Note 1 Rating of main and subsidiary taps.

Where the rating of main taps is shown as xxx/yyy –

• The lower rating (yyy) of the main secondary tap is used if the 135V tap is loaded with its rated load.
• The higher rating (xxx) may be used on the main tap if the 135V tap is not used.
• The available rating on the main tap is xxx-yyy if part load is used on the 135V tap

NT6650 intermittent rating is for direct driving of points machines. Refer to NT66XX 3.1.1 for points machine type and load conditions.

Note 2 Max fuse rating on secondary.

The Output fuse rating in table 1 is for close short circuit protection only.
Refer to the product data sheet for application data on load fuse clearance (NT66XX table 4.1.1 note 2).
The two fuse values specified are the respective values for a winding providing 110V and 135V. e.g. for NT6610 the 110V fuse maximum size is
15A and the 135V tap fuse size tap is 2A. For NT6600 the 110V fuse maximum size is 5A and the 135V tap fuse size tap is 2A.
Where the load is completely within a suite of location cases there should be no fuse between the 110V winding and the 110V busbar.
Each outgoing way on the busbar should be fused for the individual load, often 3A or 1A.

Note 3

BS88 fuses are used above 15A rating or above 250V. BS1361 or BS88 fuses are used on 230V 110V fuse range is Littlefuse 326.XXX range up to 15A.

Note 4

50V d.c. output is full wave rectified unsmoothed is expressed as “mean d.c.”

• The rating is expressed as VA where 1VA = 1 Watt at nominal voltage.
• Where an external smoothing capacitor is fitted to a 50V d.c. output the smoothed voltage will be approximately 70V depending on the design of the smoothing circuit.
• Where external smoothing circuits are used the rating of the d.c. output will be reduced by 50%, e.g. a 150V winding will be rated at 75 VA for smoothed d.c.

Note 5

The total power drawn from all windings simultaneously must not exceed the total power capability of the transformer (Total VA) e.g. NT6110 can supply up to 400VA on the 110V a.c. output and up to 200VA on the 50V d.c. output.

• However Total load on NT6610 must not exceed 500VA.
• Thus NT6610 capacity -
  • 300VA at 110V can be supplied at the same time as 200VA at 50V
  • OR
  • 400VA at 110V can be supplied at the same time as 100VA at 50V.

The outputs of multiple windings should not be connected in parallel as this will cause circulating currents that will change the thermal performance of the transformer and potentially affect reliability. NT6612, NT6623 or NT6661 should be specified if a larger single load is required than available from the multiple winding transformers. It is recommended that loads greater than 3KVA are split and more than one transformer used.

Note 1 Max fuse rating on output

The fuse rating specified is for short circuit protection only. Refer note 2.
Short circuit protection must be provided by output fuses on individual points loads when more than one point machine is driven by any rectifier and always for NQ6640.
Individual points machines must be separately fused with Littlefuse 326.XXX < 15A or equivalent.
BS88 (S) semiconductor fuses (table 2 note 1) are not required if the fuse protecting the individual points machine (Littlefuse 326.XXX < 15A) is located in the same location case or REB as the transformer/rectifier.
BS88 part 4 – 1976, IEC 269 – 4 (semiconductor fuses) are required in the output if a single cable takes 120V d.c. outside the enclosure housing the transformer/rectifier for remote distribution using Littlefuse 326.XXX range up to 15A.
Short circuit protection may be provided by primary fuses on NQ6620 and NQ6621 if only one points machine is driven. In this case 120V secondary fuse need not be fitted.
The loop impedance of the transformer/rectifier system, including the cables to the points machines shall be designed to allow more than 100A to flow in the event of a short circuit at the most remote points machine.

Note 2 Fuse type - Input

BS88 fuses are used for ratings above 15A or above 250V. BS1361 or BS88 fuses are used on 230V.