SDU 250A for Sellafield

Sub Distribution Unit generally as detailed in Sellafield Ltd Engineering Standard ES_1_2263_2 Issue 4 and designed in accordance with BS EN 61439-4.

Enclosure
Heavy duty, free-standing, double–sided enclosure designed for use in a coastal environment in an ambient temperature range of -25°C to +35°C. The enclosure is constructed from 316L stainless steel with a polyester powder finish, shade Vermilion RAL 2002. The use of high-grade stainless steel provides enhanced corrosion resistance when compared with the shot-blast and zinc sprayed, mild steel SDU enclosures previously provided. The enclosure is designed to IP54 with the doors closed and to IP2X with the doors open. Doors are provided with door stays and a padlocking facility. Guttering is provided on the canopy which projects out over the access doors both front and back.
Cable access is via bottom-entry gland plates in the underside of the unit. One gland plate is provided per compartment and there is a protective bond from each to the main earth bar. Doors have a supplementary bond to the main earth bar.
The enclosure is fitted with 2 no. M20 eyebolts for initial off-loading on site. The eyebolts can be removed and blanked off without compromising the IP rating.
Fixing holes (blanked off) are provided in the door for an ID label to be fitted on site.
All distribution switchgear is mounted behind protective inset panels.

Busbar system
A 400A TP+N busbar system (independently tested to 25kA for 0.1 seconds) is incorporated. A separate 50 x 6.3mm earth bar is provided, located within the enclosure, adjacent to the gland plates.

Incoming Switchgear
250A TP switch disconnector c/w separate fully shrouded neutral link. The switch disconnector is interlocked with the incoming door.

Distribution
2 x 63A TP Type C MCBs c/w MRCD plus separate fully shrouded neutral link.
10 x 32A TP Type D MCBs c/w MRCD plus separate fully shrouded neutral link.
Schneider iC60H Acti 9 MCBs with top and bottom shrouds are fitted, c/w shunt trip coils for control by the earth leakage devices. A separate data sheet on the Blakley MRCD variable earth leakage sensor is available on request.
For the incoming device, both top and bottom shrouds are drilled with voltage test holes (4.0Ø) so that probes can be used to check for the presence of a voltage. For the outgoing devices, just the outgoing shrouds are drilled.
The incoming cable (max. 185mm² 4c SWA) terminates directly onto the incoming device and the outgoing cables also terminate directly onto the outgoing devices (MCB/neutral link). At 63A a 35mm² SWA cable can be terminated and at 32A the limit is 16mm².

Additional equipment
An anti-condensation heater is incorporated within each compartment, controlled by a common thermostat.
A 230V 13A BS1363-2 test socket is fitted, which is protected by 16A SP+N fusing and a 30mA Type A RCCB. The 13A socket and associated protection equipment is located behind a dedicated, external, padlockable cover.