We have a tipical fuse box, fuses and neutral wires connected to a neutral bar.

Let's say we have a closed circuit with a light bulb attached to it.

The bulb is working. The neutral wire is connected to the neutral bar in the fuse box.

Other neutral wires are connected to the neutral bar.

In my opinion the other neutral wires have curent in them from the light bulb.

Are they safe to touch?

migrated from electronics.stackexchange.com Nov 11 '18 at 16:18

This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.

  • 1
    In theory, yes. In practice, never touch anything connected to the mains, whether live or neutral. There's too much risk to just assume that everything is wired correctly with no faults all the way back to the transformer. – Felthry Nov 11 '18 at 16:09
  • If everything is wired correctly then why would it be safe to touch? – Dragos Durlut Nov 11 '18 at 16:14
  • The neutral wire is supposed to be connected to ground somewhere on the line. However it is not safe to assume that this is true, because there's too much at risk if it happens not to be. – Felthry Nov 11 '18 at 16:15
  • Because the neutral bar is bonded directly to ground at that point -- or at least, it's supposed to be. YMMV. Note that this is NOT true of any sub-panel, where neutral and ground are kept strictly separated. – Dave Tweed Nov 11 '18 at 16:15

If and only if everything is working

For a theoretical panel, neutral is theoretically safe to touch if:

  • the panel is wired to modern spec
  • the panel is wired correctly
  • workmanship is all proper
  • no wire/hardware failures (note: this is a different thing than "wired correctly")
  • The supply transformer is isolating, and not leaking enough 9600V primary current to override the transformer's grounding rod (dirt isn't much of a conductor, that's why we don't just wrap it in insulation and call it wire)
  • you are not in the Philippines

But then, if all that was true, you wouldn't be opening up your panel, would you? :)

But yes. If things are in order, there will be a grounding electrode system going from ground rods, metal water pipe or Ufer tie-in to your basement's reinforcing rod, which establishes contact with earth proper. There will be one at the transformer tying to neutral, and one at each building's most main panel tying to ground.

Next, in every building the grounding electrode system will be bridged to the service-wide network of green, green/yellow or bare wire, or metal conduit, known as the equipment grounding conductor, or colloquially "ground" in the electrician's context, not to be confused with GND or Vss in electronics, which is why I steer out of my way to call this equipment safety ground. No current ever flows on this except during a fault condition.

Finally, one place in every service (i.e point fed by an electric meter, customer demarcation point, etc.), typically at the service point, has a neutral-ground equipotential bond. That has several jobs. Relevant to your question, it is to do exactly what you are concerned about: clamp neutral so it is near ground and cannot kill you. No current sgould flow on it because no current should be on ground, and transformers shouldn't leak.

By the way, the neutral-ground bond is a great place to put a clamp ammeter. Helps to wire your panel so that is easy.

In a residential setup, you optimistically have several houses sharing a transformer, and the transformer and each house's neutral-ground bonds are all wrestling neutral down to safe voltages. In an industrial setup, that is not the case, and I got a real eye-opener when a transformer's only neutral-ground was not actually attached.

I was working on a branch circuit, and to make sure the breaker was off, I brushed hot across the edge of the steel junction box. There was no blinding arc flash, but something else - the light changed subtly. Doing it again, the circuit powered back up, and a fluorescent light came on. How could that happen? If hot is grounded, neutral is -- I measured neutral-ground: 120V. Crossed wire, in my work!? No. I checked other circuits, it's the whole main panel. HMMM! Where's that coming from!? Well, after shutting off 1 circuit at a time, it finally extinguished. Turns out an unrelated circuit had a bolted hot-ground fault, which was bonding hot pole L1 to ground, for lack of a neutral-ground bond to argue the other way. Normally this would cause unlimited current in series from L1 via the breaker, L1 wire, fault, equipment safety ground, neutral-ground bond and back to neutral, and snap the breaker. As it was, it only flowed current when a second ground fault occurs, which I induced by flashing my circuit's hot to ground.

Neutral could have bitten me at any time, why didn't it? I like to credit good practices: I treat neutral and other ”known”-dead wires as if they're live. The takeaway is this:

Neutral is live until you have done a physical inspection that all the earthing hardware is in working order, and done an electrical test to confirm.

  • How are the neutral ground wrestling the voltage down? – Dragos Durlut Nov 11 '18 at 22:09
  • there is no neutral ground. There is no such thing as that. There is a neutral-ground bond, "bond" is the noun and "neutral-ground" is the adjective saying what kind of bond it is. – Harper Nov 12 '18 at 2:43

In my opinion the other neutral wires have current in them from the light bulb.

No they do not - unless they share a common neutral return wire.

You seem to be confusing voltage and current. It is the voltage between the wire and earth that presents the hazard to you - not the current through the wire.

Are they safe to touch?

If everything is correct the neutral voltage should be quite low - a few volts AC maybe. There are several things that could go wrong:

  • The 'neutral' has not been neutralised. This could happen if the link between neutral and earth is missing or broken.
  • The earth rod at the neutralising point is bad or disconnected.
  • If a very high fault current flows in the wires the resistance of the wires will cause the neutral voltage to rise high enough to kill.

Don't touch.

  • Why is the neutral voltage low? Due to the consumer? – Dragos Durlut Nov 11 '18 at 22:06
  • Also, I believe the circuits have a common neutral point in the neutral bar found in the fuse box. Am I not correct? The neutral bar is connected to the main neutral going back into the grid. – Dragos Durlut Nov 11 '18 at 22:12
  • The neutral voltage is low because that side of the feed transformer has been "neutralised" by connecting it to earth at some point - usually at the transformer and, in some countries, at the meter box or entry point to a building. Yes, there is a common live per phase and a common neutral. – Transistor Nov 11 '18 at 22:18

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.