Pre-assembled circuit breaker boxes save big money

Edited by the Engineeringtalk editorial team Jul 22, 2002

Spelsberg UK has rationalised the purchasing and assembly of components used in a new outdoor power supply unit used to power mobile phone network masts.

Spelsberg UK has rationalised the purchasing and assembly of components used in a new outdoor power supply unit used to power mobile phone network masts.

By supplying its outdoor rated EK polycarbonate junction box ready fitted with busbar, circuit breakers and cable glands, Spelsberg has reduced the overall cost of the circuit protection element in the worldwide project by around GBP 0.5 million.

At the start of the project the installation design team was initially searching for a robust enclosure with a high IP rating that could be adapted to mould-in the cable glands.

When the team approached Spelsberg for an initial quote, the company's IP65 rated TK Series polycarbonate enclosures suited the task perfectly, providing DIN rail mounts, tough physical protection, plenty of wiring space and the facility to make cable entries anywhere on the enclosure.

The TK enclosures also incorporate hinged viewing windows with integral seals providing ingress protection while allowing for physical checks on circuit breakers and resetting to be carried out without having to open a live enclosure.

The major cost benefits were achieved through the in-house custom modification and assembly service provided by Spelsberg, coupled with the supply and fitting of Spelsberg's MCB and RCB circuit breakers.

The combination of bespoke building, including the drilling and fitting of cable glands and the new circuit breakers saved an estimated GBP 0.5 million from original cost estimates.

The estimates had included separate suppliers for the enclosures, accessories, breakers, modification and assembly work, whereas Spelsberg was able to offer all these in-house.

A spokesman commented: "Having designed the power supply units, we then subcontract the building work to three companies, Spelsberg's service has not only reduced the estimated cost of the project but has helped us to ensure build consistency between the design plans and the final product by supplying the same complete circuit breaker unit to each panel builder".

There are two enclosures used in each power supply unit, an EK08 fitted with four two-pole miniature circuit breakers (MCBs) which has been modified to incorporate twelve high ingress protection cable glands at the rear of the enclosure.

The second is an EK012 enclosure containing four MCBs, a residual current circuit breaker and terminal blocks.

This enclosure also incorporates flexible membranes on the back and side for instant push-through cable entries.

In addition to supplying a very high-speed disconnection time thanks to an innovative bimetallic snap disc, the Spelsberg supplied circuit breakers also became a preferred option because of the precise width tolerance of the units.

Crossconnection links are used in the wiring of the boxes and when a previous suppliers units were installed, wiring became awkward because the terminal connections did not line up towards the end of a row.

Breakers are installed flush against each other for stability and the width tolerance is therefore crucial for fast, efficient and safe fitting in the field.

Spelsberg's circuit breakers also offer the additional benefit of accepting a maximum diameter cable into every breaker while still maintaining the option for a cross connection link to be easily fitted and remain fully insulated.

This is a significant bonus for the designers, who have the safety of maintenance personnel working in every part of the globe to consider.

The power supply unit has been developed as an international standard and is now in use in China, Brazil and throughout Europe.

(This was Engineeringtalk's Top Story on 19 July 2002).