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I have seen 200A aluminum service entrance cable described as 4/0-4/0-4/0, and also as 4/0-4/0-2/0.


When can the neutral conductor be less than the hot conductors?


Thanks,
RogerDoger
 

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As long as the calculations allow a smaller neutral.
 

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I think it's a good question..... in theory, what install conditions (calculations) allow a smaller neutral.

I can see that the balance/difference between two legs would electrically allow such,,,,,but under NEC when can that occur under what conditions and I guess why in the sense why not in other conditions.
 

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A straight 240 load like A/C or a water heater does not need a neutral
I understand.

But under normal residential installations, when and under what conditions can a service neutral be smaller than the hot conductors, or inversely, when does it have to be the same size.

Just curious from the OP's question.....I think all my se cable wires has always been the same size.
 

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The neutral only carries the inbalance of the load between phases. So if there is a 40 amp load on phase A and a 30 amp load on phase B the neutral would carry 10 amps. If the electrician balances the loads across the phases the neutral carries little current.
 

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Good Straight Honest answer....Thanks CODE..:smile:

In residential, I really don't see any instance where we would care about undersizing a neutral......very nominal$ In commercial...different story probably.

(On the other hand in residential, seems very unlikely you would have such an imbalanced load that one size smaller would be an issue.....but a possibility, so why F with it.)
 

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The neutral only carries the inbalance of the load between phases. So if there is a 40 amp load on phase A and a 30 amp load on phase B the neutral would carry 10 amps. If the electrician balances the loads across the phases the neutral carries little current.
OT....Yes, we understand that. The OP's question was:

"I have seen 200A aluminum service entrance cable described as 4/0-4/0-4/0, and also as 4/0-4/0-2/0.
When can the neutral conductor be less than the hot conductors?"


If only in theory and curiosity, what regulates/calcs that...when why where under what conditions.

Sort of an aside to the electricians in residential: Do you ever try to balance a residential load......(apart from just hitting each leg with the approx same number of circuits. I know I don't....wouldn't know how to figure it out any better.
 

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In a residential situation it's easy to see why the neutral can be reduced. Let's take a 200 amp service. If we have a 50 percent imbalance the the most current we could have on the neutral is 100 amp. 200 amp on Phase A, 100 amp on phase B. In a typical residential situation there are not enough loads to create this. The new code actually allows more than 2 size reduction s. depending on load calculations. We just finished a 400 amp. panel installation for 16 water heaters. So since theoretically there are no neutral loads we could have dropped down several sizes for the neutral but we stayed at 4/0 Al. On some computer and data equipment full size neutrals are required because they are so sensitive to imbalances.
 

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There is a sub calculation in a demand load calculation for the neutral load.
 
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Yeah, I don't get it myself. If you have a 200A service, it's because you have an all-electric house with 40A range, 30A water heater, 30A dryer and 30A A/C. All of which are 240V loads with almost no neutral current.

Maybe 20-30A of that 200A provisioning is even for 120V loads even capable of splitting, so even if you were a madman and put every single 120V load in the house on Phase L1, I don't see how you could overload a 2/0 wire.
 

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The neutral load is the difference between the loads on the two hot legs. Suppose leg A has 75 amps of load. Leg B carries 150 amps. The neutral load will be 75 amps.
 

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Accidentally came across this while looking for something else. It's
from what's known as an AltStandata and is, as far as I know, a
code amendment effective officially only in Alberta.

"Rule 4-024 Size of neutral conductor Reduced Neutral Conductor Size for Single Family Dwellings For a single family dwelling with provision for a 120/240 V electric range, or a 120/240 V electric dryer, the neutral conductor of the consumer’s service, or feeder, may be reduced to a size having not less than 70% of the ampacity of the ungrounded conductors.
This concept may be equally applied to a feeder or service supplying more than one unit of row housing or similar installations.
As explained in Rule 4-004(4), the common conductor of a consumer’s service or feeder connected to 2-phase wires and the neutral of a 4-wire, 3-phase system carries approximately the same current as the other conductors and therefore shall not be reduced.
Neutral Overload from the Effect of Harmonics on a System When designing an installation that will incorporate a number of electronic devices, a registered engineering professional should review the design to ensure that conductors will not be subject to an overload condition due to harmonic effect. Note: The standard averaging type clamp-on ammeter cannot measure the overload imposed on a system from the effect of harmonics accurately. A "true RMS" type must be used. "
 

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Final note...I think.....

Did some commercial office work years ago where the engineer required
increased neutral size.....thinking it was double that of the hots...but too
long ago to be sure. This was a feeder for a data room. Not your typical
resi stuff......
 

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Data power has issues with harmonics that I don't fully understand. I know this from talking to the UPS maintenance contractor during PM services.
 
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