Ocp 25mm singles

graham123 · Jun 27, 2015

100a tp mccb in main panel. 25mm singles suppying a db next to main panel. Length of the singles is less than a metre. Cables are in metalic trunking. Ccc of 25mm singles in trunking is 89a. This has only been installed 5 years ago. A C2 has been given on an eicr. I myself cannot see a problem because of the length of the singles. anybody else come across anything like this.

malcolmsanford · Jun 27, 2015

Graham there is every chance as you say of there ever being a problem with the installation.

I think though you are refering to the 3 metre rule in association with Reg 434.2.1 which is for fault protection and not overload

The EICR is flagging up overload and rightly it does not conform to section 433 and reg 433.1.1.

baldsparkies · Jun 27, 2015

Its an MCCB More details regarding the overload device.
Time current characteristics, is it adjustable, how is it calibrated, what if any is its current limiting range.
What type of insulation is used on those cables and what are the operating temperatures.
How will those temperatures affect the disconnection times in relation to the operating temp of the MCCB and any heat transfer that may occur.
There could be more scope with those singles and its relationship with the device protecting them !!
The code 2 may or may not be justified, but with all the above taken into account the circuit could have been designed and calibrated for compliance.

Darkwood · Jun 27, 2015

Check also the MCCB has not been derated, it is common for MCCB's to come with a adjustment dial.

Are the cables tri-rated?

Does the total value of OCPD's in the submain if full with no spare ways limit the actual current that could flow through the singles meaning the overload protection isn't required up front off the cables as the design of the install ensures the singles cannot be overloads.

If diversity has been used to calculate load and this is why the singles may be smaller then this on its own is wrong as you should not design systems with undersized cabling because diversity has been used the cables should be protected for times of higher demands where they may be subject to overload.