120V

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Little Bill said:
Someone posted a while back, (I think on this site) where they had a panel for 120V. Problem was they were using 1 leg as the neutral. That definitely was not good.
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Yup, that was true. It was in a tech building. Sub panels with 1 buss bar as a neutral. I still am not sure if its totally safe.

I spoke with the EE that wired it and he said that there is nothing wrong with a 120 volt subpanel or having 1 buss like this. He claimed that simultaneously breaking hot and neutral was much safer than the current practice in America and is common where he from.

He stated that regular setups in America were unsafe in that if the neutral to the panel becomes loose or disconnected the branch neutrals will all rise above an unsafe potential to ground and present a shock hazard to anyone doing service work. Imagine being on a ladder and getting bit even though the hot is disconnected in a traditional set up. :eek:

Being bitten by neutrals in 277 office lighting makes me think hes on to something:lol:
 
It seems wasteful to me to put the B phase of a panel to use with a neutral. If I were serving a 120V-only panel today (as I have done in the past for a panel on the load side of an inverter) I would install a #6 THHN between the lugs of a 2-pole 60A backfed breaker, supply the panel with a 2-2 SE cable and be done with it. :D
 
mbrooke said:
Yup, that was true. It was in a tech building. Sub panels with 1 buss bar as a neutral. I still am not sure if its totally safe.

I spoke with the EE that wired it and he said that there is nothing wrong with a 120 volt subpanel or having 1 buss like this. He claimed that simultaneously breaking hot and neutral was much safer than the current practice in America and is common where he from.

He stated that regular setups in America were unsafe in that if the neutral to the panel becomes loose or disconnected the branch neutrals will all rise above an unsafe potential to ground and present a shock hazard to anyone doing service work. Imagine being on a ladder and getting bit even though the hot is disconnected in a traditional set up. :eek:

Being bitten by neutrals in 277 office lighting makes me think hes on to something:lol:
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The part that is safer is that if the disconnecting means opens the neutral then the entire circuit is disconnected. The amount of voltage it is protecting you from is the amount of voltage drop that may exist on the neutral. That will vary with amount load on the neutral and distance from the system bonding jumper. This is required in some article 500-516 locations to prevent arcing of a neutral when it contacts equipment ground if the disconnect is off and someone is working on something, and result could be ignition of hazardous material.

Whether a neutral is opened by the disconnecting means or not it in no way will prevent the voltage instability that exists on MWBC's if the neutral becomes open under load, while the ungrounded conductors remain energized. It also will not prevent open circuit voltage in a two wire circuit if neutral is opened under load.

It does not matter if 120 or 277, either can kill you, knock you off a ladder, or cause other problems. Besides you don't get bit by them when you turn off all the ungrounded conductors they are serving.
 
I wired up two panels like that in a power plant, both in rooms with DCS equipment.

The two hots of a 120/240 panel were jumpered and fed by a single 120 volt circuit, with a neutral and ground bar. Also, the conductors were vastly oversized, needing pin adapters. No 240 volt present in either panel. Hot to hot was 0 volts and hot to neutral was 120.
 
kwired said:
The part that is safer is that if the disconnecting means opens the neutral then the entire circuit is disconnected. The amount of voltage it is protecting you from is the amount of voltage drop that may exist on the neutral. That will vary with amount load on the neutral and distance from the system bonding jumper. This is required in some article 500-516 locations to prevent arcing of a neutral when it contacts equipment ground if the disconnect is off and someone is working on something, and result could be ignition of hazardous material.

Whether a neutral is opened by the disconnecting means or not it in no way will prevent the voltage instability that exists on MWBC's if the neutral becomes open under load, while the ungrounded conductors remain energized. It also will not prevent open circuit voltage in a two wire circuit if neutral is opened under load.

It does not matter if 120 or 277, either can kill you, knock you off a ladder, or cause other problems. Besides you don't get bit by them when you turn off all the ungrounded conductors they are serving.
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The panel was not fed as a MWBC though, but yes its true, this setup will do nothing against the neutral opening in terms of voltage rise/fall.

I disagree that a neutral can not shock you if all ungrounded conductors are open. This is how the EE explained it. Take a standard 120/208 42 space sub panel for example. 5 wires hot 1 hot 2 hot 3 neutral and ground. The neutral that is feeding the panel is developing a high resistance connection at a lug somewhere, voltage to ground on all the 42 branch neutrals is starting to rise along with a voltage imbalance in 120volt loads that is not always noticed or to sever to be noticed immediately. ( equipment just fails prematurely)

Now a service tech opens breakers 1,3,5 to a office cubicle lets say. Hots 1,2,3 become zero to ground, ground wire is zero to building steal. But the neutral to ground voltage can be anywhere from 2 volts (usual rise) to 120 volts (fully open neutral and load not balanced across phases). Now the neutral in this disconnected circuit may shock pretty well or may even kill because the other 39 circuits in the panel are back feeding it.

The reason why I think he may be right was once I ended up getting 65 volts from neutral to ground on a 277 volt circuit even though it was off. The problem was that the gray neutral wire that was feeding the panel had its lug corroded in the switch gear. No sign anything was amiss.:dunce:
 
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Joethemechanic said:
Where was that?


