Hello all,
Let me preface by stating that I am not an electrical engineer, but have enough knowledge to get myself into trouble...
I am assisting with preliminary design for a temporary power plan.
Background[ul]
[li]We are planning to install a 50 KVA 480-240/120 1-phase transformer about 150 ft from a substation/MCC. [/li]
[li]The transformer will supply power to two electrical service panels that will be located in close proximity to the transformer (<15 ft).[/li]
[li]The two electrical service panels will be out in an open area, however due to the nature of the industrial facility, there are many underground utilities directly beneath the site.[/li]
[li]The site cannot be changed due to the requirement of other utilities and services.[/li]
[/ul]
Based on my (very) limited understanding of electrical codes, I roughly understand that NEC requires electrical grounding rods to be driven for each the...
[ol 1]
[li]50 KVA Transformer[/li]
[li]Service panel 1 -- 25 KW calculated load[/li]
[li]Service panel 2 -- 10 KW calculated load[/li]
[/ol]
I also understand that one of the requirements for electrical grounding rods is that they be driven as close to the transformer/service panel as possible, and also X feet away from each other.
Hopefully you understand my predicament by now.
It looks as though I need to drive THREE grounding rods, each around 8' long, for these three devices that are located in close proximity to each other and right above many underground utilities. As far as I can tell from my site plan, I have a 100 ft² area that I may be lucky to drive ONE rod and be within a comfortable distance to buried utilities.
My ultimate goal is to establish safe grounding, and I realize I might need to get a bit creative to achieve this.
QUESTIONS:
[ul]
[li]The substation has a grounding ring around the building that is incorporated with the building steel and very well earthed. Can I run a conductor from the transformer BACK to the substation and ground my transformer there? Can I attach the service panel grounds to the same conductors and ground everything together? In other words, 150' of conductor will be carrying power from a MCC to a transformer. The transformer and two electrical service panels will all be united to each other via a distribution block, and then a conductor connected to them all will be routed back to the substation 150' away and then connected to the substation's building ground. This option seems too easy to me to be compliant with electrical code...
[/li]
[li]Can I plan for a variation of the above? That is: Uniting the three devices (one transformer, two service panels) but connecting them to a single common grounding rod driven in the one place that is safe.[/li]
[li]Lastly, and recognize I'm spitballing ideas here, but maybe I could do a combination approach. The transformer at 480V could be grounded back to the substation, whereas the two electrical service panels at 240/120V could be grounded together at a single grounding rod. The pseudo-logic here is that the high voltage substation and transformer will be electrically isolated from the service panels via separate grounding conductors, whereas the two service panels (that so happen to share a common power supply) would share a common ground.[/li]
[/ul]
If none of the above options seem viable, I assume that I may need to trench out a road to lay conduit well away from the buried utilities so that I may drive grounding rods in a safe location. Since this is a temporary power plan, this option blows the project cost and schedule out of the water quite a bit...
I tried to give sufficient information to describe the situation without going overboard.
Thank you for taking a look into my questions
Let me preface by stating that I am not an electrical engineer, but have enough knowledge to get myself into trouble...
I am assisting with preliminary design for a temporary power plan.
Background[ul]
[li]We are planning to install a 50 KVA 480-240/120 1-phase transformer about 150 ft from a substation/MCC. [/li]
[li]The transformer will supply power to two electrical service panels that will be located in close proximity to the transformer (<15 ft).[/li]
[li]The two electrical service panels will be out in an open area, however due to the nature of the industrial facility, there are many underground utilities directly beneath the site.[/li]
[li]The site cannot be changed due to the requirement of other utilities and services.[/li]
[/ul]
Based on my (very) limited understanding of electrical codes, I roughly understand that NEC requires electrical grounding rods to be driven for each the...
[ol 1]
[li]50 KVA Transformer[/li]
[li]Service panel 1 -- 25 KW calculated load[/li]
[li]Service panel 2 -- 10 KW calculated load[/li]
[/ol]
I also understand that one of the requirements for electrical grounding rods is that they be driven as close to the transformer/service panel as possible, and also X feet away from each other.
Hopefully you understand my predicament by now.
It looks as though I need to drive THREE grounding rods, each around 8' long, for these three devices that are located in close proximity to each other and right above many underground utilities. As far as I can tell from my site plan, I have a 100 ft² area that I may be lucky to drive ONE rod and be within a comfortable distance to buried utilities.
My ultimate goal is to establish safe grounding, and I realize I might need to get a bit creative to achieve this.
QUESTIONS:
[ul]
[li]The substation has a grounding ring around the building that is incorporated with the building steel and very well earthed. Can I run a conductor from the transformer BACK to the substation and ground my transformer there? Can I attach the service panel grounds to the same conductors and ground everything together? In other words, 150' of conductor will be carrying power from a MCC to a transformer. The transformer and two electrical service panels will all be united to each other via a distribution block, and then a conductor connected to them all will be routed back to the substation 150' away and then connected to the substation's building ground. This option seems too easy to me to be compliant with electrical code...
[/li]
[li]Can I plan for a variation of the above? That is: Uniting the three devices (one transformer, two service panels) but connecting them to a single common grounding rod driven in the one place that is safe.[/li]
[li]Lastly, and recognize I'm spitballing ideas here, but maybe I could do a combination approach. The transformer at 480V could be grounded back to the substation, whereas the two electrical service panels at 240/120V could be grounded together at a single grounding rod. The pseudo-logic here is that the high voltage substation and transformer will be electrically isolated from the service panels via separate grounding conductors, whereas the two service panels (that so happen to share a common power supply) would share a common ground.[/li]
[/ul]
If none of the above options seem viable, I assume that I may need to trench out a road to lay conduit well away from the buried utilities so that I may drive grounding rods in a safe location. Since this is a temporary power plan, this option blows the project cost and schedule out of the water quite a bit...
I tried to give sufficient information to describe the situation without going overboard.
Thank you for taking a look into my questions
