How people get hurt

[chris kennedy]

Earlier this year is was swapping out a 400A 480V ATS at the largest shopping mall in Fl. Got knocked on my butt by the load neutral (literally) after opening all load, normal power and genny OCPD's and testing with two testers. After removing the load neutral from the ATS's neutral bus and scrapping myself off the floor, load neutral read 352V to ground.

Today at Miami International Airport I run into the same potential hazard. In the pic below you will see an FMC entering (bottom left) a 1900 box with an ungrounded conductor from normal power lighting PNL H1D with an EGC (330.3(B) maybe???:blink. Now top left you see a ?EMT leaving with the ungrounded conductor from PNL H1D and a grounded conductor from genny PNL EA. So what a surprise the guy changing this facilities ATS is gonna get. (I fixed it)

 

[ActionDave]

Ouch. Glad you are okay. Yes, a bootleg neutral is a bad thing.

There was a full on yelling match at our shop several years ago because one of the jw's "fixed" a 277V light at our mall by grabbing a neutral from a 120V circuit. Some people just don't think or just don't care.

 

[kwired]

I was changing out a panelboard one time (well pretty sure it has happened more than once, but one time still sticks in my mind), I had the feeder shut off and ungrounded conductors mostly all removed from their terminations and was working on removing grounded conductors. When removing one of them it arced - just a light arc, but I right away knew something was getting its neutral in an improper manner, also was hoping it wasn't part of or at least effectively part of a MWBC creating even more potential trouble.

 

[arion]

i thought red boxes were fa system only like plfa why would a box coded for fire alarm be used in non fa work? that in it self is asking to knock a fa service tec on his duff if not kill him.

 

[GoldDigger]

I think that the association of the box with fire department first responder use (since only they and maybe building management will have keys) that association overrides the other use. Also, for all we know the control writing is integrated with the FA system.
Unlike the OP's box, the new ones will typically contain low voltage or current limited wiring.

Sent from my XT1080 using Tapatalk

 

[arion]

that's what i was assuming and if its part of a dcos or cops system it would be using type ci rated cable and in a totally isolated conduit system

 

[brother]

I was taught to get an amp reading on the 'neutrals' to ensure it is not carrying a load from somewhere else if you plan on lifting it. And after you lift it you still check it to be sure especially on an ATS system. If I understand your post correctly, Sometimes they do not switch the neutrals and its not a true 'separately derived system'.

Did you do any amp readings on any of them

 

[mjmike]

Earlier this year is was swapping out a 400A 480V ATS at the largest shopping mall in Fl. Got knocked on my butt by the load neutral (literally) after opening all load, normal power and genny OCPD's and testing with two testers. After removing the load neutral from the ATS's neutral bus and scrapping myself off the floor, load neutral read 352V to ground.

Can you please clarify? You turned off the generator breaker and the normal source breaker then got shocked when disconnecting the neutral on the load side of the transfer switch which I am assuming is a solid neutral, is that correct? So where did the voltage come from? If the genset is off and the normal source feeder breaker is off, was the voltage coming from unbalanced load on the neutral bus in the switchgear where the feeder source originated? If so, sounds like a grounding/bonding issue since voltage wasn't taken to ground at the service bond. Also, why the off voltage? Other than using an amp probe, there really wouldn't be a way to know if there was voltage on the neutral because it theoretically should be 0 since you would be going from the neutral to ground which should be at the same potential. Let us know what the cause was.

 

[GoldDigger]

If so, sounds like a grounding/bonding issue since voltage wasn't taken to ground at the service bond. Also, why the off voltage? Other than using an amp probe, there really wouldn't be a way to know if there was voltage on the neutral because it theoretically should be 0 since you would be going from the neutral to ground which should be at the same potential. Let us know what the cause was.

In some cases, even with completely correct bonding and grounding (you know that grounding alone will not provide a fault clearing path, right?) there can be current flowing in the neutral and a substantial voltage available to try to keep that current flowing.
The most common problems leading to this involve the combination of a lost utility neutral (in service drop or elsewhere) and a shared grounding network between occupancies or buildings. (Think about apartments with separate meters and disconnects but a common EGC or two houses on the same transformer with a common metallic water system.)

