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Micrologic or TM-D

Tom OB

Hi all,

Currently speccing an LV system for a school and cannot justify the extra cost of using a Micrologic system (included in a previous design specification) rather than regular Thermal-Magnetic breaking.

Would anybody be able to shine a light on the main operational differences and how I could justify the extra cost to a client? If not I will de-spec to TM-D

Thanks!

Tom

  • 0

    The TM-D breaker is only adjustable for overload currents, whereas the Micrologic breaker has time/current adjustment for short circuit protection. It is often only possible to achieve selectivity by using the short time adjustments available on the Micrologic device. Only a calculation of your system will prove this of course, and if you are not in a position to calculate it and prove compliance with a TM-D at present, then I'd specify Micrologic. 

    regards, burn

  • 0 in reply to burn

    Micrologic is designed to overcome a particular selectivity problem in large installations, where MCCBs or MCBs are specified throughout. They are comparatively expensive and need a good reason to choose. Using BS88s on submains etc, is generally cheaper, but you will still need a selectivity study on your design if selectivity is required to be perfect. All this is part of the design process, you should not try to control the designer too much!

  • 0

    How many tiers of fuse or MCCB, MCB does the design need between substation and light switch ?  This will determine the 'finesse' of the discrimination/selectivity needed.

    sometimes less is more ;-)

    Mike.

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