Home»IMO Stag IS4P AC Isolator 4-Pole 20A 32A 40A 63A 100A 125A IP65 EN60947-3 UKCA Solar PV Inverter AC Switch Disconnector Lockable Padlockable Made in UK MCS Compliant
IMO Stag IS4P AC Isolator 4-Pole 20A 32A 40A 63A 100A 125A IP65 EN60947-3 UKCA Solar PV Inverter AC Switch Disconnector Lockable Padlockable Made in UK MCS Compliant
The IMO Stag IS4P AC Isolator is the standard AC switch-isolator for UK solar PV and inverter installations, available in ratings from 20 A to 125 A to suit domestic, commercial and industrial applications. Manufactured in the United Kingdom by Stag Electrical — one of the most widely recognised names in the UK wholesale electrical market — these isolators are EN 60947-3 and IEC 60947-3 compliant, carrying full UKCA, CE and SEMKO approvals. The IP65-rated polycarbonate enclosure is dust-tight and water-jet resistant, making it suitable for outdoor meter cupboards, consumer unit enclosures and any installation where moisture or dust exposure is a concern. The interlocked lid prevents the enclosure from being opened while the isolator is in the ON position, and the lockable red/yellow rotary handle can be padlocked in the OFF position — essential for safe isolation during inverter or battery maintenance. The 4th pole is an Early Make Late Break configuration, suitable for switching a neutral conductor. Multiple cable gland knockout holes (M20/M25 on smaller sizes; M20/M25/M32 on larger) provide flexibility for any installation geometry.
20–
125A
Rating range
4-pole
EMLB 4th pole
IP65
Enclosure rating
UKCA
CE
Approvals
EN
60947-3
Standard
Made
in UK
Country of origin
⚠ Competent person installation required: AC isolators are connected directly to the live AC output of the solar inverter or to the grid supply. Installation must be performed by a competent electrician in accordance with BS 7671 (IET Wiring Regulations) and applicable building regulations.
ℹ MCS requirement — AC isolator mandatory for UK solar PV installations: MCS-accredited solar PV installations require an accessible AC isolator between the inverter and the grid connection point. The Stag IS4P range is suitable for this application. The lockable handle allows the isolator to be locked in the OFF position for emergency isolation and during maintenance, as required by the MCS MIS 3002 installation standard.
Select the Correct Rating — Full Variant Table
The AC isolator must be rated at or above the maximum output current of the inverter it protects. Use the table below to select the correct IS4P variant. The 20 A or 32 A isolator covers the vast majority of domestic solar PV installations.
Part no.
Rating
Typical PV / inverter application
Enclosure (H×W×D)
Max cable
Weight
IS4P20
20 A
Single-phase inverter up to 4.6 kW (20 A output)
125×100×85 mm
10 mm²
0.52 kg
IS4P32
32 A
Single-phase inverter up to 7.3 kW; 3-phase up to 11 kW motor
125×100×85 mm
10 mm²
0.52 kg
IS4P40
40 A
3-phase inverter up to 15 kW; larger AC coupled systems
175×115×100 mm
10 mm²
0.75 kg
IS4P63
63 A
3-phase inverter up to 22 kW; commercial PV
175×115×100 mm
16 mm²
0.75 kg
IS4P100
100 A
Large commercial 3-phase inverter up to 37 kW
240×160×120 mm
35 mm²
1.34 kg
IS4P125
125 A
Large commercial 3-phase inverter up to 45 kW
240×160×120 mm
35 mm²
1.34 kg
All variants are 4-pole, 230 – 440 V AC, IP65, EN 60947-3. IS4P20L and IS4P32L are larger-enclosure variants of the 20 A and 32 A models (175×115×100 mm), available for installations requiring larger cable management space. Inverter output current = rated power (W) ÷ voltage (V). For a 3.68 kW single-phase inverter: 3,680 W ÷ 230 V = 16 A → use IS4P20. Always round up to the next standard rating.
The IS4P range is type-tested and approved to EN 60947-3, the European standard for switch-disconnectors and fuse-combination units. This is the standard cited by MCS MIS 3002 and BS 7671 for safe isolation of AC circuits in solar PV installations. Approvals include UKCA (UK Conformity Assessed, required post-Brexit for placing products on the UK market), CE (European market), and SEMKO (Scandinavian mark). RoHS compliant. Rated insulation voltage Ui: 690 V, providing substantial headroom above the 415 V operating voltage.
EN 60947-3 / IEC 60947-3UKCACESEMKORoHS
IP65 Enclosure, IP20 Body — Outdoor and Meter-Cupboard Rated
The polycarbonate enclosure is IP65: completely sealed against dust and protected against low-pressure water jets from any direction. This makes the IS4P suitable for installation in outdoor meter enclosures, external consumer unit housings, garage walls and any location where rain splash or garden hosepipe exposure is possible. The switch mechanism body itself is rated IP20. Stainless steel lid screws resist corrosion in damp external locations.
