commercial sizing compared to sizing residential wire

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tdjs

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where in the nec does it say how to size commercial wire size compared to residential wire size?
 
Not sure what you mean? The only thing that comes to mind is 310.15(B)(6) {2008} which allows for smaller conductors when installing a dwelling service. There might be some other examples but for the most part amps are amps regardless of the structure type.
 
I?m not sure what you are asking but look at table 310.15(B) (6)

A common mistake I see is guys using 200 amp service entrance cable for commercial buildings.
 
Other than the exceptions others mentioned, tables 310.16 - 310.21 covers conductors for pretty much all types of installations. Conductors are not sized differently just because they are residential or commercial.

Insulation type, ambient temperature, and termination temperature rating are the factors that may make a conductor one size at one install and a different size at another install.
 
As Kwired said, conductors are NOT sized according to residential or commercial.
 
david said:
220.61 Feeder or Service Neutral Load.
(B) Permitted Reductions.
(2)That portion of the unbalanced load in excess of 200 amps
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Very few electricians (actually none around here) calculate the load when upgrading a service to 200 amps. With residential you usually get the reduction because of the range and dryer loads but most commercial services do not involve those loads.
 
david said:
Very few electricians (actually none around here) calculate the load when upgrading a service to 200 amps. With residential you usually get the reduction because of the range and dryer loads but most commercial services do not involve those loads.
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And how often do you come up with a neutral load that needs to have same size conductor as ungrounded conductors on a multiwire feeder or service? You can subtract any straight 208 or 240 loads from the total load on ungrounded conductors as they have no effect on neutral current.
 
kwired said:
And how often do you come up with a neutral load that needs to have same size conductor as ungrounded conductors on a multiwire feeder or service? You can subtract any straight 208 or 240 loads from the total load on ungrounded conductors as they have no effect on neutral current.
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I don?t know like I said around here the calculations are never done on 200 amp upgrades So unless you do he calculations how can you reduce the neutral size.
 
iwire said:
Commercial services will often have a much higher percentage of line to line loads.
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My point is service entrance cable is used on 200 amp light commercial services all the time. Even 400 amp services with two 200 amp service panels ganged side by side. Guys have even told me I put all my equipment in the same panel and every thing else in the other panel it?s neater that way. All I am saying is I don?t know what the maximum un-balance is.

What I do know is SER is the wiring method because that?s just what a guy is used to using. When I ask what bases did you use to reduce the neutral size there is no answer given.
 
david said:
I?m not sure what you are asking but look at table 310.15(B) (6)

A common mistake I see is guys using 200 amp service entrance cable for commercial buildings.
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pete m. said:
Why couldn't someone use 4/0 aluminum SE with a 200 amp OCPD if the calculated load were 180 amps or less?

Pete
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david said:
220.61 Feeder or Service Neutral Load.
(B) Permitted Reductions.
(2)That portion of the unbalanced load in excess of 200 amps
Click to expand...
So do you know for certain they are using SE with reduced neutral... and not SE with full size neutral?
 
Smart $ said:
So do you know for certain they are using SE with reduced neutral... and not SE with full size neutral?
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I know they make SEU with a full neutral but since it is seldom used I have never seen it. The Neutral on a 4/0 seu is 2/0 and I would almost bet than many commercial jobs, barring those with high harmonics could have a reduced neutral. Also I have never seen SE cable on a large project but I suppose it may exist somewhere just not here.
 
david said:
I don?t know like I said around here the calculations are never done on 200 amp upgrades So unless you do he calculations how can you reduce the neutral size.
Click to expand...

A simple start is to ignore the straight line to line loads as they do not contribute to neutral load.
 
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