404.8(b)

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Nastro

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Can someone explain this in normal language. Is this from different systems or from the same panel? Is this for toggle switches and the like. Really confused.
 

infinity

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This could be the same system or different systems. Think about two 277 volt circuits on different phases, on the same system and adjacent to each other in a 2 gang box. The voltage between them would be 480 volts which exceeds the 300 volt limitation. So you would either need a divider between them or two separate boxes.

Welcome to the Forum. :)
 

roger

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As Rob says, it means if you have any voltage combination between two devices that will be more tha 300 volts you will need to install a barrier between the devices or use multiple boxes.
1008709181_2.gif

Roger
 

Nastro

Member
So, a 208v recp. and a 110v recp. could be in the same box under 1 cover without a barrier? This would be below 300v correct?
 

cadpoint

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Location
Durham, NC
So, a 208v recp. and a 110v recp. could be in the same box under 1 cover without a barrier? This would be below 300v correct?

I don't agree, it's over 300 Volts - The Code does not say measured voltage; that one would get if they substituted the question in #4 into the MH illustration in #3, nor does it say - measuring against two points off two different devices, of a 208 receptacle, and a 110V receptacle, would still not make it OK.

There's 208V in one device and 110V in the other.
 

raider1

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I don't agree, it's over 300 Volts - The Code does not say measured voltage; that one would get if they substituted the question in #4 into the MH illustration in #3, nor does it say - measuring against two points off two different devices, of a 208 receptacle, and a 110V receptacle, would still not make it OK.

There's 208V in one device and 110V in the other.

The the highest voltage between the devices in the OP would be 208.

404.8(B) states that the voltage between devices can't be greater that 300 volts.

Adding 120 and 208 would not give you the voltage between devices, but instead would be the sum of the voltages of the separate devices.

Chris
 

cadpoint

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Location
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Word play, I still don't agree, bad word play at that, IMO.

It doesn't say Measure the Voltage and granted it doesn't say Add them either, is my point. Well Between the two, what is that...

You won't give me the fact that the Code does not say to measure the voltage. A two Point operation on Three points of power, do they make that meter? :D

Or neither will you give me, to Add the voltage between the two devices, well between the two there isn't 300 bolts, if that's the case... back to #4 post

There's two devices and the code says "between", well 1 Device (insert some math sign((except infinity-THE math symbol)) and another 1 Device.
Whats' the between math symbol? Another later thread sure assume ADD, no I'm not assuming anything.

The the highest voltage between the devices in the OP would be 208.
I'll assume that's a two point measure with a meter, to stay with your train of thought.

404.8(B)
...so that the voltage between adjacent devices does not exceed 300 volts.

there is 208 in one Receptacle

and 110 in the other.

If you don't agree then why does MH show 308 volts Between ? He gets to measure the voltage to a summary?
Whoops it is an ADD function ~ But You won't give me that in my explanation, it doesn't say add, nor measure it says between.

One pole isn't getting metered in the 208 receptacle (staying with MH illustration against my rational) and is just dropped because not it's between, well we can't go there cause the MH-I the metered pin is on the far side, not between.

I'm not going to get into the 3 phase verses a single phase "adding" the sum for a sum number(MH Illustration), nor proof those numbers for it, here.
 
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btharmy

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Location
Indiana
I'll assume that's a two point measure with a meter, to stay with your train of thought.

404.8(B)
...so that the voltage between adjacent devices does not exceed 300 volts.

As far as i am concerned, "voltage between adjacent devices" means just that. Voltage measured between two points. I wasn't aware it could be made into such a confusing mathmatical formula. If you stick your wiggys between two devices in the same box and it measures more than 300v it gets a divider. Im kinda simple like that.
 

Dennis Alwon

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Jude, I think you are the lone wolf on this one-- I've been there. :grin:

The code states the voltage between conductors. There is only one way to know what the voltage is between conductor (well I guess more than one way) and that is to use the meter. If there are two 120v circuits on the same phase then you would have no voltage between conductors.
 

Nastro

Member
As far as i am concerned, "voltage between adjacent devices" means just that. Voltage measured between two points. I wasn't aware it could be made into such a confusing mathmatical formula. If you stick your wiggys between two devices in the same box and it measures more than 300v it gets a divider. Im kinda simple like that.

Looks like this code needs to be rewritten for a better understanding.
I am still not sure what to believe. Are there any inspectors that would like to give 2 cents on this?
 

iwire

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Looks like this code needs to be rewritten for a better understanding.
I am still not sure what to believe. Are there any inspectors that would like to give 2 cents on this?

I all but guarantee the CMP would say it is perfectly clear now and I agree with them.

In my opinion Jude is wrong on this one.
 

glene77is

Senior Member
Location
Memphis, TN
Originally Posted by Strife
So if I have 2-277V switches, I have to install a barrier, even if they're on the same phase? (277+277=554)

Well put. :)

Bob,

I don't follow you here.
Strife 'may' be fishing for something contrary to say,
but,
given Strife's illustration then I don't follow your response.

Since vector math is not used to describe Strife's illustration,
I assume that there is a measured voltage difference
greater than 300 Volts between the two 277 Volt conductors
(which Strife states to be on the same phase).

In Strife's illustration,
if there were a complete phase difference, then 480 Volts,
and if phase angles are figured in
then somewhere between 277 & 480.
None of these conditions are stated,
nor needed for the purpose of his simple illustration.

"I" simply expect to find zero volts in Strife's simple illustration.
So, no barrier required.
Just as with two 120 Volt conductors on the same phase.

Are you thinking that when two 277 Volt conductors are present in a switch box that they must be coming from Two Phases,
which I think is the normal practice.

Comments please. :)
BTW, I always read your good comments.
 
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roger

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Looks like this code needs to be rewritten for a better understanding.
I am still not sure what to believe. Are there any inspectors that would like to give 2 cents on this?

Just take a meter and read between all the conductors in the box, if any combination reads more than 300 volts you need a barrier.

The wording is quite clear.

Roger
 
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