3 ms·

> Another problem springs up. At present, some appliance manufacturers INTENTIONALLY connect the outside of their metal products to one of the power wires. This

by tjic 14y ago

> Another problem springs up. At present, some appliance manufacturers INTENTIONALLY connect the outside of their metal products to one of the power wires. This must be stopped. I disagree with this. If one side is tied to ground (and it is), then tying the chassis of a piece of equipment to that same line is the same as tying it to ground...a ground that you're already standing on. Am I missing something?

dattaway 14y ago
Voltage drop across the neutral side can and does happen. Also, loose connections often happen on the neutral side supplying the plug. This could give you the full voltage across your chassis.
- mturmon 14y ago
  "Voltage drop across the neutral side can and does happen." This is true. Even though the neutral conductor is grounded at the panel box, loading elsewhere in the circuit can cause the neutral conductor to have a potential above ground. That is, there is a small resistance of the copper wire as it goes from the electrical outlet back to the panel box. If something in the circuit is drawing significant current, this small resistance can cause a voltage to appear in the grounded ("neutral") conductor. If your home uses "shared neutral" wiring (two opposite-phase 120V hot lines sharing a single neutral wire for the return), then even throwing the circuit breaker on a given circuit can leave a potential in the neutral wire. This is because the paired hot conductor can be carrying current, causing the shared neutral wire to have potential. This can be surprising.
harpastum 14y ago
From my reading, the reason it was unacceptable was that since the wires were previously identical, the manufacturers attached an arbitrary wire to the case, so 50% of the time it wasn't the neutral one. So, once we switched the polarized plugs, some of the appliances would always have a hot chassis; unless we made sure appliance-makers always attached neutral to the chassis.
fshaun 14y ago
If everything is wired and functioning correctly I believe you are correct; the article mentions the case of electricians mixing up hot and ground wires. Presumably an appliance manufacturer could also have a mistake, but assembly lines are more consistent than humans -- if UL or CE tests a device it's likely all devices of that model are OK.
Sidnicious 14y ago
Keep reading. At that point outlets aren’t polarized and the case might end up connected either to ground or to the hot wire depending on how you plug it in. Even when outlets are polarized… > “Occasionally an electrician will accidentally wire an outlet backwards. This can't be helped, because Perfect Electricians are far more expensive than the normal human variety. And so we cannot intentionally wire appliance cases to the Wide Prong of the plug, since it would cause a lethal hazard if the appliance was plugged into a miswired wall outlet. Miswired outlets look exactly the same as the normal ones. > “The solution? Why, add a Third Prong! Connect this prong to the neutral side of the network, but do it only in one place in the circuit, and run a new third wire out to all of the wall-outlets. Give this wire a new color, one which is different from the other two. Give this this third prong a very different shape as well, so even Highly Imperfect Electricians will rarely connect the special prong to the wrong wire. Inside metal-cased appliances, insist that manufacturers connect this third wire to the case.”
- excuse-me 14y ago
  And if there is any current flowing in the circuit and you have a finite resistance in the neutral wire there will be a (small) potential difference between the case and ground.

by tjic 14y ago

dattaway 14y ago

Voltage drop across the neutral side can and does happen. Also, loose connections often happen on the neutral side supplying the plug. This could give you the full voltage across your chassis.

mturmon 14y ago
"Voltage drop across the neutral side can and does happen." This is true. Even though the neutral conductor is grounded at the panel box, loading elsewhere in the circuit can cause the neutral conductor to have a potential above ground. That is, there is a small resistance of the copper wire as it goes from the electrical outlet back to the panel box. If something in the circuit is drawing significant current, this small resistance can cause a voltage to appear in the grounded ("neutral") conductor. If your home uses "shared neutral" wiring (two opposite-phase 120V hot lines sharing a single neutral wire for the return), then even throwing the circuit breaker on a given circuit can leave a potential in the neutral wire. This is because the paired hot conductor can be carrying current, causing the shared neutral wire to have potential. This can be surprising.

harpastum 14y ago

From my reading, the reason it was unacceptable was that since the wires were previously identical, the manufacturers attached an arbitrary wire to the case, so 50% of the time it wasn't the neutral one. So, once we switched the polarized plugs, some of the appliances would always have a hot chassis; unless we made sure appliance-makers always attached neutral to the chassis.

fshaun 14y ago

If everything is wired and functioning correctly I believe you are correct; the article mentions the case of electricians mixing up hot and ground wires. Presumably an appliance manufacturer could also have a mistake, but assembly lines are more consistent than humans -- if UL or CE tests a device it's likely all devices of that model are OK.

Sidnicious 14y ago

Keep reading. At that point outlets aren’t polarized and the case might end up connected either to ground or to the hot wire depending on how you plug it in. Even when outlets are polarized… > “Occasionally an electrician will accidentally wire an outlet backwards. This can't be helped, because Perfect Electricians are far more expensive than the normal human variety. And so we cannot intentionally wire appliance cases to the Wide Prong of the plug, since it would cause a lethal hazard if the appliance was plugged into a miswired wall outlet. Miswired outlets look exactly the same as the normal ones. > “The solution? Why, add a Third Prong! Connect this prong to the neutral side of the network, but do it only in one place in the circuit, and run a new third wire out to all of the wall-outlets. Give this wire a new color, one which is different from the other two. Give this this third prong a very different shape as well, so even Highly Imperfect Electricians will rarely connect the special prong to the wrong wire. Inside metal-cased appliances, insist that manufacturers connect this third wire to the case.”

excuse-me 14y ago
And if there is any current flowing in the circuit and you have a finite resistance in the neutral wire there will be a (small) potential difference between the case and ground.