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

Here is a good explanation of the neutral and ground wires.

The standard U.S. household wiring design has two 120 volt "hot" wires and a neutral which is at ground potential.

One circuit can supply a "hot" wire to several circuits in parallel. Their neutrals are tied to the neutral tie block. The ground is a second path to the neutral block which is grounded.

This is why when you touch the hot wire you get shocked, you become the ground and complete the circuit.

When wiring sub panels you must separate the bus bars so you will have one ground bus and one neutral bus, but at the main panel they are left connected and thus both wires can be connected to the same bus bar.

Answer 2

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 3

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. So 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, but 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're created a potential parallel path for current to return via earth (ground) - so 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.