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

Hi Jorge,

Thank you for your question regarding the Neutral-to-Ground Bond in the main panel.  The short answer to your question is that the neutral-to-ground 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 ground conductor.  It should be less than 1-amp in most cases.  If the current flowing on a grounded conductor is higher than an amp, and you are not in a high-voltage (600V+) environment, it typically indicates a erroneous neutral-to-ground bond somewhere in the system.

To visualize the reason why the neutral-to-ground 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 ground, the current will flow through ground wire back to the main panel, where it will move to the neutral wire via the neutral-to-ground 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 ground, the current will flow through ground wire back to the main panel, where because it does not have a neutral-to-ground bond, the current will be forced through the ground rod, into and across the earth, and up the utility ground 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 ground 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-ground bonds can exist in the system (only one bond is allowed in the main panel).  When this occurs, both the ground 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 ground 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-ground 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 Grounding Solutions

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6 Responses

  1. I was thinking about what is said above, while it is important for breaker function to have a ground neutral bond, it is for a different reason. If a ground rod resistance is insufficient, the three wire 240 volt feed from the transformer on the pole offers the extra resistance. See in order to have 12kva to 240, it needs a center tap on the secondary and a bond to earth. High voltage wires typically have a ground wire, and they use that to ground transformers, I am not sure but they may also use a ground rod as well. So this adds the extra resistance to the system through the aerial drop to your house, or underground drop. I don’t think extra voltage on the primary side of breaker will trip a breaker, only if load is too high. There is a bimetal strip usually in a breaker and it heats up at a certain amperage and trips the breaker. GFCI’s work differently, and can put out a voltage on the neutral to be reconciled later on the ground bus. If that voltage is not the same, it will trip GFCI. Some GFCI breakers have between 30-80volts on neutral. And on spas if ground wire is loose, or water filled equipment you can have that voltage in water.

  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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