What is a double tap?

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     A double tap is when there are two conductors under a terminal which is designed for only one conductor. This a safety issue because a terminal designed for one conductor will not exert even pressure on two conductors which means one of them could come loose, arc, overheat, cause a fire etc. When we find a breaker which is double tapped then it is likely that the extra circuit would not have been calculated for the load imposed on the breaker.  So the breaker could be overloaded. Study the diagram below.

Drawing shows examples of double taps.
Example of double taps which are allowed and not allowed.
  • Fig 1 Most circuit breakers are not designed for two conductors and this is especially dangerous if the conductors are different gauges.
  • Fig 2 shows the uneven pressure exerted on two conductors especially if they are different gauges.
  • Fig 3 Some circuit breakers are designed for two conductors…. if they are then the label printed on the breaker will say so.
  • Fig 4 Double tapped neutral conductors are not allowed.
  • Fig 5 Double tapped grounding conductors are allowed.
  • Fig 4 A neutral and a grounding conductor cannot be under one terminal.

Now let’s see what we find out in the field.

Picture showing double tapped neutrals in an electrical panel.
Example of Electrical Panel with Double Tapped Neutrals.

Double Tapped Neutrals

Here you can see in the picture above the double tapping of neutrals in the main service disconnect.  This is where two wires are under one screw.  At the time this house was built the language in the NEC was vague so the practice was quite common.  More modern codes prohibit this.  In 2002 the NEC clarified the language to prohibit this although it had already been prohibited as part of the UL listing instructions for every panel manufactured since 1965.  We here at Blue Palmetto Home Inspection feel that double tapping neutrals is not a good idea because it violates the listing.  In many cases there are plenty of holes so it just involves moving the wires to a different hole. We recommend a licensed electrician do this for you.

Picture shows burnt neutral caused by double tapping.
In this picture you can clearly see that a neutral conductor is burnt and it is possibly caused by a poor connection caused by double tapping.
Picture shows double tapping at main lugs.
Here is another example of double tapping causing an unsafe condition. When the smaller gauge conductors are tapped in with the larger ones on the line side there is the issue of loose connections. However, in this case the small conductors are not protected against overload.
Picture shows double tapping of neutrals and grounding conductors.
The panel above was in a house built in the mid 1960's. It shows double tapped neutrals and grounds which has never really been allowed. Between about 1962 and 1969 however the grounding conductors were allowed to be one size smaller. So a screw tightened against two different size conductors on these homes is more likely to become loose and present a hazard.
Picture shows double tapping of neutral and grounds.
Above is a panel in a newer home with double tapped neutrals and grounds which is not currently allowed. The concern in this case is a loose connection here could mean no return path for current in that circuit because both the neutral and ground would be loose. This could be a shock hazard in case of a loose connection or short and is a little more of a concern than a double tapped neutrals condition.
Picture shows ganged neutrals and grounds.
Ganging all the conductors under a terminal meant for a larger conductor is not allowed either.
Picture shows a breaker designed for two wires.
As far as I know only one manufacturer makes a breaker designed for two conductors. As pictured above. Look and see where the conductors go. There's a really small label that tells you the allowable size and number of conductors the device is rated for.
Picture of side of a square D breaker.
This is the side of the breaker.... it has a pretty picture on it that shows how the conductors are to be secured. It also lists the number and gauge of the conductors allowed for this device.

Reference 2009 irc 3706.4, 2011 nec 408.41  Grounded Conductor Terminations.- Each grounded conductor shall terminate within the panel board in an individual terminal that is not also used for another conductor.

The Solution

Often there are enough holes for the other conductors .  You’ll just have to find an electrician to move the conductors for you. Sometimes you can pigtail the conductors with a wire nut (or other approved connector) so that only one wire goes to the breaker.

 
         

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