240V single phase to 480 single phase

Status
Not open for further replies.
R

Rock86

Senior Member
Location
new york
Occupation
Electrical Engineer / Electrician
Alright.. here is a fun one.

Without going to into mass detail.... We have a 240V SINGLE phase step up to 480v SINGLE phase transformer. 2017 NEC 250.20(B) says...1604610884481.png


And NEC 250.30(B) says...
1604610976694.png

By our understanding... because we are above 150V to ground... and because we are an ungrounded system with no GROUNDED conductor on the secondary side... do we need to provide a GROUNDING electrode conductor to the system? We do plan on carrying an EQUIPMENT grounding conductor to the transformer... but is the additional grounding required?
 
Yes, you still need a GES. See 250.30(B). Also you will need ground detectors. Is an ungounded really desirable for your situation? Kind of unusual today.
 
Agree with Texie. Grounding electrode system still needed just no phase to ground connection required.
 
texie said:
Yes, you still need a GES. See 250.30(B). Also you will need ground detectors. Is an ungounded really desirable for your situation? Kind of unusual today.
Click to expand...
augie47 said:
Agree with Texie. Grounding electrode system still needed just no phase to ground connection required.
Click to expand...
Thank you both... but I am would like to debate the grounding a touch more. Below I am attaching an article which sells me on the topic of a ground detector system... fully on board with you both about that. I had posted NEC 250.30(B) for the understanding that I had examined that section and here is my understanding...
1604610976694.png
"...shall be used to connect the metal enclosures of the derived system to the grounding electrode as specified in 250.30(A)(5) or (6), as applicable." 250.30(A)(5)&(6) say.. " It shall be used to connect the grounded conductor of the derived system to the grounding electrode in accordance with 250.30(A)(4)."

By both of your comments, you're saying I need a grounding electrode conductor but it is not connected to a phase. If my potential from phase/line to ground is 480V, by NEC 250.21 I am not required to have grounding, and because I don't have a grounded conductor I am not required to have grounding per NEC 250.30(B)... unless you can sell me on the requirement for the metal enclosure needing more than equipment grounding. Thoughts???? If you (or anyone) could maybe elaborate a little more about your interpretation about the code, i'd be happy to get a better idea on this.

Here is the article.... https://www.ecmag.com/section/codes...and-regulations-code-rules-ungrounded-systems. Thank you for the tip about the ground detection.

And yes... unfortunately this is the only system we have to work with.
 
Correction... NEC 250.20(B) leads to NEC 250.21... 250.21 kind of answers my question.
 
The only real difference in the grounding and bonding rules for grounded and ungrounded systems is that the ungrounded system does not have a main or system bonding jumper. The requirement for a grounding electrode and GEC does not change. It is only connected to the equipment grounding conductor(s) since there is no grounded circuit conductor. See 250.4(B).
 
don_resqcapt19 said:
The only real difference in the grounding and bonding rules for grounded and ungrounded systems is that the ungrounded system does not have a main or system bonding jumper. The requirement for a grounding electrode and GEC does not change. It is only connected to the equipment grounding conductor(s) since there is no grounded circuit conductor. See 250.4(B).
Click to expand...
Ok.. so based on 250.4(B)... if the primary side has grounding established, an equipment ground is carried through to bond the metal enclosure of the transformer and carried through to a device downstream and ground detector is installed in accordance with 250.21... do I need to reestablish grounding on the secondary side of the transformer when my system is not grounded on the secondary side?? 250.4(B) does not specifically say Grounding Electrode or GEC.
 
As Don pointed out in #6 above, Treat it just as you would a grounded secondary such as 480/277 except you will not have a system bond jumper (secondary to grounding system) unless you elect to ground one side and then you can omit the ground detector.
 
augie47 said:
As Don pointed out in #6 above, Treat it just as you would a grounded secondary such as 480/277 except you will not have a system bond jumper (secondary to grounding system) unless you elect to ground one side and then you can omit the ground detector.
Click to expand...
Thanks.
 
Rock86 said:
Ok.. so based on 250.4(B)... if the primary side has grounding established, an equipment ground is carried through to bond the metal enclosure of the transformer and carried through to a device downstream and ground detector is installed in accordance with 250.21... do I need to reestablish grounding on the secondary side of the transformer when my system is not grounded on the secondary side?? 250.4(B) does not specifically say Grounding Electrode or GEC.
Click to expand...
You need a GEC for the SDS, unless your primary EGC can meet all of the requirements for both a GEC and EGC.
 
Status
Not open for further replies.
Top