To bond or not to bond neutral and ground in new electric service panel?

   / To bond or not to bond neutral and ground in new electric service panel? #1  

dweitzel

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My question is the bonding screw between the ground bar and neutral bar always required in a new, stand alone entrance service panel? This is not a sub-panel, nor will I be installing a sub-panel.

I have installed a Square D, 200 amp, QO panel and need to know if I need to install the green bonding screw in the upper right corner between the ground bar and the neutral bar? The reason I ask is my HVAC contractor installed my 220v heating equipment and installed the ground wire to the neutral bar, and I believe the 220v system should not be attached to the neutral, but the ground, however; if I bond the ground and neutral bar together, isn't that the same thing?

What happens or could happen if the two are not bonded? Everything appears to be working correctly without the bonding screw.

Any help or explanation would be appreciated.
 
   / To bond or not to bond neutral and ground in new electric service panel? #2  
In the service entrance panel the “ground” and “neutral” are required to be together. With that, the green screw is required.

Bonding, per code, has a different meaning.
 
   / To bond or not to bond neutral and ground in new electric service panel? #3  
I'm not an electrician, I just pretend to be on TV.

The way I understood it as explained to me by our local electrical inspector (and this may just be our local code, so see if it applies to you):

Start at your meter base.
If the main electrical panel is more than 10' from the meter, a disconnect has to be installed outside below the meter. That disconnect is the main disconnect. Any box downstream from that main disconnect is treated as a sub-panel, even if its the only panel in your house. So the neutral and ground should not be bonded in that panel, it should be bonded in your main disconnect.

So, from your description... is there anything in the line between your meter and that panel? If not, that panel is probably considered the main disconnect, and the neutral and ground should be bonded there, in that panel.

Make sense?
 
   / To bond or not to bond neutral and ground in new electric service panel? #4  
What happens if?

The utility uses the earth as the neutral/ground. By requiring a ground at the service entrance this ensures a good “return path” for the electricity. If the two aren’t together at the service entrance the return path (neutral) is much further down the line. This can degrade your electrical service.
Because the neutral can carry power the neutral and ground are separated in the house. Neutral for “return” current flow or to complete the circuit and the ground for safety.

You don’t say where the HVAC guy attached the ground/neutral. If it’s in the panel it shouldn’t matter if the panel was set up properly. If it’s at the equipment a 240v 2 wire circuit is two hots and a ground. A 240v 3 wire circuit adds the neutral and still a separate ground. Some 240v appliances need the neutral because they use 120v for some functions (or it’s a GFCI- not covered here)- that requires the neutral. Most HVAC stuff runs on just 240v so just 2 hot wires and the ground.

With your neutral and ground not together at the main panel you run the risk of the HVAC ground (attached the the neutral) becoming the path of least resistance to utility neutral/ground.
 
   / To bond or not to bond neutral and ground in new electric service panel? #5  
Then: with the main panel going to an earth ground, what about a sub-panel 100 ft away in the barn? That one has its own grounding rod. Is this code?

Actually all the neutrals and grounds are tied together there. It's an old barn so not everything has a green wire coming back to the panel.
 
   / To bond or not to bond neutral and ground in new electric service panel? #6  
Then: with the main panel going to an earth ground, what about a sub-panel 100 ft away in the barn? That one has its own grounding rod. Is this code?

Actually all the neutrals and grounds are tied together there. It's an old barn so not everything has a green wire coming back to the panel.

The ground/neutral bond should only happen at the main service entrance. Everywhere downstream of that, ie, sub-panels, neutral and ground are to be kept separate.

Code calls for ground rods at outbuildings. That only applies to a feeder, where there is a panel and multiple circuits in the outbuilding. If it's a branch (ie, single circuit hanging off your main panel) then ground rods are not required.

250.32 Buildings or Structures Supplied by a Feeder(s)
or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) sup-
plied by feeder(s) or branch circuit(s) shall have a ground-
ing electrode or grounding electrode system installed in
accordance with Part III of Article 250. The grounding
electrode conductor(s) shall be connected in accordance
with 250.32(B) or (C). Where there is no existing ground-
ing electrode, the grounding electrode(s) required in 250.50
shall be installed.
Exception: A grounding electrode shall not be required
where only a single branch circuit, including a multiwire
branch circuit, supplies the building or structure and the
branch circuit includes an equipment grounding conductor
for grounding the normally non膨urrent-carrying metal
parts of equipment.
 
   / To bond or not to bond neutral and ground in new electric service panel? #7  
You want to keep the neutral and grounds separated outside of the main panel. So bond the main and don't bond the sub panels.
 
   / To bond or not to bond neutral and ground in new electric service panel? #8  
I don't see a ground wire from the house out to the barn sub-panel. Just two hot one neutral for 100 amp 240 service. Does that change anything?

I know the barn was wired by amateurs some 55 years ago, and I think electricity was added to the existing house in the 1920's. An outlet tester at some locations shows combinations of lights that aren't on the list of good/bad responses.

I had to remedy something that made the chrome-plated kitchen percolator tingle when touched. That could have been deadly if someone added a longer cord and filled it at the faucet while plugged in. I suspect electricity bleeding to ground somewhere was the cause of major pipe corrosion, galvanic action, that seems to have ended after I got a few things wired like they should be.

This farmhouse is out in the country, never had a building inspector sign off anything. Dad's advice was just bulldoze the place when he was gone, too much was beyond repair. Now I'm getting old and telling the same thing to my kids. It's a cute little farmhouse (and outbuildings) but everything needs attention continually to stay functional.
 
   / To bond or not to bond neutral and ground in new electric service panel? #9  
220v requires 3 wires. 1 called ground & 2 "Hot wires. Nothing more is needed.
 
   / To bond or not to bond neutral and ground in new electric service panel? #10  
The neutral and ground should be bonded at the first (main) disconnect point. This is usually the service panel. So yes, if they are not bonded elsewhere (example: an upstream service disconnect switch), bond them in your panel.
Bonding the ground to neutral insures that if a energized ( hot) conductor shorts to a case or enclosure that is “grounded” ( green wire), it has a low resistance path back to the neutral ( winding) of the transformer. Counterintuitive, but this ensure that a LOT of short circuit fault current flows and the breaker will trip. Good.
Without it bonded you are relying on the fault current to travel through the actual ground (earth) to get back to the neutral winding of the transformer (assuming transformer has its own neutral connection to ground/earth). The resistance of the earth may be high and limit the fault current so the breaker does not trip. Bad.
By code, you cannot can not rely on the earth to carry (fault) current.
It’s also possible that if not bonded in your panel, that the transformer’s neutral is not grounded to earth ( example: if not grounded at the pole), and your panel neutral will be floating. (i.e. not “locked” to zero volts) . This would lead some strange voltage splits, that is, your 240V won’t divide evenly into 2 - 120v legs.
 
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