Tvss

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anbm

Senior Member
This maybe old question but can anyone please give me some good reasons / NEC reference why TVSS won't be counted as one of main disconnect? Thanks!
 

charlie

Senior Member
Location
Indianapolis
From the 2008 Edition of the NEC Handbook, "Type 2 surge protective devices are permitted to be connected on the line side of the service disconnecting means. Such applications are permitted only in listed equipment, and the conductors connected to the surge protective device must have a disconnecting means and overcurrent protection. Field connection of these devices to the line terminals of the service equipment is not permitted."

I do not know the why unless it is to insure the lightning protection is still there when some of the service disconnecting means are open. :)
 

charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
. . . can anyone please give me some good reasons . . . why TVSS won't be counted as one of main disconnect?
I think it is simple: turning off the TVSS will not help to disconnect power to the building. The function of the main disconnecting means is to allow the building to be completely deenergized, in the event of an emergency (such as a large fire). We are allowed to set up the service with more than one disconnecting device (up to six), so long as they are close to each other. That way, if you need to turn off all power to the building, you can do it quickly (no more than six devices to turn off), and you can do it standing in one area (all six devices are grouped together). They don't count the TVSS breaker, in order to allow us all six to be used to supply loads within the building.
 
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