Arc Flash Regs and Live PLC Access

[sparky66]

Are many of you coming across problems where facilities are enforcing arc flash regs? For example, many PLC's have Run/Stop and Reset buttons. Reset buttons usually have to be held in with power on(or being applied).

 

[mk42]

Are many of you coming across problems where facilities are enforcing arc flash regs? For example, many PLC's have Run/Stop and Reset buttons. Reset buttons usually have to be held in with power on(or being applied).

What I've seen is splitting panels up into a 24V DC panel for the PLC/IO/etc, and a high voltage panel for drives, transformers, power supplies, etc. Some drive platforms can even be split up so the drive control unit can be in the low voltage panel, and the actual power sections can be elsewhere.



That way there's minimal concern when you're messing about with the PLC.

 

[Dravik]

We've also been splitting up panels where possible(cost wise) plus we have a LOT more graceport type things installed now.

For where we don't/can't, Well that's where the full suit protection comes out.

 

[Operaghost]

This is something we have been grappling with. For our people in the field, it is rare that anyone at the customer site is pushing for proper PPE and procedures. It is really us, pushing our own people to be safe.

Keep that enclosure door closed and we don't have to worry about it. Most of our panels are 120V with some occasional 240V or 480V. We don't see anything higher than that. We have determined that we don't require arc flash PPE unless we are working on 240V or greater.

But we will follow whatever rules the customer has in place beyond our own procedures. So, if they say wear it, we wear it. We might explain why according to NFPA it isn't necessary, but it is their facility, so their rules.

NFPA 70E has definitely influenced our panel design, particularly in the past couple years.

OG

 

[OysterMan]

Ive been to places where guys were changing out a vfd with the machine running and standing in a puddle and then other places where you cant open the panel without wearing the space suit. At the end of the day its 99% your responsibility to stay safe. Be extra cautious around panels that you havent worked on or built.

 

[JohnCalderwood]

Interesting to see this getting discussed.

We are a manufacturing company based in Scotland, but because we have a North American parent company, then we have to look at our potential Arc Flash situation.
We started looking at PPE and what was available, but pretty soon realised that we have no clue as to the Arc Flash energy levels that could be generated.
So we have instigated an Arc Flash Risk Assessment by a third party (can only find one in the UK), and expect to have preliminary findings later in the year.

We have MCC panels with VSDs, contactors and PLCs, as many of our panels have been installed for years.
We may end up with a lot of re-engineering to reduce levels, who knows...

 

[dogleg43]

Great topic to discuss here. Simply segregating the items into two cabinets for things >120VAC is harder than it initially appears.

1) The primary of a 24VDC power supply is typically 120VAC so it should be located in the hi voltage section.

2) All I/O needs to be low voltage, including relay contact output wiring.

3) Fuse blocks need to be in the proper section.

4) Pilot lights need to be on the door of the correct panel.

Just a partial list to consider. I’m sure there are more.