DOUBLE FUSING
- Thread starter timo
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double fusing
double fusing
Most elevator branch circuits must originate at 1 or more panelboards located INSIDE the machine room. This is both to make the branch circuits easier to locate and to prevent accidental disconnection of lighting and sump pump circuits and so forth.
The problem gets to be when you only need 3 120 volt branch circuits off of a 120Y208 volt system and the main motor runs on a single 480 volts branch circuit. Theoretically, the circuit breakers or fuses outside of the machine room would need to be 200% of the circuit breakers fuses inside of the machine room so that the external overcurrent devices count as feeder devices and so that the devices inside of the machine room trip or blow first. Feeder breakers and fusible switches outside of the machine room need to be locked ON so as to avoid accidental disconnection.
A lot of architects and engineers get this one wrong when drawing plans for a building that has only 1 elevator. The requirement for 1 or more subpanels in an elevator machine room is poorly written as a bunch of branch circuit rules - not quite so smart C average people have a hard time realizing this because of poor writing of NEC 620.23 through 620.25.
Mike Cole
double fusing
Most elevator branch circuits must originate at 1 or more panelboards located INSIDE the machine room. This is both to make the branch circuits easier to locate and to prevent accidental disconnection of lighting and sump pump circuits and so forth.
The problem gets to be when you only need 3 120 volt branch circuits off of a 120Y208 volt system and the main motor runs on a single 480 volts branch circuit. Theoretically, the circuit breakers or fuses outside of the machine room would need to be 200% of the circuit breakers fuses inside of the machine room so that the external overcurrent devices count as feeder devices and so that the devices inside of the machine room trip or blow first. Feeder breakers and fusible switches outside of the machine room need to be locked ON so as to avoid accidental disconnection.
A lot of architects and engineers get this one wrong when drawing plans for a building that has only 1 elevator. The requirement for 1 or more subpanels in an elevator machine room is poorly written as a bunch of branch circuit rules - not quite so smart C average people have a hard time realizing this because of poor writing of NEC 620.23 through 620.25.
Mike Cole
- Location
- Massachusetts
mc5w said:
They do?
That is news to me.
I have no idea what you mean.
May be a local rule?
Mike there is no requirement to provide a 'subpanel' in an elevator machine room.
Did you start celebrating the holiday early?
- Location
- Windsor, CO NEC: 2023
- Occupation
- Hospital Master Electrician
Bkaz, did you look at page 2? Don suggested fuses, Jim T suggested that you not worry about it.bkaz said:
For what it's worth, I don't think 620.62 applies to your situation. You have two feeders and two elevators, not two elevators on one feeder. However, if you have noticed a genuine selective coordination issue, you should address it. Don suggestion seems like the easiest, depending on the particulars.
- Location
- Windsor, CO NEC: 2023
- Occupation
- Hospital Master Electrician
Steve-o!milwaukeesteve said:
Check out Article 430, Part IV. A circuit breaker or fuse is the most rudimentary form of Ground-Fault protection. When a ground fault occurs within the electrical system (i.e. hot touches EGC) a circuit breaker will trip and a fuse will blow.
Above that, we have Ground Fault Protection of Equipment required by 230.95 and 215.10 in certain circumstances, defined in 100.
Above that, we have Ground Fault Circuit Interrupters for protecting people, also defined in 100.
But just because GFPE and GFCI are higher tech, don't discredit the fuse.
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