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?

Inverted fuses schematic

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.
  • 1
    \$\begingroup\$ Perhaps they are actually physically different colors? \$\endgroup\$ – Justin Jul 30 '19 at 21:01
  • 1
    \$\begingroup\$ Maybe a shorting link that is part of the distribution panel construction. \$\endgroup\$ – Spehro Pefhany Jul 30 '19 at 22:18
  • \$\begingroup\$ How are the fuseholders constructed, anyway? \$\endgroup\$ – ThreePhaseEel Jul 30 '19 at 23:38
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    \$\begingroup\$ it seems to be connected to the neutral wire. maybe that's significant. \$\endgroup\$ – Jasen Jul 31 '19 at 0:34
  • \$\begingroup\$ @SpehroPefhany -- I was thinking that too. Shorting link or maybe a dummy fuse. I just couldn't find any schematic symbols online to prove it. \$\endgroup\$ – C. Lange Jul 31 '19 at 1:09

That is the symbol for a "dummy fuse" used in a disconnecting fuse holder for the PTs. Like these:

enter image description here

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:

enter image description here


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