Sorry if this sounds a bit daft, but why in the wide wide world of sports would an engineer call for a 3/0 ground on the 400a secondary side of a separately derived system with a feeder raceway of ~10 ft? Am I missing something? Last the I checked a #3 is sufficient for a 400a panel. I understand there's nothing wrong with over sizing it, but at what point is it just a waste of money :?
overrated equipment ground per engineer.
- Thread starter wankster
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xformer
Senior Member
- Location
- Dallas, Tx
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- Master Electrician
xformer
Senior Member
- Location
- Dallas, Tx
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- Master Electrician
Could it be for future expansion? Why the concern? - If I may ask..
I was sent to a job for a start up that another electrician did the work on. As I was going though things I noticed that his install didn't match the single line, but it does satisfy NEC. I'm sure he did it to save money, and he's passed inspection, I just don't understand why they would call for such overkill.
texie
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- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
I'm reading your post as this being a SBJ and not an EGC. Table 250.66 would apply here in that case and this would require a 1/0 CU or 3/0 AL (assuming 500 or 600 MCM CU). Am I reading your post correctly?
It's not the bonding jumpers. It's the ground from the XO to the panel fed by the secondary.
The single line reads "4 #600 MCM CU, 1 #3/0 CU GND"
xformer
Senior Member
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- Master Electrician
That fits the definition of a SSBJ.... not a EGC...
Okay, then it looks like I've got some work to do.
Btw, I'm not up to speed on all the acronyms.
SSBJ = secondary system bonding jumper? :?
my original question is still valid, though, 3/0 is 2 sizes larger than that table requires, lol!
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texie
Senior Member
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- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
I think you are saying that this is an EGC and 250.122 applies. This is not an EGC but rather a SBJ that must be sized per 250.66 (2011) or 250.102(C) (2014). NEC 2011 or 2014, the end result is the same. It needs to be a 1/0 CU or 3/0 AL minimum to comply with NEC. The GEC would also likely have to be the same size assuming it is going to building steel, etc.
xformer
Senior Member
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Supply Side Bonding Jumper.. See 250.30A 2
- Location
- Massachusetts
I agree with the others about the code reasons but will add it does not matter.
If it was on the prints you bid you need to provide it even if it goes beyond minimum requirements.
If it was on the prints you bid you need to provide it even if it goes beyond minimum requirements.
texie
Senior Member
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- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
I agree. But #3 per Table 250.122 does not work here is the point I was trying to get the OP to see. So 3/0 CU it is.
- Location
- Massachusetts
I agree. But #3 per Table 250.122 does not work here is the point I was trying to get the OP to see. So 3/0 CU it is.
I agree 250.122 is not the place to go in this case.
I figured you all had covered the code issues I was trying to point out that engineers often exceed the code minimums and the reasons they do so are really not my concern.
mbrooke
Batteries Included
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If it was to a ground rod Id say huge waste, in this case Id say possibly a waste but who cares.
MasterTheNEC
CEO and President of Electrical Code Academy, Inc.
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Your topic is "overrated"..I happen to feel it's underrated
....maybe it needs a good PR Firm to represent it's interests. Sorry, I added nothing worth value to the post. I apologize Mods:angel:FWIW - if you use #3 AWG prepare for a red tag...:jawdrop:but I think you know by now that's not the right size so me explaining is moot.
- Location
- Massachusetts
The reason for this is because the secondary conductors from the transformer are not feeders they are unprotected taps until they reach the first overcurrent device.
In other words if one of these conductors faulted to ground it would not trip your 400 amp breaker in the panel. The overcurrent device on the primary side of the transformer will have to trip and this system bonding jumper must be large enough to handle that on the secondary side.
Your topic is "overrated"..I happen to feel it's underrated
FWIW - if you use #3 AWG prepare for a red tag...:jawdrop:but I think you know by now that's not the right size so me explaining is moot.
That's the funny thing about those #3's, they already passed inspection!
Edit: nvm, already answered.
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