2 or more switches of different voltages in the same metal box.

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kkdec1

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When 2 or more switches are installed in the same metal box and are fed by 2 different MC cables (one 277v. and one 120v.) do both of the MC cable ground wires need to be pigtailed to the box or can one of these grounds go directly to the switch ground screw without being pigtailed to the box?
 
All the grounds in a box must be joined together. 250.148

The one exception is if you have isolated grounds. 250.148 Exception

With a 120 and 277 switch in the same box you may want to put in a barrier. 404.8(B)
 
I don't think you need a barrier . There is not a potential of over 300 volts.I think of it as putting my tester in the box and trying to read over 300 volts.
 
tommy said:
I don't think you need a barrier . There is not a potential of over 300 volts.I think of it as putting my tester in the box and trying to read over 300 volts.
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Tommy in a building with both 208Y/120 and 480Y/277 systems you can have more than 300 volts between a 120 switch and a 277 switch.

It will depend on the phasing but barriers are cheap and easy to install so I would just toss one in.
 
Most of the jobs I work on my 480v feeds my 120v at a transformer. When I have (2) 277 volt switches together in a box on different phases then I have a potential of 480 volt. Which then I install barriers. But yea if you have the barriers for your type box and the grounds was set up not to intervere with the barrier. yea throw it in.
 
Tommy, here is an illustration to go with this thread
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The text to this section was revised to read:


(B) Voltage Between Adjacent Devices. Snap switches shall not be grouped or ganged in enclosures with other snap switches, receptacles, or similar devices, if the voltage between adjacent devices exceeds 300V, unless they are installed in enclosures equipped with permanently installed barriers between adjacent devices. Figure 404-1​
Intent: This rule in the 1999 NEC prohibited the ganging of switches in an outlet box if the voltage between them exceeded 300V. The text in the 2002 NEC prohibits the ganging of switches, receptacles and other devices in outlet boxes if the voltage between the devices exceed 300V.

Roger
 
I see what your saying but when the 480 or 277 is the same source feeding the transformer that creates your 120 volt I don't think you would be able to get 380v
 
tommy said:
I see what your saying but when the 480 or 277 is the same source feeding the transformer that creates your 120 volt I don't think you would be able to get 380v
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Yes, you can get the 380 volts between the two systems.
 
I only bring this up because I have checked. When I read From one winding 277v side to the same coil 120v low voltage.Then 277vcoil to seperate coil 120v side. I get 277v Maybe I was Mistaken When I get another chance I'll check again.
 
kkdec1 said:
When 2 or more switches are installed in the same metal box and are fed by 2 different MC cables (one 277v. and one 120v.) do both of the MC cable ground wires need to be pigtailed to the box or can one of these grounds go directly to the switch ground screw without being pigtailed to the box?
Click to expand...

I fully agree w/ the barrier but as far as the ground goes the yokes on the switches will bond to your metal box, so if you pigtail them to the box I don't see a problem.
 
kkdec1,

When useing metal boxes you do not have to ground to the switch,the

6/32 screws are allowed to ground the yoke. On the other hand, it will do

no harm.
 
benaround said:
kkdec1,

When useing metal boxes you do not have to ground to the switch,the

6/32 screws are allowed to ground the yoke. On the other hand, it will do

no harm.
Click to expand...

What if the box is surface mounted 1900 with a Mulberry cover?
 
I would say no since your mounting to the cover not to a box. The cover is being mounted to the box not the device with that type cover
 
Explain on how I can check as far as lead check Prmary (a) to Secondary (a) then Primary(a) to Secondary (b) and so on for each phases
 
celtic,

250.146(A) , only refers to receptacles, in your 1900 box with Mulbury

cover, if cover is not listed for grounding,then a jumper would be required.

IMO a switch would not. I did mention that adding one would not hurt.

Also, the discussion at the time was talking about 'flush' type boxes and

barriers.
 
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