13.4 Labelling the PV System
Key Takeaways
- Handbook 4.5.1 requires identification of the mains AC isolator as the point of emergency isolation, plus a system schematic at the point of interconnection with the DNO's distribution system.
- 'Additional supply' labels go at the service termination, the meter position, and all points of isolation between the inverters and the main incoming supply.
- The DC switch-disconnector is labelled 'PV array DC isolator' (or equivalent) with ON and OFF indicated; its enclosure carries the Regulation 712.514.102 warning; off-load-only isolators and BS EN 62852 DC connectors must say they must not be opened under load.
- DC cables read 'PV array cable – live during daylight' (or equivalent); the inverter warns to isolate all AC and DC supplies before work; the inverter AC isolator reads 'PV system main isolator' (or equivalent).
- A building warning that a solar PV system is installed is part of 4.5.1; fire crews at the meter cupboard rely on additional-supply labels, the schematic, and emergency-isolator identification, and they must still treat DC as live in daylight.
Labelling is not decoration for the handover pack. City & Guilds 2922 handbook v1.3 4.5.1 lists labelling requirements in accordance with BS 7671 and Engineering Recommendations G98 and G99. The list runs from (a) to (k). The paper can ask any letter. Learn the wording, the location, and who the label is for — the next electrician, the DNO, or a fire crew who has never seen the loft.
(a) Identification of the mains AC isolator
Identify the mains AC isolator as the point of emergency isolation. This is the AC device people operate in a hurry to separate the PV system from the incoming supply at the origin end. It must be obvious: not an unlabelled rotary handle among three identical isolators. On a simple board-mounted layout this may be the dedicated PV isolator at the consumer unit. On a split layout (hall plus loft) you still designate and mark the emergency point — typically the origin device that a firefighter or occupier can reach without climbing into the roof.
(b) System schematic at the DNO interconnection
Display a system schematic at the point of interconnection with the DNO's distribution system. That point is where the installation meets the distributor — commonly the meter / service position — not a drawing left in a kitchen drawer. The schematic shows inverter location, AC and DC isolators, and how the generator sits on the installation. G98/G99 interconnection paperwork and BS 7671 identification rules meet here: someone standing at the cut-out can see what else is on the building.
(c) 'Additional supply' labels
Fit an 'Additional supply' label at:
- the service termination
- the meter position
- all points of isolation between the inverters and the main incoming supply
Multiple sources are the hazard. A person opening the cut-out cover or operating a meter isolation point must be told this installation is not a single incoming DNO supply. Every isolator on the path from inverter to main incoming supply gets the same warning, including the loft AC isolator and the hall PV isolator on a two-isolator job.
(d) Off-load isolation only
Isolators only suitable for off-load isolation must be labelled to this effect. DC connectors used as a point of isolation, or a disconnector that must not break load, are the usual examples. If someone opens them under load they draw a DC arc that the device was never designed to extinguish. The label is the last barrier when the handle looks like any other isolator.
(e) PV array DC isolator, ON and OFF
The switch-disconnector shall be labelled 'PV array DC isolator' (or equivalent) with the ON and OFF positions clearly indicated. This is the DC device, not the AC isolator. Mixing the two names is a standard exam fail: the AC device in (j) is 'PV system main isolator'; the DC device in (e) is 'PV array DC isolator'. ON/OFF must be unambiguous in poor light.
(f) Switch-disconnector enclosure — Regulation 712.514.102
The enclosure of a switch-disconnector shall have a warning notice in accordance with Regulation 712.514.102 of BS 7671. That regulation is the DC live-parts warning: after isolation, live parts on the DC side can remain energised (the array is a current source in daylight). The notice belongs on the enclosure people open, not only in the O&M manual. Item (e) names the device; item (f) warns about what is still live inside and around it.
