# Neutral Double Tap



## CallMeVilla (Sep 26, 2014)

Oh boy has the debate been raging ...  Got talking over beers with electricians about "things we've seen."

Here is the question:  To add circuits, can you double stab the neutral/ground bus when it is full?

"NEC versus field" was part of the discussion.  What do you say?


----------



## bud16415 (Sep 26, 2014)

NEC 408.21 says No


----------



## nealtw (Sep 26, 2014)

But I think you are allowed to have mar cannectors in the box and you can run 2 circuits on one ground and one common. No?


----------



## Kabris (Sep 26, 2014)

Generally you can double lug grounding conductors only (max 2 per screw terminal), but not the grounded (neutral), only 1 per screw.  This is code and what I have always practiced in "loaded" panels.


----------



## Kabris (Sep 26, 2014)

Also I see in the OP picture that the neutral and ground share a lug, also a no no and looks like garbage.


----------



## Kabris (Sep 26, 2014)

nealtw said:


> But I think you are allowed to have mar cannectors in the box and you can run 2 circuits on one ground and one common. No?




2 circuits can share a ground but I would only share a neutral with a 3-wire only.


----------



## Kabris (Sep 26, 2014)

nealtw said:


> But I think you are allowed to have mar cannectors in the box and you can run 2 circuits on one ground and one common. No?




2 circuits can share a ground but I would only share a neutral with a 3-wire only.o


----------



## nealtw (Sep 26, 2014)

Kabris said:


> 2 circuits can share a ground but I would only share a neutral with a 3-wire only.o





That is why I asked.


----------



## CallMeVilla (Sep 27, 2014)

Since my first post, here is what I found written up about this issue:

_408.21"Each grounded conductor shall terminate within the panel-board in an individual terminal that is not also used for another conductor."

Now, was this always a requirement? No. However, the reason this requirement was implemented was for safety concerns (which most electrical requirements are). One of the concerns is that an unsuspecting contractor or individual may trip a breaker thinking that he has isolated a circuit in-order to work on a given item (possibly a ceiling fan or such). Well, if the grounded conductors are double tapped under the same buss screw, the contractor who &#8220;thinks&#8221; he has isolated that circuit may very well be surprised to find out otherwise. Basically, this is a safety concern.

Knowing what we know today, it is ill-advisable to continue to use outdated methodologies (due to safety concerns) when we now know better. If we know an item has the potential to cause a safety or overheating concern, it is our policy to always alert the client to make the necessary upgrades/ repairs._


----------



## Kabris (Sep 27, 2014)

I'm not following Villa, the grounded and grounding conductors all share the same bus in a main panel anyway. 

I think the double tapping issue under one lug is so 2 circuits do not need to be disrupted to work on 1.  Let's say 1 breaker needs to be removed and an AFCI breaker put in its place. The electrician needs to take the neutral off the bus. If there are 2 neutrals sharing one screw terminal then he may have to turn off both circuits.  For residential this doesn't seem like a big deal, but it is a big deal for commercial places like hospitals.


----------



## oldognewtrick (Sep 27, 2014)

That's the thing I didn't understand. What difference does it make if the share the same slot or different, it's the same bar. Other than pointed out above.


----------



## beachguy005 (Sep 28, 2014)

Here's an explanation on the neutral issue.  It's 408.41 in the 2011 NEC also. 


http://ecatalog.squared.com/pubs/Electrical Distribution/Panelboards/0100DB0705.pdf


----------



## oldognewtrick (Sep 28, 2014)

Ok, that makes sense.


----------



## Kabris (Sep 28, 2014)

Yeah when I used to do old work residential it was always scary removing a neutral from a terminal shared with another neutral, bc I had no idea what load the other circuit was under. Generally once the panels were fully loaded like that (and looked like a rat nest of wires), any panel schedule/directory was totally unreliable. That code explanation makes perfect sense. 

So the solution, if you had to add a circuit, would be to double lug a couple of grounds to free up space on the bus, then you could terminate the added neutral.


----------



## hornetd (Nov 20, 2014)

Kabris said:


> Yeah when I used to do old work residential it was always scary removing a neutral from a terminal shared with another neutral, bc I had no idea what load the other circuit was under. Generally once the panels were fully loaded like that (and looked like a rat nest of wires), any panel schedule/directory was totally unreliable. That code explanation makes perfect sense.
> 
> So the solution, if you had to add a circuit, would be to double lug a couple of grounds to free up space on the bus, then you could terminate the added neutral.



An even better solution is to add an equipment grounding buss bar







 to the panel enclosure so that the Equipment Grounding Conductors (EGCs) can all be moved from the neutral buss leaving plenty of room for new circuit neutral terminations.  

Another reason that it is a bad idea to terminate two different circuits neutral conductors in the same lug is that the conductors expand and contract as they are loaded and then the load shuts off. This small change in the diameter of the conductor stresses the pressure screw or clamp.  The terminations are tested to withstand this when used for a single conductor.  When two wires that are expanding and contracting at different times and rates are under the same pressure screw or clamp the pressure on the two wires will not be even.  If the loading is markedly different the lighter loaded conductor will no longer have an airtight connection.  That connection will slowly corrode, develop a higher resistance in its connection, and begin to heat beyond it's design temperature rating.  Arcing and connection failure can then occur.

--
Tom


----------



## Kabris (Nov 21, 2014)

Yes adding a bus would be the better solution, in addition to cleaning up the "rat nest" of wires, but when I did residential work for a contractor, unfortunately, the cheaper and faster solution was generally the way to go. Sad to say, but true.


----------

