High & Low voltages

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tommyh

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Can I run 277 volt ckts & 120 volt ckts in seperate conduits, but then they terminate in one 12x12 junction box for lighting and power purposes.

Is that legal?? per NEC 2008? I thought as long as the insulations of all wires is 600 volts or less it's ok??
 
tommyh said:
Can I run 277 volt ckts & 120 volt ckts in seperate conduits, but then they terminate in one 12x12 junction box for lighting and power purposes.

Is that legal?? per NEC 2008? I thought as long as the insulations of all wires is 600 volts or less it's ok??
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Welcome to the forum.

In general, you can even have them inside the same conduit, legally.
 
300.3(C) Conductors of Different Systems.
(1) 600 Volts, Nominal, or Less. Conductors of ac and dc circuits, rated 600 volts, nominal, or less, shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.

Given that most building wire insulation is rated 600V, you're golden.
 
277 120 same box

277 120 same box

i dont recall any thing exact from the code about 120 and 277 in the same box. but i would have the different circuts from two panels in two different boxes good rule of thumb personal preference. either way it should not hurt as long as the insulation rating on each conductor is higher than the highest voltage used.
 
277 volts & 120 volts in the same junction box (without barrier)

277 volts & 120 volts in the same junction box (without barrier)

Question: Can I run 277 volt ckts & 120 volt ckts in seperate conduits, but then they terminate in one 12x12 junction box for lighting and power purposes.

Is that legal?? per NEC 2008? I thought as long as the insulations of all wires is 600 volts or less it's ok??

RE: Now someone told me that if you have say, one conduit with (600 volt rated wires) @ 277 volts in a juntion box and another conduit with (600 volt rated wires) @ 120 volts in that "same" junction box:

He said that if between the two voltages it reads over 300 volts it's illegal???
So a 277 volt leg metered to 120 volt leg (in that same junction box)
= 397 volts (over 300 volts)

Where is that in the new 2008 NEC, or is he wrong?? Need help!
 
next time someone tells you something like that, ask them to help you find it in the codebook.

I don't believe there is any such code. There is an article 4o4.8 B which applies to 300volts between two adjacent switches in the same box, and I think maybe your friend has confused this with junction boxes.
 
He is wrong about them occupying the same box it is legal, if you have two devices fed from the two different systems in the same box they must be separated by a barrier.

Roger
 
as long as you comply with 300.3(C), 200.6(D) and 210.5(C), there is no probloem with them sharing the same j box.
as mentioned, your fried is probably thinking of 404.8(B)
 
tommyh said:
Can I run 277 volt ckts & 120 volt ckts in seperate conduits, but then they terminate in one 12x12 junction box for lighting and power purposes.

Is that legal?? per NEC 2008? I thought as long as the insulations of all wires is 600 volts or less it's ok??
Click to expand...

Not in NYC 300.3(C)(1) Exception No.2
Barriers shall be provided to isolate conductors energized from different sources when systems voltage exceeds 250 volts :cool:
 
nyhockey said:
Not in NYC 300.3(C)(1) Exception No.2
Barriers shall be provided to isolate conductors energized from different sources when systems voltage exceeds 250 volts :cool:
Click to expand...

What's their reasoning?

Roger
 
roger said:
He is wrong about them occupying the same box it is legal, if you have two devices fed from the two different systems in the same box they must be separated by a barrier.

Roger
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Roger,

Care to explain what you mean by two different systems? 208/120 vs. 277/480?
 
roger said:
Rob, that is what I was refering to.

voltagebarrier.jpg


Roger
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If I remember correctly there is a phase arrangement (with the graphic that you've shown) where you could end up with less than 300 volts between the devices and therefore a barrier wouldn't be required.
 
infinity said:
If I remember correctly there is a phase arrangement (with the graphic that you've shown) where you could end up with less than 300 volts between the devices and therefore a barrier wouldn't be required.
Click to expand...

You are correct, it would depend on which phases of the high and low sides are present. The wording in the illustration below would seem to be taking this into considertion.

1008709181_2.gif


Roger
 
roger said:
You are correct, it would depend on which phases of the high and low sides are present. The wording in the illustration below would seem to be taking this into considertion.

1008709181_2.gif


Roger
Click to expand...

But just from electrical theory, if the this is comming from a different source, you would not read 381 volts between the 2 systems right?? Like current returning to a different sourch. And no, Im not trying to start 'that' thread again :)
 
brother said:
But just from electrical theory, if the this is comming from a different source, you would not read 381 volts between the 2 systems right?? Like current returning to a different sourch. And no, Im not trying to start 'that' thread again :)
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You would need to test between the two devices to know for sure. I do believe that there is a phase arrangement that would give you less than 300 volts between a 277 volt switch and a 120 volt receptacle.
 
brother said:
But just from electrical theory, if the this is comming from a different source, you would not read 381 volts between the 2 systems right?? Like current returning to a different sourch. And no, Im not trying to start 'that' thread again :)
Click to expand...

The separate systems are all connected to ground so yes you can measure voltage between them.

Depending on which phases you where reading between you could measure 380.
 
Brother, yes you read these numbers. The next time you have a 480 - 208y/120 v transformer open read all the combinations.

Roger
 
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