physis
Senior Member
Really? I've only seen that like twice. I guess my experience is somewhat limited.
Contradiction
- Thread starter e57
- Start date
- Status
Really? I've only seen that like twice. I guess my experience is somewhat limited.
e57
Senior Member
- Location
- San Francisco, CA
If I were to put stat's to it ~ it would be:
Neutral connection failure:
<10% in the main.
15% meter to main connection (In the meter enclosure)
15% POCO side of meter connection (In the meter enclosure)
The other 50% weather head and pole connections.
<5% in feeders or branch circuits.
Why? Feeders, Branch, and Main OCP enclosures (at least around here) are usually more protected from weather, and changed/serviced/inspected more often. Meters - once sealed - stay sealed/consealed, not seen until failure happens, and usually exterior enclosures. And OH conductors are exposed to the environment, with bare AL neutral conductors, and vibrated constantly by wind. POCO UG conductors and terminations are water/air-tight and essentially submersable.
physis
Senior Member
I'm curious about something here. Are we talking about straight out neutral loss or degradation of continuity? Not that it really matters I guess, but objectionable current usually comes from loss of integrity on the load side of the service and it seems like what's mostly being talked about here is total neutral loss on the power company side. But maybe I'm seeing this funny.
- Location
- Massachusetts
- Location
- Massachusetts
Even with perfect neutral connections under normal operating conditions the conduit will pick up a large portion of the imbalanced neutral current. Of course if the neutral starts to degrade the current on the conduit will rise.
- Location
- Illinois
- Occupation
- retired electrician
Yes, the conduit may carry half or even more of the grounded conductor current, but I don't see it as a hazard. If there is a poor connection, the resistance of the connection will limit the current and the only voltage available to drive the current is the voltage drop on the grounded conductor.
physis
Senior Member
It's more like this.
The current is limited by the resistance but the current across any conductive system is the same all the way across it.
A voltage drop exists across any and every resistance. This is where a shock or a fire hazard might exist.
If you multiply the current through the system by the voltage across a junction you get the wattage or power at that junction. That's where the fire hazard comes from.
The voltage across that same junction is where the shock hazard comes from.
SAC
Senior Member
- Location
- Massachusetts
If the neutral was properly connected, and the conduit was poorly connected, the conduit would carry less than 50% of the current because the current will choose the lowest path of resistance - the properly connected neutral. The worse the connection on the conduit, the less current it would carry.
- Location
- Illinois
- Occupation
- retired electrician
My post was based on a system with a grounded conductor that is in good condition. If there is a high resistance connection in the parallel path (conduit) more current will flow on the grounded conductor. The only voltage to drive the current through the poor conduit connection will be the voltage drop on the grounded conductor. The voltage drop across the poor conduit connection cannot exceed that of the grounded conductor itself. Of course if the neutral has a problem we can have both a shock and fire hazard at the conduit.
SAC
Senior Member
- Location
- Massachusetts
Yes, for example - what would be required to heat up a conduit and enclosure to the point of igniting surrounding material? I'd guess 1KW could do it. Let's consider 100A of load - it would require about 0.1Ohm in order to dissipate 1KW (100A * 100A * 0.1Ohm = 1KW). Now, consider that same 0.1Ohm in parallel with a nice #2 neutral - at about 0.001Ohm for 5 feet. We'll keep the math clean here - since the parallel resistance will be less than the smaller of the two, we'll just use 0.001Ohm, and calculate that at 100A the voltage drop would be ~0.1V (100A * 0.001Ohm = 0.1V). Now, the power dissipated in that crummy 0.1Ohm conduit connection is only ~0.1W (0.1V * 0.1V / 0.1Ohm). Even though the neutral and the crummy conduit are in parallel, pretty much all the current (and power) goes through the neutral.
physis
Senior Member
The neutral and grounding paths are parallel resistances, whatever they might be, R=1/R/1+R/2 (if this poorly writen equation makes sense).
And after looking at how to respond to your post, you're right. Except that you seem to favor the neutral as having lower impedance while, for the sake of argument, both resistances are arbitrary. But you are none the less right.
e57
Senior Member
- Location
- San Francisco, CA
Seriously - I am on the fence of whether it is 'safer' or not :wink: (My ealier post mostly in jest.) - but it does make a good 'back-up' (if well connected) for not burning the place down via your electric blanket - or by the conduit most likely outside that may shock the bejesus out of you when you go to shut it all off. Both are a bad time.....
The conduit will be carrying current either way if metalic.- Status