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Why do you have to bond the neutral and the earthing wire in the main panel?

Hi Jorge,

Thank you for your question regarding the Neutral-to-Earth Bond in the main panel.  The short answer to your question is that the neutral-to-earth bond is needed to properly operate the circuit breakers.  Over Current Protection Devices (OCPD) such as circuit breakers and fuses actually require a short and intense INCREASE in electrical current (a short) in order to detect the fault and cut the circuit off.    Without a sharp and drastic increase in electrical flow, a fault could go on without triggering a circuit breaker to stop the flow.  This actually occurs quite often and can be measured easily by checking the amount of current flowing on your earthing conductor.  It should be less than 1-amp in most cases.  If the current flowing on a earthed conductor is higher than an amp, and you are not in a high-voltage (600V+) environment, it typically indicates an erroneous neutral-to-earth bond somewhere in the system.

To visualize the reason why the neutral-to-earth bond is required, you must consider the entire electrical circuit from a 120-volt outlet all the way back to the utility transformer hanging out on the pole:

  • In a properly designed circuit, if a fault were to occur on the 120-volt outlet between the hot-wire and the earth, the current will flow through earthing wire back to the main panel, where it will move to the neutral wire via the neutral-to-earth bond, up to the utility transformer, back down the hot wire to the circuit breaker, tripping the breaker.
  • In an faulty designed circuit, if a fault were to occur on the 120-volt outlet between the hot-wire and the earth, the current will flow through the earthing wire back to the main panel, where because it does not have a neutral-to-earth bond, the current will be forced through the earthing rod, into and across the earth, and up the utility earthing rod and in to the utility transformer, back down the hot wire to the circuit breaker.  The resistance of the earth is almost always to great to allow sufficient current flow to trip the breaker, and you end up with a steady-state earth fault, that never trips the breaker, and this is a hazardous situation indeed.  You cannot use the earth as a conductor.

Another issue that can occur, is that multiple (and illegal) neutral-to-earth bonds can exist in the system (only one bond is allowed in the main panel).  When this occurs, both the earthing wire and the neutral become current-carrying conductors, which effectively means that you have two (2) neutral wires running in parallel.  This divides the current and places electrical energy on to the chassis of all metallic objects within the system.  Another hazardous situation.

Also, Arc-flash energy exposure can also go up if you don’t have a solid neutral to earth connection because of the inverse-time curves of circuit breakers.

This subject can be a very difficult concept to understand and the improper application of neutral-to-earth connections can have very serious and life-threatening consequences.  If you have any doubts at all, we highly recommend getting a licensed electrician to assist you.  We hope this information helps.

Best regards,

The Engineering Team at E&S Earthing Solutions

Photo Credit: http://www.flickr.com/photos/deltamike/2637796725/sizes/o/in/photostream/

7 Responses

  1. Rob

    I thought that neutral and ground are isolated in the breaker panel and bonded at the service entrance/meter, outside the building in most cases. The breaker box is bonded to ground with neutral isolated inside the panel. Am I missing something here?

  2. joe

    I am trying to find out how to bond the neutral bus and the ground bus at the main electrical panel. The panel is a GE Powermark Gold Load Center 100/125amp. There is no bar connecting the 2 buses. One person told me you can screw the green ground screws, 1 through the neutral and 1 through the ground buses into the back of the panel box and that is how the box was designed. Any info would be greatly appreciated.

  3. Rory Aguilar

    What constitutes a multiple (illegal) neutral – to – ground bond. I am installing a 50 amp spa disconnect circuit connecting to the main with 2 (30) amp breakers poled together. I am connecting 4- #6 AWG stranded wires (black, white, red, green) from the spa disconnect to the main. I am connecting the black to one of the 30 amp breakers and the red to the other 30 amp breakers. I am also connecting the green to the ground buss bar and need to know where to connect the white wire. This main box has all the neutral (white) wires connected to the buss that has all the ground wires connected. Do I connect the white (neutral) #6 AWG wire from the spa disconnect circuit to the buss bar that has all the other neutral wires ? Or is this considered a multiple (illegal) neutral – to – ground bond ? Please help !

  4. Deepak

    Thank you very much for detailed explanation. I have one doubt, though. If, in a properly designed circuit, current should not flow to the earth at all, even in case of a fault, then why is the ground rod required at all? Please excuse me if this is a silly question.

      1. Pawan

        Thanks for both the links. Indeed they are crystal clear.
        I got the same doubt as you Deepak and was very happy to find an answer for it.
        So, the purpose of a local Ground rod is to dissipate any Surge/Transients or Harmonics and NOT providing earth path for Line fault. am I right?

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