Why An Open Neutral Kills 120V Devices

[Mike Sokol]

Re: Why An Open Neutral Kills 120V Devices

In that diagram would there not be a link between the utility neutral to the secondary neutral as per standard distribution practice?

Actually, if the pole transformer is one phase of a 3-phase Delta distro (very common) there isn't a neutral on the primary side of the transformer at all. The grounding rod at the pole would be for the topmost utility wire on the poles acting as the lighting safety. If the transformer primary is one phase of a 3-phase WYE distro, then the Neutral bus would exist, but not be tied across to the secondary side. Essentially the bond point of the ground rod, secondary neutral and safety ground bus in the service panel creates a local ground plane for your facility or residence.

In my diagram I'm showing one phase of a 3-phase WYE transformer primary with an earth-grounded neutral bus, but it just as easily have been one phase a 3-phase Delta primary as well.

 

[David Buckley]

Re: Why An Open Neutral Kills 120V Devices

If the transformer primary is one phase of a 3-phase WYE distro, then the Neutral bus would exist, but not be tied across to the secondary side.

Yeah, that's the point at which we differ. It is my understanding that standard USA practice is that in urban areas, WYE distribution is the norm, and thus there is a neutral conductor that goes pole to pole in addition to the phase conductor(s). Further I understand that normal practice is that this supply neutral is bonded to the secondary drop. This is a peculiar (evil) American practice, called the Multi Grounded Neutral.

From a helpful diagram on Florida PSC website on a page entitled What's on a Utility Pole?

There are two hots coming out of the transformer, and also the centre tap, the neutral, which is commoned to the utility neutral as well as going on the drop to the consumer.

Thus I continue to contend that your diagram should show a link between the utility neutral with its ground rod, and the secondary neutral with its ground rod.

As someone brought up in the European way of doing electricity, the MGN arrangement is nuts. For reasons why its evil, see an article entitled The Hazardous Multigrounded Neutral Distribution System And Dangerous Stray Currents.

Boy, are we off topic here

 

[Mike Sokol]

Re: Why An Open Neutral Kills 120V Devices

Yeah, that's the point at which we differ.

There are two hots coming out of the transformer, and also the centre tap, the neutral, which is commoned to the utility neutral as well as going on the drop to the consumer.

Thus I continue to contend that your diagram should show a link between the utility neutral with its ground rod, and the secondary neutral with its ground rod.

Boy, are we off topic here

Gosh, I had to review Delta to WYE and WYE to Delta transformer theory and practices over the weekend, and I think you're correct for WYE connected residential transformers, when I was envisioning Delta connections for industrial power. I've done much more industrial power than residential back in the day, so it's time for a refresher course.

I hope you realize that we're picking nits here and that most of this has nothing to do with internal building neutral wiring, but what the heck....

Notice how I brought this thread bock On Topic by also noting that we're Off Topic... :roll: