Bonding screw main panel/ grounded neutral

Hi, thanks for any help! I just realized that there wasn't a bond screw in my main panel. I know it is supposed to be installed only in the 1st/ main panel. What could happen if it isn't in? Second question maybe more complicated? Subpanel with three wires hot/hot/ neutral no bond screw but accidently connected neutral to ground and powered on. Two smoke alarms popped and I turned breaker off. I fixed the neutral wire and tried again and the two alarms that popped then smoked while watching them. Cut power and removed the alarms that popped and smoked. What happened electrically? I know I was stupid but want to understand what happened. All other breakers and neutral now connected in that box without any problems. Just alarm breaker is off. I guess it powered the neutral somehow and blew them? Be nice please

I will leave the bonding issue for those that know for sure.

Okay we know the mistake you made, what were you actually doing when you did it. Are the detectors interconnected? When you pulled them, did you un wire them or just pull the little plugs out?

It would help if you posted pictures of both the panels so we can see what you have. Also you state the first main panel does not have a bonding screw. How many wires are going into that panel. Are you sure you do not have a disconnect prior to that panel.

Also, what do you mean by you fixed the neutral. What was wrong with the neutral?

Yes, the sub panel needed 4 wires going to it not 3. Hot, hot, neutral and ground.

Yes the detectors were interconnected. I unplugged each one to quiet. The subpanel is connected with conduit so maybe that's why there isn't a separate 4th wire for ground. There is a disconnect at the meter socket 100 ft from house. Could it be bonded there? Not sure? What did the power up with the neutral actually do? Fixed neutral, was accidently connecting to ground and then returning it to neutral. That is what I don't really understand? Thanks

nealtw said:

I will leave the bonding issue for those that know for sure.

Okay we know the mistake you made, what were you actually doing when you did it. Are the detectors interconnected? When you pulled them, did you un wire them or just pull the little plugs out?

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By Code , the first panel or disconnect must have the neutral & earth ground bonded together . If you have an outside main , that is it .

All other panels do not have the neutral and ground bar bonded . And must be feed with the neutral , hots & an earth ground .

Wyr
God bless

js5518 said:

Yes the detectors were interconnected. I unplugged each one to quiet. The subpanel is connected with conduit so maybe that's why there isn't a separate 4th wire for ground. There is a disconnect at the meter socket 100 ft from house. Could it be bonded there? Not sure? What did the power up with the neutral actually do? Fixed neutral, was accidently connecting to ground and then returning it to neutral. That is what I don't really understand? Thanks

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Sounds like you wired the detectors with a dead short. Hooking neutral to ground is wrong but it would not have caused your problem.

Thanks. Yes, it was wrong. To be clear, it was the feed neutral and not the detector neutral. That is fixed. If the subpanel was energized with hot/hot and no neutral would that then be 240 to connected breakers? Something definitely popped and smoked the detectors? It is all back the way it was now. I think it is correct but still want to understand what caused it, short, 240 or what? WyrTwister I have a meter socket outside 100 ft from house with a 200 amp breaker and would it be bonded in there and then not bonded at the house circuit panel? Is that what you were saying?

js5518 said:

Thanks. Yes, it was wrong. To be clear, it was the feed neutral and not the detector neutral. That is fixed. If the subpanel was energized with hot/hot and no neutral would that then be 240 to connected breakers? Something definitely popped and smoked the detectors? It is all back the way it was now. I think it is correct but still want to understand what caused it, short, 240 or what? WyrTwister I have a meter socket outside 100 ft from house with a 200 amp breaker and would it be bonded in there and then not bonded at the house circuit panel? Is that what you were saying?

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So you had it hooked to ground and then discovered the mistake and moved the neutral with out turning off the main?

No, the main and breaker feeding the subpanel was off. The neutral was in the subpanel. Then yes it was fixed. The only question now is what actually happened and not what is right or wrong. The exception being that bonding screw in the house main panel which is # 1 in the house but after the outside meter with 200 breaker 100 ft away.

