Is there any rule against 480 volt pushbuttons or switches on equipment? TYpically we use 120 volt control but I have a situation wher it would be much less expensive to use 480 volt devices. I realize there is a safety aspect to consider but I'm looking for documentation for additional information.
480 Volt Control Switches
- Thread starter sherwin
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jimdavis
Senior Member
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- salt lake city, UT USA
480 volt control circuits are permitted by the NEC. However as you noted already there is a safety aspect to consider and weigh against the cost of installing a control transformer.
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- Licensed Electrician
Not the most common but not unusual to see 480V on HOA switches for some irrigation pumps I work on.
kwired
Electron manager
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Do you have remote switches or are your controls all mounted in same enclosure as motor controller?
I don't think the NEC has any objection with 480 volt control circuits, possibly some specific conditions but not in general, some other safety standards may have issues with it.
Timbert
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What type of equipment? Is it covered under NFPA 79 Industrial Machinery?
just the cowboy
Inactive, Email Never Verified
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what are you controling
what are you controling
Machine control is limited to 120 volts , but a combination starter is all in one enclosure and not restricted I believe. You said manual starters what do you need 480v control for.
what are you controling
Machine control is limited to 120 volts , but a combination starter is all in one enclosure and not restricted I believe. You said manual starters what do you need 480v control for.
- Location
- San Francisco Bay Area, CA, USA
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- Electrical Engineer
That used to be the case, because the Power Tool Association held sway over the NFPA committee for a long time, so they had exceptions put in that applied to combo starters on bench / pedestal power tools 2HP and under, and stand-alone automatically controlled machines like air compressors. But that changed a long time ago, I think in the mid 80s? Enforcement was never retroactive however, so there were/are still a lot of stand-alone machine tools out there with "Full Voltage Control" (as it is called) used in the combo starters, so I for one have had to work on them often.
As to "safety"? Are we going to start saying that 120VAC is "safer" than 480VAC if you touch it? Because EITHER one can kill you, or just hurt you. It is not based on the voltage level. You are not supposed to touch either one, nor let either one touch conductive surfaces.
Bingo, my thought too. A MMS has no control coil, so that restriction would not apply. That's why you see a lot of people going that route on small simple On-Off machine tools like grinders and sanders.
As a general statement yes we are going to say that. And 24VDC is even safer. As a specific statement to a specific application then no.
In general practice deciding to say, use 120V pushbuttons instead of 480V pushbuttons, means a control relay was put in place. The contacts carry the 480V not only at full voltage but at full amperage. The 120V coil side is typically fused at a fraction of the amperage. The power at a broken pushbutton, say a stray strand from the wire attached, is a tiny fraction of the power available at the contacts.
The misunderstanding of the physical argument is that neither Voltage nor Current are stuff let alone independant. Voltage and Current are only measurements of the stuff that kills you. They're properties of energy not a thing unto themselves. Akin to arguing over whether it's the Mass or Velocity of a bullet that kills you. Frankly the most important property of electricity and bullets alike is whether it hit you. But if it does - any reduction of available voltage or available current probably makes it more survivable.
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