Guides

Transformers and fuses

Due to the megnetizing current which is released when starting up a transformer the following should be observed when choosing fuses and connecting the transformers.

The total resistance in an installation is the product of:

• The line-voltage and it's stiffness
• Choice of type of fuse
• The resistance in the leads of the installation
• The resistance in the fuses
• The resistance in the primary side of the transformer

and all these factors thus limits the start-up current.

The following points should be observed in this connection.

• Diazed/Neozedfuses (slow) should be chosen (or fuses with the same release-characteristics)
• Automatic fuses with B- or C-characteristics should not be chosen, use preferably fuses with D-characteristic
• As long common lead as possible up to a group of transformers (For an estimation of the resistance-values in installation cables, see Guides, Resistancetable)
• For the connecting mode on-off-on at least 1250 ohm is required in order to connect a power of 2300 VA to a 10 A installation fuse. Please observe that this figure includes the marked power of the transformer and the power-loss. This means that for practical use it is feasable to connect 6 pcs of 300 VA transformers to one 10 A installation fuse if the resistance is 1250 Ohm (It is not always practical to calculate exactly the resistance value, therefore it is wise to have a marginal, for instance max 4 pcs. of 300 VA transformers to one 10 A installation fuse of Diazed/Neozed type)