Elevator motor(s)

[hhsting]

I am confused two questions:


1. How is it normally done? If you want to size overcurrent protection and branch circuit cables to elevator motor(s) do you get the MOCP (maximum overcurrent protection) and MCA ( minimum circuit amps) from manufacturer or do I need to use Article 620 and 430?

2. Article 620 shows how to size cables to elevator motor but not the overcurrent protection. Where do you look for sizing the overcurrent protection?

 

[hhsting]

I am confused two questions:


1. How is it normally done? If you want to size overcurrent protection and branch circuit cables to elevator motor(s) do you get the MOCP (maximum overcurrent protection) and MCA ( minimum circuit amps) from manufacturer or do I need to use Article 620 and 430?

2. Article 620 shows how to size cables to elevator motor but not the overcurrent protection. Where do you look for sizing the overcurrent protection?

Nobody here knows? Thanks for your input.

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[sii]

Nobody here knows? Thanks for your input.

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You gave it all of two hours friend. Lots of very intelligent people here but I assume elevators are a fairly niche industry so not everyone has your answer. Chill out for a bit, your answer will come.

 

[gadfly56]

You gave it all of two hours friend. Lots of very intelligent people here but I assume elevators are a fairly niche industry so not everyone has your answer. Chill out for a bit, your answer will come.

To add to that, a lot of them are, well, working. Someone has to pay the bills.

 

[infinity]

Lately all of the elevator motors that we've wired were fed from controllers with VFD's. The conductors and OCPD were sized according to the VFD nameplate. A nameplate current of 67 amps would get a 70 amp circuit.

 

[paulengr]

In general ampacity on motors uses larger size conductors than name plate to cover the extra load during for instance starting. 430 now has a whole table of factors for intermittent duty. 440 similarly increases ampacity, as do the rules for fire pumps and elevators as examples.

On VFDs you size cables between the VFD and motor at the same as if it was a starter. So size by elevator rules. It is oversized for the duty. VFDs might blunt the high starting currents but it just spreads the thermal load out over more time. The load (kilowatt-hours) is not decreased...same inertia in the car. Maybe a little less I2-R losses but that’s splitting hairs.

I would think that the line side should be as per the VFD. When it comes to derating a VFD certainly qualifies as a nonlinear load so you use the 125% factor. So a VFD rated at 100 A continuous load rating would use an ampacity of 125 A. I would think you’d size the same as an elevator motor but the Code really doesn’t cover VFD driven elevators.

With overloads regardless of the application the goal is to thermally model and protect the motor. You go by name plate amps always. This may mean motor replacement requires swapping heaters. If we swapped a 1950s vintage 25 HP motor for a new energy efficient model it will never reach the FLA of the old motor without overheating. So the overload always needs to be checked and sometimes changed. Can’t tell you how many times I’ve found them jacked to the maximum size and then people wonder why the motor burned up and why now it’s a gearbox problem too and why nobody caught it on the first troubleshooting call...




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[hhsting]

Post #1 assume their is no VFD being used. How would the two questions be answered? Thanks for input.

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[infinity]

I would think that the line side should be as per the VFD. When it comes to derating a VFD certainly qualifies as a nonlinear load so you use the 125% factor. So a VFD rated at 100 A continuous load rating would use an ampacity of 125 A. I would think you’d size the same as an elevator motor but the Code really doesn’t cover VFD driven elevators.

Do you have a code reference as to where the 125% factor requirement in the NEC for elevator VFD's?