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Anonymous
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Well we know Hbiss is the final word....
So please explain how that short circuit on the load side or ground fault on the load side will trip the OCPD protecting this panel?
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Joined: Mar 2001
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" Connect the control panel earth ground screw through a #16 AWG or larger wire to a cold metal water pipe or a buried ground rod. DO NOT use a gas pipe, plastic pipe, or AC Ground connections.... Isn't the cold water pipe an AC ground connection(provided it's metallic and the service is using it as a GEC)? steve
Steve
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Joined: Dec 2003
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Isn't the cold water pipe an AC ground connection(provided it's metallic and the service is using it as a GEC)?
Yes if it's as you say but it's not code because a cold water pipe does not guarantee a ground back to the service.
...please explain how that short circuit on the load side or ground fault on the load side will trip the OCPD protecting this panel?
I'm assuming by "load side" you are refering to the wiring after the security, fire or other panel. If the panel is powered by an external transformer the panel, wiring and any devices connected to the wiring are floating- there is no ground reference because of the transformer.
In the not unlikely event that this wiring should become energized due to a cross with a class 1 circuit anyone coming in contact with any part of the system would be in danger. The condition would go undetected because no current would flow- and the panel, wiring and devices would be "hot" with reference to any grounded object.
The ground screw is meant to provide a return path to ground in this instance. If the wiring is such that enough current can flow the OCPD on the class 1 circuit will trip. At the very least fuses internal to the panel will blow or small gauge wiring will melt which in turn will disrupt operation of the system.
-Hal
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Joined: May 2003
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Ok vote time:
A:To the Service.
B:To the EGC in the box serving it.
C:To the water line 5' from entering the building.
D:Any water line 15' away with #16 per instructions.
E:Not at all.
Mark Heller
"Well - I oughta....." -Jackie Gleason
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Joined: May 2003
Posts: 2,876
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Mark Heller
"Well - I oughta....." -Jackie Gleason
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Joined: May 2003
Posts: 2,876
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I almost flip-flopped, no still 'B'!
Mark Heller
"Well - I oughta....." -Jackie Gleason
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Joined: Jun 2004
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I have to go with "d" . I have an old '96 NEC. In it under grounding seperately derived grounded systems, it lists the nearest effectively grounded metal water pipe as grounding electrode to be used. Not sure when they deleted this phrase in the NEC, but it may explain where it came from. Apparently the engineers haven't gotten the update.
[This message has been edited by trekkie76 (edited 09-13-2004).]
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Anonymous
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But is this a separatly derived AC system?
All of the premisis wiring is 12V DC and in no way phisically connected to the ground.
I asked a honeywell tech what the ground was used for and was told it was only to protect the P.C. board from damage caused by arcs as well as surges coming off of the monitoring phone lines.
Will add that a note in an install manual makes the statement that if a grounded water line is not available then a 6' ground rod MUST be used
[This message has been edited by kentvw (edited 09-13-2004).]
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Joined: Jun 2004
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the plug in trans. is 12 VAC. no connection to the nuetral, no direct electrical connection to the regular electrical system.By def. it is a seperately derived system.I have seen that same note in an FBI panel manual.
[This message has been edited by trekkie76 (edited 09-13-2004).]
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Anonymous
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Still do not think it is required to be grounded at all.
250.20(D) "Separatly derived systems, as covered in 250.20(A) or (B) shall be grounded as specified in 250.30"
250.20(A).."Alternating-current circuits of less than 50volts shallbe grounded under any of the following conditions:
(1) Where supplied by transformers, if the transformer supply system exceeds 150 volts to ground
(2)Where supplied by transformers, if the transformer supply system is ungrounded
(3) Where installed as overhead conductors outside of buildings
In this case the transformer supply is is 120 volts. My duplex feeding the transformer is grounded and I have no outside wiring.
So I am not required to ground the system.
HERE IS THE CATCH
250.20 ......Other circuits and systems shall be permitted to be grounded. If such systems are grounded, they SHALL comply with the applicable provisions of this article.
Taking the ground wire the nearest cold water pipe ain't gonna meet code.
I stand corrected! THANK YOU
What a great code question!
As trekkie pointed out this did change between 99 and the 02 code. 99 said nearest available effectively grounded water pipe and the 02 changed to within 5' of entrance.
[This message has been edited by kentvw (edited 09-13-2004).]
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