Originally Posted by mpoulton
Whoa, there! Hold on a minute. This looks like a 3-wire feed, not 4. He can only separate neutral and ground if there is a separate grounding conductor back to the main. Otherwise this would be disastrous - the panel would be ungrounded. A 4-wire feed may not have been required at the time this was installed, in which case a 3-wire feed with neutral and ground bonded is perfectly acceptable.
While you are correct that I SHOULD have asked if the panel was fed with a metal conduit, a grounded conductor is not required to separate the grounds and neutral. It very well could be a 3 wire feed with the conduit supplying the ground path.
If the panel is is done in PVC with 3 wires, then the panel isn't grounded anyway (no bond screw from the neutral bar and the case) and we could debate which is more dangerous, bonding the neutral and ground or having no ground.
Judging by the age of that panel, a ground would be required. There is new(er) THHN's feeding the panel and romex thruout. I don't know when the code changed that required neutrals and ground not be bonded, but I know it was well before romex came along.
I'll ask the question now, how do the feeders arrive at the panel? Metal conduit or PVC?