Contradiction

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e57

e57

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In terms of objectionable current....

How is this:

1113845784_2.jpg



Different from this?

1113921646_10.jpg

(Power supply originating in enclosure in opposite direction and the fault will take BOTH paths... Or attempt to.)
 
My own personal theory, which has never been substantiated, is that we want as much bonding on the line side of the service disconnect as possible because of the high available fault current. In that case, the objectionable current is the lesser of the two evils.
 
e57 said:
In terms of objectionable current....

How is this:

Different from this?
Click to expand...

One is objectionable current and one is fault current.

Edit: The only differnce between the two is that objectionable current is pretty much constant and fault current is only supposed to last a very short time, not that it should be there to begin with.

I like the different electron behaviour idea. :grin:
 
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e57 said:
You're going to have to elaborate Bob... The electrons can differentiate what enclosure they are in? :rolleyes:
Click to expand...

Yes, that has to be the explanation because other then that the two examples are identical to me. I also wonder why 250.32(B)(2) had to be removed in the 2008 NEC, that was just the same as every service in the USA. Apparently safe on the supply side of the service disconnect but unsafe on the load side of the service disconnect.
 
physis said:
One is objectionable current and one is fault current.

Edit: I like the different electron behaviour idea. :grin:
Click to expand...
I wasn't goin to edit the graphics but the OP is about "objectionable current" - not the fault current which I have abused, and may abuse again in another thread.... :rolleyes:

I was really hoping Bob and Roger would collectively come up with more on that line - of how the electrons know where they are....
 
One is apparently a touch voltage danger and fire hazard - but the other is not?

It also makes me wonder about this:
1113921429_2.jpg


Since there apparently is a grounded neutral on possibly in the gutter, and main - and possibly each meter enclosure too.
 
The gutter, the conduits the meter and breaker enclosures are all required to be bonded to the neutral, the entire set up is one big combined neutral.:confused:

Its one of those things I just accept and move on, I have started intentionally using PVC nipples to avoid the issue.:smile:
 
iwire said:
~the entire set up is one big combined neutral.~
~ I have started intentionally using PVC nipples to avoid the issue.:smile:
Click to expand...
Not available to me and some others. (POCO and local AHJ require RMC/IMC for service conductors above grade.)

Now - if it is one big neutral. If say one main neutral was carrying one current, and each of the others carrying a different current - with PVC nipples - they would all be at a different voltage potential on the exterior of the enclosure? Or if one lost the neutral all together - it could be upwards of 120v on the exterior? (if say 120/240 single phase - more if 277/480)

Almost seems safer to use metal nipples - so the enclosures are closer in voltage to eachother on the exterior?????
 
e57 said:
Not available to me and some others. (POCO and local AHJ require RMC/IMC If say one main neutral was carrying one current, and each of the others carrying a different current - with PVC nipples - they would all be at a different voltage potential on the exterior of the enclosure?
Click to expand...

I can't imagine the voltage difference would exceed 50 volts which is considered safe.

Or if one lost the neutral all together - it could be upwards of 120v on the exterior? (if say 120/240 single phase - more if 277/480)
Click to expand...

That is always an issue if the service equipment is outside and the supply neutral is lost all the service enclosures could be close to the L to N voltage compared to the earth your standing on.
 
I don't agree with Mike's graphic saying that the current through the conduit is a fire or safety hazard assuming the grounded conductor is in good condition. I also see no technical or electrical difference between the installation on the line or load side of the service...just a code rule that tells us one is ok and one isn't...hence the idea that the electrons change their behavior at the service disconnect.
 
iwire said:
I can't imagine the voltage difference would exceed 50 volts which is considered safe.
Click to expand...
50 volts is safe? What/where is that based on?

Even if there was very little voltage difference - touching the gutter and one of the main panels puts your body in parallel with the current of the neutral if using PVC nipples. Using steel/metalic puts you in parallel with the hopefully well joined/bonded enclosures and raceways - which should in therory be the same potential. (even if they are carrying current)
 
Isn't the first graphic showing a grounded conductor detached at the load end and its terminal incorrectly rebonded to the enclosure? That leaves the loose raceway connections to carry the full neutral current until repaired.

That leaves the raceway as the only grounded cirucit conductor. Said objectionable current would be avoided if the grounded conductor was not rebonded.

The second is just showing how proper bonding will ensure a good path when needed for fault current, though I don't know why the text says "only one end".
 
In the first picture, the service neutral conductor is not connected to the neutral bus but the grounding conductor is, this causes current to flow along the conduit which is described as being a loose connection. Continuous current through a bad connection results in heat.
 
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