A useful rule of thumb is to allow for a temperature rise from 20 degrees to 70 degrees by multiplying the listed value by 0. In other words – in the final distribution electrical switchboards of buildings in which the nominal current does not exceed 125A. Alternatively, the maximum Z s value can calculated using the time- current characteristic of the MCCB being used, as shown in Fig. An MCCB with a rated current value (I n) of 32 A is connected to a circuit forming part of a TN supply system which has a U 0 value of 230 V.

Usually, these circuit breakers are sold by electrical retailers: they are simple to install, safe, and easy to use even after many years without maintenance. These certified CBs are intended for indoor use, and under pollution and humidity-free conditions: households or similar installations where overcurrent protection will not likely be maintained by unskilled users.

But having looked at the fuse curve characteristics in the BS7671 - P199, the Graph straight lines from 0.

Any installer who plans to substitute a different cb must obtain authority from the assembly manufacturer to do so in compliance with Regulation 536. k it could be because the house was very old and damp when we started wiring or should i change the RCD. The maximum earth fault loop impedance values (Z s) in BS 7671 – or the equivalent tables in the IET On-Site-Guide (OSG) and IET Guidance Note 3 Inspection and Testing (GN 3) – are essential references when carrying out Z s tests.

I would also suggest that if your U0 is not subject to the +10% tolerance then disconnection times as per Table 41. Circuit-breakers for overcurrent protection for household and similar installations Circuit-breakers for a. The NICEIC just say refer to manufacturer, but I cant find the information for 60947-3 mcb’s starting from 2A and also for a lot of the motor starters GV2,3 etc etc. Although cbs from different manufacturers may appear similar, the technical performance, dimensions and terminations are not always compatible. Infrequent switching of cbs on load is admissible for the purposes of isolation or emergency switching.

The most suitable solution is for MCBs that are certified by both IEC standards since their performance meets requirements for use in residential installations and is high enough for use in industry and infrastructure applications. Dear Sahad, it is normal having MCCB certified as per 947 in commercial/small commercial buildings with MCB’s certified as per 898. When contractors wish to make additions to circuits protected by BS3871 circuit breakers, or are carrying out a periodic inspection and test of an existing installation, they will need to verify that the measured value of earth loop impedance will permit ADS. It is convenient when the performance of a cb meets the requirements of both standards and is therefore suitable for residential, industrial and commercial installations. The ‘Stablok’ circuit breakers, manufactured by Federal Electric Type, are indicated by the colour of the operating handle; white for Type 1, green for Type 2, orange for Type 3 and black for Type 4.

The earth fault loop path from which the earth fault loop impedance (Z s) is derived in shown in Fig. The table is based on nominal rather than actual voltage - 230V nominal is usually taken to be anything within the -6% to +10% range - i. A cb designed for Pollution Level 2 conditions would not be suitable for harsh outdoor or humid applications that require Pollution Level 3. If you want to claim you've got a higher nominal voltage than 230 V, and hence can use higher loop impedance values, then some appliance manufacturers would be within their rights not to guarantee their equipment if it fails in your installation.

The rated voltage currently required in industrial use CBs is 400 V, 440 V, 690 volts, or higher values up to 1000 V. But it is not really a sudden step in risk between 230v and 231, more of a gentle rise in risk from quite safe at about 50V to really very bad for you by perhaps 1500V , from which 2 handy values have been converted into safe times for the table. The concept behind it evolved in the 1970s-80s when it was a single standard for all low-voltage switchgear. That notion, combined with a lack of knowledge or technical expertise, may have led to the misconception that there is only one standard for all CBs.RCD as a term used without any further additional information would revert to the most commonly used general purpose version when quoting tripping times.