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I'm trying to replace the wires from the boom to connectors that go into the wiring harness and into the ground. The existing wire is 13 mm with a 2000 volt rating and the replacement my boss ordered is 8 mm, rated at 600 volts. I'm concerned that the new wire may be too small. I'm afraid of overloading it and arcing. He says it will work but I don't think so.

Something like this, I suspect:

material handling crane with magnet

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    The insulation voltage rating needs to be enough for the volts the machine actually uses. The mm cross-section needs to be enough for the amps the machine actually uses. Who knows, the old cable might have been oversize because they used what they had in-stock.
    – Harper
    Commented Dec 29, 2016 at 18:51
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    While I'm not sure this is a great fit for Mech.SE, before anyone gets hostile with it, I told DIY.SE to send it over after they asked. It's probably about the only SE where this could fit. Let's give it a chance to get answered before we decided to do something else with it, please.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Dec 29, 2016 at 20:52
  • Is this about a material handling crane with an electro-magnet instead of a hook for picking up metal objects? Are the wires going from the boom (instead of 'bom')? Also, what is the load (current and voltage) that the wires are supposed to carry?
    – dlu
    Commented Dec 29, 2016 at 23:00

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Assuming that this is for a material handling magnet on a crane of some sort, I have a few observations based on working on locomotive cranes with large magnets used for handling scrap metal:

  • 600 V insulation is likely to be fine. 2,000 V is a lot of voltage and it would be very unusual to find that anywhere where untrained people are likely to be able to get close to it. The old wire was probably either DLO (diesel locomotive cable) or Type W mining cable. The new wire is probably welding cable or maybe finely stranded UL Style 1284.

  • If the conductor (the copper part, not including the insulation) is 8 mm in diameter it is roughly equivalent to 1/0 AWG wire and will carry about 245 Amps, a 13 mm conductor is roughly 4/0 AWG with an ampacity of 380 Amps. That's a big difference, so it would be good to check the magnet for markings or trace the wire back to the source in the crane and see how the controller is rated / fused.

  • The wires supplying a magnet are subjected to very rough service and larger wires may be used just for their mechanical strength even if the size is not needed for the current to be carried. We used welding lead wire which has lots of small strands which made it very flexible and less likely to be broken by the flexing it encountered connecting a swinging magnet to the crane.

  • The wire run is likely to be pretty long (at least twice the length of the boom of the crane) so the size of the wire may have increased to manage the voltage drop due to the resistance of the wire. If you're running over 100' (~30 meters) then you probably want to step the wire up one size (e.g., if you need 1/0 for current carrying capacity, you'd go to 2/0 to manage the voltage drop).

Without knowing the details of the crane and magnet it is hard to be more specific, but hopefully this will help you to evaluate the situation and decide if the new cable is adequate.

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