IP65 enclosureIP20 bodyPolycarbonate + SS screws
Interlocked Lid — Cannot Open in the ON Position
A mechanical interlock prevents the enclosure lid from being opened while the rotary handle is in the ON position. This is a critical safety feature: it is not possible to inadvertently touch live terminals while the circuit is energised. The handle must be rotated to OFF before the lid will release. This interlock is required by the wiring regulations for accessible isolators in consumer-facing installations.
Lid interlocked in ON positionCannot access live terminals
Lockable Red/Yellow Rotary Handle — Padlockable in OFF
The distinctive red and yellow rotary handle follows the BS 7671 colour convention for isolation devices. A padlock can be fitted through the handle when it is in the OFF position, preventing the circuit from being re-energised during maintenance. This is an MCS installation requirement for solar PV AC isolators: the firefighter or emergency service must be able to lock off the supply before approaching the roof or inverter. The lockable handle also serves for energy company meter testing isolation and general contractor lock-off/tag-out procedures.
Red/yellow handlePadlockable in OFFMCS compliant
4th Pole — Early Make Late Break for Neutral Switching
All IS4P variants are 4-pole. Three poles switch the line conductors (L1, L2, L3 in three-phase; L1 plus two additional poles in single-phase use). The 4th pole is configured as Early Make Late Break (EMLB) for neutral switching: when closing the isolator, the neutral connects before the live poles; when opening, the neutral disconnects after the live poles. This sequence ensures the neutral is always in place before current flows, preventing overvoltages from neutral loss. The 4th pole can also be used to switch a neutral in a 3-phase+N system.
4-pole4th pole: Early Make Late BreakNeutral switching
Multiple Gland Knockouts — Flexible Cable Entry
The enclosure features multiple pre-formed gland knockout holes on the base, top and sides. Sizes: M20 and M25 on the 20A, 32A, 40A and 63A enclosures; M20, M25 and M32 on the 100A, 125A and 150A enclosures. These accept standard IP65 cable glands, allowing the installer to choose cable entry positions to suit the specific installation geometry and maintain the enclosure’s IP65 rating (unused knockouts should be plugged with appropriate blanking glands).
M20/M25 knockouts (20– 63A)M20/M25/M32 knockouts (100– 125A)Top, base and side entry
Flame-Retardant Polycarbonate — UK Manufactured
The IS4P enclosure is moulded from flame-retardant polycarbonate, a material with excellent electrical insulation properties, impact resistance and UV stability for external use. In the event of an internal fault, the enclosure is self-extinguishing and does not propagate flame to adjacent materials. Made in the United Kingdom by Stag Electrical, the IS4P range is a staple of the UK wholesale electrical and solar trade and has been specified by UK installers for decades.
Flame-retardant polycarbonateUV stableMade in UK
Optional Auxiliary Contacts (SAC) — Remote Status Monitoring
Optional SAC auxiliary contact modules are available for the IS4P range, fitting onto the left-hand side of the isolator body. Each SAC provides 1 normally open (NO) and 1 normally closed (NC) contact (rated 6 A at 230 V AC15; 1.1 A at 125 V DC13). These allow the isolator’s switch position to be signalled remotely to a monitoring system, inverter, or energy management controller. Three SAC variants cover the full IS4P range: SAC32-11 (for 20A/32A), SAC63-11 (for 40A/63A), SAC150-11 (for 80A–150A).
1NO + 1NC auxiliarySAC32-11 / SAC63-11 / SAC150-11Remote status signalling
Technical Specifications
All IS4P Variants — Common Specifications
Poles
4 (L1, L2, L3 + Early Make Late Break neutral)
Rated voltage (AC21)
230 – 440 V AC
Rated insulation voltage Ui
690 V
Frequency
50 / 60 Hz
Protection class (enclosure)
IP65
Protection class (body)
IP20
Enclosure material
Polycarbonate, flame-retardant, UV stabilised
Lid screws
Stainless steel
Lid interlock
Prevents opening in ON position
Handle
Lockable red/yellow rotary (padlockable in OFF)
Mechanical life
10,000 operations
Rated cond. short circuit current
20 × Ie
Short time withstand (1 s)
12 × Ie
Rated make/break capacity
8 × Ie
Gland knockouts
M20/M25 (20 A – 63 A) · M20/M25/M32 (80 A – 150 A)
Standards and Approvals
Product standard
EN 60947-3 / IEC 60947-3
Approvals
UKCA, CE, SEMKO
Environmental
RoHS compliant
Country of manufacture
United Kingdom
Variant Specifications
IS4P20 (20A)
Dims: 125×100×85 mm · Cable: 10 mm² · Torque: 2 N m · Weight: 0.52 kg
IS4P32 (32A)
Dims: 125×100×85 mm · Cable: 10 mm² · Torque: 2 N m · Weight: 0.52 kg
IS4P40 (40A)
Dims: 175×115×100 mm · Cable: 10 mm² · Torque: 2 N m · Weight: 0.75 kg
IS4P63 (63A)
Dims: 175×115×100 mm · Cable: 16 mm² · Torque: 2 N m · Weight: 0.75 kg
IS4P100 (100A)
Dims: 240×160×120 mm · Cable: 35 mm² · Torque: 3 N m · Weight: 1.34 kg
IS4P125 (125A)
Dims: 240×160×120 mm · Cable: 35 mm² · Torque: 3 N m · Weight: 1.34 kg
Optional Accessories
Auxiliary contacts (20A / 32A)
SAC32-11: 1NO + 1NC, 6 A @ 230 V AC
Auxiliary contacts (40A / 63A)
SAC63-11: 1NO + 1NC, 6 A @ 230 V AC
Auxiliary contacts (80A – 150A)
SAC150-11: 1NO + 1NC, 6 A @ 230 V AC
Frequently Asked Questions
Which rating do I need for my solar inverter?
