Plugging/Unplugging 480v cords

[GSTeat]

I've seen related questions in past posts but no clear answers. I'm working with a plant that uses cord and plugs as the electrical lockout point for a few machines that are 480v. I know this is not the correct way and that 480v plugs should be de-energized prior to plugging or unplugging them to prevent arcs and/or shocks. But for more credibility in my recommendation, I'm looking for a code or regulation that supports this but can't seem to find it.

Is it just a best practice?

Second, what about lesser voltages? I'm thinking anything over 120v should be de-energized first. Is this correct?

 

[iwire]

What makes you think 480 volt receptacles need to be de-energized before use?

The NEC recognizes a cord and plug as a disconnecting means.

Second, what about lesser voltages? I'm thinking anything over 120v should be de-energized first. Is this correct?

I disagree with that.

I would not even call it best practice.

 

[GoldDigger]

One reason that horsepower ratings are listed on some NEMA plugs and receptacles is that they are rated to break the connection to a running motor of that power or lower. The ampere rating is what it can break (or make) for a resistive load.

Sent from my XT1080 using Tapatalk

 

[jim dungar]

One reason that horsepower ratings are listed on some NEMA plugs and receptacles is that they are rated to break the connection to a running motor of that power or lower. The ampere rating is what it can break (or make) for a resistive load.

A horsepower rating means the device can make the inrush current of a motor and break the locked rotor current. I believe the PF assumed for these conditions is 35%.

 

[petersonra]

I am inclined to shut the machine down first but I don't see it has to be de-energized.

 

[zbang]

Playing the devil's advocate for a moment- single pole connectors should definitely not be disconnected under load, and ought to be de-energized. OTOH, I'm sure that's not what the OP was talking about.

 

[jtinge]

One company (XXXXXXXXXX) offers a connector that removes power prior to disconnecting to limit exposure to live parts and thus eliminating the source of arc flash exposure. Don't know of any code requirement for such a device but it is certainly any interesting marketing strategy.

 

[iwire]

As much as like the products mentioned by the poster above we can't allow advertising. I had to remove the link.

 

[GSTeat]

I was always taught that you should disconnect power to a 220v, and up, cord prior to plugging the cord in, to avoid potential arcs and shock from plugging them in under load. Seems as though it's an NFPA70E thing but I lent my manual out and didn't get it back so I can't verify or deny it. That's what I'm asking. Sounds like the general consensus is that nobody thinks it's a requirement.

 

[iwire]

Sounds like the general consensus is that nobody thinks it's a requirement.

I would say the consensus is that it is not a requirement.

From the NEC.

430.110(F) Cord-and-Plug-Connected Motors. For a cord-and-plug-connected motor, a horsepower-rated attachment plug and receptacle having ratings no less than the motor ratings
shall be permitted to serve as the disconnecting means. A horsepower-rated attachment plug and receptacle shall not be required for a cord-and-plug-connected appliance in ac-cordance with 422.33, a room air conditioner in accordance with 440.63, or a portable motor rated 1?3 hp or less.

Notice there is no limitation for voltage.

 

[jim dungar]

...Seems as though it's an NFPA70E thing ...

NFPA70E seems to be more worried about moisture:

110.4 Use of Equipment Connecting
(B)(4)Attachment Plugs.
(a) Employees' hands shall not be wet when plugging and unplugging flexible cords and cord- and plug connected equipment if energized equipment is involved.
(b) Energized plug and receptacle connections shall be handled only with insulating protective equipment if the condition of the connection could provide a conductive path to the employee's hand (for example, if a cord connector is wet from being immersed in water).