460VAC as control for motors?

Status
Not open for further replies.
B

bp_redbear

Member
I work in an industrial plant where we use many start/stop stations for electrical motors. I have seen some cases where someone wired the station with the control tapped off L1 and L2 of the motor starter (where the coil of the starter is a 460V coil).

1.) I have been told that it is "code" to limit control voltage to 120VAC max. I have been unsuccessful in finding this written in the 2002 NEC. I have also been told that the practice is acceptable, but that the control circuit must be fused.

If there is a fault in one of the buttons, but no short to ground, there would be approx. 260V potential between a metal part of the button and ground (or the panel, if it is metallic, and grounded).
2.) We have a washdown/refrigerated environment and experience water entering our enclosures and condensation problems, also. I have seen some cases where a pushbutton having a metal locknut will have a 120V potential between the locknut and ground (non-metallic enclosure and 120VAC as control). A-B 800T/800H pushbuttons, specifically.

What is code?
What is safe?
My co-workers are getting shocked by the 120V faults where a NM panel is used. If these panels were metallic, I am sure our breakers would be tripping constantly.
3.) Are mineral deposits penetrating these pushbuttons, and making them conductive where they should be insulated? Perhaps rubber boots over the PB's would be a solution.

Before we have a serious shock, with someone being seriously hurt (120 bad enough, let alone 240 or 460). :(
Thanks in advance for any help.

bp
 
Re: 460VAC as control for motors?

I can't say about limiting control voltage to 120vac, altho I would certainly reccomend, I'm in no shape to look it up this late at night.

For the rest of it, really you need to use enclosures and devices that are suited for your application. If that means using nothing but marine type gear with no exposed metal at all, then that's what it's going to take.

One of my regular customers is a plating facility, and we are gradually replacing their enclosures with NEMA4X because nothing else will withstand the generally corrosive atmosphere. It's costing a ton of money, but it's what's safe for their application.

If you're working in a washdown environment, it sounds like you may need to use NEMA6 rated gear, make sure everything has the code required clearance from the walls to allow for drainage in such environments.

[ October 13, 2004, 03:22 AM: Message edited by: noxx ]
 
Re: 460VAC as control for motors?

I have seen some cases where a pushbutton having a metal locknut will have a 120V potential between the locknut and ground (non-metallic enclosure and 120VAC as control). A-B 800T/800H pushbuttons, specifically.
Click to expand...
You can't use 800T devices in nonmetallic boxes without providing a bonding jumper to the device. You can bond 800T selector switches by connecting a bonding jumper to one of the screws that holds the contact block in place, but I know of no way to bond any other type of 800T device in a nonmetallic box. This problem does not occur when you use 800H devices as all of the exposed parts are nonmetallic.
As far as the control voltage question, the code does not prohibit the use of 480 volt control circuits,but in many cases 430.72(B) will require overcurrent protection for the control circuit conductors.
Don
 
Re: 460VAC as control for motors?

Line voltage coils are pretty common, espcially for larger starters. you can often avoid providing OCPD on the control conductors by making the wire bigger in many cases but its just as easy to put in a small set of fuses, and its a good practice to do so.

I don't see how 800H buttons could have any potential to ground as they are all plastic, at least on the exterior of the enclosure.

[ October 13, 2004, 09:20 AM: Message edited by: petersonra ]
 
Re: 460VAC as control for motors?

The control circuit voltage is not an NEC issue, however OSHA and NFPA79 may have a 120V limitation.

As far as protecting the control circuit, there are several things to consider:

a) size of the branch OCPD

b) size of control circuit conductors

c) does ungrounded control circuit conductor exit the starter cabinet/enclosure
 
Re: 460VAC as control for motors?

Originally posted by don_resqcapt19:
You can bond 800T selector switches by connecting a bonding jumper to one of the screws that holds the contact block in place, but I know of no way to bond any other type of 800T device in a nonmetallic box.
Click to expand...
According to AB:

"We sell bonding brackets: 800T-N300 for back-of-panel or 800T-N300F for front-of-panel."

I learn something new every day. I was a lot suspicious of the idea of using the contact mounting bracket as a bonding point but its probably adequate.
Click to expand...
 
Re: 460VAC as control for motors?

