Extended Coverage - Pressure?

[Bagge]

I have been using Tyco’s EC-11 sprinkler for some time now. And I just somehow know that when I’m using the sprinkler in OH for a length and width of (example) 4.3 m x 4.7 m - I have to find the start pressure at the sprinklers in the tables for 4.9 m x 4.9 m. But why is that? I can’t find the exact written rule for this in NFPA13. And the funny thing is that when I would like to use the Tyco EC-17 or EC-25 in Extra Hazard - I don’t have to use that rule (!) Then it’s okay to use 4.3 m x 4.7 m. But why? I’m confused – somebody that could please help me with a good, or just an explanation? And could tell where the exact rule is listed – NFPA13? I don’t think the data sheet is very helpful.

If someone could help me out here I would be very grateful…

 

[cdafd]

accepted practice???

not a meter guy, but

if the question is do you have to bump to the higher coverage/ pressure, if you are in between???

would say if you are say using a head that covers 10x10 feet or 14x14 feet at certain required pressures, and you are covering say 12x12 feet, it looks like it would make sense to bump to the higher coverage 14x14, and higher pressure to assure that you will hit the 12x12 coverage.

if that makes any sense

I know they do the same thing with smoke detector coverage

 

[cdafd]

maybe this says better what I tried to say, and is from nfpa 13 2002 edition



A.8.8.2.1 The protection area for extended coverage upright and pendent sprinklers is defined in the listing of the sprinkler as a maximum square area. Listing information is presented in even 2 ft (0.6 m) increments up to 20 ft (6.1 m). When a sprinkler is selected for an application, its area of coverage must be equal to or greater than both the length and width of the hazard area. For example, if the hazard to be protected is a room 13½ ft (4.1 m) wide and 17½ ft (5.3 m) long as indicated in Figure A.8.8.2.1, a sprinkler that is listed to protect an area of 18 ft × 18 ft (5.5 m × 5.5 m) must be selected. The flow used in the calculations is then selected as the flow required by the listing for the selected coverage.



8.8.2.1* Determination of the Protection Area of Coverage.
8.8.2.1.1 The protection area of coverage (As) for extended coverage sprinklers shall be not less than that prescribed by the listing