3AUSA30400CG0C Series 300SE - ASCO | Automatic, 400 AMP

The ASCO Series 300 Service Entrance (SE) version combines the transfer function with a service-entrance rated disconnect in a single listed enclosure, so the switch can be installed at the point where utility power enters the building instead of requiring a separate service disconnect ahead of it. This unit is rated 400 A, 208V, 3-pole, NEMA 1, open transition. Typical loads are a whole-building distribution panel, a rooftop packaged unit group, a small data or telecom room, a clinic or a restaurant — installations where the transfer switch is sized to the full service and must coordinate with the upstream overcurrent protection. The NEMA 1 enclosure is intended for indoor installation in a dry, protected space such as a mechanical room or an electrical closet. Terminations and footprint. Two conductors per pole from 1/0 AWG to 250 kcmil, or one from #4 AWG to 600 kcmil, in the same 24 in by 56 in by 14 in cabinet at 250 to 270 lb. 400 A is the largest rating that still shares that enclosure with the 260 A unit, and it is the practical ceiling for a wall-adjacent installation: beyond this the switch is a floor-standing assembly with a different footprint and a different rigging plan. Service arrangement. This is a 208Y/120 V three-phase four-wire switch — the service found in office buildings, retail strips, clinics and small data rooms, where one panelboard feeds 208 V three-phase loads and 120 V receptacle circuits off a solid neutral. The neutral is not switched, because it is bonded at the service and opening it would defeat ground-fault sensing. Neutral configuration. The grounded conductor is solid: it runs straight through on a bolted neutral plate and is never opened. That is the correct choice when the transfer switch is not a separately derived source — the generator neutral is bonded to the same grounding electrode system as the utility, so the neutral is one continuous current-carrying conductor end to end and breaking it would serve no purpose. It is also the cheaper of the two arrangements and has one fewer set of moving contacts to inspect, which is why it is the default on most commercial retrofits where the existing service neutral is already bonded. Enclosure. The Type 1 cabinet is for indoor use in a dry, protected space — a mechanical room, an electrical closet, a plant room — where the only thing it has to keep out is incidental dust and the occasional touch. It is not rain-tight and not watertight: mounting one on an exterior wall, even under a soffit, invites water in through the door seam and the conduit knockouts, and the first sign is usually a rusted mechanism rather than a tripped breaker. If the switch has to live outdoors, the 3R version of the same rating is the one to order. Service-entrance rating. This is the SE version, which means the assembly is listed as service equipment in its own right: the utility disconnect and the transfer mechanism share one enclosure, and there is no separate main breaker or service disconnect ahead of it. Three things follow from that. The neutral bus is the service neutral and the main bonding jumper lands inside this enclosure, so the grounding electrode conductor terminates here rather than at a separate disconnect. The short-circuit current rating applies to the whole assembly, not just to the switch, and it has to be checked against the available fault current at the service point. And the utility will want to see the listing before they energise it — a standard transfer switch installed ahead of the service disconnect without an SE rating is a common inspection failure. What the extra cost buys is one enclosure, one set of terminations and one less place for a bonding error. Matching generator. At 208V with an 0.8 power factor this switch carries approximately 115 kW of load (400 A × 208V × √3 × 0.8 = 115 kW, three-phase). Size the standby generator so that its standby rating meets or exceeds that figure, and confirm the generator's two-wire automatic-start contacts are compatible with the transfer switch controller. Controller. This unit carries the ASCO Group G controller: a 128 × 64 graphical LCD with switch-position, source-availability, common-alarm and not-in-auto indication. Transfer and re-transfer delays, engine cool-down and the in-phase transfer timer are all set from the membrane keypad rather than from DIP switches, with ranges up to 60 min 59 s. The Group G controller supports both open transition and delayed transition, and accessory 11BE adds RS-485 communication at 9,600–115,200 bps, a seven-period programmable exerciser and a 300-event log. Three-pole configuration. The three phase conductors are switched with a solid neutral. This is the standard arrangement where the neutral is bonded at the service and must not be opened by the transfer switch. Supply. Supplied as a genuine ASCO Power Technologies (Schneider Electric) unit, brand new and factory original, packed for export from our Dongguan warehouse. Ask us for the outline drawing, wiring diagram and data sheet for this exact catalog number.