We designed a project that is currently under construction. The project involved replacing a number of incorrect 1200A 480V feeders (wrong size and wrong ground) that were fed from a 4000A switchboard.

Originally the board was going to be shut down and then the old feeders were going to be removed and replaced with new (over the weekend). After the main breaker in the board was shut down, it was quickly realized that the board fed a critical data center which cannot be shut down (which is another story in itself...bad UPS and no generator backup)

So now they want to replace the feeders with the board live, and the E.C. is asking what the Flash Hazard Boundary is so that they can select the correct PPE.

An arc flash study has not been performed yet, and although we would recommend it, I want to provide options to the owner.

Would an acceptable option be to have the E.C. follow NFPA 70E table 130.7(C)(9) & (10) in lieu of having the study conducted now?

Any help would be appreciated!

Thanks,

Tom

If the project is still under construction, why can't it be shut down? I would suggest that you rent a generator, back feed the comp center, and de-energize the board. Removing and re-installing multiple parallel KCMIL circuits would be very taxing while wearing any category of PPE.

Another option would be to have them shut down the data center. The data guys never like it but sometimes it is better to have an controlled shut down than run on "dirty" power and take a chance. We used to shut down the data center (very large) to do substation maintenance. It makes the data guys very nervous because they are always afraid something might not come back up smoothly. It's risky for the data guys but not life threatening like the alternative.

Unfortunately the owner cannot any under circumstances shut down the data center. I agree with your comments, but they are not options for this client.

I would say do the study now, so that the workers could possibly use a lower category of PPE than what the tables stipulate. However, if you are going to use the tables pay close attention to the "Specific Notes".

I find it hard to believe that you will be able to perform this work live.

As cbauer pointed out, it is extremely unlikely that you will meet the "notes" that are integral to table 130.7(C)(9).

If you are worried about an arc flash occurring, you must be concerned that a fault will occur during the project. How does the data center like the idea they may experience another unintended shutdown?

Don't see you or the owner winning this one with OSHA if something happens. Shutting down a data center is inconvenient, but not infeasable.

Do Calcs or Do the Study?

The purpose of the tables is to use them. I would agree that you MUST see if you meet the tables by doing a hazard assessment (fault current, clearing device check). If this is done and you meet the tables you are in in good. Good practical question. I'd differ with Zog. Shutting down most data centers is infeasable. Especially if it shuts down Arc Flash Forum!!!

Ok, we'd live but a bank or Google or other large data center users would probably NOT think is is just inconvienent.

I have been doing work at data centers for 15 years, always during a shutdown (Besides battery testing). Most recently for one of the largest banks in the country.

The OP stated the problem in the original post: "(which is another story in itself...bad UPS and no generator backup)...................."

If its so damn important (and they always are ) Why don't they simply get a "Good UPS" and a back up generator.

Sorry if it sounds sarcastic, but like Zog, my firm also works at some of the largest data centers in the country and they manage to have regular shutdowns.

We have several UPS systems at our data centers. Occasionally there are failures. We place the UPS or the system in bypass and repair the UPS. Are your customers aware that any failure will shut them down possibly for a very long time.

tell the owner that if they cant shut it down then they should build a better data center so concurrent maintenance can be performed.