Thread: Two Ground Wires Under One Screw (not lug)

Hi,

I see there are plenty of discussions about double / triple tapping but they all show examples of ground wires or neutral wires under a tap / set screw (and that two, maybe even three is OK as long as the manufacturer states it's OK).

But, is it ever OK to wrap two ground wires under a single screw head as shown in the attached photo?

It doesn't look like a tight connection can be guaranteed.

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Here's a photo of the entire panel.

Originally Posted by Ian Currie

...is it ever OK to wrap two ground wires under a single screw head as shown in the attached photo?..

Nope.

Originally Posted by John Arnold

Nope.

Thought not. Thanks.

Ian,

I doubt that screw was intended for grounding purposes. I would recommend installation of a grounding terminal bar.

Gunnar,

I wondered about that too. . . Here's another photo, showing the neutral bus, with another bar above it (empty).

Does anyone know what that's about?

Looks like the panel does not have enough neutrals to need the second buss.

Was this the service panel?

That is stablok panel in Canada. They are equipment grounding terminal screws. They can have 2 wires under them only I believe you do not wrap the screw head but land each wire on opposite sides of the screw. The raised ridges on each side of the screw trap the wire under the screw. Here is a different panel above

Roger, check your picture. Those breakers look like they are held in by screws and unless they are all turned off, face the wrong way to be StabLoks.

But you are correct about the screws for ground wires. Those are the correct screws and 2 wires can go straight in under opposite sides of the screw head. That is what I see, but I had to search through dozens of Stabloks to find an example. The newer panels have a short bus bars added for the grounds.

Old Westinghouse panels also used those cheezy ground screws.

BTW, Ian, in Canada, you should never see ground wires going into the neutral bus, whether it is service equipment or not, simply not allowed. Be careful what you learn on forums like this, because there are dozens of differences between the codes, eh?

Sorry John I completely messed up what I was trying to say.....tornado warning going on here at the moment ....

See my edit..... Going to the basement back later.

This is a good example of how things are a bit different in Canada, and that the US based training makes it a bit of a challenge for me (and other Canadian's too, I'm sure).

Even more importantly, this shows the power that the forum has to help educate the new guy.

Thanks to all. I'll keep digging.

Originally Posted by Ian Currie

But, is it ever OK to wrap two ground wires under a single screw head as shown in the attached photo?

Not unless the label shows/states that is okay.

Those are 'binding screws' and, as Roger said, the ridges help keep the wires wrapped around the screw while tightening the screw down, however, those binding head screws are only rated for (at least here in the states, and I would suspect in Canada too) *one conductor* under each binding head screw.

From the three binding head screws shown in the photo, none of the ground wires are properly terminated at those screws.

Jerry (and anyone else),

Do you have a photo of ground wires held in place by binding head screws that are properly terminated?

Thanks again.

Originally Posted by Ian Currie

This is a good example of how things are a bit different in Canada, and that the US based training makes it a bit of a challenge for me (and other Canadian's too, I'm sure).

Even more importantly, this shows the power that the forum has to help educate the new guy.

Thanks to all. I'll keep digging.

Ian. check my edited post above.
Yes, you can copy that pic. It's a rare one.

Originally Posted by Ian Currie

Jerry (and anyone else),

Do you have a photo of ground wires held in place by binding head screws that are properly terminated?

Thanks again.

Ian,

Here is a drawing showing wires properly terminated under binding head screws.

Originally Posted by Jerry Peck

Ian,

Here is a drawing showing wires properly terminated under binding head screws.

Jerry,

The resolution makes it difficult to see any details. However, it looks like the end of the ground wires are bent back to form a 180° 'loop', but the loop is placed to one side of the screw, offset from the 'shank' (instead of looping around the 'shank' as seen in my photo).

It looks that way to me because it appears that there is a short bit of wire poking out, facing down. Am I right?

Originally Posted by Ian Currie

Jerry,

The resolution makes it difficult to see any details. However, it looks like the end of the ground wires are bent back to form a 180° 'loop', but the loop is placed to one side of the screw, offset from the 'shank' (instead of looping around the 'shank' as seen in my photo).

It looks that way to me because it appears that there is a short bit of wire poking out, facing down. Am I right?

I'll describe it and see if that is what you are saying:

After stripping the insulation from the conductor, wrap the stripped end of the conductor around the screw shank in a clockwise direction (which is the direction the screw tightens), pull the conductor around the screw shank snugly, cutting off the excess so the conductor wraps around under the binding screw head to the greatest extent possible (which is why you do not see the conductor shown - it is hidden behind the binding screw head), then tighten the binding screw down to the specified inch-ounces of torque for a properly tightened connection.

According to Jerry, the wire must be snuggly wrapped around the shank. If so, it seems that running a wire straight through, making contact with only one side of the screw shank is not permitted (which rules out double tapping).

John, can you site the CE Code reference that states it's proper to run a wire straight through a single side of the screw (and that two can be placed under a single one).

Regardless, a wire making contact all the way around the head is certainly more secure than one that is only making contact with one side of the screw head.

Ian

Somewhere I have a file or internet source saved about this subject at hand. It wasn't about panels but about the bonding screw in the back of a Iberville metal box commonly used in Canada. Anyway the same bonding (binding crew) is identical as shown below. I just can't get the documentation for how may wires can be terminated to it.