 

[kwired]

I was taught to get an amp reading on the 'neutrals' to ensure it is not carrying a load from somewhere else if you plan on lifting it. And after you lift it you still check it to be sure especially on an ATS system. If I understand your post correctly, Sometimes they do not switch the neutrals and its not a true 'separately derived system'.

Did you do any amp readings on any of them

If the neutral only has a few milliamps of load it may not register on a clamp meter, but can still knock you on your butt when you put yourself in the circuit.

i thought red boxes were fa system only like plfa why would a box coded for fire alarm be used in non fa work? that in it self is asking to knock a fa service tec on his duff if not kill him.

I don't think that is an NEC requirement, but may be for some other code. Kind of is an industry standard at the very least.

 

[GoldDigger]

I don't think that is an NEC requirement, but may be for some other code. Kind of is an industry standard at the very least.

And do those other codes require FA boxes to be red, prohibit all other boxes from being red, or both?
"Never assume" is always good, although annoying, advice when on the job.

 

[brother]

If the neutral only has a few milliamps of load it may not register on a clamp meter, but can still knock you on your butt when you put yourself in the circuit.

They make meters that can read milliamps and like I stated before, even after you remove the neutral, if it was still live a tic tracer (non contact voltage tester) would pick up a reading. I still see no reason for this not to be checked out before you put your bare hand on it to become 'part of the circuit'.

 

[kwired]

They make meters that can read milliamps and like I stated before, even after you remove the neutral, if it was still live a tic tracer (non contact voltage tester) would pick up a reading. I still see no reason for this not to be checked out before you put your bare hand on it to become 'part of the circuit'.

I was just trying to point out that most of us probably will not be using a clamp on meter that can read milliamps very accurately, many multimeters will read milliamps but involves breaking the circuit and inserting the meter in the circuit to take a reading. A low impedance volt meter is just as effective for the intended purpose here.

 

[mjmike]

How about in the case of adding a branch circuit to an existing panel? Could mean you could get shocked when loosening a screw on the neutral bus to terminate the branch neutral. Seeing how the ground and neutral are to be tied together (can't check voltage with ground as the reference), how else can you check to see if the system is safe without a mA clamp meter? I would think you could do a continuity test between the neutral and ground? Or, check for voltage between the neutral and ground. If there is voltage, then the bond is bad, if there is no voltage then the neutral is bonded.

 

[kwired]

How about in the case of adding a branch circuit to an existing panel? Could mean you could get shocked when loosening a screw on the neutral bus to terminate the branch neutral. Seeing how the ground and neutral are to be tied together (can't check voltage with ground as the reference), how else can you check to see if the system is safe without a mA clamp meter? I would think you could do a continuity test between the neutral and ground? Or, check for voltage between the neutral and ground. If there is voltage, then the bond is bad, if there is no voltage then the neutral is bonded.

If you are complying with 408.41 you will not be adding a conductor to an individual terminal that already is used by another conductor. If the terminal bar is full, you have a problem with complying with 408.41, unless you are able to combine equipment grounding conductors landed on that bar - this should only be an option if the panel happens to be the service equipment.

 

[mjmike]

If you are complying with 408.41 you will not be adding a conductor to an individual terminal that already is used by another conductor. If the terminal bar is full, you have a problem with complying with 408.41, unless you are able to combine equipment grounding conductors landed on that bar - this should only be an option if the panel happens to be the service equipment.

I'm talking about using a spare screw on a neutral bus. Let me clarify; the neutral bus in the panel that has lets say 20 screws for neutrals and a spare screw, hole, or whatever you want to call it is being used. this screw is still electrically connected to the neutral bus even if there currently is not a neutral wire under it.

 

[kwired]

I'm talking about using a spare screw on a neutral bus. Let me clarify; the neutral bus in the panel that has lets say 20 screws for neutrals and a spare screw, hole, or whatever you want to call it is being used. this screw is still electrically connected to the neutral bus even if there currently is not a neutral wire under it.

How is it that you would be opening any circuit if that is what you have? Only voltage you are possibly subjected to in that circumstance is any voltage drop present on the supply side neutral conductor, which if there are no bad connections involved is probably going to only be just a few volts, unlike opening the neutral conductor of a loaded circuit, whether it is a big or small load, you will be subjected to full voltage of the circuit if you touch it and anything grounded.