Inverter to Step-up Transformer EGC or SSBJ ?

[hill900505]

Even ungrounded systems are required to have a grounding system and bond noncurrent-carrying metal parts. They are also required to have a ground detection. With other grounded systems on the premises, the grounding systems should be coupled IMO but as SDS's, the NEC does not require such unless part of the same building or structure. So with that said, I still agree with your inspector... and add that there needs to be ground detection installed somewhere if the secondary is truly ungrounded. Whoever engineered this project should know that. I do not know the circumstances why they decided to go ungrounded, but as I see it, the secondary should be grounded, if not solidly, at least go with high impedance grounding, especially if there will be no one to monitor ground detection on a frequent basis.


PS: the other system, especially the grounding transformer part, sounds weird. Can you post the one line (please verify non-proprietary status and/or censor the qualifying data before posting).

Here is the oneline for the project. The inverter and main transformer are on the far right.

 

[Smart $]

You should come out here and talk to some of the AHJ's I work with.
Yes, but then there's that 10ft requirement instead. :slaphead:

Ohh, I figured my interpretation would not fly in all areas.

Within 10ft of its respective equipment can be a lot further than 10ft apart under 'certain' interpretations... regardless, still far from what I'd consider grouped under most interpretations.

 

[Smart $]

Here is the oneline for the project. The inverter and main transformer are on the far right.

Definitely ungrounded secondaries. One line shows ground detectors. But the one line only shows system grounding. It does not show equipment and non-current-carrying metal parts grounding. I'm still leaning in agreement with the inspector. SSBJ sized per 250.102.

 

[jaggedben]

Here is the oneline for the project. The inverter and main transformer are on the far right.

Not to open another can of worms, but I hope the ground detectors don't run afoul of 705.32.

 

[hill900505]

Definitely ungrounded secondaries. One line shows ground detectors. But the one line only shows system grounding. It does not show equipment and non-current-carrying metal parts grounding. I'm still leaning in agreement with the inspector. SSBJ sized per 250.102.

On one note, If there is a second SDS again after one SDS, what is the right way of grounding them? (From oneline number 15 aux transformer to number 27single phase transformer) Is the 40A breaker in 27 considered as the first disconnect for aux transformer 15 OR No.27 single phase transformer is a separate SDS and make GEC connection twice both in No.15 and 27?

 

[Smart $]

Not to open another can of worms, but I hope the ground detectors don't run afoul of 705.32.

Ground detectors do not interrupt power. They only provide visible and audible warning of one-of-three lines to ground fault(s). A two-of-three lines to ground fault situation is assumed to be capable of tripping the supply OCPD.

On the other hand, ground-fault protection does interrupt power on detection of a ground fault exceeding a preset milliampere-level threshold.

 

[Smart $]

On one note, If there is a second SDS again after one SDS, what is the right way of grounding them? (From oneline number 15 aux transformer to number 27single phase transformer) Is the 40A breaker in 27 considered as the first disconnect for aux transformer 15 OR No.27 single phase transformer is a separate SDS and make GEC connection twice both in No.15 and 27?

Each SDS must comply with the rules by itself. You need to run a GEC to each system.

Under current Code you can run an EGC/GEC combo with the feeder to the panel. It must comply with all the rules for both EGC and GEC (there are a lot of installation details I am not aware of so I cannot add further). But seeing as this is a stamped project you need to check your feeder schedule to see if the grounding conductor is sized appropriately. If not, RFI the engineer of record explaining what you want to do...