single point near the consumer's terminals (Figure 3.9B).

Is PNB a new earthing arrangement created by A4:2026?

No. The arrangement existed before; A4 added it to BS 7671 with its own definition, figure and notes in Regulation 312.2.1.1, and a separate box on the model forms.

Do PME bonding sizes apply to a PNB supply?

It depends whether PME conditions apply. On a private network with the source earth and neutral-earth link inside the consumer's installation they do not (NOTE 3 to Figure 3.9B). Where a PNB system is connected to a public network they could (NOTE 4). Where they apply, Table 54.8 sets the minimum main bonding size; confirm with the distributor.

Do I need to reissue old EICRs that just say TN-C-S?

No. An EICR records the installation on the form in use at the time. The next periodic inspection on the A4 form will record TN-C-S (PME) or TN-C-S (PNB).

How do I know whether a supply is PME or PNB?

Ask the distributor or the owner of the private network. A typical domestic TN-C-S supply from the public network is PME. PNB is the arrangement where a single installation is supplied from its own source with the PEN earthed at one point close to its supply terminals.

A4:2026 CHANGE

TN-C-S PNB vs PME explained

Amendment 4 to BS 7671, issued on 15 April 2026, added protective neutral bonding (PNB) to the earthing arrangements in Regulation 312.2.1.1 and gave it its own tick box on the certificates. Both PNB and PME are forms of TN-C-S. What separates them is how many points the combined neutral and earth (PEN) conductor is earthed at, and how many installations hang off the source.

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7 min readUpdated 2026-10-28Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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The short answer

What is TN-C-S (PNB)?

TN-C-S (PNB), protective neutral bonding, is a TN-C-S arrangement in which there is only one point in the network where consumers' installations connect to a single source, and the PEN conductor is earthed at a single point, as close as practicable to the consumer's supply terminals (BS 7671 Figure 3.9B). TN-C-S (PME) is earthed at two or more points along the supply network (Figure 3.9A).

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Key takeaways

01PNB and PME are both TN-C-S: neutral and protective functions share one PEN conductor in part of the system, and separate N and PE conductors run inside the installation.
02PME (Figure 3.9A): the supply PEN conductor is earthed at two or more points. It is the usual public network arrangement for homes and small businesses.
03PNB (Figure 3.9B): only one point in the network at which consumers' installations are connected to a single source, with the PEN earthed at a single point, between the transformer and the consumer's supply terminals and as close to the terminals as practicable.
04PNB can apply to single-phase and three-phase supplies (NOTE 1 to Figure 3.9B).
05On a private network with the source earth and neutral-earth link inside the consumer's installation, PME conditions do not apply. Where PNB is connected to a public network, PME conditions could apply (NOTES 3 and 4).
06A4 did not invent PNB. It added the figure and the requirements to BS 7671 and a separate TN-C-S (PNB) box on the EIC, EICR and Minor Works forms.

01 · A4:2026 Change

What Amendment 4 changed

Before A4, BS 7671 described one TN-C-S arrangement, the PME one. A4:2026 added a second figure under Regulation 312.2.1.1 for TN-C-S (PNB), added definitions of both terms to Part 2, and split the TN-C-S tick box on the model forms into TN-C-S (PME) and TN-C-S (PNB).

Protective multiple earthing (PME), Part 2: an earthing arrangement, found in TN-C-S systems, in which the supply neutral conductor is used to connect the earthing conductor of an installation with Earth, in accordance with the ESQCR.
Protective neutral bonding (PNB), Part 2: an earthing arrangement, found in TN-C-S systems, where there is only one point in a network at which consumers' installations are connected to a single source of voltage.

02 · A4:2026 Change

PME vs PNB: the difference

Both arrangements combine neutral and protective functions in a PEN conductor up to the origin of the installation. The difference is upstream of the consumer.

Earthing points. A PME supply PEN conductor is earthed at two or more points, and an earth electrode may be necessary at or near a consumer's installation. A PNB supply is earthed at a single point.
Where the earth is. In PNB the PEN is connected to an earth electrode at a point remote from the transformer, between the transformer and the consumer's supply terminals, as close to the terminals as practicable. That limits the voltage rise if the PEN goes open-circuit (NOTE 2).
How many installations. PNB has one point at which consumers' installations connect to a single source. PME networks feed many properties from the same PEN.
Supply type. PNB can be single-phase or three-phase (NOTE 1).

When PME conditions apply to a PNB supply

NOTE 3 to Figure 3.9B: on a private distribution network where the source earth and neutral-earth link are within the consumer's installation, PME conditions do not apply, and PNB is typically used for multiple-source supplies (Regulation 444.4.6 and Appendix 9). NOTE 4: where a PNB system is connected to a public distribution network, PME conditions could apply, and ENA Engineering Recommendation G12 Issue 5 is the reference. Ask the distributor which applies.

03 · A4:2026 Change

Bonding and the PEN conductor

Whichever TN-C-S arrangement it is, the PEN conductor stops at the origin. Regulation 543.4.1 says PEN conductors shall not be used within an installation except where it permits, and its NOTE points to regulation 8(4) of the Electricity Safety, Quality and Continuity Regulations, which prohibits using a PEN conductor in a consumer's installation.

Where PME conditions apply, main protective bonding conductors are sized from Table 54.8 on the supply PEN conductor: 10 mm² copper for a PEN up to 35 mm², more for larger PEN conductors. Where PME conditions do not apply, the general sizing rule of Regulation 544.1.1 is used instead. That is why it matters which box you tick: the box tells the next person which bonding rules the installation was designed to.

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04 · A4:2026 Change

Recording it on the A4 certificates

The A4:2026 EIC, EICR and Minor Works forms list TN-S, TN-C-S (PME), TN-C-S (PNB), TT and IT as separate options under supply characteristics and earthing arrangements. Choose PNB only where you know the supply is arranged that way: the distributor, or the owner of a private network, can confirm it. A typical domestic TN-C-S supply from the public network is PME.

Older certificates

Certificates issued before A4 had a single TN-C-S box. They were correct for the form in use at the time and do not need reissuing. The next EICR on the A4 form will record PME or PNB.

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