# ungrounded delta systems



## charlie Bob (Jul 26, 2009)

I've never worked onsuch a system but as i'm reviewing grounding and bonding something came to my attention.
as the name discribes it, the system is ungrounded, therefore a ground fault will not tri any OCP but a second will cause it will be a short fault of the two phases. So if all the metal parts of the system are connected together by a EGC to ground:
- how safe this system is against ground faults?
- I guess one should check potential between metal parts and ground before 
working on them?
- Am i missing anything?

Thanks.


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## RePhase277 (Feb 5, 2008)

Ungrounded systems should have some means to indicate a ground fault. But if not, you can still test by using a volt meter. If there is no ground fault, a volt reading between any phase and ground will give an odd reading. If there is a ground fault, two phases will read full system voltage to ground, and the faulted phase will read 0.


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## charlie Bob (Jul 26, 2009)

thanks inphase


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## Toronto Sparky (Apr 12, 2009)

Most I have seen have three neon lights on the main switch gear. 
If there are all the same brightness all is ok.. On Fault one goes out the the other two get brighter.


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## goose134 (Nov 12, 2007)

I believe some of these have an audible alarm as well.


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## augie47 (May 4, 2009)

Keep in mind that equipment grounding is extremely important on these systems. Picture a 480v ungrounded system. Machine #1 has "A" phase to ground. Machine #2 has "B" phase to ground. If by changes these two are not grounded & bonded together the potential between the two wold be 480 volts.

Incidentally the ground fault detector is required by 250.21(B)


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## brian john (Mar 11, 2007)

augie47 said:


> Keep in mind that equipment grounding is extremely important on these systems. Picture a 480v ungrounded system. Machine #1 has "A" phase to ground. Machine #2 has "B" phase to ground. If by changes these two are not grounded & bonded together the potential between the two wold be 480 volts.
> 
> Incidentally the ground fault detector is required by 250.21(B)


If "A" phase is grounded then the system is no longer ungrounded and then if "B" phase becomes grounded, GROUND FAULT.


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## MDShunk (Jan 7, 2007)

By the way, charlie bob, if this system has no indicator lights or alarms to indicate a ground, this can be pretty easily retro-fitted. There's some pretty slick turn-key solutions to add that feature. I'm not sure if you're in a position to recommend that upgrade or not. It will save a lot of heartache later on.


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## augie47 (May 4, 2009)

brian john said:


> If "A" phase is grounded then the system is no longer ungrounded and then if "B" phase becomes grounded, GROUND FAULT.


my "grounded" term was in error... I was attempting to say (poorly) if "A" phase "connects" (as in a fault) to a piece of equipment and "B" to another that isn't grounded, you have a potential. Why it is important that everything be grounded.
I have seen portable equipment where this has occurred..sometime just a leakage and not the full voltage..
probably one reason the Code wants the fault detectors...so that potential


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## Toronto Sparky (Apr 12, 2009)

Ground is a relative term.
A lot of these new machines require a ground rod at the machine (Fanuk comes to mind) 
Depending on the conductivity of the soil under the concrete. I'm thinking it would be easy to get a significant potential between machines.


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## MDShunk (Jan 7, 2007)

Toronto Sparky said:


> Ground is a relative term.
> A lot of these new machines require a ground rod at the machine (Fanuk comes to mind)


Ever wonder why or how that requirement got put in the manual?

I've had to drive ground rods for paper converting equipment so that the static discharge equipment worked properly.


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## ale13 (Sep 6, 2013)

augie47 said:


> my "grounded" term was in error... I was attempting to say (poorly) if "A" phase "connects" (as in a fault) to a piece of equipment and "B" to another that isn't grounded, you have a potential. Why it is important that everything be grounded.
> I have seen portable equipment where this has occurred..sometime just a leakage and not the full voltage..
> probably one reason the Code wants the fault detectors...so that potential


In an ungrounded delta system there is no such thing as a ground fault. Unlike a wye or grounded delta system there is no reference to ground. So if A phase became "grounded" in any location within the system no breaker or fuse would trip or blow. Now if B phase then became grounded at a location near the same location that A phase is grounded you wouod have a dead short between 2 phases. If the grounds on A and B phase are far enough apart the resistance of the wire, conduit, or any combination of any conductive material is great enough there will be no fault that will occure. This why code requires a "ground detection device" be installed withing the system.


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