VFDs & PLC in same enclosure?

I also agree with Paully's recommendations. Cost and space savings from common enclosures are usually offset by the arc flash issues. You can expect insurance carriers to start getting nasty about this in the future.

I have seen split enclosures with a dividing wall and a dead front over the 480 VAC side. I'm not sure if this meets all arc flash access limiting requirements, and I'm not convinced it has advantages over two enclosures, but it might be worth looking into.
 
Arc flash should and MUST become a concern for everyone designing and working in control panels.
at present, we have a classification for everyone in regards to control panels they can access and the calories dissipated in an enclosure, mcc bucket, vfd panel, disconnect if an arc flash occurs.

No one wants an arc flash to occur, but it does happen.
Opening an mcc bucket and dust fell in the bucket causing an arc. electrician had on ppe and faceshield. damage to face shield and it was replaced.
Bolt / screw fell out of component as bucket was being opened causing an arc. all headgear had to be replaced.
Cheap voltmeter used to measure 480 volts blew up, this was mine before I knew any better in 1985. I now use a fluke 87 with cat 4 leads.

these had no serious injuries.
unfortunately, we have had a bad one within the last 18 months and I will say no more about it.

We are now required to wear rubber gloves and leather protector gloves even when working on 110 volts. Its a pain, but it's either obey the rules or get fired after the 1st offence. Killing all power to the control panel is the preferred way to do the work, but in a lot of situations, its not practical when you are trying to debug a wiring issue.

let's all be pro active and work safely.

james
 
Last edited:
The company I work for does

Just about every company I know does, unless they are a union shop. And then, if there are restrictions, its for union protection reasons, not safety.

Some controls guys come from electrical backgrounds, but many don't, and they are all expected to troubleshoot in live panels just the same.

As an industry we've historically been terrible about safety. The big arc flash push is helping a lot.
 
Never do it - would probably need a big A/C unit to cool the cabinet as it would overheat.
 
For the last 12 - 15 years we've been building everything doing the two enclosure thing. All controls are 24VDC in one cabinet, and all drive hardware is in a second cabinet. The controls cabinet uses a sealed externally mounted 24VDC/5 amp power supply that has its own lockout switch and external 120VAC fusing. So absolutely everything in this panel is low voltage = live work rules don't apply. The VFD panel uses all finger safe hardware including fuse and power distribution block covers.

If you make it easy to comply with Arc Flash requirements, then everybody gets on board a lot sooner.
 
For the last 12 - 15 years we've been building everything doing the two enclosure thing. All controls are 24VDC in one cabinet, and all drive hardware is in a second cabinet. The controls cabinet uses a sealed externally mounted 24VDC/5 amp power supply that has its own lockout switch and external 120VAC fusing. So absolutely everything in this panel is low voltage = live work rules don't apply. The VFD panel uses all finger safe hardware including fuse and power distribution block covers.

If you make it easy to comply with Arc Flash requirements, then everybody gets on board a lot sooner.

That certainly is a great way to comply w/all of the safety rules. However it drives the initial cost up a certain percentage. The trick is to get the bean counters to buy into it.
 
True - but what's the cost of safety? It really comes down to being the cost of doing business.

It's also how you'll determine if your company is wanting to actually practice electrical safety or just talk electrical safety.
 
What is this american obsession with Arc Flash? Do you use nails as MCBs?

You put a .37kw drive in an enclosure with a PLC and the country goes into panic mode.
 
What is this american obsession with Arc Flash? Do you use nails as MCBs?

You put a .37kw drive in an enclosure with a PLC and the country goes into panic mode.

Here in the US it's no longer a topic you where you can plead ignorance.
 
You can expect insurance carriers to start getting nasty about this in the future.
Is this the real issue ? The fear of litigation in turn makes insurance prices skyrocket. Litigation is a much bigger concern over by you than by us.

I have seen split enclosures with a dividing wall and a dead front over the 480 VAC side. I'm not sure if this meets all arc flash access limiting requirements, and I'm not convinced it has advantages over two enclosures, but it might be worth looking into.
That is how it is typically done over here. The difference is, there is no separate main switch.

No one wants an arc flash to occur, but it does happen.
Opening an mcc bucket and dust fell in the bucket causing an arc. electrician had on ppe and faceshield. damage to face shield and it was replaced.
Bolt / screw fell out of component as bucket was being opened causing an arc. all headgear had to be replaced.
Cheap voltmeter used to measure 480 volts blew up, this was mine before I knew any better in 1985. I now use a fluke 87 with cat 4 leads.
In these examples it would not make a difference if the low voltage was in a separate cabinet.

Here in the US it's no longer a topic you where you can plead ignorance.
I dont think it is a question of pleading ignorance or not.
You cannot plead ignorance over here either.

To me the separate enclosures thing sounds as an extra safety precaution.
In principle it ought not be necessary, but your authorities say you must do it, so be it. It is definitely safer.
 
What is this american obsession with Arc Flash? Do you use nails as MCBs?

You put a .37kw drive in an enclosure with a PLC and the country goes into panic mode.

Initially, the insurance carriers discovered that the bozos running uninsulated wire around houses, supported by nails, were causing fires. That led to UL. Then the carriers discovered people were getting electrocuted by shorts in appliances. That led to more UL and double insulated power tools etc. Then they found that people were apparently taking baths with toasters. That led to GFCI outlets in NFPA/NEC.

Now they have discovered arc flash is a hazard. The hazard isn' new, and knowing it exists isn't new. The fact that other, more severe hazards have been tamed is new. As a result, the insurance carriers turn their attention to arc flash to reduce their liability exposure further, increase job security, and do it at someone else's expense.

Arc flash is a real hazard and real people are hurt by it. I'm not saying the regulations aren't beneficial. I'm saying that as technology evolves and safety improves there is always another opportunity. I'm certainly not in a position to say when the point of diminishing returns is reached.

You fellers in Europe and Australia shouldn't get too smug. The arc flash mitigation is coming soon to an insurance carrier near you.
 
What is this american obsession with Arc Flash? Do you use nails as MCBs?

1) Its a real danger that it is a good idea to try to mitigate

2) In my experience Americans aren't big on actually taking the time to think about things and design them. We follow black and white rules of thumb, or we just do whatever dumb thing comes into our head.

3) Come on we have ONE THING we're doing right in regards to safety, let us have this :p
 

Similar Topics

I'm new to PLC. Have little knowledge of VFDs. I've 5 nos of Delta M series VFDs and all are connected to motors running the conveyor belts...
Replies
3
Views
2,838
I'm looking for a PLC solution to control multiple variable frequency drives at one time. I have a testing setup that uses Yaskawa V1000 VFDs to...
Replies
9
Views
4,982
This is a little OT, but I know there are some experts here on the forum with the relevant experience. I have a project that expects a very long...
Replies
6
Views
1,054
This is a little OT, but I know there are some experts here on the forum with the relevant experience. I have a project that expects a very long...
Replies
4
Views
1,099
I have a project where the customer specs will not allow the use of the VFD's STO safety function. They demand dual safety contactors in front of...
Replies
18
Views
1,822
Back
Top Bottom