Hot Work on a Live Six-Sigma Site: Designers and Technicians Must Work Together
Every critical power site is in a constant state of flux, driven by changes in technology, business protocols and more often than not, finances. It's clear that when the need for improvements and upgrades to the system do pop up, what's paramount is to execute remedies with extreme care and caution. More often than not, a client will wish to make these modifications without any disturbance or o...
Every critical power site is in a constant state of flux, driven by changes in technology, business protocols and more often than not, finances.
It's clear that when the need for improvements and upgrades to the system do pop up, what's paramount is to execute remedies with extreme care and caution. More often than not, a client will wish to make these modifications without any disturbance or outage whatsoever to the critical operations.
Ideally, the planning and design of each new critical power system would include maximum-rated spares —or space for such—in draw-out or equivalent main panels, switchboards and switchgear. Also taken into account would be schemes for tapping these busses temporarily for back-feeds via other routes during construction and cutover operations. The equipment also would be large enough within the enclosure guttering and wire-lay space so that temporary or new feeders could be placed without difficulty or jeopardy.
But, alas, this is the real world. One good design practice for the use of "future" switches and breakers is to pre-install conductors having an ampacity that matches the maximum rating of the device, bringing these out to a junction box. This allows the circuit to be easily extended in the future without having to access the hot panel or switchgear. Splices are normally not wanted, but again, designers should weigh the consequences and future worth of design decisions; in this case bussed junction boxes can be used for larger conductor sizes if compression splices are shunned.
It's also desirable to have in place either: manual load-rated throwover switches on the mains of large distribution panels, so they can temporarily or permanently be re-fed from another source; or future services to increase reliability or meet load growth.
However, in my 35 years of experience, I have learned a way to accomplish transparent cutovers in nearly every existing situation. The analysis of more complex systems through a planned multi-phased changeup is rather like a chess game: One must clearly see the moves all the way to the end of the game. It is only with such a proven work plan (known as method of procedure or MOP in the telecom world) that one can convince users and management to relax.
Most system modifications of this type require executing the work in coordinated stages. For instance, load may need to be shifted onto a temporary transfer scheme using a "roll up" diesel generator for backup, or even to operate on a genset for tens of minutes while otherwise hot connections are worked.
So the key to success is planning and designing so that each stage meets an acceptable risk level based on actual, concurrent business functions. And each stage must have been reviewed and have the buy-in of users.
But what about situations that do require electricians to perform hot work inside equipment? Is this acceptable?
Believe it or not, I've known some users who seem to feel their operations are more valuable than human life. Any electrician, whether a contractor or direct employee, must be highly trained and routinely practice this type of work in real situations. Owners must pick their contractors on this basis—above all other criteria. Hot work requires meeting OSHA directives and requires the use of specially insulated hand tools, insulating blankets and barriers. I've witnessed aggressive contractors who have performed such work without these measures. It is the kind of attitude that leads to disaster.
Some contractors, however, will view this work as rather routine and will convince an owner/user of their ability to "pull it off." The engineer should point out the challenges—and the consequences, should something go wrong. Engineers should definitely not acquiesce to violations of safety law.
Overall coordination of work from conception to completion should be managed by a small team that includes design engineers, electricians, users and owner. This team must be led by a commissioning manager or facilitator, who may be the design engineer or a third party commissioning agent .
In fact, commissioning must be embedded in these processes, as it may be impossible to do any testing after the work is completed and the live load is humming. The process must include a highly detailed checklist and must be run much like a real-time military operation-with dress rehearsals in advance to detect bugs in the planning.
The need for performing this type of mission-critical work is one that will become more and more prevalent as technology becomes increasingly embedded in every aspect of our lives. Regardless of the complexity, however, the need for good old human common sense in the planning of such critical operations is an absolute.