But this doesn’t tell you about the overhead lights, of which there are several.
Just for the hell of it I turned off the two ganged breakers that the legend identified as cuisine and then went to the kitchen and everything I checked was still on. Two of the four receptacles I looked at (the other two are hard to access), the lights as well as the appliances which of course have their own breakers. I don’t see any reason why 4 receptacles need two circuits anyway. I guess the toaster over draws a lot, but the microwave has its own circuit. At least there is breaker labeled micro-onde. The whole thing is obviously f**ked-up.
There’s an adapter that screws into a bulb socket the works for those types of fixtures. Otherwise you might have to pull the fixture to access the leads.
I have my aquarium electrical equipment protected by a GFCI in a two wire circuit. It does interrupt the circuit. I would think this is because in a two wire circuit, neutral is ground.
No. Neutral is never ground, and regardless a ground wire is not relevant to the operation of a GFCI. GFCI circuitry doesn’t even connect to ground. A GFCI monitors hot and neutral (in US-style 120V circuits) to make sure that the exact same amount of current is flowing on each wire. If there is an imbalance, all the load side terminals get disconnected from their corresponding line-side terminals. If any additional receptacles are being fed from the load terminals of a GFCI receptacle, they will all be cut off. It doesn’t matter if the fault is current from hot going directly to a ground wire, getting back to neutral upstream of the GFCI, going to a water pipe, going into the actual dirt ground, or extra current coming in from the hot of a different circuit somehow. They’re all faults and the circuit will be interrupted.
A 220v grounded outlet has four wires.
Hot 1, Hot 2, Neutral, and Ground.
There is 120V between each Hot and Neutral, and 240V between the two Hots.
Ground is electrically the same as Neutral. It’s just another wire that is run from the Grounded bonding bar in the breaker box.
The Neutral is used so that 120V loads can be powered (like a motor in a clothes dryer, while the heating element is powered from 240V). The ground should never have any current flowing in it - it’s just for safety.
Note that older 240V-only appliances (like some dryers and stoves) used to bond the Neutral to the chassis, which was probably not a great idea if there were loads in the appliance that used Neutral - if the Neutral wire was unbonded at the breaker box, the chassis of the appliance would become a shock hazard. Hence the 4th wire as a dedicated ground.
While all true, which is unsurprising since you’re in the biz, that’s probably way above @carnivorousplant’s head.
You need to be precise about whether you’re talking about ground level voltage, a physical ground wire, or one of the other many uses of the word “ground”.
An electrical system runs on the difference between the input and output wires. Here in the US that 120V nominal at an ordinary outlet. Neither of those wires need to be at the same voltage as the Earth. And absent any explicit connection to the Earth neither one will be at the same voltage as the Earth is.
Ground wires (not “grounds”) were added to household power circuits back in the 1960s as a third unpowered wire to provide a separate permanent escape ramp for any electricity leaking out to the exterior of the plugged-in lamp or appliance. Back in the day when nothing was plastic and most lamp and appliance bodies were made of metal.
The fact you mentioned 220V and center tap in the same breath as “ground” suggests to me that you’ve got just enough terminology and understanding to get everything turned sideways half inside out. I don’t say that to be mean or dismissive. Just that untangling those misconceptions would be easy in a face to face convo, but maybe prohibitively hard over a messageboard.
It’s bedtime here, but If you want to try again I’m willing to see if I can add value, not further confusion, in the morning.
Before the three-prong era, there were many electronic devices that were breathtakingly dangerous.
Have you ever heard of a musician being electrocuted by his guitar amplifier? That’s because in the good-old-days, when Amps used tubes, some early designs were transformerless. That meant that there was a 50% chance that each time the amp was plugged in, the chassis (and the “ground” connection on the guitar plug) was “live.” Even amps that did use a power transformer were dangerous, since they didn’t have a ground wire, and a fault in the amp could make the chassis “hot”.
It was not uncommon in the early part of the 20th century, in the USA anyway, for many, meaning more than one but less than all, to be transformer less. Manhattan for many a year had DC power to many areas. So radios and such did not have transformers in their design. My Grandparents has two such radios that I’ve seen and used.
Nothing.
Note how the leg marked “Neutral” is grounded.
But - that doesn’t mean that in your house Neutral=Ground.
When power is run from a step-down transformer on a pole, or in a box on the side of the street, only three wires are run to the break box at your house. Just like the diagram shows. But, inside the breaker box, a 4th circuit is created - the “Earth Ground” (or Safety Ground). In the old days, this ground was clamped to a nearby water pipe, “bonding” the neutral to Earth Ground. There days that’s frowned upon (because modern plumbing is often PEX, not copper), and a separate copper ground rod is driven into the ground and used. Or, for concrete construction, something called a Ufer ground is used.
In any case, Neutral and Ground are connected at the breaker box, and run throughout the house. Electrically they are identical, but their functions are different. The only time current is supposed to flow in the ground connection is during a fault, which will (hopefully) trip the breaker.
And houses from the 50s won’t have any ground wiring in them at all. At least in the original installation; upgrades since then are a crapshoot loosely based on common practice whenever they were done.
Which original two-wire systems lacking dedicated ground wires are inherently rather dangerous and generally are (and long have been) required to be upgraded when significantly altered.
Aside from the “ground” vs. “grounded” issue, the other issue is that you said (my bold):
The voltages, with respect to ground, of the lines passing through a GFCI are entirely irrelevant. The fact that neutral is bonded to ground at the service entrance does not matter to the functioning of the GFCI.
A GFCI can be designed to handle any of the following, and more:
one phase that’s 120V from ground and one that’s 0V from ground
one phase that’s 520V from ground and one that’s 400V from ground
two 60V phases 180 degrees apart (120V difference, used in UK worksites)
two 120V phases that are 180 degrees apart (240V difference)
two 120V phases that are 120 degrees apart (208V difference)
three phases
All that matters is that the current coming in over the monitored wires is exactly equal to the power going out over the monitored wires. If there is an imbalance (whether due to current leaking out - possibly through a human - or coming in from another source) it disconnects
(For the nitpickers, yes, the voltages with respect to ground must be within some reasonable limit such that the exposed terminals don’t just start arcing to other nearby chunks of metal - inputs of 1,000,120V and 1,000,000V with respect to ground [still 120V apart] wouldn’t fly with a regular household GFCI)
It’s worth noting that a GFCI would not save you if you somehow managed to touch one of its protected terminals with one hand and another with the other hand, while otherwise insulated from the electrical system. There would be no imbalance, so no detectable fault to interrupt. Fortunately that’s very