Good thing I have a small meter

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wyreman

wyreman

Senior Member
Location
SF CA USA
Occupation
electrical contractor
So I I have an old tenement apartment building
?
And the distribution has some major problems! =0

That's all fine!

So here's the first stupid question
1.
We know the white wire carries the unbalanced load.
But I also know that on my meter that's hardly ever true!
In single phase 240 V. Residential distribution am I dreaming to expect that the white wire will be Close to the unbalanced load between the two phase wires?

2.
If it's not somehow we are either talking about
It's really a three-phase system and there's some other use of the full boat somewhere Beahm

Or it's an installation where there is some kind of leakage to the ground

3.
The reason current will flow from the neutral busbar to the ground
is because the ground is has a lower impedance path
back to the centerpoint of the transformer

If the white wire is intact, how can this be?
Only if it's undersized
or the utility grounded is has higher impedance then
the system grounding to the cold water pipe
IMG_9145.jpg


I just uploaded the video and you guys can't hear the buzzing
but I have a little bit a chip paint
That's bare metal
there and when the neutral goes
through the screwdriver to the box
we can hear the buzz
 
Were you turning off and on a load? Why were the amps bouncing around so much?

Definitely an interesting problem.
 
the answer to #1-thats what its supposed to do. its not clear what question 2 & # is. and what conductor are you clamping on to in the video?
please don't tell me a homeline is the distribution panel.... that's the house panel, right? most of these wiremen on this forum are sticklers for details if help is needed... as long as its betwist trade men.
 
The service neutral will seldom carry only the unbalance of the loads. It can carry additional current due to it being bonded to the GEC and that being connecting it the municipal water system. The utility neutral and the metallic water system are essentially in parallel with each service neutral bonding them together. The utility neutral and the metallic water system have vastly different impedances hence the voltage differential at different points resulting in current flow in the service neutrals.

Measure the current on the GEC and see what you get.

-Hal
 
wyreman said:
So I I have an old tenement apartment building
������
And the distribution has some major problems! =0

That's all fine!

So here's the first stupid question
1.
We know the white wire carries the unbalanced load.
But I also know that on my meter that's hardly ever true!
In single phase 240 V. Residential distribution am I dreaming to expect that the white wire will be Close to the unbalanced load between the two phase wires?

2.
If it's not somehow we are either talking about
It's really a three-phase system and there's some other use of the full boat somewhere Beahm

Or it's an installation where there is some kind of leakage to the ground

3.
The reason current will flow from the neutral busbar to the ground
is because the ground is has a lower impedance path
back to the centerpoint of the transformer

If the white wire is intact, how can this be?
Only if it's undersized
or the utility grounded is has higher impedance then
the system grounding to the cold water pipe
View attachment 15719


I just uploaded the video and you guys can't hear the buzzing
but I have a little bit a chip paint
That's bare metal
there and when the neutral goes
through the screwdriver to the box
we can hear the buzz
Click to expand...

Do you have a 120/240 single phase source? You mentioned this is an apartment building, and I presume this is one of the tenant panels.

If you have a 208/120 wye source but are only using two phases and the neutral for this feeder - neutral doesn't carry unbalanced current in this scenario. In fact if both phases are loaded the same the neutral will read approximately the same as well. You only get true imbalance on a three phase wye neutral when you have current from all three phases involved.

If panel is wired correctly there should be separation of neutral and equipment grounding conductor beyond the service disconnecting means. Shorting the neutral to EGC will make the EGC a parallel conductor to the neutral, potentially other conductive items with continuity to the EGC as well. When there is parallel paths all paths will have some current on them. Those with least resistance will see the most current, but all paths will see some current.
 
kwired said:
Do you have a 120/240 single phase source? You mentioned this is an apartment building, and I presume this is one of the tenant panels.

If you have a 208/120 wye source but are only using two phases and the neutral for this feeder - neutral doesn't carry unbalanced current in this scenario. In fact if both phases are loaded the same the neutral will read approximately the same as well. You only get true imbalance on a three phase wye neutral when you have current from all three phases involved.
Click to expand...

Great point to bring up. :)


wyreman you really need to determine if you have a 240/120 service or a 208/120 service.
 
Hi guys, I am going back to that old bldg early next week and will post
What I remember is that has 120/208 but that can is just single phase

That is a distribution panel on the 5th fl hallway that feeds many units!
The inrush is from 5 or 6 refrigerators kicking on at the same time.

I will have to maximize the volume of the existing chases out of the can to pull individual 30a panels for those studio units, at least give them a SA1 & SA2 plus a hairdryer, then gen power1 and gen light1
as units come vacant

Sure that is a 120/208 wye in the basement with a separate DC feed to the elevator =0
but the hallway distrib on 5th fl I remember as single phase which is why I was scratching my head about the unbalance load.

Any thoughts on the big current flow from the grounded to the grounding - that is the neutral bus to the can>?
If the white wire is intact, how can this be?
Only if it's undersized compared to the resistance of the grounding path [pipe path lower impedance than white wire]
or the utility grounded is has higher impedance then
the system grounding to the cold water pipe​
 
Last edited:
Three phase service to the building with 2 hots and a neutral to each unit will ensure a larger unbalanced load on the neutral to each unit. Now, if the neutrals are isolated as they should be, there will be current flow via your screwdriver to the can when you short accross to it. You made the EG, conduit etc, a parallel path with the neutral back to the transformer at that point. More current will flow on the path with least resistance. You should expect a spark at the screwdriver.

My summary as I see your question.
 
wyreman said:
Any thoughts on the big current flow from the grounded to the grounding - that is the neutral bus to the can>?
If the white wire is intact, how can this be?
Only if it's undersized compared to the resistance of the grounding path [pipe path lower impedance than white wire]
or the utility grounded is has higher impedance then
the system grounding to the cold water pipe​
Click to expand...

About half the neutral current will flow on the EGC if you short them together and they are about the same resistance. If you have 20 amps on the neutral and then short it to the EGC you will have about 10 amps on both, that will make a fairly noticeable arc when you make that connection.
 
While you are experimenting with this, put a good VOM between the Neutral and EG or can before you make the N-EG connection with the screwdriver. Note voltage. Make the connection and note the voltage again.

Remember where your hands are and realize nothing of what you are doing is considered "safe" anymore. Wear your PPE.
 
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