A dead break allows an increased current rating (up to 600A) and can be used on basically all cable types. At 100% insulation level a 750kcmil cable is rated 610A in underground duct. When would you use a 750kcmil? In most non-utility cases you would design or install sets of 500kcmil or smaller if you needed more than one 500kcmil could handle. Even from a 1200A breaker, two sets of 500kcmil per phase would be sufficient for distribution (about 1000A), if the load was even that high. Most of the time you set the relays down to the actual load in order to limit the copper used.
A dead break when used in man-holes for splicing cables allows the flexibility of connecting more than two cables together as well as future expansion if required. Say another building was added that needed power, you could just connect that building to the existing array of dead break elbows. This also works great when temporary power is needed for construction or even if the circus is in town and they need medium voltage (it happens!). They can pick up power from the man-hole with the dead break elbows or from a piece of equipment with dead break elbows. I’ve heard that ships are now starting to use medium voltage shore power, I wonder what kind of connections they use.
A dead break still provides flexibility during maintenance it just requires a brief outage to allow the splice to be broken. This outage could be scheduled at an off-peak time or after ensuring that all back-up systems were already running and/or transferred to another source such as a generator. I wouldn’t trust a UPS alone in this case unless it was connected to a second source of power like a generator. The amount of time to disconnect the splice and coordinate the outage would cut it real close.
Deadbreak elbows are fairly large, so make sure to check the space restraints of the location you are installing them. If you do run into a space problem, their are various other seperable splices on the market that may be suitable, check with the manufacturers.
Although I prefer Richards Manufacturing for these products (just my preference) they are also manufactured by ABB and Thomas and Betts (Elastimold) and they can be ordered with all sorts of accessories.
Keywords: Hammerhead Splice, Dead Break Elbow, Load Break Elbow, Richards Manufacturing, Seperable Splices, Temporary medium voltage connections