How to...install a three-phase distribution board

Installing a three-phase distribution board is both a technical challenge and a big responsibility. Mike Lawrence of Havells sets out the key steps so you’ll get it right first time.

Step #1

As with most distribution boards the location will be determined by the incoming supply. However, when fixing it to the wall don’t forget to use your spirit level. As Part L2 of building regulations becoming an increasingly important factor in electrical installation, this board has a fully wired integral meter.

Step #2

Once on the wall, you can populate the unit with your outgoing devices. Make sure each MCB/RCBO is sitting on the PAN assembly correctly, ensuring that the bus bar stubs are correctly inserted into the box clamp of the device and tighten correctly. Fit full form blanks to any unused outgoing ways to ensure maximum IP protection.

Step #3

When connecting three phase incoming supply cables (if you’re using brown cable) you will need to label the incoming cables as above; brown, black, grey from L-R, ensuring that this can be clearly seen. Use the free cable interface kit to mark the trunking and cut outside of the marked line to ensure protection against sharp edges once the interface kit has been fitted.

Step #4

Make sure when you connect up the incoming neutral the ‘connecting link’ is dropped out and not reconnected until you are ready to switch on. Alternatively a 4 pole device can be used to switch the neutral when switching the phases.

Step #5

Always make sure that your cables are nicely dressed and secured with cable ties. Ensure that the radius bend is neat and that there are no sharp kinks or bends in the cables. You’ll note here that it’s only the three poles, neutral and earth of this individual circuit that are joined together. This makes things easier for identifying and testing individual circuits.

Step #6

Complete all testing as per the requirements of BS7671 ensuring that all dead tests are carried out prior to energizing. If you are using an integral meter distribution board, remember to open the blade fuses before carrying out insulation resistance tests, this will ensure that the meter is not affected. Before energizing the board, ensure that the main Neutral link is reconnected and connect the blade fuses and neutral to the integrated energy meter.

Step #7

Depending on the location (or client requirement) you may need to lock the door for security. A door barrel lock can be easily fitted to this board by removing the plastic door knob and replacing it with a barrel lock accessory.

Step #8

Once all live tests have been correctly carried out, ensure that all circuits are easily identifiable. Ensure that you have a schedule of circuits attached to the inner side of the door, and that all test certificates and user documentation is handed to the customer. Also make sure to use an appropriate label to indicate ‘date tested’ and ‘next test required’.

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