If you are trying to be as accurate as you can on diversity then installing meters (like @VTer suggested) on the incoming section will give you a more accurate representation. The NEC even addresses it in determining existing load. Reference NEC Article 220.87. I was on a reliability project...
>>>HCBFlash (Electrical)20 Nov 16 18:41
>>>Interesting.
>>>I find myself "building per print", and questioning things less and less as the years pass, but I can say that only very, very rarely (if ever) do I >>>recall having dealt with equipment grounding conductors of the same circular mils...
We have multiple feeders from a piece of SWGR to multiple SWBDs. These feeders are 1600A’s each so we are running parallel feeders using a separately run #4/0 AWG Ground. The Contractor wrote an RFI in order to try a save the owner money and requested that we run a single ground cable for the...
I came into the project late and I don't believe we have the ability to change the PO without schedule and cost implications. I agree with your proposal and this will be my approach going forward! I have learned that the NESC is the code for substations and that the 10' from live parts to...
If the steel has a proper connection to the Grounding electrode system (see definition in Part III of Article 250(specifically2 250.52 (A) (2) of the NEC) then yes connecting to the steel is permitted.
If you have access to the NEC handbook that have nice illustrations that convey the above...
My standard answer is that it depends...
Typically Codes are adopted to a project based on when the Purchase Order was signed or as dpc said if the engineering scope was written in a language that points to a specific adoption. Ethically, if the consultant has a maintenance argeement on the...
My background is Industrial so I am coming into this arena with little to no Utility experience. I am working on a design tie a 12 ohm NGR to a wye delta grounding XFMR (The Fault current of the NGR is 1658A for 10sec.) The L-L voltage is 34.5kV. During a fault the NGR can see as much as 20kV...
Sorry Gents. My ratings were going from memory when I wrote this the value of the NGR is 20 Ohms.and the 10 sec rating is closer to 1000A.
I believe that if my coworker were to plug the SLG fault values to the cable thermal damage equation they would get similar results as what SKM is...
I am trying to size the NGR's conductor from a wye delta isolation transformer. I believe the NGR is rated 75A continuous and can allow ~900A for 10 sec and has an 8 ohm impedance.
When I model the system using SKM the damage curve of the conductor requires a 500kCMIL cable to withstand the...
OK here's the thing. I normally research my topic thoroughly prior to coming into the eng-tips forums, but I am on a tight deadline to have answers on this topic very soon. So I am apologizing up front for now making attempts at due diligence.
Now that I got that out of the way...
My...
I got an opinion from a seasoned veteran electrical engineer with 30+ years of Pulp and Paper and he said when the copper prices sky rocketed the 575V drives allowed for a cost savings in reducing cable sizing. Since coordinated drives use 1000s of HP the bump in voltage can translate to a...
I have been on several Pulp and Paper Projects in the recent past where the project direction took the coordinated drives on a 575V power system and the 480V loads consisted of FVR/FVNR/non coordinated VFDs, etc.
Is this a client preference or is there a motive to doing this? I have tried to...
I am in the middle of attaining pricing and deliveries for Medium Voltage Cable for a MV VFD motor (4000V) application. Some common denominators I am getting from the various players are 5kV 133%/8kV 100%, CLX or CCW or IAC Armor Tape shield, all of the vendors are specifying 3 connectric...
Thanks RonShap & dpc for your valuable responses!
dpc, the overall goal should be to protect the worker at all cost. My request was sent to better understand what NFPA 70E says about circumstances where the worker will have very limited working tasks. I realize that when an electrical fault...
I am working with a Client who has given me a reference to a table from NFPA 70E Table 130.7(C) (15) (a).
The line item from that table states that the task when opening hinged covers (to expose bare, energized electrical conductors and circuit parts) in Metal Clad Switchgear, 1kV through 38kV...
Yes I am in the US. Project is in Ohio.
I enjoyed reading that technical write up and it looks like it supports the argument to advise the client to save the dollars.
Thanks for sharing.
Distinguished Forum Members!
I have a 250HP 480V Centrifugal Circulation Pump that supplies water to a Heat Recovery Steam Generator (HRSG) that we have in our specification to Supply an HMCP for short circuit protection and Motor Overloads for Long Time Thermal limit protection. I have been...
Fellow Code Guru’s:
I have a question concerning the NEC's Article 250 stance on tying in new structures to existing. We have this Railroad elevated tie off structure that will allow the factory workers to tie off to an elevated rail and access the railcars as they enter the area. The owner...
