VFD Location?
- Thread starter wsbeih
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
It always depends...
There are way too many variables on this kind of thing to be able to make a blanket declaration.
Just a few things that come into play.
Distance from the VFD to the motor. Shorter is usually better. 150 feet is not all that far.
Environmental concerns. The MCC room or electrical room is probably a better place for a VFD than out on the plant floor.
Protection from meddlers. Out of sight is out of mind. if it is someplace easy to get at, people will fiddle with it.
There really is no right answer to this issue.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Great list, I can only add a couple of things:
The general rule is that the closer the better, but almost all distance issues can be mitigated, so the other things stated above are probably more valuable.
Arc Flash concerns must now be added to the mix, which puts the issue back into the best location being an electrical room where ostensibly this is already addressed. Putting a 480V VFD next to a motor, especially with vents in the doors, means the Arc Fash Boundary may make it difficult for mechanical people to work on the equipment if it is even energized. I don't mean work on the electrical portion because that obviously involves LO/TO, but imagine a guy having to don the "bunny suit" just to grease bearings or check vibration while a motor is running.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I am having a hard time understanding this. How would there be an arc flash hazard just hooking up to a zerk and pumping grease into a motor?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If the VFD is right next to the motor and it is energized, the zert fitting is likely within the Arc Flash Boundary that technically exists around the VFD at a radius of 4ft. Closer than that and he could be in the Limited Approach Boundary, and if the VFD is right next to the motor connection box as I have seen people do, he might even be within the Restricted Approach Boundary. The rules do not require him to be doing anything electrical, they require him to stay away or be wearing the appropriate PPE.
It's a brave new world...
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
How would this be any different than a closed panel board? Are you saying no one can walk within the AFB of a closed up panel board?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
It depends on the established hazard based on the incident energy inside. Small 120/208 or 240V panelboards, not very often. But switchboards and most 480V panelboards now? Yes, that is becoming the case! It is, needless to say, a controversial issue.
captainwireman
Senior Member
- Location
- USA, mostly.
Where can I read up on this? I have been through NFPA 70E training and this was not addressed.
eHunter
Senior Member
- Location
- North Texas & Georgia
Hopefully this helps.
From:
NFPA 70E, Standard for Electrical Safety in the Workplace
2012 Edition
ARTICLE 100
Definitions
Arc Flash Hazard. A dangerous condition associated with
the possible release of energy caused by an electric arc.
Informational Note No. 1: An arc flash hazard may exist
when energized electrical conductors or circuit parts are
exposed or when they are within equipment in a guarded or
enclosed condition, provided a person is interacting with
the equipment in such a manner that could cause an electric
arc. Under normal operating conditions, enclosed energized
equipment that has been properly installed and maintained
is not likely to pose an arc flash hazard.
Informational Note No. 2: See Table 130.7(C)(15)(a) and
Table 130.7(C)(15)(b) for examples of activities that could
pose an arc flash hazard.
Boundary, Arc Flash. When an arc flash hazard exists, an
approach limit at a distance from a prospective arc source
within which a person could receive a second degree burn
if an electrical arc flash were to occur.
Informational Note: A second degree burn is possible by
an exposure of unprotected skin to an electric arc flash
above the incident energy level of 5 J/cm2 (1.2 cal/cm2).
Boundary, Limited Approach. An approach limit at a distance
from an exposed energized electrical conductor or
circuit part within which a shock hazard exists.
Boundary, Prohibited Approach. An approach limit at a
distance from an exposed energized electrical conductor or
circuit part within which work is considered the same as
making contact with the electrical conductor or circuit part.
Boundary, Restricted Approach. An approach limit at a
distance from an exposed energized electrical conductor or
circuit part within which there is an increased risk of shock,
due to electrical arc-over combined with inadvertent movement,
for personnel working in close proximity to the energized
electrical conductor or circuit part.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
It bothers me that someone conducted training and did not go into why it was necessary... leaving those who got the training in the dark, which can lead to misinterpreting things that were not very specifically outlined in the training. I like to empower people with at least the basic concepts when I do training.
What I've noticed with 70E training, or any training for that matter, is that usually the company is not willing to pay for all the time it would take to teach the employees the material. I've been through many classes where the instructor was rushing through everything because they only alloted him 5 days to teach a 2 week course.
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