At a Glance. A switch disconnector has to interrupt current safely, and the difficulty of that job depends almost entirely on whether the current is AC or DC. The Socomec range we stock reflects that split. SIRCO PV 4X600A F 1000Vdc (order no. 27PV4060) is a direct-current switch disconnector built for photovoltaic circuits. CT LBS 4P 160A IP65 S2N (order no. 30324016) is an AC load break switch supplied in a steel enclosure. A third family, CDE FE 4 4X D-G (order no. 143E3113), combines switching with fuse protection. All three are catalogued under Switch Disconnectors & Transfer.
1. Why DC switching is the harder task
In an AC circuit the current passes through zero twice per cycle, and that zero crossing is where the arc naturally extinguishes. A DC arc has no zero crossing, so it must be stretched, cooled and split by the arc chute. The higher the DC voltage, the more chute stages are needed and the wider the contacts must open.
The practical consequences for a specification are straightforward:
- Never substitute an AC-rated switch into a DC circuit. The contact rating on the label is only valid for the current type and voltage printed beside it.
- Number of poles matters more in DC. Series-connected poles share the arc voltage, which is why PV isolators are often multi-pole devices rated for a high system voltage.
- Load break capability must be stated. A switch that only isolates an already-de-energised circuit is not the same as one that can break full load current.
2. SIRCO PV versus CT LBS at a glance
| Criterion | SIRCO PV (DC) | CT LBS (AC) |
|---|---|---|
| Current type | Direct current, photovoltaic | Alternating current |
| Voltage class | Up to 1000 Vdc on the version we stock | Low-voltage distribution level |
| Typical location | String combiner boxes, inverter DC side | Distribution boards, machine incoming supply |
| Enclosure | Depends on the installation; often panel-mounted | Painted steel enclosure, IP65 on the CT LBS version |
| Poles | Multi-pole, series connection common | 3-pole and 4-pole versions |
| Main selection risk | Under-rated DC voltage or missing load break rating | Confusing isolation duty with load break duty |
3. When to add fuse protection
Switching and protection are two functions, and a switch disconnector does not provide overcurrent protection on its own. In photovoltaic combiner boxes the string fuse is normally a separate device; on AC boards a fused switch disconnector — the concept behind CDE FE 4 4X D-G — lets one device isolate and protect at the same time, which saves panel width. Choose a fused device when the protective device and the isolator would otherwise sit side by side.
4. Specification checklist
- System voltage and current type. State the DC voltage of the string at its coldest expected condition, which is the highest value, not the nominal one.
- Rated current. Use the continuous current of the string or circuit, then check the derating for the enclosure and ambient temperature.
- Utilisation category. Confirm what the switch is expected to break before ordering.
- Mounting. Panel cut-out, enclosure IP rating and cable entry positions all change the part number.
- Accessories. Auxiliary contacts, extended handles and shaft extensions are separate items and are frequently forgotten on the first order.
- Marking. Confirm the SCCR / short-circuit rating against the upstream protection.
5. Cross-referencing an existing installation
Socomec has changed part numbering several times across the SIRCO and CDE families. Two switches that look identical in a photograph can differ in pole configuration, handle position and enclosure rating. The reliable way to cross-reference is from the order number printed on the device or the panel schedule, not from the family name.
Send us the order number, the required pole count and a photo of the installed device and we will confirm the current equivalent and availability from our switch disconnector stock. Common requests such as 27PV4060 and 30324016 can usually be quoted the same working day.