Divide the inverter’s rated output power (in watts) by the circuit voltage to get the output current, then select the next standard IS4P rating above that figure. Examples: a 3.68 kW single-phase inverter at 230 V outputs 16 A → use the IS4P20. A 5.0 kW single-phase inverter at 230 V outputs 21.7 A → use the IS4P32. A 10 kW three-phase inverter at 415 V outputs 13.9 A → use the IS4P20. If in doubt, select the next size up. Never select a rating lower than the inverter’s rated maximum output current.
Is this isolator required for MCS-accredited solar installations?
Yes. MCS MIS 3002 requires an accessible AC isolator between the inverter and the grid connection point. The isolator must be lockable in the OFF position so that the supply can be isolated and locked off for emergency services or during maintenance. The Stag IS4P meets this requirement: it is lockable, accessible, EN 60947-3 compliant, and carries UKCA approval for the UK market.
What is the Early Make Late Break 4th pole, and do I need to use it?
EMLB (Early Make Late Break) describes the switching sequence of the 4th pole relative to the other three poles. When the isolator is turned ON, the 4th pole connects before the other three poles. When turned OFF, the 4th pole disconnects after the other three. This is the correct sequence for a neutral conductor. In a standard UK single-phase PV system (230 V AC), you have L + N. Connect L to one of the numbered poles and N to the EMLB pole. The other two numbered poles remain unused (or are wired as part of a multi-pole scheme). In a three-phase system, use L1, L2, L3 on the three numbered poles and N on the EMLB 4th pole.
Can this isolator be mounted outdoors?
Yes, the IP65 enclosure is rated for outdoor surface mounting. IP65 means the enclosure is fully dust-tight and protected against low-pressure water jets from any direction (e.g. rain, garden hose spray). It is not rated for submersion (IP67/68), so do not install where it may flood. The polycarbonate material is UV stabilised for long-term outdoor use. Stainless steel lid screws prevent corrosion. Ensure all unused gland knockouts are fitted with appropriate IP65-rated blanking glands to maintain the enclosure’s ingress protection.
What is the difference between IS4P20 and IS4P20L (the ‘L’ variant)?
The ‘L’ suffix denotes a larger enclosure. The IS4P20L uses the same 20 A switch mechanism as the IS4P20 but is housed in the larger 175×115×100 mm enclosure (the same body used for the 40 A and 63 A models). This gives more room inside the enclosure for cable management, particularly useful when the installer needs to bring larger cables to the isolator or where there are multiple cables entering the same enclosure. Weight increases from 0.52 kg to 0.75 kg. Electrically identical to the IS4P20.
Can I fit auxiliary contacts for remote monitoring?
Yes. Optional SAC auxiliary contact modules clip onto the left-hand side of the isolator body. Select the correct SAC for your isolator: SAC32-11 for IS4P20 and IS4P32; SAC63-11 for IS4P40 and IS4P63; SAC150-11 for IS4P80 through IS4P150. Each SAC provides one normally open (NO) and one normally closed (NC) contact rated at 6 A at 230 V AC. These can be wired to an inverter’s external signal input, a building management system, or a remote alarm panel to indicate whether the isolator is open or closed.
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BTU & WATT Calculator
Room Dimensions
Room Type
Living Room
Bedroom
Kitchen
Bathroom
Conservatory
Hallway
Glazing Type
Single Glazed
Double Glazed
Triple Glazed
External Walls
0 Wall
1 Wall
2 Walls
3 Walls
4 Walls
Insulation Level
Poor
Average
Good (New Build)
Required Heating
0
Watts
0
BTUs
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