Without the pictures someone already asked for we can only guess but here's mine. With the panel energized without the neutral connected to the main bonding jumper at the outside disconnect; no matter where the break in the neutral occurred; the voltage across the individual branch circuit would depend on which of the energized conductors had the most load connected to it. The voltage of the more heavily loaded energized conductor will be lower than the voltage of the less heavily loaded energized conductor. The greater the disparity in the loading the greater the voltage difference will be. Keeping in mind what I said about this being a guess; or in other words pure speculation on my part; what may have happened is that the smoke detector circuit may have been subjected to a voltage which was markedly higher than the smoke detectors could withstand. Unlike the 600 volts which the entire wiring plant can be expected to be insulated to, individual devices such as smoke detectors, GFCI receptacles, built in timer switches, appliance controls... may fail at a much lower voltage to ground. It is entirely possible that an imbalanced load and no neutral connection was the cause butt that does not mean that it was the cause! The only way we may be able to give you a much more reliable answer is if you provide a picture which clearly shows the connection which was previously open. So if you want to actually know the cause of your problem then take the picture and post it. If my purely speculative guess is good enough then good luck to you and the Boston Red Sox because you'll both need it!

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Tom Horne

js5518 said:

No, the main and breaker feeding the subpanel was off. The neutral was in the subpanel. Then yes it was fixed. The only question now is what actually happened and not what is right or wrong. The exception being that bonding screw in the house main panel which is # 1 in the house but after the outside meter with 200 breaker 100 ft away.

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A huge issue, which is not yet clear to me; is whether the Feeder from the outdoor Service Disconnecting Means has a separate Equipment Grounding Conductor (EGC) run with the Grounded Current Carrying Conductor (Neutral) and the energized conductors. I believe that you said that the Main Bonding Jumper; in the form of a machine screw that connects the neutral buss to the panel cabinet; was not installed in the house panel when you first energized that panel. If that is true then even if there is an EGC run with the feeder from the outdoor disconnect the bonding screw would be unlikely to prevent the damage. Whether the Feeder to the house was required to have an EGC run with it when it was installed would depend on which addition of the electrical code was in effect when the permit for that work was issued. Providing that the work was finished in the time allowed by the permit, the permits issue date carves the code which was in effect at that time into stone in regards that installation.

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Tom Horne

js5518 said:

Some original text deleted so as to limit my reply to one question. The exception being that bonding screw in the house main panel which is # 1 in the house but after the outside meter with 200 breaker 100 ft away.

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The answer to this question is; If an Equipment Grounding Conductor (EGC) was run with the other feeder conductors supplying the house the installation of a bonding jumper between the neutral buss and the House panel's cabinet is not merely not required but it is actually prohibited. What is required, regardless of whether or not an EGC was run with the feeder, is the installation, at the house, of a Grounding Electrode System which includes all of the electrodes named in the article 250 which are present. In the absence of one of the named electrodes that is not an underground metal water pipe an additional electrode is required consisting of a minimum of two driven rods at least eight foot long and six feet apart.

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Tom Horne

Tom. Thanks! This set up has been operating for about 18 years. I did not actually do this neutral myself but have been trying to help. Don't know about the EGC being run with the feeders? I do know there is at least 1 rod near the house. I was asked what happened and was not able to explain it. Yes, I know that it would only be bonded at the first location and didn't really think about it being outside at the meter disconnect. No water pipe to connect with here, well water. The bonding screw is definitely not in the main panel inside the house. Not in the sub. Your answer about the smoke detector circuit is probably the answer I was trying to understand. The connection was fixed and don't what I would take picture of now? I will open the outside meter box tomorrow and see if there is 3 wires and ground. I think there is a rod at meter and at the house and just the 3 wire feed. Don't really know the code from 18 years ago. If safety would be better with another rod at either location it would be simple enough! The subpanel is located 2 ft away from the house main and connected with conduit with no separate ground but three wires, hot/hot and neutral which was the incorrectly attached wire to ground bar of sub which attached to the neutral in the house main panel. The sub panel is not bonded. The subpanel is now connected correctly minus the possible bare ground to main panel ground bar. The whole house is conduit pipe which was code.

Is the water pipe to the pit adapter metal? Is the well casing metal? If the well has a metal casing it makes a very effective grounding electrode. If the water pipe to the pit adapter is plastic, as many are, then the challenge will be to run a Grounding Electrode Conductor (GEC) to the well casing if it is metal.

If there is no Equipment Grounding Conductor run with the Feeder from the outdoor Service Disconnecting Means (SDM) then the house panels cabinet should be bonded to the feeder neutral just as it would be if that panel were the location of the SDM. Each building that is supplied by a Service which is located outside that building has to have a Building Disconnecting Means that meets all of the requirements for an SDM. That includes the requirement that the building be disconnected with six throws of the hand. In other words not more than six Switches, Fused Pull Outs, or Circuit Breakers can be needed to completely disconnect the building. Does the house panel have a main breaker? This all makes it fairly important that you find out whether or not an EGC was run with the Feeder Conductors which supply the house.

