PPE for PLC panel within MV switchgear

[rpg]

We have a MV switchgear supplier who wants to incorporate the emergency generator PLC controls within the lineup. They claim that they can put the PLC controls in a separate compartment isolated from any other voltage that's >120 and put individual arc flash stickers on each compartment; therefore eliminating the arc flash PPE requirements for the PLC controls compartments per NFPA 70e Table 130.7(C)(15)(A)(a) which states "Work on control circuits with exposed electrical conductors and circuit parts, 120 volts or below without any other exposed energized equipment over 120 volts including opening of hinged covers to gain access". Is this an accepted procedure and are the reduced PPE claims true?

 

[Jraef]

Well it's done all the time with Arc Resistant gear, but without details it's hard to know if the heat in question is truly certified as Arc Resistant.

 

[jim dungar]

Is this an accepted procedure and are the reduced PPE claims true?

It is up to your company to perform the risk analysis and establish their Electrical Safe Work Practices.
You will not find any official 'one size fits all' answer.

 

[gray.one]

PPE for PLC panel within MV switchgear

That is pretty normal. Metal clad switchgear gets different arc flash ratings for the line side of the main and the bus because the gear is designed to segregate sections/compartments. Same goes for control compartments.

Arc resistant gear is a step further in that any arc is vented out a plenum. It is unnecessary in my opinion. Add a bus differential and do away with arc resistant swg...


Sent from my iPhone using Tapatalk

 

[jim dungar]

Arc resistant gear is a step further in that any arc is vented out a plenum.

Typically the arc resistance gear venting is not effective when doors are open on the gear. Though I am not sure if that caveat also applies to instrumentation compartments.

 

[Jraef]

Typically the arc resistance gear venting is not effective when doors are open on the gear. Though I am not sure if that caveat also applies to instrumentation compartments.

It does. In order to attain certification to ANSI C37.20 as Arc Resistant Class 2B, which is what most mfrs attain, workers wearing minimal PPE must be protected from harm while standing in front, sides, back and with the LV compartment door open. The LV compartment cannot therefor share the same air space with the MV compartment and what you see is that control conductors passing into the MV space are either sealed or pass through a restricted or baffled chase of some sort that would cool the gasses.

 

[rpg]

Thank you all for your responses. Just to let you know, this is not arc resistant gear. The original design had the PLC controls located in separate panels, but still in the same electrical room across from the switchgear. The customer wants to make sure the PPE requirements would not be higher with the PLC panels located in the switchgear vs. being located in their own panel.

 

[Jraef]

Thank you all for your responses. Just to let you know, this is not arc resistant gear. The original design had the PLC controls located in separate panels, but still in the same electrical room across from the switchgear. The customer wants to make sure the PPE requirements would not be higher with the PLC panels located in the switchgear vs. being located in their own panel.

If it's not AR, then the HRC would be based upon ALL DOORS being closed and latched. So opening any door exposes the worker to the higher HRC.

 

[jim dungar]

The customer wants to make sure the PPE requirements would not be higher with the PLC panels located in the switchgear vs. being located in their own panel.

The customer needs to make their own decision based on their ownrisk analysis. There is no single 'look up in a table' answer that applies to all installations.

While I would say the majority of companies are so risk adverse that they will rate the LV control compartment PPE requirements to be equal that of the main buss compartment, I do work with some companies that evaluate the AF incident energy for LV compartments to be independent of the rest of the equipment.

 

[rpg]

I have now found out that there is a 7200:120 volt PT in a draw out compartment within the controls compartment. The MV side is isolated, but could potentially be opened up by an untrained person. Wouldn't this disallow the rule of no voltage >120 being accessible and the LV compartment having to take on the higher rating?

Sorry, I know this is an internal matter. I am in the CM team trying to provide the safest system for the customer who I know does not keep trained electricians on his I&C staff and would need to coordinate with the electrical department to even look in the PLC compartment to see if a module had faulted. The contractor and vendor naturally argue to put the controls in the switchgear for cost reasons, but I'm still not convinced once the AF analysis is complete, they will be allowed to open the door for inspection with minimum or no PPE which is what the customer is asking for. Thanks and I appreciate all your comments.

 

[jim dungar]

I have now found out that there is a 7200:120 volt PT in a draw out compartment within the controls compartment. The MV side is isolated, but could potentially be opened up by an untrained person. Wouldn't this disallow the rule of no voltage >120 being accessible and the LV compartment having to take on the higher rating?

I believe my company's energized work permit process would have an issue with MV CPTs in the same area as the PLC.