Incoming supply
The mains supply should be clean – not connected to any other distribution that might affect it. Large facilities may have the supply taken from a dedicated transformer. We may even provide a standby transformer for facilities where the risk of damage to the mains incomer – accidental or deliberate cannot be discounted.

Transient protection at this point will protect the facility from the effects of lightning strikes to the premises or the ground around.
Capacitors may prove to be cost effective – depending on the load on the facility.

The feed is connected – in the case illustrated above, into a changeover cubicle, where an alternative supply from a standby power source is also available.

For any reasonably sized facility, the provision of an alternative source of electrical power, in the event of a mains failure, is essential. The cost of such provision is small when related to the cost of facility downtime.

For smaller facilities, the same comments apply, although the relative cost may be higher.

Diesel generation is the most popular solution and gas turbines, running on similar fuel, are used for larger loads.

The generating equipment simply comprises an engine, which drives the alternator, which produces electricity.

A generator emits noise and exhaust fumes and requires a supply of aspirating air for the engine and fresh cooling air for its radiator.

However, it can be contained in a weatherproof, acoustically attenuated housing and placed outside the facility it is protecting. Alternatively it can be housed inside a premises and the acoustic and anti-vibration treatments applied.

Fuel is usually held in a day tank built into the frame supporting the generator. As the term suggests, this will enable the set to operate for
8 hours under full load conditions. It is usual to provide a bulk storage tank to extend this period. Fuel tanks need to be bunded to contain leakage.

Permissions will be required from all relevant local authorities and owners of the premises

Where there is an alternative standby electrical power source, we feed cables from it and the main provider, into a changeover panel.

Inside are a changeover switch, sensors and breakers. The changeover switch automatically disconnects when a supply is lost and then switches over when a supply is present.

The switch is mechanically interlocked so that both supplies cannot be connected at the same time. Once thrown, it is usually arranged that it be manually changed back to the original source.

Opportunity may be taken at this panel to split the supply, where part is intended to be UPS supported.

UPS are the initial letters of, Uninterruptible Power Supply. As the description suggests, its purpose is to provide a source of uninterrupted AC electrical power.

This is achieved by providing the power from a battery bank.

A UPS contains an inverter to convert its input to DC, a battery bank, and a rectifier to convert the DC to AC.

When the main source of power is lost, the battery bank continues to provide power seamlessly.

When the batteries are no longer being replenished by the outside electrical power source, the UPS supply continues until the battery bank has run down.

This expensive and limited resource is intended to protect any equipment that would be damaged or have adverse consequences on the business activity, if its operation were interrupted in any way. An example would be computer disc drives. UPS support prevents them crashing and provides time for operators to make backups and close down in an orderly manner.

A UPS also gives time for any standby power source to be brought on-line and take over – in the event of a mains power failure.

This costly but effective facility needs careful sizing and consideration as to what to connect to it – which is the computer equipment.

We do not connect air conditioning, because its loss for a few minutes will not affect the room equipment. We do not connect the room lighting – because sufficient fittings throughout the room will be fitted with 3 hour backup batteries, to enable operations to continue.

Some telecoms equipment is supplied complete with its own UPS battery pack. This still needs to be connected to the UPS – see Pitfalls.

Whilst a UPS will have a bypass switch inside to enable the unit to be switched off whilst being serviced, we need a speedy means of isolating the UPS when it is removed/replaced.

This facility is provided by means of an external bypass switch. It provides an alternative route for the mains electrical power, avoiding the UPS.

The mains incoming electrical feed is fed through this switch before connecting to the UPS

This distribution panel is fed from the UPS – assuming one is provided, otherwise it has a clean supply and separate earth.

It may contain voltmeters, ammeters and sometimes an emergency stop shunt switch.

From it emanate all the electrical power circuits feeding the server and telecoms equipment and any others requiring UPS support.

Requirement
Although all power supply cabling in the room, and the breakers protecting them in the equipment PDU, will be clearly labelled, this does not prevent accidents. Access to connections within equipment racks is difficult by definition of their location and packing density of equipment inside them.

Engineers are required to work in pairs, and in the event of one receiving an electric shock – remembering that 400v 3-phase may be installed – a means of immediate electrical isolation may save life.

The large number of connections means that immediate identification of the source of the incident is not always possible.

Only where this risk is considered to be present, we fit a shunt trip to the computer PDU. This immediately shuts off all supplies from it.

Location
The emergency stop button may be mounted on the PDU and/or adjacent to the main entrance door.

This is a drastic installation measure and needs careful consideration.

Alternative
An alternative is investment in cable management installation and maintenance together with strict instructions regarding location and verification of power supplies before works are carried out. None however can entirely remove the risk of an electrical accident.

The method of distributing the power supplies to the various items of equipment in the room depends on the size and shape of that room.

A long narrow room may be suitable for only two rows of equipment down its length. In this case it may be considered acceptable to install the power supplies in perimeter dado height trunking, drop feeds to floor level opposite the item of equipment, and lay floor trunking up to it.

The floor trunking becomes a hazard to foot traffic, but this is acceptable as long as its presence is notified and it is not the main route through the room.

A wider room, in which there is space for more than two rows of equipment, may be treated as above for the equipment nearest to the walls. The inner rows may be fed from electrical trunking run through the suspended ceiling void, to drop into each item of equipment via a power pole.

The alternative is to install a raised floor with removable panels providing access, and the void a route for cables.

For other than small rooms, the raised floor option will be found to be the most cost effective and practical. Engineers climbing above equipment to install or remove supplies are both risky and expensive in terms of time involved.

Small power supplies emanating from the essential services PDU may be dealt with via a network of trunking – from which supplies are taken via socket outlets. This is has the advantage of tidiness and clarity.

The area in which the racks are likely to be located needs predicting - rather than the installation of general networks – the majority of which are then never used.

Where the supplies are required in an existing room, the laying of such trunking is usually impractical because of access disruption and pollution. We therefore opt for the laying of armoured cabling terminated in metal clad socket outlets.

Because of the large number of these supplies usually required, we bring the outlets from the floor void and mount the outlets on the floor tile inside or near to the rack being served. From here the multi-gang outlets can be safely connected.

A problem with the multiple single-phase supplies required in server racks is phase separation.

We always need to balance the phase loading on the Computer PDU, and in sufficient number, server racks need to be fed from different phases. Because racks are installed in rows and abutting one another, there is the risk of phase mixing – 400v – that can be lethal.

A 2m-distance phase separation may not always be possible and engineers seem to be constantly plugging in new equipment. It is therefore of prime importance that supplies, cabinets and rooms, carry appropriate warnings and that the operations department carefully monitor new installations.

Other than the computer servers and telecomunication related equipment, there are other items of equipment which should have UPS support:

Equipment not requiring UPS support:

The computer equipment manufacturer may specify lighting levels. Some are satisfied with the usual 600 lux, others demand 1000 lux on the basis that it assists their service engineers.

Recessed light fittings are fitted as they reduce airflow restriction.
Low glare is achieved by fitting parabolic grids to the luminaries.
A level of background illumination needs to be maintained in the event of a power failure – Fire Regulations.

Apart from illuminated escape signs above the exit doors, we can either fit mains maintained battery packs into some of the luminaries, or fit separate light fittings containing batteries.

It is necessary to ensure that the mains feed into the room has its own clean earth.

The whole of the room installation needs to carry earthing in accordance with the 6th Edition of the IEE Regulations.

Pedestals supporting the raised modular flooring need earth bonding.
The computer installation engineers are responsible for earthing their equipment.