More fun electrical questions!

[Jeff7]

Originally posted by: Paperdoc
Hey, you've lost focus by asking the wrong question. The problem is not just that you have only one outlet box with a ground lead in it. The real problem is that you have ONE circuit into the room with a maximum capacity of 20 amps. I don't care what you hook into that outlet box, you will not change the total capacity of the circuit, because that's set by the new breaker in the panel.

Now, you could connect all sorts of things into the single 20-amp circuit to give you many grounded outlets for plugs. (Well, actually, there are code limits on how many outlets can be on one circuit.) BUT then you would have to monitor your uses and ensure that you never exceed 20 amps total at one time. In fact, the breaker will do that for you, sort of - it will pop off if you run too much load. But if you plan to use more power than that, the only solution is to add more 20-amp new circuits, starting from the panel with a new breaker and wiring. Before you have that done (I would guess you cannot do it yourself), you need competent advice on whether the panel itself, and its supply, can accomodate more 20-amp branch circuits.

By the way, a GFCI is NOT a substitute for a ground lead! A ground lead ensures that the chassis of the load device (saw, toaster, whatever) is grounded just in case a fault causes a live wire to touch it. If that happens, the presence of a ground connection ensures two things: the current flow to ground will be VERY high and it will trip the breaker; and, the chassis should remain at nearly zero volts during that brief mishap. A GFCI, on the other hand, checks the currents flowing in the supply line and ground line; if it detects that they do not match within 5 mA, it trips itself open because there is current flowing someplace it should not. This does NOT guarantee that the unexplained current is flowing to a safe place - it could be through you! But the 5mA limit is low enough that it will prevent serious injury to you.

To be honest, I am not sure whether GFCI units need to have a good ground to "refer to" for their operation. I have no doubt they are designed for installation in modern circuits that have good grounds, but I cannot say whether they work without them.

Just to clarify, there are multiple circuits being run into the room. Only the one circuit, which has only one pair of outlets, has a genuinely good ground.
The rest of the circuits have a current capacity of at least 15A.

And monitoring current use could be tough, as the startup draw of some of these motors can be close to 20A. That's part of why I want to spread out the usage across multiple circuits.


So if I do this:
Grounded vacuum on Circuit 1 + Ungrounded GFCI-protected outlet on Circuit 2
would that be ok?



(Oh, and you don't want to ground a toaster's chassis. )

 

[BigJ]

Originally posted by: Paperdoc
A GFCI, on the other hand, checks the currents flowing in the supply line and ground line; if it detects that they do not match within 5 mA, it trips itself open because there is current flowing someplace it should not. This does NOT guarantee that the unexplained current is flowing to a safe place - it could be through you! But the 5mA limit is low enough that it will prevent serious injury to you.

To be honest, I am not sure whether GFCI units need to have a good ground to "refer to" for their operation. I have no doubt they are designed for installation in modern circuits that have good grounds, but I cannot say whether they work without them.

Absolutely incorrect.

The GFCI will look for the difference between the hot and neutral. They are the only receptacles approved for replacment of non-grounded receptacles besides other two-prong outlets (no I'm not going to mention GFCI breaker + 3-prong/grounded outlets). They absolutely do not need a ground to work, although you can run into very severe problems if your neutrals aren't wired properly.

 

[Paperdoc]

Sorry and Thanks, BigJ. I mis-typed ground when I should have said neutral line. And thanks for answering my unknown - a GFCI does not need a proper ground to function, OK. I certainly understand that a GFCI can yield protection similar to a good ground. But it ONLY cuts off the circuit after there is actual unbalanced current flow through some unintended path. On the other hand, a ground without GFCI will not protect a person who mistakenly contacts a live wire which is NOT grounded. In that case the person becomes a conductor and may NOT cayse a breaker to pop open, even thought the current through the person may be lethal. That's why both systems are required in some applications. For example, where I live a GFCI is required for all outlets in a bathroom.