Neutral Bus Bar Question

[89MustangGX]

Hello,

In a main panel, I understand that in an electrical panel on the bus bars, grounds can be combined with like size grounds, however neutral wires must be separate for each terminal.

First question, is my understanding correct?

Second, what would or could happen if this was not followed? For example, two neutral wires of same size were combined in a terminal. What is the reasoning for this and potential or immediate consequences?

I feel pretty comfortable with most basic electrical but I am having difficulty wrapping my head around this if neutral and ground are bonded in the panel anyway.

Thanks for any help you can give!

Adam

 

[sberry]

The neutrals are Current carrying conductors subject to thermal expansion. I had a call a while back where a handyman install did this and it loosened up.

 

[wyliesdiesels]

Yes your understanding is correct.

The issue is as sberry said above and also if u have to remove one of the neutrals both would become loose and if the second one feeds a MWBC then u could fry 120v equipment because it may see voltage above 120v all the way up to 240v. That is unless u turn off the other circuit.

 

[sberry]

Good reason for this rule, happens all the time.

 

[89MustangGX]

Thanks for the replies.

So I understand this correctly- it is not for a reason of electrical function, it is "mechanical" in the sense that might loosen up with temperature changes? How often or likely is it that thermal expansion in neutral wires happens? Example a standard 12 gauge wire. Or, does it depend on other factors?

Or, potentially if someone was working on the panel with it energized and there was a shared neutral circuit (do I understand MWBC?) that it could cause an electrical problem if that neutral was removed while still energized? Do I have that right?

Thanks again.

 

[matt_i]

Second, what would or could happen if this was not followed? For example, two neutral wires of same size were combined in a terminal. What is the reasoning for this and potential or immediate consequences?

Imo, the reason for two wires not landed under the same screw even if same-sized is the large potential for one to be very tight and taking all of the clamp load and the one next to it being very loose.

I experienced this exact problem in the plant where I work. A piece of electrical-test equipment had a set of large DC contactors that wouldn't operate when commanded, caused hours of downtime. I finally fixed it because I drew my own wiring diagram...the "as builts" were completely jacked up and wrong, and eventually I found the common neutral wire feeding both coils had 2 wires landed under the same screw. You guessed it, one was super tight and the other fell out in my hand, black from arcing. It had run for about 3 years successfully, and finally in year 4 the trouble started.

 

[sberry]

You open a neutral and its not a grounded conductor anymore, it is 120 to ground. 120V in series. with 1 leg still energized. After the Y a breaker kills the circuit provided the N remains hooked to the bar before the Y if the other leg happens to be in use. Turning both poles off in this type of circuit completely de energizes it.

 

[sberry]

You could open the N in part of the circuit with 1 breaker off without issue but the other part could have current flowing on it.

 

[sberry]

Not only 2 neutrals but the one I recently found was simply 2 wires, the ground wire and the white from the same circuit. I aint scared to run a screw driver over the screws in a panel that has been in service a while, doesnt mean reef everything tighter but look for loose screws, lots of them loose on bars. Nothing wrong with firming them up a little.

 

[89MustangGX]

Thanks again guys- I feel like I understand much more now.