VanmBuilders
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Separately derived system transformer
- Thread starter VanmBuilders
- Start date
- Location
- New Jersey
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- Journeyman Electrician
Okay makes a little more sense. Let's see if I have this correct the service is attached to the building a feeder fro a 125 amp breaker in the service feeds a 200 amp disconnect with125 amp fuses which feeds the transformer primary to the 208Y/120 volt panel.
Service>125 OCPD>200 amp Disconnect>XFMR Primary>Panel
Where are you installing the SBJ in the transformer or in the panel? In that location you'll need to land the GEC which connects to the existing building GES.
VanmBuilders
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Yes you’re correct……primary side 480volt to secondary 208v panel.
was planning on sbj with transformer and get my GEC using ground rod by transformer. Building steel is 20ft away. However a little unaware of how sbj would be executed in the 208 panel.
It says your a contractor in California so your general contractor? I don't know what the laws are in CA if they allow general builders to work on 480V systems and set transformers, but here that would need to be done by a licensed EC. My apologies if you are an EC but I am new here an I don't know what the forum rules are around giving advice to a general contractor, does that fall under DIY advice?
VanmBuilders
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New C10 as well? Just first one in career.
Ahh well sounds like your an EC then,
You don't need a ground rod at the transformer, here I often run a GEC all the way back to a main electrical room where there is a grounding electrode busbar and all the building ground come together. Since your more of an outdoor setup I'd imagine you would run back to the main building switch-gear with a grounding electrode conductor. Sometimes we use building steel. Its mostly all covered in 250.28 - 250.30 in the NEC, I gather CA is on the 2020 NEC.
VanmBuilders
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- California
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Ya we’re 2020 out here with jurisdictions sometimes some recognize 2023
VanmBuilders
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Reason why I came to forum was had another c10 tell me to use a ground rod at transformer then to XO then neutral out to 208 panel. I’ve seen one done that way as well so wanted to confirm.
250.30(C) says you need to connect to a grounding electrode, 250.30(A)(5) covers the grounding electrode conductor you run for a single transformer back to the building grounding system.
I believe this needs to be a wire type conductor or busbar but others will chime in here and correct me.
When I have a outdoor transformer its often on a roof so I have never thought of adding a ground rod, that would really look odd in a 10th floor roof (perhaps in one of those roof garden planters)
Seriously though If you add a ground rod at a outdoor transformer you still need to run back to the grounding electrode system for the 600A service at the building main electrical gear.
I believe this needs to be a wire type conductor or busbar but others will chime in here and correct me.
When I have a outdoor transformer its often on a roof so I have never thought of adding a ground rod, that would really look odd in a 10th floor roof (perhaps in one of those roof garden planters)
Seriously though If you add a ground rod at a outdoor transformer you still need to run back to the grounding electrode system for the 600A service at the building main electrical gear.
VanmBuilders
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I just opened the cabinet and seen the neutral that runs with the feeders is attached at the building main electrical gear. And goes down to what appears to be grounding conductor but there all marked white.
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VanmBuilders
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VanmBuilders
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I’m just going to use the neutral that was inside that raceway with the other 125amp conductors because it is attached to the building main gear system. That will give me my bond to the electrical grounding system At that 600amp service.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I'm not sure why someone installed that bonding jumper, the neutral bus is factory bolted directly to the enclosure.
VanmBuilders
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This appears to be there grounding wire goes back to that neutral buss.I'm not sure why someone installed that bonding jumper, the neutral bus is factory bolted directly to the enclosure.
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kwired
Electron manager
- Location
- NE Nebraska
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- EC
All separately derived systems ultimately need to tie to the GES of the building/structure. There can be many ways to do so but that is the basic intent there. The idea is to avoid potential between the grounded/grounding conductors of each system. Water pipe electrodes and building steel electrodes both require a GEC fully sized to table 250.66, Ground rods/pipes, ground rings, or CEE's may possibly have smaller conductor allowed to be run to electrode itself is a reason it may not be so desirable to try to use those items or the conductor run to them for interconnection between systems
re-read 250.30(C), now that I just did I could see how someone would get the impression you need to establish a ground electrode system at a outdoor transformer, all I am saying is if you did that you'd still have to tie into the building's grounding system with a GEC that is wire or busbar.
I am not really sure what the point of that item (C) is, it does not seem to add anything not covered in A or B.
All I know is I can't have two grounding electrode systems at a single structure, no matter how big that structure is, you always tie them into one single grounding system.
The cool thing about that neutral in the OP's situation is that since it originates at the service equipment, it can be used as an EGC, and since it is large enough to be a neutral, it is probably also large enough to serve as the GEC as well, so no extra rods or any lugs to steel or anything.