1
\$\begingroup\$

I have a three cable circuit in the kitchen1, I know that one is live, one neutral and one is ground. However, there is no colour2 matching between the standard and the real cables, so I can't use the usual easy way, furthermore, from my brief research on the topic I've found that:

"...Typically Neutral is connected to earth ground at some point, usually at the breaker box. This pretty much makes earth and neutral very close in voltage. And Hot is always 220V (or the nominal line voltage) measured with reference to Neutral (and earth for that matter)..."

thus, a voltmeter would measure the same values between "hot" and neutral , and "hot" and ground.

How to figure out which is ground and which is neutral?


1. EU - Greece - 220V, 50Hz

2. Real cables colours: grey, brown, white.

\$\endgroup\$
  • 2
    \$\begingroup\$ You might want to fix the complete wiring to adhere to code (unless in your country code doesn't include wire colouring). Anyways usually neutral is a bit above GND when appliances nearby are operating. \$\endgroup\$ – PlasmaHH Oct 10 '16 at 9:24
  • 1
    \$\begingroup\$ Consult a qualified electrician, since you obviously don't know what you are doing and a mistake could prove very dangerous. \$\endgroup\$ – Leon Heller Oct 10 '16 at 9:25
  • 1
    \$\begingroup\$ @PlasmaHH It is a relatively old apartment. OK, so if I turn on an appliance nearby the neutral should change value, right? \$\endgroup\$ – Ziezi Oct 10 '16 at 9:26
  • 1
    \$\begingroup\$ Open up another socket or appliance and see how its wired, then copy that. \$\endgroup\$ – Steve G Oct 10 '16 at 9:36
  • \$\begingroup\$ @LeonHeller You were probably right, but everything worked beautifully. \$\endgroup\$ – Ziezi Oct 11 '16 at 16:25
4
\$\begingroup\$

If you have proper protection in your house, connecting a small load (e.g. a light bulb) between earth and live will trip the circuit breaker, while a load placed between live and neutral will stay powered.

If the load stays powered no matter which wire you pick, then the wiring in your apartment is really screwed, to the point your insurance company may decline your claim in case of electricity-related accident.

\$\endgroup\$
  • \$\begingroup\$ So, earth has lower resistance and will cause large current, right? \$\endgroup\$ – Ziezi Oct 10 '16 at 9:59
  • 4
    \$\begingroup\$ No, there is a special device that checks that current on live and neutral are equal -- that's why the answer is qualified with "if you have proper protection". \$\endgroup\$ – Simon Richter Oct 10 '16 at 10:02
  • \$\begingroup\$ OK, I understand. \$\endgroup\$ – Ziezi Oct 10 '16 at 10:05
  • 2
    \$\begingroup\$ After cross checking using a light bulb I confirmed what I've already knew, additionally the power went off when I connected phase with ground, so everything seems to be in order. Thanks, for the answer! \$\endgroup\$ – Ziezi Oct 10 '16 at 17:27
  • \$\begingroup\$ GFCIs/RCDs have only been required to be installed relatively recently (the last 20-ish years), and it is perfectly reasonable to expect a place not to have it. \$\endgroup\$ – Someone Somewhere Apr 14 at 10:56
0
\$\begingroup\$

After a brief experimentation with the voltmeter, three measurements are needed to determine ground, neutral and phase:

  1. Voltage between phase and any of the other two should be around 220V.
  2. Voltage between neutral and ground should be 0V. (determine phase)
    3. After shutting down supply, the lowest Resistance between phase and the rest of the two determines the ground.
    3. Connect a heavy load to generate enough voltage drop and determine the neutral, which will be less. In other words, when you plug in another device the voltage between phase and neutral will be less than the voltage if the same device is not plugged.

Following the above, in my case, grey = neutral, brown = phase, white (yellowish (old)) = ground.

\$\endgroup\$
  • 1
    \$\begingroup\$ Not sure whether your method actually works. When you shut down the power, both live and neutral must be cut off, so the resistance between both of them and ground should be "infinite". \$\endgroup\$ – Dmitry Grigoryev Oct 10 '16 at 10:10
  • \$\begingroup\$ @DmitryGrigoryev You are right, it shows 1. \$\endgroup\$ – Ziezi Oct 10 '16 at 10:16
  • 1
    \$\begingroup\$ This is not a definitive test, be careful. If you do as suggested in a comment above and load a different KNOWN GOOD socket and then measure voltages between the live (found using test 1 or 2) and the two others you should see slight reduction of voltage between live and neutral and less reduction between live and earth. The difference may be slight enough that it could be misinterpreted. If the RCCI test works that will be much safer. Local reputable electrician will know what to do. \$\endgroup\$ – KalleMP Nov 27 '16 at 16:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.