A fun rabbit hole to dig into is how a transformer can have one wire going in, and three going out to your house. Where does neutral/ground go? How does the high voltage circuit complete?
Short answer: they don't. A residential transformer has an input connection to a 'hot' and the neutral line. The neutral connection just isn't as obvious, because it may be to the body of the transformer itself.
Sure, but the transformer still has 2 connections on the input (HV) side. The neutral path just doesn't run on a continuous wire all the way back.
I think it's interesting that a similar idea can actually be demonstrated in your own home. Because current takes all available paths in relation to their impedance, the household 'neutral', which is also connected to physical ground at multiple points, return path isn't just through the wire itself. The ground connected to your incoming water/gas/UFER will have some small amount of the current your house is using. Most will be on the triplex wire running to the transformer, but a few amps may be on those alternative grounds.
(Basically, and probably wrong in all the right ways, if you are using ground as neutral somewhere, you can be shocked because a breaker will NOT throw when it should, and you can be shocked to death by a neutral/return line just as easily as a hot line when it is being used.)
(This does NOT mean that your single connection to ground shouldn't be multiple ground rods, as you want that connection to be as low-impedance as possible, as it helps to ground out large surges such as lightning, etc.)
A modern GFCI will trip if you accidentally ground the output neutral. IMO this is a very good thing, in part because it prevents problematic wiring practices like this downstream of the GFCI.
Modern GFCIs are kind of a wonder-device, in that they prevent bad wiring but also make other types of bad wiring safe - you're much better off putting an UNGROUNDED GFCI in instead of miswiring a 3 prong outlet or adapter in an ungrounded box. It's my go-to now to "fix" two prong outlets.
> If neutral is connected to the physical ground at multiple points you have a quite dangerous electrical fault, and should get it resolved.
Mostly true, except that neutral will also be re-grounded at the service transformer.
The NEC actually requires this (or more specifically it requires it to be grounded before it gets to the building, see NEC 2020 250.24(A)(2)). This is honestly a little weird, as typically that grounding would be before the service point, and thus outside the NEC's jurisdiction. The service point cannot be before the transformer, as only instrumentation transformers are allowed on the service before the service disconnect. But in any case, the utilities code has a similar requirement.
This means that neutral current absolutely can go though the bond at the service disconnect, down into your grounding electrodes, though the earth, and out at the transformer's grounding electrode, and up to neutral wire grounding at the transformer. Which is not really ideal. As long as the neutral has not failed, it is not a huge deal, as any interruption in the path would not cause significant voltages or spikes, but instead more current would travel over lower impedance neutral service conductor. It is more of a problem if the neutral service conductor has failed.
The connection between the transformer and the main breaker (including the service entry point at the top of the house/underground, and the meter) is not breakered, so it's understandable it would have weird/different protection requirements.
Yeah, I was saying the feeder neutral has ties to ground at the pole and usually at multiple points near the house: multiple ground rods, UFER, copper water pipe, etc.
The equipment grounding conductor (typically referred to as the 'ground') for branch circuits shouldn't touch physical ground. Unless of course the circuit is a feeder to a detached building, which needs its own ground rods.
Not in California! IMO this practice is dangerous (it intentionally runs current in a path that will divert some of it through the ground), and California has banned it for a long time. In CA, there may be a “primary neutral” that is grounded, but it’s not grounded in multiple places, and the transformer inputs are insulated as if the primary neutral is not grounded.
(I think the actual motivation for the ban is that ground currents are dangerous to cattle.)
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[ 0.28 ms ] story [ 48.0 ms ] threadI think it's interesting that a similar idea can actually be demonstrated in your own home. Because current takes all available paths in relation to their impedance, the household 'neutral', which is also connected to physical ground at multiple points, return path isn't just through the wire itself. The ground connected to your incoming water/gas/UFER will have some small amount of the current your house is using. Most will be on the triplex wire running to the transformer, but a few amps may be on those alternative grounds.
https://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Neutra...
https://www.houzz.com/discussions/2649182/so-why-is-it-bad-t...
(Basically, and probably wrong in all the right ways, if you are using ground as neutral somewhere, you can be shocked because a breaker will NOT throw when it should, and you can be shocked to death by a neutral/return line just as easily as a hot line when it is being used.)
(This does NOT mean that your single connection to ground shouldn't be multiple ground rods, as you want that connection to be as low-impedance as possible, as it helps to ground out large surges such as lightning, etc.)
https://www.electricallicenserenewal.com/Electrical-Continui...
Mostly true, except that neutral will also be re-grounded at the service transformer.
The NEC actually requires this (or more specifically it requires it to be grounded before it gets to the building, see NEC 2020 250.24(A)(2)). This is honestly a little weird, as typically that grounding would be before the service point, and thus outside the NEC's jurisdiction. The service point cannot be before the transformer, as only instrumentation transformers are allowed on the service before the service disconnect. But in any case, the utilities code has a similar requirement.
This means that neutral current absolutely can go though the bond at the service disconnect, down into your grounding electrodes, though the earth, and out at the transformer's grounding electrode, and up to neutral wire grounding at the transformer. Which is not really ideal. As long as the neutral has not failed, it is not a huge deal, as any interruption in the path would not cause significant voltages or spikes, but instead more current would travel over lower impedance neutral service conductor. It is more of a problem if the neutral service conductor has failed.
The equipment grounding conductor (typically referred to as the 'ground') for branch circuits shouldn't touch physical ground. Unless of course the circuit is a feeder to a detached building, which needs its own ground rods.
(I think the actual motivation for the ban is that ground currents are dangerous to cattle.)