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 250 A, 220V, 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. Two conductors per pole from 1/0 AWG to 250 kcmil, or a single conductor from #4 AWG to 600 kcmil, in the same 24 in by 56 in by 14 in cabinet as the 260 A unit at 250 to 270 lb. 250 A is a rating that appears on Canadian services and on older US switchboards rather than on new design, and it is the last size before the lug stack changes for the 600 A frame: the practical difference from 260 A is the breaker and the feeder, not the switch. 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 β 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 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 220V with an 0.8 power factor this switch carries approximately 48 kW of load (250 A Γ 220V Γ 0.8 = 48.0 kW, single-phase two-wire). 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.