Jerry very well could be right but I remember a Canadian electrician on another forum explaining two accepted methods. Problem is I can't find my source .... I'll look some more today. I believe he quoted or copied code backing up what he said.

Also a link that might be of some help in understanding the difference in terminology between NEC and CEC

Grounding and Bonding CEC/NEC – How Different Are They? | IAEI Magazine Online

Ian

I have a request in on a Canadian code forum to explain how these type bonding screws are terminated. I'll link you to that forum and supply any documetnation they might provide to this thread when the electricians there respond..

Ok the electrician on that site referenced documentation to the electrical safety authority of Canada.

At this link below ....choose grounding and bonding as your catagory that will lead you to this

ESA - FAQ's


Quote:
Originally Posted by ESA - FAQ's
Question
Where there is more than one bare ground wire entering a box what are the acceptable methods for bonding and splicing these and connecting them to the receptacle. Can one wire be left long and run straight to the bonding screw on the receptacle with the other wire(s) wound around this wire or does there have to be a pigtail and an insulated cap in all cases?
Answer

There are two methods that are considered Code compliant.

The first is the pigtail connection. One of the bond conductors is looped around the outlet box bonding screw and left long enough to be connected together with the other bond wires and with a pigtail that goes to the receptacle bonding screw. The wires must be joined together using a suitable wire connector.

Note- there are manufactured wire connectors available that incorporate a "built in pigtail".

Note that twisting the bond wires together without a wire connector does not comply with the Code.

The second method can be done with metal boxes that have two bond screws in the back with a raised metal ridge on either side of the screws. Each bond conductor may be terminated by laying it under and on one side of the screw in such a manner that the tightening of the screw will pull the conductor rather than push it (note- only two bonding conductors per screw can be done in this manner). Each bond conductor may have any excess cut off with the exception of one which is connected to the bonding screw of the receptacle (note this conductor must be at least 150 mm or 6" long between the box bond screw and the receptacle bond screw).

Rule 10-906.


Which I believe is saying this (below) with one of the bonding wires extended to the receptacle bond screw..this for a metal box. Now I suspect that somewhere on the specifications sheet of the panelboard Ian posted it should say how many wires under those screws as Jerry mentioned. If it doesn't say then only one wire....IMO.

Further if you look at the location of those screws on the panel Ian posted .. IMO it would be very difficult to land two bonding wires (Canadian lingo) in opposite directions on each side of those bonding screws so that they are pulled and not pushed.

I believe Jerry is going to end up correct for the bonding screws in the panelboard IAN is referencing.

As for the panel John posted I'm not so sure.

Originally Posted by Ian Currie

According to Jerry, the wire must be snuggly wrapped around the shank. If so, it seems that running a wire straight through, making contact with only one side of the screw shank is not permitted (which rules out double tapping).

Unless the terminal is designed and listed for two conductors, in which case it would have been tested and approved for that use, and would probably have a larger diameter head to contact enough of the conductor.

John, can you site the CE Code reference that states it's proper to run a wire straight through a single side of the screw (and that two can be placed under a single one).

That would be shown or stated on the label, which is why it is a good practice to get into taking photos of the label, or, if you can't take a photo of the label because of where the label is, read the label and check certain things, such as the number of conductors for the terminals, the rating of the panel, and other things which might be of use. Once you see several of the same panels and they all say the same thing, go by that.

The electricians over on self help and more are saying two equipment bonding wires allowed for both panels shown in this tread. However no documentation addressing panels with these type bonding screws was given. Both panels are incorrectly terminated. The bonding wires must terminate like the diagram I posted.

So it all circles back to the listing on the panel label. Panel listing label must say two wires and if it does I guess the electricians know how to land those bonding wires. Either that or there is some other rule that addresses bonding screws in panelboards.

I'll be reading the panel labels more closely from now on, that's for certain.

For now, I bet that any panels / boxes that permit two wires to terminate beneath one binding screw have raised ridges that are similar to those shown in the photo Roger posted.

If you look closely at the photo the ridges are located beneath the screw head in such a way that an inserted wire cannot slip out from underneath the head.

Now, if you look closely at the photo I supplied (see closeup attached to this post) there are ridges alongside the screws but they are not located under the screw head, or even close enough to keep a wire in place. I think it's a safe bet that this panel only allows one wire under each screw and that it needs to be terminated in the manner Jerry described. The ridges likely don't perform any function in this case.

Originally Posted by Ian Currie

For now, I bet that any panels / boxes that permit two wires to terminate beneath one binding screw have raised ridges that are similar to those shown in the photo Roger posted.

Also note that if this is one of those terminals the conductors would need to come in under the binding head from the left (as shown in your photo).

Also keep in mind that the connection is not being made to the back of the enclosure in Roger's drawing but to the underside of the screw head - the enclosure is painted and the paint acts as an insulator, so the contact is simply with the underside of the terminal screw head.

Ian

I just have to suspect from all the observations we have made about those bonding screws in the posted panels that they are one wire only. It will have to be proven to me otherwise.


So next time you inspect a panel like this see if you can get a good picture of the panel specifications label. See if it addresses number of equipment bonding wires under those screws. I'd like to know as would others here ....