Number of conductors under one screw terminal .

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guschash

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What article ( if any ) talks of terminating one wire under one screw. I'm thinking it has to do with the listing of the screw or terminal. I have a white book and figure it's in there someplace but can't find it.
 
Also in the 2011

408.41 Grounded Conductor Terminations. Each grounded
conductor shall terminate within the panelboard in an individual
terminal that is not also used for another conductor
Click to expand...
 
Thanks Dennis . The question that was put to me was meter panel. But I also knew I readied some place about one wire under one screw.
 
408.41 Grounded Conductor Terminations. Each grounded
conductor shall terminate within the panelboard in an individual
terminal that is not also used for another conductor
Click to expand...

is a "terminal block" considered "an individual terminal"? all bare's in my service panel are on this single/dedicated terminal block, but some of the screws on that TB are squishing two bare's. i guess next Q is, why is having two a bad thing?
 
The main reason in having two, without proper design support, is the risk that either one wire will not be as tightly held as the other or that relative movement if the two wires might loosen them both.
The hazards of loose connections are well known, so I will not go into them.
 
110.3 Examination, Identification, Installation, and Use of Equipment.
....
(B) Installation and Use.
Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

This is an indirect reference to the UL White book. NEC does quite a tap dance to not say UL or NRTL but that is the intent.

In the White Book there is a section called

AALZ ELECTRICAL EQUIPMENT FOR USE IN ORDINARY LOCATIONS

which is filled with rules for a whole bunch of things found on lots of listed devices. The rule relevant to your question is:

Terminals ? Product terminals, including wire connectors and terminal screws, are acceptable for connection of only one conductor, unless there is marking or a wiring diagram indicating the number of conductors which may be connected.
 
FionaZuppa said:
is a "terminal block" considered "an individual terminal"? all bare's in my service panel are on this single/dedicated terminal block, but some of the screws on that TB are squishing two bare's. i guess next Q is, why is having two a bad thing?
Click to expand...
Each "opening" is considered an individual terminal. Listing of the block will tell you if each opening is intended for single or multiple conductors, and what size of conductor(s) is acceptable.
 
GoldDigger said:
The main reason in having two, without proper design support, is the risk that either one wire will not be as tightly held as the other or that relative movement if the two wires might loosen them both.
The hazards of loose connections are well known, so I will not go into them.
Click to expand...
And when a terminal is designed for two conductors they often are designed only for two of the same size so there will be even amount of pressure applied to both conductors. If you placed a 12 solid and a 14 solid in same termination there is greater chance of less pressure being applied to the 14 especially in most set screw type devices with no other type of pressure plate or other clamping method and it may develop continuity problems because of this.
 
If I put more then 1 wire under a terminal I use ring terminal crimps, and sometimes star washers too. Spades or forks will squeeze out.
But it depends on what kind of terminal you are talking about. But this is new to me I hadn't considered the rules about this one.
 
jxofaltrds said:
And what if it is a?:

Neutral Conductor. The conductor connected to the neutral
point of a system that is intended to carry current under
normal conditions.
Click to expand...
In most cases, the neutral conductor is a grounded conductor. For the cases where the neutral conductor is not a grounded conductor, that section would not apply.
 
Aleman said:
If I put more then 1 wire under a terminal I use ring terminal crimps, and sometimes star washers too. Spades or forks will squeeze out.
But it depends on what kind of terminal you are talking about. But this is new to me I hadn't considered the rules about this one.
Click to expand...
I recall there being a fairly lengthy thread about screw terminals on devices, receptacles I believe, but perhaps others, such as wall [snap] switches. Can't remember the consensus... perhaps someone will find it and provide a link... ;)

Anyway, doing what you describe on screw terminals of typical yoke mounted devices is not a violation that I know of. But I think using ring terminals should be avoided on these. My reasoning is the manufacture process nowadays uses thread forming screws to make the threads in the mating back-plate contact. When you back the screw all the way out to put on one or more ring terminals, you remove a little more of the back-plate thread mass. There's little there to begin with. Then you remove a little more putting the screw back in. This degrades the thread to the point where adequate compression torque may not be possible. You also create filings in the device that may aid in the formation of an arc fault. The preceding isn't a substantially significant reason to not do it, but I believe something to consider before doing it (or doing it again :)).
 
Smart $ said:
I recall there being a fairly lengthy thread about screw terminals on devices, receptacles I believe, but perhaps others, such as wall [snap] switches. Can't remember the consensus... perhaps someone will find it and provide a link... ;)

Anyway, doing what you describe on screw terminals of typical yoke mounted devices is not a violation that I know of. But I think using ring terminals should be avoided on these. My reasoning is the manufacture process nowadays uses thread forming screws to make the threads in the mating back-plate contact. When you back the screw all the way out to put on one or more ring terminals, you remove a little more of the back-plate thread mass. There's little there to begin with. Then you remove a little more putting the screw back in. This degrades the thread to the point where adequate compression torque may not be possible. You also create filings in the device that may aid in the formation of an arc fault. The preceding isn't a substantially significant reason to not do it, but I believe something to consider before doing it (or doing it again :)).
Click to expand...
Anyone know exactly how they put the screws described in here in such items? They can't really be thread forming screws as that would tap the hole and they would thread back out easily, they are somehow designed and installed in a way that they can not easily be backed all the way out the hole yet need to be inserted in the hole the first time somewhow.
 
Smart $ said:
I recall there being a fairly lengthy thread about screw terminals on devices, receptacles I believe, but perhaps others, such as wall [snap] switches. Can't remember the consensus... perhaps someone will find it and provide a link... ;)

Anyway, doing what you describe on screw terminals of typical yoke mounted devices is not a violation that I know of. But I think using ring terminals should be avoided on these. My reasoning is the manufacture process nowadays uses thread forming screws to make the threads in the mating back-plate contact. When you back the screw all the way out to put on one or more ring terminals, you remove a little more of the back-plate thread mass. There's little there to begin with. Then you remove a little more putting the screw back in. This degrades the thread to the point where adequate compression torque may not be possible. You also create filings in the device that may aid in the formation of an arc fault. The preceding isn't a substantially significant reason to not do it, but I believe something to consider before doing it (or doing it again :)).
Click to expand...

I see your point on not backing the screws all the way out on some devices. I don't use a lot of terminals and usually just one on a screw and those will be fork types.
But I have noticed the fork types squeeze out when stacked. That's where I use a ring.
 
GoldDigger said:
I believe that the end threads are either pre-distorted or are distorted after they are threaded in.
Click to expand...
I would think they have to distort them somehow after installation otherwise they would back out easier then they do. Many times when you do fully remove such a screw it no longer has that resistance that keeps it from easily backing out.
 
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