Is it ok to have mixed grounds and neutrals on bars in a breaker box?

Question

So to continue my line of electrical questioning (and perhaps narrow down my flickering light problem), I took a look through the two panels in this house. There is a 200amp main service in the basement, which then feeds up to a 100amp sub-panel for the main floor. This 100amp sub feeds a kitchen (fridge, microwave, dishwasher, gas range), a bathroom, 3 bedrooms, and a living room. The 200amp main feeds the 100amp sub, 2 bedrooms, a living room, a washer/dryer (gas dryer), a utility room (well pump, pressure tank, gas water heater, gas furnace), and an A/C.

My first concern is that the main service panel has the bare ground and neutral wires mixed on the two bus bars. Reading around, some say this is OK, other's say it is bad. Any thoughts? The sub-panel is wired with grounds and neutrals on separate bars.

My second concern- is a 100amp sub sufficient for the main floor?

Answer 1

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.

Answer 2

The wiring issue is not a matter of pride, neatness or whatever... it's a safety issue. :)

At the service panel (ONLY AT THE SERVICE PANEL - HUGELY IMPORTANT) the neutral bus bar is bonded to ground. You should see the ground lead and neutral tied to the same bus (the neutral bus bar). Based on your description, it sounds like your panels are wired correctly. It just doesn't "look right" based on how the other panel is made up. I can completely understand how this can seem incorrect from a common sense perspective.

However, any sub-panel after the primary service from there MUST have an isolated neutral. DO NOT DO NOT DO NOT bond neutral to ground in a sub-panel.

Why is this? When you tie neutral to earth ground in a subpanel, you create a potential parallel path for current to return via earth (ground). In the event of a fault, your ground conductor has assumed the role of the return path for current and now everything that you've grounded (sub-panel, appliances, metal fixtures, etc) to that sub-panel is now hot.

All it takes is a preexisting fault, one rainstorm, or wet feet, whatever... and you touching something energized - and you're doing the 60 cycle shuffle.

Answer 3

You can just use whichever bus is easier to get to in the main panel since they are wired together, either with a large wire, or they can be physically the same piece of metal.

That being said, any electrician who take pride in their work will make sure that all of the neutrals run to one bus-bar, and the grounds the other.

Also it makes it so that later down the line, you can add a new panel as the main one, using the old main panel as a sub-panel without a lot of rewiring.

Answer 4

Your panel wiring may start out nicely dressed, but after a couple changes it won't be. I've got wiring out of all 4 sides now, and a sub-panel, And I now keep wiring a prudently short as possible; so Ground and neutral go together on the closest bus.

Answer 5

If you tie both neutral and ground to earth ground, or both to utility ground (AKA neutral), you have then defeated the purpose of having redundant grounding paths. You have in effect removed the fail safe by combining them and placing them on one leg/ground.