Hi, I was wondering if it is safer to break both live and neutral wires with a switch, instead of the live wire. Is there any disadvantage by doing this?

One accident that might happen is if the neutral wire is somehow electrified, you switch off one room, that only kills the live wire, and the neutral is still connected to the rest of the circuit.

By killing both neutral and live in a switch you make sure that you broke any possibility of current passing by any cable.

 

You might want to switch the Neutral to something on your Bench,
but You shouldn't have Mains Wiring floating around on your Bench in the first place.

The National-Electrical-Code (US) specifically forbids switching Neutrals, (Grounded-Conductors).
It would also add an unnecessary expense to the Mains-Wiring-System in your House.
There is always a remote chance that some clown will create a dangerous condition,
but if You follow the Rules, it's not "safer" to switch the Neutral.

As far as I know, no country allows switching Neutrals.
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Externally for house wiring etc, especially with RCD-protected circuits, its usual, and in many locations, legally required, just to switch the live, leaving the protected neutral in place, UNLESS the switch is designated as an isolator, in which case both circuits are isolated (typically for high-power dedicated circuits for cookers, water heaters, etc.) ; such switches are usually clearly of a different design to normal wall switches (often rotary).

Within equipment its always considered safer to use a DP switch to isolate both wires and, in my experience, its rare to find a modern piece of equipment that doesn't do so.. The switch should normally be after any live-side input fuse.

 

Mi point is this one:


The left room is what we do now, the neutral wire is always connected to the system, we only break the hot wire in the switch, and there is a possibility that if the neutral somehow gets electrified anywhere in the circuit, you would touch it and the switch at the wall would not cut it.
However, the right room has a double switch that breaks all the wires that enter that room, hence no matter what happens outside the room, there would be no possibility of you touching a cable that carries current.

So, my question is... is there a reason why this is not done, besides "it's not really necessary and the installation would need a bit more neutral wire"?
Any safety reason?
Something that could go wrong in the right room that would not happen in the left room?

 

The "neutral" is also called a grounded conductor. That is, the neutral in a system properly built is bonded to ground and should have the same potential as ground.

This being the case, neutral serves in a safety role additional to it being the return path for the live wire. Disconnecting it makes things less safe, not more. There is no advantage to interrupting it since it will never, in normal conditions, be at a potential substantially above ground, and if it is, it is because of a fault that needs to be corrected and switching it off is not protective from such a fault which will also exist when it is switched on.

 

Something that could go wrong in the right room that would not happen in the left room?

Yes. Suppose the the two pole switch fails such that the live is connected but not the neutral. You can now get electrocuted by touching the neutral wire.

Bob

 

The "neutral" is also called a grounded conductor. That is, the neutral in a system properly built is bonded to ground and should have the same potential as ground.

This being the case, neutral serves in a safety role additional to it being the return path for the live wire. Disconnecting it makes things less safe, not more. There is no advantage to interrupting it since it will never, in normal conditions, be at a potential substantially above ground, and if it is, it is because of a fault that needs to be corrected and switching it off is not protective from such a fault which will also exist when it is switched on.

Just deviating slightly off topic here. . . But does your electrical code require (for the same reason) that you connect the neutral output of an inverter to ground?

 

Just deviating slightly off topic here. . . But does your electrical code require (for the same reason) that you connect the neutral output of an inverter to ground?

This is a good question, I don't know.

 

I would guess not since some pickup trucks have built in inverters and I don’t think they require you to put in a grounding rod when you use them.

Bob

 

Just deviating slightly off topic here. . . But does your electrical code require (for the same reason) that you connect the neutral output of an inverter to ground?

Found this: (from Samlex https://samlexamerica.com/resources-support/faq/inverters-grounding-and-neutral-bonding/)

The UL standard for this type of inverters- UL458 does not have a requirement for a bonded neutral on the output of inverters. As long as the installation requirement of grounding the chassis of the inverter has been accomplished, loads that are plugged in will have their chassis held at the same ground potential as the chassis of the inverter and the house or RV. The only difference is that the neutral slot of the receptacle has approximately 60V on it instead of the usual 0V.

The impact of this is minimal, since parts of wiring and equipment that are connected to the neutral side of the circuit are required by safety standards to be treated as if they were at 120VAC, since there are many receptacles that are wired backwards or 2-prong plugs that are not polarized.

Therefore, a voltage of approximately 60VAC of the Neutral slot is not accessible to the user, and any shock hazard presented is mitigated by lack of access. The main safety agencies, CSA, UL, and ETL, have all approved inverters with this half-voltage on the neutral scheme.

 

I would guess not since some pickup trucks have built in inverters and I don’t think they require you to put in a grounding rod when you use them.

Bob

This is heading in the same direction as the joke about a man who builds his own electric car, and when asked if he is going to increase the range replies “Yes, as soon as I can afford a longer cable”.
But seriously, you could equipotentially bond the neutral to the vehicle chassis.

 

Mi point is this one:
View attachment 244056

The left room is what we do now, the neutral wire is always connected to the system, we only break the hot wire in the switch, and there is a possibility that if the neutral somehow gets electrified anywhere in the circuit, you would touch it and the switch at the wall would not cut it.
However, the right room has a double switch that breaks all the wires that enter that room, hence no matter what happens outside the room, there would be no possibility of you touching a cable that carries current.

So, my question is... is there a reason why this is not done, besides "it's not really necessary and the installation would need a bit more neutral wire"?
Any safety reason?
Something that could go wrong in the right room that would not happen in the left room?

The neutral(grounded) wire just might save you (or someones) life from electrical shock one day.
I'd leave the neutral connected and break only the Hot/Live side.

 

tripp-lite puts breakers incorrectly in both line and neutral in their 120 VAC medical power strips.

They claim for reverse polarity protection. They should be different ratings.

I think the hot should be a lower rating. e.g. 12A for hot and 15A for neutral.

if it gets switched the now hot and case gets 15A and the now ground gets 12.
If there is a short to case, the 15A fuse blows and the 12 should be in-tact.

When they are both 15A and separate, you don't know which will blow first.

Inside a piece of equipment, you can switch neutral. It happens all the time with 240/120 switchable stuff.

I did have the experience of seeing a front-panel mounted neutral, non-ganged breaker on a 3-phase 90A 208 electron beam power supply from Telemark.

I can't remember how it was connected, but it did contain a high current 15 kV power supply.

 

Found this: (from Samlex https://samlexamerica.com/resources-support/faq/inverters-grounding-and-neutral-bonding/)

Thanks. There seems to be a disproportionately large number of threads on this forum on the subject of inverters!
Just in case you’re interested, UK regs allow a single piece of equipment To be connected to a floating supply (it behaves like an mains isolating transformer and becomes an IT earthing system), but for inverters supplying multiple loads, neutral must be earthed (TN-S) so that fuses blow in the case of a live-to-earth fault.