grounding MCC to building structural steel
- Thread starter mobo
- Start date
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Why would you need to bond the MCC to the building steel? If the service is bonded to the steel then the MCC would not have to be. Maybe there is something I don't know about this- let's see what others say
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Unless it is also the service equipment for the building (or an SDS), there is no such code requirement.
- Location
- Illinois
- Occupation
- retired electrician
It is very common for industrial specs to require all large electrical equipment to be bonded to the building steel in addition to the code required EGC.
We recently inspected a new auto manufacturing facility and every one of the hundreds of MCCs required a 4/0 back to structural steel. A few of the contractors overlooked that on their bids and the tears were flowing.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
He did not ask about specs though.
I wonder why such a thing would be found in a spec. What possible benefit is there to doing this?
talked to a pla.t personnel, who is no engineer, and he said they're very overkill on grounding here, but was the only explanation given.
can anybody give a code reference for the 4/0 wire? I'm waiting on feedback
from our office from one of our guys who is an electrical engineer. He's working in an undergound mine today so it'll probably be late before i hear from him.
i found this site and thought i'd hear some input from others in the field.
Strictly a design choice if the MCC does not contain the service or SDS (separately derived system) disconnecting means. As such, no Code reference can be given. The largest GEC (grounding electrode conductor) required by Code is 3/0 Cu (250kcmil Al) per 250.66. An EGC (equipment grounding conductor) can be much larger under 250.122 (but not the issue here).
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I did a project once where the engineering company required a 2/0 ground lug on everything, including junction boxes and control panels. it was very strange to see a control panel with a 10A, 120V power feed with a ground lug on the sheet iron sized for 2/0.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Of course, if the plans spec 4/0 then you must use what was designed and approved. As stated the NEC does not req. more than a 3/0 in any case. Table 250.66 is for GEC
I haven't been involved in SubStation design in quite some time but if I remember correctly ,oft times the Job General Specications will list all standards and codes the design engr'ng company must follow and adhere to.............IEEE is or was usually one of those listed and the document standard within was quite extensive.I don't recall the # or name of the standard.Owner Plant standasrds were also in the mix.
dick
dick
good input guys, our engineer finally got back with me and pretty much said the same thing. Said the code is grey on the issue and that we're gonna go with 4/0
The specs simply said "per NEC requirements". problem is, like stated, the NEC
is grey on the issue. so, 4/0 it is.
The specs simply said "per NEC requirements". problem is, like stated, the NEC
is grey on the issue. so, 4/0 it is.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The NEC is not gray on this issue. 3/0 is all that is required for a GEC if you are talking copper conductor.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The NEC gets blamed for everything.
The City of Chicago code would require this bonding jumper to be sized to the 'area of the circuit conductors', they do not stop at 3/0 like the NEC does.
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