Add Split Circuits

Add a 1-Phase Split Circuit

Some might say a strange terminology to use, however, say you had a fuseway with 2 x circuits connected to it, which might be true for an over-populated board. Not ideal, but it does not mean that it is unsafe for continued use. The first circuit is from a single phase fuseway which has an item of equipment capable of causing an overload, wired in a 2.5m m 6242Y cable. The cable is covered with insulation material in a roof space and as such, cable is at risk of overload. The second circuit supplies a fire alarm which is wired in 1.5 mm mineral insulated cable clipped to the surface. The circuit is very long and suffers from high earth loop impedance. Here we have two completely different circuits wired from the same fuseway and as such, having requirements that are not the same.

  1. In the left tree right-click circuit 2L1, then select “New” -> “Split Circuit”.

    The “Create Split Circuits” dilaog will appear with the chosen circuit greyed out.

  1. The “Number of Legs” defaults to 2, if any more, enter the number of circuits “Legs”. Click OK to accept “2”.
Now you can see the circuit icon reflects the “split” status and the 2 x circuits 2L1a and 2L1b have been added.
As this is a “Split Circuit” there is no “Specification” or “Results” to enter. You do need however, to fill in the “Protective Device” details here, as this is common to both “split” circuits.
../../../_images/137_Split_circuit_staus_showing_nothing.jpg ../../../_images/138_Split_circuit_no_results_shown.jpg
  1. Select the “Protective Device” tab and fill in the details. We have chosen a BS 60898 / C MCB rated at 20 amps.
Now that the protective device details have been entered, you can see that as it is a “Split Circuit”, certain information will not be entered.
  1. Highlight the first “Split” circuit (2L1a) and enter the details. As you can see, we have chosen a 2.5 mm 6242Y cable which, for part of the route, is clipped direct, it is also for part of the route, above a ceiling covered by insulation in excess of 100 mm.
The “Installation Methods” have now recorded both current ratings for both methods of installation with 17 amps being the maximum allowable rating of the cable.
../../../_images/142_Split_circuit_1st_method_of_showing_cable_capacity.jpg ../../../_images/143_Split_circuit_protective_device_details.jpg
  1. Open the “Protective Device” tab and you can see that the protective details have been copied through from the “Split Circuit” details, with the “Edit” button greyed out. If you need to change the protective details, go back to the “Split Circuit” “Protective Device” tab and make the required changes. You can also see that the “Lowest Capacity Cable” has 17 amps recorded. This will offer the relevant overload automatic observation applied to this “leg” only when all data has been recorded and a “Compliance Check” is carried out. Now enter in the details for the second “split circuit” 2L1b. The current carrying capacity of the cable is rated at 23 amps, therefore, this “leg” will not be subject to an overload risk both in terms of the size of cable and the nature of the load.
Although the second “split circuit” has, as the “Lowest Capacity Cable” of 23 A, but the earth loop (1.2 Ω) exceeds the maximum “Allowable Zs” for the protective device (0.92 Ω). Again, this will offer the relevant earth loop automatic observation applied to this “Leg” only, when all data has been recorded and a “Compliance Check” is carried out.

Add a 3-Phase Split Circuit

We will now create a “split” 3-phase circuit. Initially we follow the same procedure as when creating a split single-phase circuit.

  1. In the left tree, right-click the first fuseway and select “New” -> “Split Circuit”.
  1. In “Number of Legs” enter the number of ways to split this circuit into.
  1. Repeat steps 1 and 2 above on fuseways 3L2 and 3L3. You can either enter the same number of “Legs”, or for example, if you had 2 x 3-phase circuits and a further single phase circuit fed from one of the fuseways (3L2) it will be listed as 3L2a, 3L2b and 3L2c.
The fuseway groupings in the left hand pane should now look like the screenshot below. If any of the fuseways are “shrunk”, open them up by using the “+” button.
  1. Select the first phase way 3L1 (Split Circuit) and enter the protective device details only.
  1. Repeat step 4 for fuseways 3L2 (Split Circuit) and 3L3 (Split Circuit).
You cannot copy and paste between the primary Split Circuits.

We now need to define the phaseway grouping of the first split circuit.

  1. In the left tree select the first leg of the first fuseway (3L1a), then in the “Specification” tab click “Other Fuseways”.

    The “Select Phaseways” dialog box opens.

  2. Hold down the Control key and click circuits 3L2a and 3L3a to select them, then click “Add”.

  1. Click OK and confirm that the “Other Fuseways” list is updated.
  2. Enter the circuit description and cable details. This circuit is wired in a 6.00 mm XLPE cable.
  1. Select the “Protective Device” tab and confirm that the protective device details reflect the fuse entered on the root of the split circuit. As with a single phase split circuit, the “Edit” button is greyed out.
  1. Select the “Results” tab and fill in the details.

That is the first “phase leg” finished. We now need to enter the cable specification and results for the other 2 “legs”.

  1. In the left tree, right-click the phase leg circuit completed above, then select “Copy Circuit”.
  1. In the left tree, hold down the Control button and click the two other “phase legs” (3L2a and 3L3a) to select them.
  2. Release the Control button, right-click on one of the selected circuits (3L2a or 3L3a), then select “Paste Circuit”.
The first finished 3-phase circuit should now look like below.

We now need to supply a switch fuse off the second 3-phase “legs”.

  1. Create the switch fuse off the first of the second group of “legs” by “right” clicking on 3L1b and choosing switch fuse. When we have filled in the details consisting of the supply cable and test results (the protective device details are already entered) copy 3L1b.
  1. Now paste the copy of 3L1b to fuseways 3L2b and 3L3b.
  1. Now go to Switch Fuse 1/2L1/3L1b “Board Fed From” and then “Select”.
  2. High-light the relevant circuits (3L2b and 3L3b) and “Add”.
  1. Verify that the “Board Fed From” details are correct and carry on entering the remaining details and results.

➲ Next: Reset a Circuit.