Archive for the ‘Transformers – Liquid filled’ Category

A quick overview guide to The London Building Act (Amendment) Act: 1939 Section 20

Saturday, June 13th, 2009


Section 20 of the London Buildings Acts (and subsequent amendments) is concerned with the danger arising from fire within certain classes of building which by reason of height, cubic extent and/or use necessitate special consideration. The principles incorporated the provision of fire-fighting facilities that would enable the fire brigade to tackle the fire with utmost speed, but also provide warning of fire, contain an outbreak of fire and to prevent its spread.

This is quick guide to section 20 building requirements. But remember, always seek professional guidance.

Especially in relation to escape routes, building services, sprinkler or other automatic fire extinguishing,  or suppressant system, including hose reels; smoke extraction / venting system,  and vertical transport (including fireman’s lifts).

The London Building Act (Amendment) Act: 1939 Section 20
(Buildings of excess height and / or additional cubic extent)
(As amended 1985 & 2005)

Do the proposed works attract an application under this Legislation?

Application will be required if the building is:

  • More than 30 metres in height;
  • More than 25 metres in height with an area of any floor more than 930m 2.
  • A building of the warehouse class, or is a building or part of a building used for the purpose of trade or manufacture exceeding 7100m3 (250,000ft3) in cubical extent  unless it is divided  by division walls (with 4hr FR) such that no part of the building exceeds 7100m3 (see note 1).


If the proposed works bring the building into one or more of the above listed categories the building will then become subject to the above legislation requiring an application.


An Application is necessary if the works affect any of the following:

  • Sprinkler or other automatic fire extinguishing or suppressant system, including hose reels;
  • Smoke extraction / venting system;
  • A change to the access to the site for the Fire & Rescue Service;
  • Work that affects or impacts on any special fire risk areas (see Note: 2).

Where Approved Inspectors propose works within a building subject to LBA Section 20 it is mandatory that this local Legislation is recognised in the Initial Notice; failure to do so will result in rejection of the Initial Notice. Please note that this is irrespective of whether the proposed works impact on the criteria listed above or not. If the Council decides that a Section 20 Application is necessary then the Council will ask for this but will not delay validating the Initial Notice, providing that this local Legislation is expressly referred to in the Initial Notice, and confirmation is given that if necessary an application will be submitted in due course.

1)A building of the warehouse class means a warehouse, manufacturing, brewery, distillery with a cubic extent exceeding 4,247m3 (150,000ft 3) which is neither a public nor a domestic building. Please note for the purposes of this legislation the definition of a domestic building includes office use.
Height is taken from street level at the centre of the face of the building to the ceiling level of the top storey. Where more than half the roof is covered by a plant room such room becomes the top storey.

Cubic extent in relation to the measurement of a building means the space contained within the external surfaces and roof and the upper surface of the floor of its lowest storey but including any space within any enclosure on the roof of the building used exclusively for accommodating a water tank of lift gear or any like apparatus.

2.  Special Fire risk Areas:

  • Heat producing appliance above 220 kilowatts (heat);
  • Internal combustion engine producing above 44 kilowatts (power);
  • Oil-filled transformer or switchgear over 250 litres of oil and voltage above 1000 volts;

Flammable or combustible solids, liquids or gas manufactured, treated, handled or stored in quantities likely to constitute a fire hazard including any of the following:
i.    Fuel oil, diesel or petroleum;
ii.    Nitrate film or celluloid;
iii.   Cellulose or flammable liquid spraying

Substations and transformers – The basic considerations

Saturday, June 13th, 2009

The location of a site sub-station needs to be carefully considered, the key factors being:

Proximity to the heaviest loads
Equipment with heavy loads is generally grouped together into what is termed a load centre, and ideally the sub-station should be located as close as possible to the load centre. This avoids the need for lengthy runs of low voltage cable which is relatively expensive and can cause a degree of power loss under heavy loads. Large installations may have several load centres located at different points around the building and may consequently require multiple sub-stations.

Supplier access:
The supplier must have easy access to their high voltage switchgear. This can either be located in the same area as consumer’s switchgear or alternatively in a separate switch room.

Transformer type:
There are a variety of different types of transformers that can be used, all of which fall into two basic categories: liquid-filled and dry type.

Liquid filled transformers:

Key points:

  • Mineral oil transformers are relatively cheap but present a slight fire risk
  • Liquid-filled transformers are generally more energy efficient than dry transformers


  • Mineral oil transformers generally need to be located outside due to the fire risk
  • Internally located mineral oil transformers may require automatic fire extinguishers and a purpose built soak-away to deal with any oil spillages
  • Synthetic ester filled transformers provide a non-flammable alternative but cost approximately 30% more than the mineral oil option

Dry transformers:

Key points:

  • Available with high grade insulation that renders them fire resistant enabling them to be used in locations where an oil-filled transformer may not be suitable
  • Transformer performance can be boosted by using mechanical ventilation to enhance cooling
  • Limitations:

    • More expensive than oil-filled transformers, especially the cast resin type
    • Dry transformers tend to be significantly heavier and larger than oil-filled transformers, which can be a problem where space is restricted
    • At low to medium loads, dry type transformers tend to be less efficient, which results in more electrical energy being converted to heat and lost to the atmosphere. This wasted energy must be paid for by the consumer and represents a significant operating cost

    High voltage distribution:
    In many buildings such as offices, a single sub-station is often all that is required to supply the low voltage distribution system. In such cases, the incoming high voltage supply and substation can be located in a single area and that will be the extent of the high voltage system.

    Larger commercial buildings and industrial applications may have several load centres and will require a high voltage distribution system to serve multiple sub-stations. There are two systems which can be used, each of which has advantages and disadvantages. These systems are:

    • Ring main

    The high voltage distribution circuit is arranged in the form of a ring which starts and finishes at the high voltage intake. The load centres are connected at convenient points around the ring main. The benefit of this system is that each load centre effectively has a high voltage supply from either side of the ring main, so if a fault occurs with one of the supplies, the load centre can still operate.

    • Radial feeder

    In a radial feeder system each load centre is fed separately from the consumer’s main high voltage switchboard. The main benefit of this system is that a fault in the supply to one of the load centres should not affect the others.