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After having issues with lights flickering, I noticed the main 100A breaker was warm and arcing slightly. Instead of just replacing the breaker, I decided to call in a electrician to install a larger panel with spaces for more breakers, as I was planning to install an air conditioner in the future.

He said the existing ground wire wasn't long enough, so he connected it to the metal wall of the panel with something that looks like a miniature bus with one screw. (sorry, I forgot exactly what it was called)

Is it really safe to do this? Is there any advantage/disadvantage to connecting the grounding wire to the metal casing of the panel instead of directly to the neutral bus?

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Most panels have a neutral bus and a ground bus both of which are connected to each other, the service entrance neutral, and the panel. All of this is bonded to the grounding electrode. However, without knowing exactly what he did, what brand panel it is, and your location, it's impossible for us to tell you if it's acceptable or not. If you could add some more information and a few pictures, that would help a lot. –  Tester101 Feb 3 '13 at 22:05
Their should be a seperate neutral and ground bus in the panel and the panel box should be grounded to the ground bus. The neutral and ground however should be connected by a wire as well. The important thing is, if the main breaker is still warm and if your lights are still flickering. Simply adding more slots for additional breakers and properly grounding your panel isn't going to fix this by itself. –  maple_shaft Feb 4 '13 at 13:11
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3 Answers

The panelboard will be bonded to ground, and according to the National Electrical Code (NEC) it must be done so using specific methods.

250.8 Connection of Grounding and Bonding Equipment.
(A) Permitted Methods. Grounding conductors and bonding jumpers shall be connected by one of the following means:

(1) Listed pressure connectors
(2) Terminal bars
(3) Pressure connectors listed as grounding and bonding equipment
(4) Exothermic welding process
(5) Machine screw-type fasteners that engage not less than two threads or are secured with a nut
(6) Thread-forming machine screws that engage not less than two threads in the enclosure
(7) Connections that are part of a listed assembly
(8) Other listed means

(B) Methods Not Permitted. Connection devices or fittings that depend solely on solder shall not be used.

If the specific method used in your situation fits one of the methods listed above, then the panelboard is likely grounded properly. The ground and neutral bus bars inside the panel are surely bonded to the panel itself using one of these methods. Which means as long as the panel is connected to the system grounding conductor using an approved method, the system should be properly grounded.

If you have doubts as to whether or not the installation is correct. Contact your local government and check on any permits that were obtained for the work, and/or request the installation be inspected by the local electrical inspector.

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Nope, the box breaker wall is not designed to serve as a ground bus.

Yes, it is grounded so that if a stray wire falls onto the wall this incurs a leak or a short and protection trips but it is not meant to serve as the primary path to ground.

You have to extend the actual ground wire and use it as a ground.

So although from the common sense point of view you're perhaps okay (I've seen much worse installations and noone was shocked), the described installation violates the idea of how grounding is designed and so is not proper grounding.

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Yes this is probably fine. Usually grounds and neutral are connected to the same bus but if that is full you can add a ground bar that connects to the housing.

Only grounds should be connected to it though not neutrals.

For instance this Square D Catalog has a "Grounding Bar Kit" designed to add additional ground terminals to the Load Center.

This Instruction manual for the Grounding Bar kit shows that it may be installed with a single screw.

As mentioned in the comments both proper installation and a compatible grounding bar is required for it to be safe.

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"probably fine", and electricity don't mix. There is no way of telling if this installation is done properly without seeing it, so this answer is completely speculation. Please provide some facts to support your statements. –  Tester101 Feb 4 '13 at 12:06
I added links to specific products the can be used for this purpose. –  Craig Feb 4 '13 at 16:15
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