Adding ground bars

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Since this panel does not have a main breaker, is there a situation in which the MBJ screw would be used in this type of panel?
If no main then it must be sub panel, main lug, even if only to a service disconnect, neutral and grounds must be seperated already, any other condition would be a violation of code, and MBJ would not be used. The panel in picture is a main breaker type, breaker not really clear in picture.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
Since this panel does not have a main breaker, is there a situation in which the MBJ screw would be used in this type of panel?
It is a main breaker, but if it was just a MLO, you could add a main, either with a main breaker kit or a breaker on the bus with a hold down bracket, then you could use the MBJ. Otherwise, it is as was stated, a subpanel and the MBJ is not to be used.
 
My panel had those 4 holes that were for future ground bars on each side. If it did not have those holes and I added a ground bar then I would have had to connect with a wire? The enclosure I don’t think would have been thick enough to get enough threads in.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Since this panel does not have a main breaker, is there a situation in which the MBJ screw would be used in this type of panel?
Well, one, technically speaking: No loads require a neutral and you use the neutral bus as the EGC bus.

I did that when I added a second 200a main breaker outside for a tankless water-heater panel inside.

I used SE cable; two hots and ground; no neutral. The inspector failed it until I got him to call his boss.
 

Jerramundi

Senior Member
Location
Chicago
Occupation
Licensed Residential Electrician
You've lost me, what does the MBJ have to do with attaching the EGC bus to the metal enclosure?
I'm not asking about that. I'm asking about 250.24(B)'s explicit use of the word "unspliced" in its' reference to the MBJ being used to connect (1) the equipment grounding conductor(s) and (2) the service-disconnect enclosure to the (3) grounded conductor.

The use of the word "unspliced" to me implies the use of a continuous length of wire used to connect these (3) components.

250.24(B) Main Bonding Jumper. For a grounded system, an unspliced main bonding jumper shall be used to connect (1) the equipment grounding conductor(s) and (2) the service-disconnect enclosure to the (3) grounded conductor within the enclosure for each service disconnect in accordance with 250.28.
 

Jerramundi

Senior Member
Location
Chicago
Occupation
Licensed Residential Electrician
I'm well aware of the magical green screw and how things are typical done. I'm just at that point in my career where I'm studying the code for myself, independent of another electrician telling me what's what, and deciphering it for myself (for better or for worse).

And to me the above wording implies that a continuous length of wire should be used to connect the enclosure and the GECs to the ungrounded conductor.

Something about utilizing the enclosure to transfer a ground fault to the neutral doesn't seem right to me unless of course, that fault is within the enclosure itself, then it's unavoidable. Otherwise I feel like faults on EGCs shouldn't rely on the enclosure as a conductive pathway.
 

Jerramundi

Senior Member
Location
Chicago
Occupation
Licensed Residential Electrician
Although I suppose one could argue that it's similar to a metal conduit raceway being used to conduct a ground fault back to the system neutral, the only argument against this I would/could make would be that a metal conduit raceway is actually NEC approved as an EGC, whereas the same is not true of a panel enclosure as far as I'm aware.
 

Jerramundi

Senior Member
Location
Chicago
Occupation
Licensed Residential Electrician
My panel had those 4 holes that were for future ground bars on each side. If it did not have those holes and I added a ground bar then I would have had to connect with a wire? The enclosure I don’t think would have been thick enough to get enough threads in.
These debates can muddy up the original question. Let me see if I can clarify this discussion for you a tiny bit...

If this is the first point of disconnect (i.e. the main panel and not a sub panel), the answer to the question...

"Do you have to connect (1) the 'Ground Bar' (more precisely referred to as the 'EGC Bus' or 'Equipment Grounding Conductor Bus') to (2) The Main System Neutral (more precisely referred to as the 'Ungrounded Conductor')".... is YES.

This is how you clear a ground fault. A fault current flows on the green Equipment Grounding Conductor back to the system neutral... allowing the circuit to pull a large amount of current and trip the circuit breaker.

What we are debating is whether or not the connection between (1) the 'Ground Bar' and (2) The Main System Neutral or 'Ungrounded Conductor' can be done by just tightening that green screw on the neutral bus (which you may or may not have available depending on the type of panel). This green screw connects to the neutral bus to the enclosure and the enclosure is connected to the ground bar.

Most people just tighten the green screw and they are done. I myself have done it this way for years. If you don't have this green screw, you need a wire-type connection sized according to Table 250.102(C)(1).

It's just in the last 5 or so years I've started reading the code for myself, as opposed to just taking direction from others, and am arguing that perhaps the panel connection may not be acceptable... but I admit I could be wrong.

Either way. If this is a main panel, you need that connection... either via the enclosure or via a wire type jumper.
 
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