coordination of breaker with the fused disconnects
coordination of breaker with the fused disconnects
(OP)
As per Canadian electrical code(section38), the elevator needs a fused disconnect switch inside the elevator machine room. I have an application where, the elevator is fed from a circuit breaker in a remote panel and the fused disconnect switch(type D) is in the elevator machine room. The code guides me to calculate the size of the fuse and the clips. But How can I calculate the size of the breaker in the panel? My understanding is it can't be the same size as the fuse as it will give rise to a loss of coordination between the fuse and the breaker.
Thanks in advance for any guidance
Thanks in advance for any guidance






RE: coordination of breaker with the fused disconnects
RE: coordination of breaker with the fused disconnects
Then whats the meaning of the fused disconnect switch if the breaker does the same job? Why can't we use a non fusible disconnect instead? Is there anybody out there who could address the issue based on Canadian electrical code. I have seen in US the same situation(Breaker with a fuse) to the same feeder. Breaker is not only magnetic but thermal-magnetic.
RE: coordination of breaker with the fused disconnects
RE: coordination of breaker with the fused disconnects
RE: coordination of breaker with the fused disconnects
As jgrisht indicated, when loss of either device in series results in loss of the same load, coordination becomes immaterial. Opeing of the breaker before the fuse may be a inconvenience but it is NOT a safety hazard nor a code violation!
Your Code may require a fused disconnet but that does not preclude use of a breaker upstream of that.
No Codes defy engineering principles. They could, sometimes, be misinterpreted or over interpreted.
Sometemes Codes may become overzealous in inisting the safety than coveniences.
For example, the elevator inspectors may not want to look beyond the local disconnect to make sure that elevator drive and its wiring is adeuately protected and there is positive service disconnet in the vicinity to ensure saftety of person working on the elevator system for repairs. He would not care as to how the disconnect is fed or in case of a fault upstream device opens.
Speaking of physics or engineering, you would not be able to achieve coordinatoin between two devices of equal rating ( or closely rated). And yes, cricuit breakers in fact does the same job as the fuses (lets not get into their finer characteristics). Meaning, a 200A breaker protects a 200A rated condcutor and so does a fuse. But you also have the motor so they should be sized per the applicable seciton of codes for a motor branch cicuit.
Side Note: NEC (I beleive CEC is based on the NEC) suggests that for motor branch circuit protection, the following is applicable:
Non-time delay fuses: 300% max. (of FLA of the motor)
Time delay fuses: 175% max.
Thermal CB : 250% max.
RE: coordination of breaker with the fused disconnects
RE: coordination of breaker with the fused disconnects
I see no reason for having two points of fault / ovecurrent protection on one supply, from a maintenance point of view it would make life more dificult if there was no co-ordination between the cb & the fuses (i.e if they are the same rating). Maybe the Canadian standard should be simplified & require a disconect switch, then you could fit copper links in place of the fuses whilst having fault / ovecurrent protection at source.
RE: coordination of breaker with the fused disconnects
Elevator...
Humans in elevator....
Local fusing for elevator...
If service personal, or rescue workers need to 'adjust' local fusing to make it move, then let them.
RE: coordination of breaker with the fused disconnects
Many HVAC packages such as chillers, etc have long required fused disconnects for protection since this was the basis for their UL approval. The fuses can provide current-limiting that can help in short circuit tests. When it comes down a choice between doing something logical or following the code, you just follow the code, unless it appears to obviously unsafe.
RE: coordination of breaker with the fused disconnects