As I already wrote a Grounding Electrode System that meets all the requirements for a Service must be installed at each separate structure which is supplied from the outdoor SDM enclosure. Although the code required Grounding Electrode System can be a minimum of two driven rods which are eight feet long or longer and are driven at least six feet apart that is not a very effective electrode system in most soil types. If you can you will want to install a Ground Ring. That is a number two American Wire Gauge copper conductor which circles the entire house at a minimum depth of 30 inches. If it would be less wire to reach the well, and the well has a metal well casing, than that makes a very good Grounding Electrode. That conductor would need to be buried at two feet below the finished grade so there is no reason not to bury it as deeply as is practical. If you use a machine to do the trenching then the maximum practical depth for that machine should be used. The deeper a bare GEC or Ground Ring conductor is buried the more effective a part of the Grounding Electrode System it will be until you are down to the permanent moisture level. Once you get to a foot under the permanent moisture level there is no point of going any deeper if the other requirements for depth of bury have been met. If you cannot install a Ground Ring and attaching the Grounding Electrode Conductor to a metal well casing is impractical then you will need to drop back to rearranging the two driven rods to be more effective. To do that you drive the second rod at least twice the length of the longest rod away from the first rod in a trench that is at least 30 inches deep. The two rods are driven through the bottom of the trench, which puts the entire rod 30 inches underground, and the Grounding Electrode Conductor is laid in the bottom of the trench. You also use the number two copper which would be required for a Ground Ring rather than the much smaller number six AWG which the code allows for the GEC to a Driven Electrode. Testing done by the National Institute of Standards and Technology (NIST) show that this in the minimum practical Grounding Electrode System which will be effective in providing an adequate ground for a home.

Do let us know what you find at the Service Disconnecting Means. A picture of that assembly would be really helpful.

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Tom Horne

I will look tomm. Well is not metal. For sure when house was built 1 rod was required, pretty sure? Ring not possible. Adding another rod is possible assuming this is now required or better safety? Detached garage is shut off completely from house main and garage has main breaker for shutting off circuits while in garage. Subpanel is shut off with breaker in main. House has main shut off and then everything is shut off from meter breaker at meter. All this stuff was inspected and approved????????????????I do see things done wrong, based on what I am learning here!

js5518 said:

Thanks. Yes, it was wrong. To be clear, it was the feed neutral and not the detector neutral. That is fixed. If the subpanel was energized with hot/hot and no neutral would that then be 240 to connected breakers? Something definitely popped and smoked the detectors? It is all back the way it was now. I think it is correct but still want to understand what caused it, short, 240 or what? WyrTwister I have a meter socket outside 100 ft from house with a 200 amp breaker and would it be bonded in there and then not bonded at the house circuit panel? Is that what you were saying?

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That is how I interpret code and what I would do . However there is a distinct possibility the installer may not have run the earth ground for that 100 foot ( just 2 hots and the neutral ) .

That 200 amp breaker is THE MAIN . All other panels must , by code , have neutrals and grounds separated .

By design , neutral is a current carrying conductor . By design , the earth ground kind of " stabilizes " the neutral . But the only time it carries a true current is when one of the hots shorts out to earth ground . To facilitate tripping / blowing the over current device .

The neutral is there for function . The earth ground is there for safety .

If you hook up the hots to a panel ( with some / all the CB's ( circuit breakers on ) , the 120 VAC circuics will experience any where from 0 - 240 VAC . Depending on what is actually turned on .

Wyr
God bless

So, you would consider the outside 200 amp breaker as the main? This is where it should be bonded and everything after is separated ? Then each other box would require it's own means of ground to earth? They are but I think only 1 rod per box. I figured that the smoke alarm components couldn't handle whatever was put through them. The wires supplying them seem fine it was just the alarm itself. I know for sure the detached garage ground from rod goes to the neutral bar with other neutral connections. Will change that by adding bar in the box for ground wire. Been that way for 18 years! Thanks

The 200 amp CB is the main . That is where the neutral should be bonded to earth ground and where the ground rod ( or other grounding electrodes ) should be terminated . From there downstream , they are essentially feeder grounds or equipment grounding conductors .

In practice , at the house , other grounding electrodes may or may not be terminated at the ground ( not neutral ) bar . Not sure about the best interpenetration of code on that , but if it is , not at any sub panel . As far as I know , in our area , metal conduit is still considered a legal ground . But we always run a ground conductor .

We do a few residential service calls , but have not done new houses for ages .

I agree , the wire to the smoke detectors would not normally be damaged in such a case , even though the smoke detector is toast .

In the case of a detached garage , I would have to look that up .

Wyr
God bless

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