VFD right to motor no Disco?
- Thread starter zappy
- Start date
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
The VFD doesn't have a disconnect? The ones I have seen recently are fused VFD's with a disconnect handle.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
There's no code requirement to locate a disconnecting means downstream of a VFD.
There is a code requirement that every motor have a disconnecting means. That disconnecting means can be upstream of a VFD as long as it meets all of the requirements of a disconnecting means.
My suggestion is you look in the code and see if what you are doing is acceptable. He might well be right but you have not given us enough information to make that determination.
Typically you don't want a disconnect between the VFD and the motor since disconnecting the circuit while the motor is running could damage the VFD. If a disconnect is used between VFD and motor, it should have early break auxiliary contacts to signal to the VFD to shut off output power right before the circuit is isolated.
ptonsparky
Tom
- Occupation
- EC - retired
You are getting optional upgrades.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
look at 430.102(B), specifically the exceptions.
the informational note to exception (a) might be instructive.
the informational note to exception (a) might be instructive.
- Location
- Illinois
- Occupation
- retired electrician
If you must have a disconnect on at the location of a motor supplied by a VFD, you can get one with a set of early break control contacts. You use those contacts to tell the drive to go into "coast to stop" mode so that when the power conductors are opened, there is no output from the VFD.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
MOST disconnect switch aux. contacts are “early break”, meaning the aux. contact opens BEFORE the main contacts open.
I have never seen one that wasn’t, but if I make a claim that they all are, someone will show me one that isn’t…
I have never seen one that wasn’t, but if I make a claim that they all are, someone will show me one that isn’t…
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
That would be for pilot devices. I’m talking about the aux contacts for disconnects. Different animals.Challenge accepted
Could be mistaken but I seem to recall Allen-Bradley makes both an early break and late break auxiliary contact 800X ******
ptonsparky
Tom
- Occupation
- EC - retired
I specified early break late makes for my CH safety switches. I never timed them, but that is what they supposedly sold me. Special order.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Lol, they likely sold you the standard ones, but told you they were special so they could charge you more… ;-)
ptonsparky
Tom
- Occupation
- EC - retired
If it was AB, I'd agree.
ptonsparky
Tom
- Occupation
- EC - retired
It's called a control pole and has overlapping contacts. They mount on the left side of the disconnect. Not next to the handle on the right.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
https://www.eaton.com/content/dam/e...rols-systems/swiching-devices/TB00801002E.pdf.
Page 13 of 40, 3/4 of the way down, they say that they are all EM-EB…
Edit:
Ah, if it was added as a power pole, that would explain it.
Page 13 of 40, 3/4 of the way down, they say that they are all EM-EB…
Edit:
Ah, if it was added as a power pole, that would explain it.
ptonsparky
Tom
- Occupation
- EC - retired
Yes this is what he said.
I worked on & performed PM'S on hundreds of VFD'S. We tried to have drives installed close ( less then 50' ) from motors. If a safety switch is installed on the load side of a drive it shou!d have a micro switch that will open NC contacts before handle opens. I talked to several drive tech about the dangers from turning off a safety switch on load side while drive is operating. All told me that you might not blow anything up maybe 9 out of 10 times. We had four 75 HP cooling tower fans on drives. Drives were two floors below the first floor and non fused safety switches were outside next to towers. Contractor who did maintenance inside cooling towers would use the safety switch to turn a running drive on & off rather then walk a distance then down over 50 steps to use drive control panel. One day he blew up two drives. These outdoor non fused safety switches did not have a micro switch to shut down drive. Forget how much the IGBT'S cost for them but it was over a $1,000 for the IGBT'S for 125 HP drives awhile ago. So I'm all for safety but if the VFD is within say a 50' sight would never install a safety switch on drive output. I always ordered drives with a built in disconnect switch. When I had to change a bad motor I installed LOTO on drive disconnect and the circuit breaker that feed it. We had over 50 air handlers from 40 to 125 HP that drives were on the outside but had a non fused safety switch from air handler company mounted inside of walk in air handlers.