I'm looking at a schematics of a power system, and encountered some schematics I find quite strange.

As you can see, the schematic contains a lot of bent lines. I have two hypothesis:

  1. It indicates jumpers, see this question.
  2. It indicates fuses

As you can see, the horizontal line in the bottom is labeled "30m Cross Over Jumper Spectron 10". This of course, strengthens hypothesis 1. I think it also makes sense, seeing there are connectors you can connect/disconnect. However, I don't see why you would need three of them for just one single branch. Also, the system is subsea, I don't know if you can use jumpers the same way you do in "normal" systems.

I think it looks similar to common symbols for fuses, but again, I don't see why there should be so many. (And fuses on the bottom of the ocean doesn't seem like a particularly good idea).

Additional information:

  • The distances are small (from the red arrow and down, the schematic has been updated. Above the red arrow, the cables may be long). The transformer is very close to the load (compressors).
  • The horizontal cable at the bottom goes to an identical parallel setup (100kVA transformer, 36.5 kW load etc.).
  • The entire system is subsea.
  • The power umbilical is several km


Here's a more complete schematic.

enter image description here

Does anyone know what the symbol means?

  • 3
    \$\begingroup\$ My experience suggests that sort of thing would indicate some arbitrary length of cable, as in "it could be 10mm, it could be 1000m, don't assume" \$\endgroup\$
    – John U
    Commented Feb 27, 2014 at 12:50
  • \$\begingroup\$ That was my first thought too @JohnU, but the horizontal one is labeled 30m, and the other ones are short (true, I don't know the exact length, but it shouldn't be many meters). From an electrical point of view, such a short cable won't have much influence. \$\endgroup\$ Commented Feb 27, 2014 at 13:12
  • 1
    \$\begingroup\$ Again, from my experience, that sort of symbol would indicate "some" quantity of cable, typically external to the device, EG a cable between two different units / PCB's, a transmission line, etc., could be 5mm, could be 5km. \$\endgroup\$
    – John U
    Commented Feb 27, 2014 at 14:01

5 Answers 5


It's a flexible connection of some kind. In this drawing, it is likely to represent a trailing or reeling cable (I will explain this a bit more below.)

Supporting my claim - from AS1102.3 Graphical symbols for electrotechnical documentation - Part 103: Conductors and connecting devices, we have:

enter image description here

Note AS1102 is based on IEC 617 Graphical symbols for diagrams.

Contrast the symbol for a jumper ("connecting link"), also from AS1102.3, and a fuse, from AS1102.7.

enter image description here enter image description here

What's a trailing cable?

A trailing or reeling cable is used to power mobile equipment, i.e. a mobile drilling rig, or mobile substation.

In this application, I think the 'sub-sea' transformer is in some kind of waterproof container, connected to the surface supply by trailing cables. Flexibility is required for the transformer to be moved around, or to move with the water currents.

Note that trailing cables are a special breed, not like regular cables. See Olex catalogue for trailing and reeling cables. Generally these cables are much more flexible than normal cables, are designed to withstand cars running over them, etc. There are also special protection features to detect if the cable has been damaged - these aren't required for normal cables which spend most of their life living in a protected environment, i.e. conduits.


It means you have to twist the cable to make it work :-)

Just kidding, how about it only indicates an arbitrary length of cable ? Then there may indeed be a notion of "twistability", i.e. the cable does not have a fixed position.

The reason for the many cables is the different types of connectors used, necessitated by the water element.

  • \$\begingroup\$ Could be a possibility, but then again, the horizontal one is labeled 30m. \$\endgroup\$ Commented Feb 27, 2014 at 10:36
  • \$\begingroup\$ @RobertP I'm sure one of the more experienced contributors will have a more definitive answer. \$\endgroup\$
    – FredP
    Commented Feb 27, 2014 at 10:52
  • \$\begingroup\$ Thanks for your input Fred! I updated the schematic, I don't know if it helps =) \$\endgroup\$ Commented Feb 27, 2014 at 15:43

Given that the star-delta (\$Y-\Delta\$) transformer is connected on slip rings, some amount of rotation will be expected and as a half-guess I'd say the symbol might imply that the cable could be expected to be twisted (due to the turret rotating).

  • \$\begingroup\$ I believe it means flexible cable / connection gallery.proficad.com/Symbols/electrical-installations/… see flexible connection \$\endgroup\$
    – Spoon
    Commented Feb 27, 2014 at 13:04
  • \$\begingroup\$ Thanks for answering Andy! The slip rings referred to in the schematics (the circle) are further up in the system. Do you know if "wet mate connectors" act like slip rings (i.e. you can spin the cable around)? The twisting part makes sense for the transformer feeder, since the cable is 30km long. Do you think this explanation holds on the secondary side too? I don't know the exact length, but it shouldn't be more than a few meters (except for the 30 meter one). \$\endgroup\$ Commented Feb 27, 2014 at 13:09
  • \$\begingroup\$ @RobertP. Maybe more data about the diagram would help resolve these extra questions. I believe wet-mate connectors probably can be joined in the presence of water yet are able to stop the water affecting the connection. \$\endgroup\$
    – Andy aka
    Commented Feb 27, 2014 at 14:42
  • \$\begingroup\$ @Andyaka: Thanks for your input! I have updated the question with a more complete schematic. I hope it helps =) \$\endgroup\$ Commented Feb 27, 2014 at 15:37
  • \$\begingroup\$ Simple questions.... what is it? What is the underwater thing? What's above water feeding it? \$\endgroup\$
    – Andy aka
    Commented Feb 27, 2014 at 16:02

I think you can rule out the fuse idea, the fuse symbol is more of a laid down "S", this is too steep a curve to be a fuse. It doesn't seem to be any valid symbol but I would suggest it means either flexible, indeterminate or long length. It is similar to the AC signal symbol but again the curves are a bit steep for that.


In technical drawings if I remember correctly it is called a foreshortening line indicating something longer than the scale of the drawing can represent. In an electrical drawing a length of wiring or cabling of a specified of variable length. The symbol is also used in architectural and plumbing drawings as well.


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