Sub panel grounding question

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Old 08-30-05, 05:43 PM
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Sub panel grounding question

I have a 400 amp main panel outside my house that feeds two sub panels inside my house. They are both fed with aluminum wire. One of the panels comes off the main feed with it's own 100 amp main breaker. This panel has the aluminum ground running back to the main box as well as two copper grounds that go to the main water pipe where it enters the house. That is what is raising a question about my second sub panel.
This panel is fed by a 90 amp breaker off of the main 400 amp panel. The only thing attached to the ground bar is an aluminum ground that feeds back to the main panel. It doesn't have the copper ground like the other box, but I realize it is also fed differently. Is this acceptable or should I be adding another ground in this panel as well? Sorry this is so long but I'm trying to be accurate. Thanks in advance... Andrew
 
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Old 08-31-05, 08:27 AM
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Do both bare copper wires run from the 100A panel to the same water pipe?

Your installation is a little odd in that the bond to the water pipes usually would come from the main (400A) panel, but I suspect that the subpanel is "on the way" from the main panel to the water pipe entrance, and the installer wanted to conserve wire. The local inspector must have allowed it.

What is certain, however is that the 90A panel does not need a ground rod or a bond to the water pipes. I assume the 90A panel is in the same building as the main 400A panel, if there are detached buildnigs involved then it's a totally different situation.
 
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Old 09-01-05, 06:11 AM
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Both copper wires do run to the same pipe about three inches apart on the pipe and about one foot in from where the water pipe enters the house.

The configuration on my house is very odd. My drop comes into my meter, then a 400 amp disconnect switch, which is connected to a 400 amp main panel outside the house. The only breaker in the 400 amp panel is the 90 amp that is feeding the second sub panel I had mentioned. The 100 amp panel is fed off of the leads inside the main panel and not by a breaker. Both panels are inside the house next to eachother so a seperate building doesn't apply. The 100 amp panel feeds almost everything in my house. The 90 amp panel only feeds my dryer, double oven, and cooktop.
 
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Old 09-01-05, 08:39 AM
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If you'r assement of the existing conections is correct, and my understading of you'r decription is correct, you have an EXTEREMLY SERIOUS Code-violation.

Certain exceptions aside,Conductors MUST be protected at the point where they connect to the "supply".This means that conductors with an ampacity of 100 must be protected by an over-current protective device (OCPD)with the "Line" terminals of the protective device connected directly to the "supply" conductors, which in you'r system appears to be the "bus" of the "Main" panel.The 100 amp conductors connect to the "Load" side of the OCPD.

I suggest you adress this problem immediately. I hope you are wrong in concluding that the 100 amp Feeder is not connected to a 100 amp OCPD at the connection-point in the "Main" panel.

Good Luck and Learn & Enjoy from the Experience!!!!!!!!
 
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Old 09-01-05, 09:21 AM
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It might be code compliant if it meets the feeder tap exceptions. How far away is the 100 Amp panel from the 400 Amp panel? Less than 10 feet? I do think it is strange that the 90 Amp panel is fed from a circuit breaker, but the 100 Amp panel is not. How far away is the 90 Amp panel from the 400 Amp panel?
 
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Old 09-01-05, 03:33 PM
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Both the 100 amp panel and the 90 amp panel are next to eachother inside the house and they are both about ten feet away from the the main outside the house. The house was renovated in the mid-eighties and that was when the 90 amp panel was added to accomodate a kitchen renovation. All the electrical work was signed off on at that time, because the stickers from the inspector are still on the panels from back then. I will double check on the feeds to the 100amp panel, but I'm almost positive they are they way I described.

I WAS MISTAKEN !!! Sorry for the confusion but there are two 90 amp breakers in the main box. One feeds each sub panel inside the house. It just happens that the original box still is using the 100 amp breaker to feed the bus I guess. But now back to my original question, The second sub box has an aluminum ground back to the main. Should it be bonded to the water pipe like the other one?? Thanks everyone for your valuable input!!!
 

Last edited by Drew2672; 09-01-05 at 03:54 PM. Reason: Overlooked second breaker
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Old 09-02-05, 10:04 AM
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Re: "2nd. sub-box (panel)"

You'r ? pertains to an Aluminum Equiptment Grounding Conductor (EGC)between the "Main" (?) panel and the 2nd sub-panel.This is the "Feeder" EGC.

The Feeder EGC is connected to conduct a "Fault-Curent" back to the "source", which is where the Feeder Conductors to the 2nd. sub-panel are connected at the "Main".Essentialy, the Feeder EGC is connected so that it forms a conducting path seperate from the Neutral , but"in parallel" with the Feeder Neutral, back to the "source" where the Feeder EGC connects to The Neutral, not the Grounding Electrode Conductor.

In the 2nd. sub-panel, the Feeder EGC is "Bonded" to both the metallic surface of the enclosure, and the EGC's of the Branch-Circuits that extend from the 2nd. sub-panel. The Feeder EGC DOES NOT connect to the Neutral.

IF--- repeat IF--- the Service Dis-connecting Means is located in the "Main" panel, then the Feeder EGC connects to the Grounded Service Conductor ( the Neutral). If the Service Dis-connecting Means is an an enclosure seperate from the "Main" panel, then there should be an EGC between the enclosure for the Service Dis-Connect and the "Main" panel.


Good Luck & Enjoy and Learn from the Experience!!!!!!!!!!!
 
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Old 09-02-05, 03:22 PM
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Thanks for your reply. I do understand what you mean even if my terminology isn't the best. Thanks again... Andrew
 
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