Pete,
According to AB:
"We sell bonding brackets: 800T-N300 for back-of-panel or 800T-N300F for front-of-panel."
Click to expand...
The following is from the AB online catalog.
Bonding Bracket
The bonding bracket establishes an electrical circuit between the mounting surface and metal operator bushing for grounding purposes; recommended for installations which require CSA approval. Necessary mounting hardware is included. Order 800T-N300 for back-of-panel bracket. Order 800T-N300F for front-of-panel bracket.
Click to expand...
This item only insures bonding when the device is installed in a metallic box, and does nothing when the device is installed in a nonmetallic box. There is no way to leagally install an AB 800T device, other than a selector switch, in a nonmetallic enclosure.
Don
 
Re: 460VAC as control for motors?

Originally posted by don_resqcapt19:
There is no way to legally install an AB 800T device, other than a selector switch, in a nonmetallic enclosure.
Don
Click to expand...
Sure there is, use a class 2 circuit. :D , I don't many opportunity's to dispute you, I gotta grab em when I can. :D

Bob
 
Re: 460VAC as control for motors?

Thanks for the input.

I will suggest to our director of plant maintenance that we consider NEMA6 hardware.

I was aware of the bonding kit for the AB 800T devices, and was going to suggest utilizing them, but, did not know that 800T's were not acceptable for NM enclosures. I will suggest 800H types. (My reference of 800T/800H devices was from memory -it was late last night- I am sure that we are using 800T's.)
Devices with no exposed metal sounds like a great solution (and NEMA6 hdwe)

Is NEMA 6 marine/underwater rated?
Are A-B 800H devices NEMA 6 rated?

Our cleaning crew uses high pressure hoses with caustic cleaning/sanitizing agents, so our stuff is basically "underwater".
Thanks again!
bp
 
Re: 460VAC as control for motors?

bp,
I have had good luck with the 800H devices installed in the 800H-xHZ4R nonmetallic enclosures. We use the sealed magnetic reed type of contacts in the wet areas. This combination is also suitable for Class 1 Division 2 locations.
Don
 
Re: 460VAC as control for motors?

Do not think you will find a very big selection of NEMA 6 equipment. But NEMA 4X is readily available.

I believe that Nema 6 is submersible & NEMA 6P is prolonged submersible. Nema standards books define all of that & describe the tests they use.

I agree that NEC does not limit the control to 120V. but it is likely that NFPA79 (as referenced in NEC Article 670) does. Part VI of Article 430 covers O/C protection, etc. of motor control circuits.
 
Re: 460VAC as control for motors?

UL/NEMA Type 4 equipment is all that is required for washdown environments. UL/NEMA Type 4X (non-metallic or stainless steel) equipment is required for caustic as well as washdown environments. Boots are always optional but do not change the environment rating of the devices.

UL/NEMA Type 6 devices are rated for submersion to a specific depth for a specific amount of time. AB 800T/H operators are not UL/NEMA Type 6.

While not common, it is possible to purchase some non-metallic pushbutton enclosures with internal grounding plates. This is from the Stahlin literature "CF-22 enclosures designed to receive 22mm diameter compact devices metal grounding strap furnished".
 
Re: 460VAC as control for motors?

Most of our enclosures are either stainless steel or non-metallic. Though our enclosures are not submersed in water, they are exposed to corrosive/caustic chemicals.
I believe that a NEMA 4X enclosure exposed to direct spray from a high pressure, hot water hose may exceed the pressure that may be exerted by simply being dunked unredwater or exposed to falling rain. (So it would seem that NEMA 6 may be best, although our food processing machines are sprayed while the enclosures may be hit with indirect spray.
I will look into the NEMA specs.
I will look up the code articles mentioned by my fellow posters, including OCPD's.
I will look up the NFPA specific codes.
Thank you all, again.
bp
 
Re: 460VAC as control for motors?

Don,
Are 800H-xHZ4R enclosures A-B co. products? I believe we use Hoffman brand NEMA 4X enclosures, but still get water inside them (maybe due to poor connection where the conduit enters the enclosure-slight amount of strain and cracks appear). These have hinged doors with gaskets, butbp have only 2 screws securing the doors closed.
bp
 
Re: 460VAC as control for motors?

bp,
Yes they are AB products. The 'x' is for the number of pushbutton openings that are required. I think that you can get up to 6. (I could be wrong about the exact part number of the enclosure, but it is close)
Vertical conduit runs always leak in wet locations, so you have to run the conduit to a point below the enclosure, provide a drain of some type and pipe into the bottom of the enclosure.
Don
 
Status
Not open for further replies.
Top