A customer of mine had a friend wire his basement. He did a neat job, but when I opened up the mailnpanel to add a circuit, I noticed he had installed ground bars and separated them from the neutral bus bars. The neutral and grounds are not connected at all (like you would do in a sub panel). I talked to the guy about it and he said, "it is an isolated ground system which is better for electronics." I cannot find any info on where this is legitimate. Let me know your thoughts. Thanks.
Electrical – Main Panel with separated neutral and ground
electrical-panelgrounding
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National Electrical Code 2014
Article 250 Grounding and Bonding
II. System Grounding
250.24 Grounding Service-Supplied Alternating-Current Systems.
(A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).(1) General. The grounding electrode conductor connection shall be made at any accessible point from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.
This means that the grounded (neutral) from the service must be connected to ground, and that the connection can be made by bonding the neutral bus bar to the grounding electrode.
(5) Load-Side Grounding Connections. A grounded conductor shall not be connected to normally non–current carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article.
This means that the grounded (neutral) conductors should only be grounded at the main service disconnnect.
If the main service panel happens to be the same place that the grounded (neutral) conductor is bonded to the grounding electrode, then there is no problem mixing grounds and neutrals on the same bus bar (as long as there is an appropriate number of conductors terminated under each lug). If the two bus bars are not connected; as would be the case anywhere other than the main disconnect (exceptions exist), then you cannot mix them.
Notice how the grounded, and grounding bus bars are connected in the main service panel. This means that; electrically speaking, they can be considered a single bus bar. Which means that both grounded (neutral), and equipment grounding conductors can be terminated on either bus bar.
In the subpanel, the bus bars are kept separate. So grounded (neutral), and equipment grounding conductors cannot be mixed.
You'd have to remove the bonding jumper, and install a separate grounding bar.
Notice in this image, there are clearly separate grounding bars installed.
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Best Answer
This isn't what "isolated ground" means in the NEC
What your customer has is not an isolated ground -- it's an ungrounded system, which is only permitted for specific industrial applications in the NEC where electrical system availability is critical and ground-fault detection can be provisioned separately. In an ungrounded system, there is no neutral wire, just hot wires and an equipment grounding wire -- this doesn't work well with the split-phase neutral system, so 120/240V split phase services are required to be grounded (neutral on this type of service is grounded at the transformer anyway, for that matter).
An isolated ground system, on the other hand, has a normal neutral/ground bond, but runs a dedicated ground wire to the receptacle ground contact from the main bonding point, perhaps via isolated busbars on its way, but not bonded to the main equipment grounding system; likewise, the receptacle ground contacts on isolated ground receptacles are isolated from the receptacle yoke.
As to fixing this...
Go to your local electrical supply house and ask them for a Square D 4028345850K, as per this FAQ entry, then, with the main breaker turned off, install it into the mating screw hole on the loadcenter's neutral tie bar (the metal busbar behind and below the main lugs or main breaker load connections that connects the two neutral bars together).