And way back in the day, here in the USA we use to fuse neutrals. We stopped doing it because it was dangerous
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Somewhere in eastern Europe. He did mention that in great Brittan it is now code to open the neutral at the main and sub main (RCD) in case it was to open in the system. By the way he also said 30ma GFCI protection is required on all circuits in Europe:blink:

He swears its safer and NEC legal as long as both open (hot and neutral):eek:hmy:
 
mbrooke said:
The panel was not fed as a MWBC though, but yes its true, this setup will do nothing against the neutral opening in terms of voltage rise/fall.

I disagree that a neutral can not shock you if all ungrounded conductors are open. This is how the EE explained it. Take a standard 120/208 42 space sub panel for example. 5 wires hot 1 hot 2 hot 3 neutral and ground. The neutral that is feeding the panel is developing a high resistance connection at a lug somewhere, voltage to ground on all the 42 branch neutrals is starting to rise along with a voltage imbalance in 120volt loads that is not always noticed or to sever to be noticed immediately. ( equipment just fails prematurely)

Now a service tech opens breakers 1,3,5 to a office cubicle lets say. Hots 1,2,3 become zero to ground, ground wire is zero to building steal. But the neutral to ground voltage can be anywhere from 2 volts (usual rise) to 120 volts (fully open neutral and load not balanced across phases). Now the neutral in this disconnected circuit may shock pretty well or may even kill because the other 39 circuits in the panel are back feeding it.

The reason why I think he may be right was once I ended up getting 65 volts from neutral to ground on a 277 volt circuit even though it was off. The problem was that the gray neutral wire that was feeding the panel had its lug corroded in the switch gear. No sign anything was amiss.:dunce:
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Opening the neutral that supplies breakers 1,3 and 5 will make that voltage go away.

Even if there is no bad connection on the feeder there is voltage drop on that conductor and you likely will see some voltage anyway but probably very little unless voltage drop is rather significant and neutral has a heavy load on it.

This is why neutral needs isolated from ground once past the service or first disconnect for separately derived systems, So equipment ground conductor, and anything connected to it, does not become raised above earth level because of voltage drop or an open circuit condition.

Neutrals are grounded conductors(normally), but they are also current carrying conductors and you must still treat them like current carrying conductors when working on things or one will get you sometime. When disconnected they are no longer grounded.
 
kwired said:
Opening the neutral that supplies breakers 1,3 and 5 will make that voltage go away.

Even if there is no bad connection on the feeder there is voltage drop on that conductor and you likely will see some voltage anyway but probably very little unless voltage drop is rather significant and neutral has a heavy load on it.

This is why neutral needs isolated from ground once past the service or first disconnect for separately derived systems, So equipment ground conductor, and anything connected to it, does not become raised above earth level because of voltage drop or an open circuit condition.

Neutrals are grounded conductors(normally), but they are also current carrying conductors and you must still treat them like current carrying conductors when working on things or one will get you sometime. When disconnected they are no longer grounded.
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I agree with your statement.:D Just because a neutral is grounded at the service disconnect does not mean that it will be 100% at ground potential all the time. Im guessing this is what the EE was protecting against.
 
Yeah but how do you make sure that the breaker for the neutral, and the breaker/breakers for all the phases open simultaneously?

I wouldn't trust the handle tie. And if one of the phase breakers failed to open due to an internal malfunction you could end up opening a loaded neutral.
 
Hey, I didn't think most of Europe even used neutrals. I wonder if this EE even understands neutrals
 

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Joethemechanic said:
Yeah but how do you make sure that the breaker for the neutral, and the breaker/breakers for all the phases open simultaneously?

I wouldn't trust the handle tie. And if one of the phase breakers failed to open due to an internal malfunction you could end up opening a loaded neutral.
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Where you are allowed to put a breaker in a grounded conductor in the NEC it must operate simultaneously with ungrounded conductors - IOW common trip - no handle ties would be allowed, fuses are not allowed because there is no way to insure common trip.
 
Joethemechanic said:
Yeah but how do you make sure that the breaker for the neutral, and the breaker/breakers for all the phases open simultaneously?

I wouldn't trust the handle tie. And if one of the phase breakers failed to open due to an internal malfunction you could end up opening a loaded neutral.
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Double pole breaker that is normally used for 120/240 systems was used for the application. It meets the requirements. A handle tie would not work because it does not have internal common trip which assures that any 1 pole that trips causes the other(s) to open.

As for an internal malfunction on a double pole breaker, it would be just as bad if it failed in standard 208/240 operation leaving 120 on one phase.
 
mbrooke said:
Double pole breaker that is normally used for 120/240 systems was used for the application. It meets the requirements. A handle tie would not work because it does not have internal common trip which assures that any 1 pole that trips causes the other(s) to open.

As for an internal malfunction on a double pole breaker, it would be just as bad if it failed in standard 208/240 operation leaving 120 on one phase.
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That is just wat I'm saying, If a phase failed to trip. Who really cares about if the neutral failed to open, no problem. But if a N opens up, and a phase does not, now we have a hot neutral conductor all the way back to the panel.

Believe me, I grew up in a K&T house with fused neutrals. I can tell you a N opening up and it's phase staying closed is a really sucky situation.

When I go into something, I want to at least have a reasonable expectation that my N is going to be at the same potential as my G.


And think of this, you finish your work, go back to the panel, snap the breaker handle to the on poisision. and the phases close but the N fails to close.
 
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I have done that when there is no utilty power and homeowner didn't want to spend the money on 2 inverters from his generator/solar panel system. But I planned on him someday going to utility power and ran correct wire so he would be already setup with 2 phases with minimum cost when he did.
 
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