Replacing old two prong outlets?

I recently purchased a home built in the late 1950s. ALmost all outlets in the house are 2 prong.
Upon further investigation at several outlet boxes, I found that the wiring, although old (it's that old silver colored cable) it does actually have 3 wires , black,white and copper.

Looking in the outlet boxes, I can see that they actually took the ground wires and twisted them together.
These are all metal boxes btw.
I also checked a couple of the ceiling light boxes and found the same. Metal boxes, 3 wire cables, with the grounds twisted together.

Of these boxes I checked, some are grounded via a connection to these twisted together ground wires, and some are not.

I used a meter and checked from the hot leg, to the ground and it checks out in all cases.

next I went to the main breaker panel to see how that end of the circuits was and what I found was that the ground wire in each of these older cables (there are 4 or 5 of them total, leaving the breaker panel) are all actually 'grounded' to the cable connectors on the box, except for one of them, which is appropriately grounded to the ground bar in the breaker panel. Not sure why this was done this way, unless it was a left over from the original,old fuse panel and they didn't want to or couldn't extend this ground wire and attach to

So, a couple of questions.....

1- does anyone know why this was done this way (ie. i'm talking about the ground wire being attached to the cable connector where it enters the box, instead of the ground bar

2- is this considered an appropriate ground (thinking the ground wire is connected to the cable connector, which is on the box)?
3- I have no idea why this was done this way as the cable is 3 wire(hot,neutral,ground). The ground is there, but not
used in the fashion I would expect it to be
4- TO convert these two prong outlets to 'safe' 3 prong, can I just pigtail at each box the two ground wires in each cable and attach to the ground screw on the new 3-prong outlets AND ground to a ground screw on each box? h

 

Your lucky they are inside the box. In many cases the early cable grounds were connected to the outside of the box. Assuming the boxes are metal as you wrote you will need to pigtail to both the box and the receptacle to meet current code.

The electrician that probably installed them was probably trained on ungrounded circuits and just did them the way he understood.

 

ok. I figured as much, but wanted other opinions as I've never seen anything like this. I'll then proceed with the pigtail

 

OK, so, I forgot and have another question then.
In my first post I mentioned how the ground was made at the service panel.

THe ground is NOT connected to the ground bar, but rather, it's looped around
the cable connector, where the cable enters the service panel box and its securely fastened to the cable clamp/connector.

It this OK, or do I also have to somehow try to extend this ground(they or course cut it off short) and attach it under one of the open grounding screws in the ground bar?

 

If the service panel is the first service panel you must connect either to the ground bar, if there is one, or the neutral bar. If it is a subpanel and new enough to have a ground bar then it must go to the ground bar otherwise to the neutral bar. You can add a short pigtail using a wire nut if you need to.

 

Many times you can unwrap the grounding conductor and slip it into the connector to reach into the panel.

 

OK thx for the additional information.