How does a fused disconnect switch (for an elevator motor) get tied back to a load center?

[EPSQ]

Do the conductors get clamped onto the panel bus or is there a second OCPD at the panel? If so, how does this breaker get sized with respect to the fuse size?

In this case I am given a 35A fuse size for a 208v 3P traction elevator motor.

Thanks in advance for your time.

 

[waross]

It depends.
1. Where in the world are you and what is your governing code.
In North America:
Conductors must be adequately protected at there source of supply, unless:
Variation for short conductors.
Variation for shorter conductors.
Panel board main protection adequately protects the conductors.
Transformer primary protection adequately protects the secondary conductors.
etc.
Check the National Electrical Code or the Canadian Electrical Code or other code for the details.
In most cases there will be a breaker in the panel sized for ampacity of the conductors.
For motor feeders the over current device may be oversized to allow motor starting. See the code.
Check both the motor section and the elevator section of your code.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[EPSQ]

Apologies,

This is in Florida, USA. 2014 NEC. Per the NEC I am aware that you rate the OCPD and conductors based on the duty rating (intermittent), and the conductor on the OCPD.

In this case the elevator shaft houses the motor / disconnects as this is a non-machine room traction elevator.

The thing that I cannot find anywhere in code or online is how do engineers size the OCPD (and conductors) when all thats given is the fuse rating for the elevator? I am aware that sometimes fuse is used interchangeably with OCPD and thus breaker, but is this such a case?

Thank you,

 

[waross]

It depends.
Motor only or mixed load?
Use the motor nameplate current.
For motors you must have overload protection. This may be provided by the motor overload relay or device.
You must have over current (short circuit ) protection at the source.
Overload protection at the source may be greater than the conductor ampacity.
Check your code for the percentages to apply to;
Code fuses.
Time delay fuses.
Circuit breakers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

OCPD is sized to protect the conductors. Conductors are sized to carry the load. Local disconnect fuse size is also often dependent upon having to protect the motor windings, so may be different from those of the Feeder going to it.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[rhatcher]

The conductors from the disconnect will connect to an individual motor starter or VFD, not to a 'bus'. As mentioned by previous posts, the conductor sizing should be based on local code but in general they will be rated for no less than 125% of the full motor load current. The motor overload protection will be provided by the starter or VFD and the motor disconnect fuses will usually only be selected to provide short circuit protection. The elevator manufacturer should have specified the type of fuse to be used so you should check this and be certain to use that specific fuse.