DC Isolation in UK Solar: Installer Guide to Safety & Compliance

Safe, fast isolation on both the DC array side and the AC output side is essential for maintenance and compliance with BS 7671 Section 712. The right switchgear and a clean installation reduce DC arcing, prevent water ingress, and cut avoidable call-backs for installers.

In the UK, most formal DC isolator standards are paid publications, but there are free resources that provide practical guidance and context, including manufacturers’ installation guides. Key compliance and guidance references include:

(NICEIC-2024) - Connection of DC isolators - pratical installer guidance on safe PV installation.
BSI – BS 7671 (paid access) - the UK wiring regulations.
BSI – BS EN 60947-3 (paid access) - standard for switch-disconnectors and isolators, core for PV duty.

What is a DC isolator?

A DC isolator is a switch-disconnector on the PV string side. It separates the array from the inverter for inspection, testing, maintenance, or emergency shutdown.

High-quality units use a snap-action mechanism with arc chutes to interrupt current quickly, extinguish arcs, and protect the contacts.

Key Features and Functions of DC Isolators

Switch-disconnector: safely opens a DC circuit under load.
Safety & maintenance: ensures PV strings are electrically isolated before work.
Arc suppression: fast make/break with arc chutes to minimise fire risk.

How to Choose a Compliant DC Isolator (UK)

Correct ratings: voltage/current above worst-case Voc and Isc at minimum site temperature.
Compliance: IEC/BS EN 60947-3 with DC-PV1 or DC-PV2 marking.
Safe operation: fast make/break, lockable OFF, clear ON/OFF.
Durability: IP66+ enclosure, UV-resistant housing, properly sealed cable glands.

What is an AC isolator?

An AC isolator is a switch-disconnector on the inverter’s AC output. It provides a manual, visible air-gap to separate the inverter from the grid and any AC loads, enabling safe work, simpler fault-finding, and rapid shutdown for first responders.

What to look for in AC isolators

Correct ratings: suitable voltage/current with utilisation category (typically AC-22A or AC-23A).
Placement: adjacent to the inverter or as site policy requires; clearly accessible.
Durability: IP66+ and a robust, UV-stable enclosure for outdoor use.

Both DC and AC isolators are required for a safe, compliant PV installation in the UK.

Why DC Isolation Needs Special Attention

Unlike AC, DC current flows continuously and never crosses zero. Opening a DC circuit under load can sustain a plasma arc that will not self-extinguish.

A compliant DC isolator must:

Open quickly with snap-action contacts.
Extinguish arcs using arc chutes or magnetic blow-outs.
Be rated to the correct DC-PV category for string or parallel operation.

DC Isolator Selection Checklist for UK Installers

Voltage rating: always above string Voc at lowest site temperature.
Current rating: confirm against Isc and factor in potential back-feed from parallel strings.
PV categories: DC-PV1 for single strings; DC-PV2 for parallel strings.
Safe operation: lockable OFF, clear labelling, easy access for maintenance and emergencies.
Correct installation: IP-rated glands, torque to spec, mount to avoid water tracking.
Compliance & placement: provide isolation on both DC and AC sides in line with BS 7671 Section 712; place isolators close to the equipment and label clearly (e.g. “PV array dc isolator”).
Documentation: record test results and include isolator details and photos in the handover pack.

Fire Risk: What the Evidence Shows

UK data indicates most PV-originated fires start on the DC side, with external DC isolators the largest single source, followed by PV DC connectors.

Root causes typically include moisture ingress, incorrect crimps, cross-mating look-alike connectors, incomplete engagements, and loose switch terminals.

Sources:

PV fire risk from DC isolators and connectors | Alternergy

Sources:

Where Not to Install a DC Disconnector

In UK practice, installers should avoid putting a PV DC disconnector in any location that increases fire, water-ingress or access risk.

On the roof/under the array (unless explicitly required).
Hidden or hard-to-reach spots (behind modules, loft corners, plant areas without clear access).
Where water can track into the enclosure (beneath gutters, drip lines, or with top/side-upwards cable entry). Outdoor units must be rated for the environment and are best with bottom cable entry to reduce water ingress.
Locations outside the device’s environmental rating (direct sun/heat beyond spec, corrosive atmospheres, wash-down zones, or flood-risk areas).
Publicly accessible areas without protection/signage (risk of tampering or unsafe operation). Place isolators in clearly signed, safe areas and include them in emergency plans.
Scattered, multiple sites that confuse shutdown (e.g., one on the roof, another elsewhere).

Example of unsuitable PV DC disconnector placement next Solar Panel| Alternergy

Example of unsuitable PV DC disconnector placement Water | Alternergy

➛ Practical rule of thumb: If the inverter includes a built-in DC isolator, prefer locating isolation at the inverter and avoid additional external rooftop DC isolators, unless the manufacturer, client spec or site policy explicitly requires them.
Always size and mark per BS EN/IEC 60947-3 and select DC-PV1/DC-PV2 as appropriate.

IMO DC Isolators UK: True DC Safety for Solar PV Systems

Among UK PV isolator brands, IMO is widely trusted by installers and wholesalers. IMO stands out because it combines purpose-built PV design, proven compliance, and real-world durability.

Poorly made or incorrectly installed isolators often fail under load or let in moisture, which leads to the majority of PV fire incidents. IMO has built its reputation by eliminating those weaknesses.

Why installers choose IMO

“True DC” design & safety: patented design "snap-action", very fast make/break (typically <3–5 ms) for reliable arc suppression.
Reliability & durability: UV-resistant materials and IP66/IP67 enclosures for harsh outdoor conditions.
Proven trust: selected by leading inverter manufacturers and installers worldwide.
Certified compliance: IEC 60947-3 and EN 60364-7-712.
Range & flexibility: IMO offers a wide range of DC isolators for the UK residential and light commercial markets.

Safety depends on specification & installation

Correct PV category: DC-PV1 for single strings; DC-PV2 for paralleled strings (never DC-PV0 for on-load).
Verified rating: BS EN/IEC 60947-3 marking, voltage/current above calculated maxima.
Fast snap-action: essential for arc suppression (a defining IMO feature).
Proper installation: IP66 glands, correct torque, drainage orientation, water-ingress prevention, lockable handle, clear labelling.

Choosing the Right IMO DC Isolator

Match the isolator rating to the expected string current and application. IMO’s flexibility means a safe, compliant solution for everything from small residential to multi-string commercial PV systems.

IMO DC Isolator Options:

Current ratings:
- 16 A → Ideal for single-string residential systems (Isc + 125% < 16 A)
- 25 A → Suitable for hybrid/off-grid inverters with ~25 A inputs; balances safety and cost-effectiveness
- 32 A → Designed for parallel string applications where combined current exceeds 16 A but remains under 32 A
Pole configurations: 2-pole (single string), 4-pole (two strings, most common in UK), 6–8 pole (larger multi-string installs).
Mounting options: Enclosed IP66/IP67 units for outdoor use, or panel/base-mount versions for integration in cabinets and string boxes.

➛ These ratings are the most common in UK solar installations and provide installers with confidence in both performance and compliance.

Get Special Trade Pricing on IMO DC Isolators

Account customers receive preferential rates on IMO “True DC” isolators.

➛ Explore DC Isolators

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