Product Overview
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 150 A, 480V, 3-pole, NEMA 3R, 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 β installations where the transfer switch is sized to the full service and must coordinate with the upstream overcurrent protection. The NEMA 3R enclosure is rain-tight and rated for outdoor mounting against a wall or on a pad, so the switch can sit next to an exterior generator without an additional weather shelter. Terminations and footprint. The lug range stays at #14 AWG to 4/0 AWG on a single conductor per pole, and the cabinet becomes an 18 in high by 31 in wide by 13 in deep arrangement at roughly 69 to 75 lb. The layout is wider and shallower than the 30 to 104 A box, which matters when the switch has to fit between a panel and a wall: the footprint changes shape, not just size, and that is what usually decides the mounting location. Service arrangement. This is a 480Y/277 V three-phase four-wire switch, the standard industrial and large-commercial service in North America: 480 V for motors, chillers and process equipment, 277 V for lighting, with the neutral bonded at the service and carried solid through the transfer switch. This is the voltage at which arc-flash energy climbs fastest, so the upstream coordination study matters more here than at 208 V. Neutral configuration. The neutral is switched β it opens and closes with the phase poles as one more pole. You need this when the generator is wired as a separately derived source with its own grounding electrode and its own main bonding jumper: leaving the neutral solid would tie the two grounding systems together through the neutral, put objectionable current on the grounding conductor and leave the generator frame at a potential above earth during a fault. It costs one more pole and one more set of contacts to maintain, but on a separately derived system it is not optional, and an inspector will look for it. Enclosure. The Type 3R cabinet is rain-tight, not watertight: it is built for outdoor mounting against a wall or on a pad, with a hooded or sloped top that sheds water and a gasketed door that keeps driven rain out. What it does not do is keep out dust or hose spray, and the installation still has to do its part β conduit entries need drip loops or sealing hubs so water running down the conduit cannot track into the enclosure, and the mounting surface has to drain. A 3R unit on a north wall in a coastal yard will outlast three indoor units in the same spot, which is why it is the default for anything not under a roof. 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 β 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 480V with an 0.8 power factor this switch carries approximately 100 kW of load (150 A Γ 480V Γ β3 Γ 0.8 = 100 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 Γ 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 9,600β115,200 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.
