The following diagram shows fuses off each of the PT connections (standard IEC fuse symbol) but it also shows a fuse symbol with inverted colouring on the neutral connection.
This second fuse also looks like the IEC fuse but what is the reasoning for the colour inversion? Is there a special neutral fuse that no one has told me about?
More info:
- GE 869 Motor Protection Relay
- Schematic is from this manual. PDF page 42, manual page 2-8.
- PTs connected in wye configuration (shown above)
- PTs and fuses are external (i.e. not included) to the motor protection relay.
Best Answer
That is the symbol for a "dummy fuse" used in a disconnecting fuse holder for the PTs. Like these:
When a circuit is grounded (i.e. the "Neutral" in this case), you cannot have a fuse in it, but because this is for a meter, you want to use disconnecting style fuse holders so that the PT can be easily isolated for testing. So to avoid having the fuse in there to make it work, you use a "Neutral Dummy Fuse", like this: