# Ground Fault Detection Scheme



## brian john (Mar 11, 2007)

Make one, lamp to ground


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## Bob Badger (Apr 19, 2009)

DipsyDoodleDandy said:


> Looking for a design for a cost sensitive GFDS for a compressor on a 3 phase ungrounded delta system. The key word is "Cost Senstive" or "Cheap Customer". Been looking around for some type of ground lamp setup. The customer is having some "Cash Flow Problems". This cash flow problem story is really starting to get old.


Three lamps of equal wattage, one hot of each to each phase. The line from the screw shell of each lamp connected together and to ground.


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## Zog (Apr 15, 2009)

DipsyDoodleDandy said:


> Looking for a design for a cost sensitive GFDS for a compressor on a 3 phase ungrounded delta system. The key word is "Cost Senstive" or "Cheap Customer". Been looking around for some type of ground lamp setup. The customer is having some "Cash Flow Problems". This cash flow problem story is really starting to get old.


Unless you are an engineer you should avoid designing such a system, you try to do something cheap and easy and you might be on the line for liability issues if something were to happen. My advice, pass on this one, tell them to do it right or don't do it at all. 

That said, the simplie way is to connect 3 PT's delta connected from each phase and connect each phase secondary to groud with a lamp in series. All 3 lights on is good, one phase sees a ground and it dims and the other 2 get brighter. Now this requires someone to look at them every once in a while, you want anything with a protective function and it gets more complicated. 

I stock both GF monitors and relays, reconditioned and tested. Depending on what equipment they have it might be pretty easy. How about some details of thier system?


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## Zog (Apr 15, 2009)

Bob Badger said:


> Three lamps of equal wattage, one hot of each to each phase. The line from the screw shell of each lamp connected together and to ground.


Looks liike you are assuming this is lower voltage system and I am assuming (As usual, my bad) this is either a 480V system or a MV system. 

OP, whats the voltage?


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## Bob Badger (Apr 19, 2009)

Zog said:


> That said, the simplie way is to connect 3 PT's delta connected from each phase and connect each phase secondary to groud with a lamp in series.


The 'simplest way' needs PTs?

I did not get the impression this was a high voltage system.


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## Bob Badger (Apr 19, 2009)

Zog said:


> Looks liike you are assuming this is lower voltage system and I am assuming (As usual, my bad) this is either a 480V system or a MV system.
> 
> OP, whats the voltage?



LOL yeah my bad as well, but they do make 277 volt lamps.


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## Bob Badger (Apr 19, 2009)

Here is another way to handle 480 delta


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## DipsyDoodleDandy (Dec 21, 2009)

*...*

I already ran the light bulb frame to ground rod past him. Too cheesy, yet he is broke. The machine is already hooked up and active on an ungrounded 3 phase delta system. Currently they have it on a 90 amp 3 pole OCPD 300 ft away. Fuseable disconnect at machine on 30 amp dual element time delay fuses which they are using as overcurrent and overload protection. No ground rod at machine. This is not even a job of mine. This is all from a phone call of a friend Maintance man. There are still a few places around here that grandfather in the 3 phase delta ungrounded systems around here.


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## DipsyDoodleDandy (Dec 21, 2009)

*...*

Sorry, this is a 240 delta ungrounded system. 240 V Phase to Phase


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## Bob Badger (Apr 19, 2009)

DipsyDoodleDandy said:


> I already ran the light bulb frame to ground rod past him.


No, never to a ground rod.

You would connect it to the systems EGC.




> Too cheesy, yet he is broke.



Well then I guess he is SOL and will have to step up and pay the price for the correct equipment.







> The machine is already hooked up and active on an ungrounded 3 phase delta system. Currently they have it on a 90 amp 3 pole OCPD 300 ft away. Fuseable disconnect at machine on 30 amp dual element time delay fuses which they are using as overcurrent and overload protection. No ground rod at machine. This is not even a job of mine. This is all from a phone call of a friend Maintance man. There are still a few places around here that grandfather in the 3 phase delta ungrounded systems around here.


Ungrounded delta is still a used system and no grandfathering is required.

Why would a ground rod be required at the machine?


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## DipsyDoodleDandy (Dec 21, 2009)

*GR*

Don't know. He said they have it next to other machines there as added protection. He is maintainance guy at large machine shop. Another odd thing is technically with the locked rotor amps at machine I think it should be kicking out the 90 amp Instantaneous Trip Breaker yet it isnt (according to him. I think he said it should be 140amp Class H,7.5 HP motor) ? I'm sure Brian will ring in on that.


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## DipsyDoodleDandy (Dec 21, 2009)

*f...*

Bob, you must mean because of this

http://www.groundperfect.com/cncmachframe.htm

I'll forward this article to him.


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## brian john (Mar 11, 2007)

DipsyDoodleDandy said:


> I already ran the light bulb frame to ground rod past him. Too cheesy, yet he is broke.


This is how some "store bought" systems work.


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## Bob Badger (Apr 19, 2009)

DipsyDoodleDandy said:


> Bob, you must mean because of this
> 
> http://www.groundperfect.com/cncmachframe.htm
> 
> I'll forward this article to him.


There is much grounding voodoo out there but my point was the NEC does not require a ground rod at the machine and as far as what the computer geeks want I think they are clueless. Most CNC communication issues can be fixed with data line isolation boxes that break the ground loop created by the grounded conductor in the RS-232 cable.

I could install an ungrounded system today although I think the modern choice is a high resistance grounding scheme.


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## DipsyDoodleDandy (Dec 21, 2009)

*...*

Ever done this or know of anyone who has? This appears to me like the latest most cost effective and long term grounding scheme out there. 

http://www.groundperfect.com/deepframe1.htm

P.S. He said they only set ground rods on their 3 wire delta no ground machines (5.... I think). I know, your probably cringing right now


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## DipsyDoodleDandy (Dec 21, 2009)

*oops*

go to page 4


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## Bob Badger (Apr 19, 2009)

DipsyDoodleDandy said:


> Ever done this or know of anyone who has? This appears to me like the latest most cost effective and long term grounding scheme out there.
> 
> http://www.groundperfect.com/deepframe1.htm
> 
> P.S. He said they only set ground rods on their 3 wire delta no ground machines (5.... I think). I know, your probably cringing right now


From the link




> ABSTRACT
> 
> Low resistance earth grounding is essential for safety and protection of sensitive electronic equipment. It is the basis for any facility’s power quality assurance program.


I think the above is a for the most part a fallacy.

Is a connection to dirt required for electronics?

How is that accomplished in a plane? Or the research stations in the Antarctic?


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## brian john (Mar 11, 2007)

> Low resistance earth grounding is essential for safety and protection of sensitive electronic equipment. It is the basis for any facility’s power quality assurance program.



IMO (and many with real world experience) this is a fallacy, I have had systems that were accidentally left ungrounded then had a branch circuit phase to ground fault, The system was operating N-G 120 VAC, B-G 240 VAC, C-G 240 VAC, A-G - VAC. No one knows how long this was like this. This was in a skiff with racks and racks of "sensitive" electronic equipment.

But the profit margins go up as the grounding systems get more elaborate.


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## micromind (Aug 11, 2007)

I've had good luck with these, you can set the fault current level to 5, 10, or 30 ma. They need 120 AC, and cost about $200. 

Cutler/Hammer #EGF3NOACNET3. 

The CT is solid core, so you have to disconnect the 3 wires and run them through the 3/4" hole in the middle. 

Rob


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