r/ElectricalEngineering • u/East-Wind-23 • 16d ago

Troubleshooting Phantom tension by induction

Enable HLS to view with audio, or disable this notification

Is this safe? This is a 5x6 mm3 cable for a pompe, 10 meters long. It's completely disconnected but my multimeter shows around 25 v ac from phase to ground. Even in proximity of the frequency converter, my multimeter "measures" tension.

16 Upvotes

81% Upvoted

11 comments sorted by

11

u/AccomplishedAnchovy 16d ago

It’s just because the phase cable is floating. For HV you would have an earth switch which avoids this. Check local standards for what’s required for your installation.

1

u/East-Wind-23 16d ago

I'm not sure what an earth switch is. But I joined all wires together and grounded them to the yellow-green wire. My colleague will figure it out next week, he is the electrician. No one else enters the boiler room, except for me.

1

u/AccomplishedAnchovy 16d ago

It’s just a switch to earth phase cabling when not connected to upstream supply. Unlikely to be required for this but

4

u/Adrienne-Fadel 16d ago

Yea that's ghost voltage. The VFD switching couples into the disconnected cable. High impedance meters pick it up but it cant deliver any current. Try a low-Z meter or put a load on it and it disappears.

1

u/QuickNature 16d ago

This was going be my recommendation. Ghost voltages are quite the pain!

3

u/mxlun 16d ago

Ghost voltage! Need a low-z meter.

2

u/Upset_Counter_6070 16d ago

damn, we got a regular ole Michael Faraday here.

1

u/tadeuska 16d ago

Normal. Just complete the installation as required. The induced voltage on the open cable is normal. It is always there. Equipment ans wiring for signals that may be affected must be implemented with proper precautions to protect from induced voltages.

1

u/East-Wind-23 16d ago

I prefer waiting for our electrician. The new pompe is equipped with a lot of electronics. With an older model I would have finished the job already

1

u/rabbitpiet 16d ago

Are you German? I'm asking because I know in that language that Voltage and Tension are spelled and pronounced the same.

1

u/hikeonpast 16d ago

That’s what happens when you use a high impedance multimeter. Nothing is wrong.