Thank you both. I just got confirmation from the utility that says something similar, stating that the main service is not to protect the utility transfomrer, but to protect the load side on the customer.
Logically, between the utility that tends to undersize (being conservative), and the...
At one of the job site we have, the service transformer at the utility pole is 3x 75KVA which gives 225kVA max capacity. Our contractor has previously procured a 1200A main service panel with a 1200A main circuit breaker, before he realized what the utility service will be. At 225KVA, the max...
Hi Bill, just want to say thanks for explaining. I think your suggestion for adding a isolation transformer should do the trick, where the isolation can isolate ground circuit. I need to think about this more. Thank you so much for the idea!! And thanks again for your explanation on this...
For single generator scheme, I would connect the generator neutral to the main neutral bus at the service entrance. There you have a single bond to the ground for both the main distribution and the generator system and not separately derived.
When you have parallel generator (emergency standby, permament installation) in operations, through a set of parallel switchgear, is there any special consideration that requires the ATS to also switch the neutral? In the case of a single emergency generator, I always prefer to solidly bond the...
In the past when I did the short circuit study on the one line diagram and try to determine the AIC rating for devices, I was taught to make sure the AIC of the device can handle the fault current available at the point of my calculation. Lately, I wonder, as long as I know what the SCCR...
Thank you all for all these comments. One thing I am puzzlled when I post the question was, the purpose of Table 430-52, at least for general polyp[hase AC motors, was to compenstate for motor starting current, which could be as high as 6 times the FLA. Although it states the exception for...
I just want to consult others on the following. In general for motor protection(typical 3-phase motor) using circuit breakers, reading the NEC, I got:
Branch ckt ground fault & overcurrent protection = not to exceed 250% FLA per Table 430.52
Disconnect device = min 115% - 125% FLA
Branch ckr...
Recently I was running into increasing the size in the electrical room and trying to account for all NEC clearances around the equipment, when a thought hit me. The equipment I was dealing are low voltage, from 208V to 480V as the highest. The thought was what about arc flash. I was merely...
Hi PHovnanian, thanks you're probably right. As for grounda fault, you would want the current to return back to building system groundo, is that what you mean? Or are you saying conduits underground inside a building will be subjected to fault current going back to the building system ground?
We are installaing conduit system. Perhaps a picture will help. Here is my detail how the conduit/j-box will be installed below grade. They are in effect inside the floor slab with 6-inch embedment all around.
I guess my original intent of my question is what constitues outside exterior...
I read an article that mentioned a similar scenario that when conduits installed below grade (when they are in contact with the subgrade, e.g. soil) will be subjected to temeperature difference between below grade temperature and inside the building. But I wonder, and as my argument, that if...
Hi, has anyone heard of problems installaing premise distribution CAT 6 cables under (or within) floor slabs in open office environment? One of our customer has requested to install outside plant cables under the floor slab. His arguement anyting under the floor slab is considered exterior...
Actually, the problem happened at the bus ducts between the transformer and the switchgear. The bus ducts were fabrciated and certain locations you can see gaps between the metal. It is questionable it is rated for NEMA 3R. The bus inside the ducts had low points that is close to the bottom...