(g) DC plug and socket connectors — BS EN 62852
All DC plug and socket connectors shall be marked to indicate that they should not be disconnected under load, in accordance with BS EN 62852. Typical PV connectors arrive with that marking; replacements must keep it. Accessible connectors for ordinary persons also need to be of a locking type (DC-accessories content), but 4.5.1(g) is specifically the under-load marking. Do not unmate them as if they were extra-low-voltage appliance couplers.
(h) DC cables — live during daylight
DC cables shall be labelled 'PV array cable – live during daylight' (or equivalent). Isolating AC does not make the roof dead. Isolating the DC switch-disconnector does not make the array side of that switch dead in daylight. Fire crews and later electricians cut what they can see; the cable label is how they know those conductors are a daylight-live PV array, not a discarded aerial.
(i) Inverter notice — isolate AC and DC before work
The inverter should contain a notice giving warning to isolate all AC and DC supplies before carrying out work. Two sources, two isolations. This matches the practical safe-isolation sequence and the BS 7671 inverter warning (commonly discussed alongside 712.514.103). A sticker that only says 'isolate mains' is incomplete on a PV inverter.
(j) Inverter AC isolator — PV system main isolator
The inverter AC isolator shall be labelled 'PV system main isolator' (or equivalent). That is the AC device associated with the inverter — on a one-room job it may be the same handle as (a); on a loft job it is typically the adjacent loft AC isolator from 4.4.1(e), while (a) still identifies the emergency point at the origin. Learn both phrases: emergency identification in (a), this exact AC label in (j).
(k) Building warning — solar PV installed
Provide a warning of installation of solar PV system installed on a building. External or origin-position warnings tell arriving fire and rescue that the roof is a generator. Combined with (h), they should not assume that pulling the DNO fuse killed every conductor on the premises.
Label versus location
| Item | Typical wording or content | Where it goes |
|---|---|---|
| (a) | Identifies the mains AC isolator as the point of emergency isolation | On/at the designated emergency AC isolator |
| (b) | System schematic | Point of interconnection with the DNO's distribution system |
| (c) | Additional supply | Service termination, meter position, and all isolation points between inverters and the main incoming supply |
| (d) | Off-load isolation only | On isolators that must not break load |
| (e) | PV array DC isolator, ON and OFF | DC switch-disconnector |
| (f) | Warning notice to Regulation 712.514.102 | Enclosure of that switch-disconnector |
| (g) | Do not disconnect under load | Every DC plug/socket (BS EN 62852) |
| (h) | PV array cable – live during daylight (or equivalent) | DC cables |
| (i) | Isolate all AC and DC supplies before work | On the inverter |
| (j) | PV system main isolator (or equivalent) | Inverter AC isolator |
| (k) | Solar PV system installed on this building | Building / origin warning for arriving crews |
Scenario: fire crew at the meter cupboard
It is 02:00. There is a roof fire. The crew goes first to the meter cupboard — service termination and meter position — because that is how they shut off a dwelling. If 4.5.1 was installed properly they immediately see (c) Additional supply at the service termination and meter, so they know this is not a single-supply house. They see (b) the schematic at the DNO interconnection, showing a loft inverter, hall and loft AC isolators, and a DC isolator. They can identify (a) the mains AC isolator as the point of emergency isolation without guessing among unmarked handles. (k) on the building has already told them solar PV is installed.
What the meter cupboard cannot do is make the roof safe by AC isolation alone. (h) on the DC cables and (f) on the DC isolator enclosure exist because array conductors remain live during daylight. (e) tells them which handle is the PV array DC isolator; (d) and (g) tell them not to pull connectors or off-load devices under load. (i) on the inverter, if they reach it, repeats isolate AC and DC. (j) marks the inverter AC isolator so it is not confused with the DC device.
If any of (a)–(c) or (k) is missing, the crew at the meter cupboard has to invent a model of the installation while the roof burns. That is why 4.5.1 is a list, not a choice of favourite stickers.
Where does handbook 4.5.1(c) require 'Additional supply' labels?
What wording does 4.5.1(h) require on DC cables (or equivalent)?
How shall the inverter AC isolator be labelled under 4.5.1(j)?