Delta-Delta Ungrounded

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MrJLH

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Need some help understanding how messed up this is.

The picture is a breaker that is fed off a transformer that is delta-delta to my knowledge. There are 6 wires coming in an six wires leaving, 2 per phase. I can clearly see the enclosures of the transformer grounded.


The client wants to replace the breaker to feed some new gear without having to modify the feeder off the transformer. Can this be done? Per the code I cant see how. There is ground fault detection installed.

Sorry about the photo

Thanks

BigBox4.jpg
 
electrofelon said:
What do you think the problem might be? Only caveat other than load being within limits of the upstream equipment is you won't be able to use slash rated breakers and equipment.
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For starters the load is being reduced but I don't want to focus on that just yet.

I see the problem being that since the breaker fed off transformer is ungrounded delta-delta, there is no supply side bonding jumper from the transformer to the OCP enclosure.


So I don't see how this can be re-used without having to pull a new SSBJ.

Thanks
 
I’m not sure what you’re asking. Guessing the lugs are rated for two wires and they are sized properly. I would think there should be a grounding conductor somewhere, unless the raceway is suitable. I can’t see if anything is bonded. Is this the service entrance?
 
ptonsparky said:
I’m not sure what you’re asking. Guessing the lugs are rated for two wires and they are sized properly. I would think there should be a grounding conductor somewhere, unless the raceway is suitable. I can’t see if anything is bonded. Is this the service entrance?
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No service entrance is at the utility substation outside the facility fence.
 
You are correct that there is no bonding jumper and thus in the event of a ground fault the breaker won't trip.

This however is permitted for intentionally 'ungrounded' systems if you follow the rules for such systems.

Ungrounded systems have specific rules you need to follow and have specific problems that might make them bad design, but they are permitted by code.


Jon
 
MrJLH said:
Picture of transformer that breaker is fed from
View attachment 22389
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First thing I would look at is the transformer nameplate for the winding diagram, to verify it is delta / delta. It may not matter but it's a puzzle piece. You would want to be sure of the whole picture including the available windings. Looks like three bushings at the transformer secondary, but i would peek at the nameplate.

The underground load side stubs up look like RGS. The next thing I would be looking at is if the sitewide equipment ground, the RGS with the feeders, is consistently all connected together intentionally and solidly. The RGS common bonding system is not shown in the picture. I would be looking for a three wire four conductor system.

Next would be looking at the load and making sure everything is line to line connected. People unfamiliar with the floating delta supply may come along and try to get 277 V off it (thinking they may have a neutral) or loading a drive on it.

If the survey checks out and they know what they're doing, just changing the breaker may happen routinely.
 
MrJLH said:
For starters the load is being reduced but I don't want to focus on that just yet.

I see the problem being that since the breaker fed off transformer is ungrounded delta-delta, there is no supply side bonding jumper from the transformer to the OCP enclosure.


So I don't see how this can be re-used without having to pull a new SSBJ.

Thanks
Click to expand...

In an ungrounded system, everything still needs to be bonded together and to a grounding electrode system. The only difference between ungrounded and grounded is there isn't a system bonding jumper connecting ine of the system conductors to the egc/ground system. See 250.4(B) and 250.30(B).
 
I tend to agree with __dan's post. Although we don't see the conventional supply side bonding jumper, you can see a grounding conductor on the transformer case and in all likelihood on an install this large, all equipment is bonded to a grid of some type and you end up essentially with the same bond..
I would not hesitate in changing the breaker.
Just make sure the new breaker is fully rated for a delta connection (240.85)
 
I worked with an installation that was the same method as the picture but from an earlier era. With a mix of PVC and RGS stubbing up out of the ground to a weatherhead, just like the picture. They had a three phase three wire installation mostly, frame and structure grounding for an effective fault clearing (or carrying) path was not assured. EGC conductor or connections were missing.

Let's say the primary stepdown transformer was installed by company A and the load side feeders were installed by companies B, C, ... over the years. So there's a difference in implementation strategy (if any). The visible grounding wire at the transformer may just go to a ground rod, but the expected to be seen grounding method for the GRS is water pipe clamps hanging on the stubs (and the EGC hanging from that). There has to be a material and visible method to connect the RGS to each other and to the transformers case ground, along with contiguous frame and structure grounding to the EGC system.

A survey of the EGC would be indicated.
 
electrofelon said:
In an ungrounded system, everything still needs to be bonded together and to a grounding electrode system. The only difference between ungrounded and grounded is there isn't a system bonding jumper connecting ine of the system conductors to the egc/ground system. See 250.4(B) and 250.30(B).
Click to expand...
Correct, even if ungrounded we still bond all non current carrying parts and install grounding electrodes in same manner we do for grounded systems - this is done to put all the non current carrying components at same potential.
 
kwired said:
Correct, even if ungrounded we still bond all non current carrying parts and install grounding electrodes in same manner we do for grounded systems - this is done to put all the non current carrying components at same potential.
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To be more thorough, to lower touch potentials, for functionality of ground detectors, and for the tripping of line to line faults.
 
electrofelon said:
In an ungrounded system, everything still needs to be bonded together and to a grounding electrode system. The only difference between ungrounded and grounded is there isn't a system bonding jumper connecting ine of the system conductors to the egc/ground system. See 250.4(B) and 250.30(B).
Click to expand...

Thanks

Just out of curiosity can you explain why in NEC 2017 250.186(B) is so specific to systems above 1000V?
 
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