vartz04
Well-known member
I can't find a clear answer on this if I am powering a 60 amp sub panel with 6 awg wire and you can use 10 awg as the ground can you downsize the neutral as well? If so what size is appropriate 10 as well or 8?
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downsize neutral in subpanel feed?
- Thread starter vartz04
- Start date
pattenp
Well-known member
If you look at a #6 manufactured cable such as NM or SE the neutral is the same size only the ground is smaller.
Highbeam
Well-known member
Can't downsize the neutral. The neutral could possibly carry as much current as any one of the hot lines if only one of the hot lines is maxed out and the other is unloaded. For every amp that both are passing simultaneously, the neutral carries an amp less than the fully lopsided loading that drives the neutral size.
The ground is downsized since it only needs to carry enough current to pop the breaker.
The ground is downsized since it only needs to carry enough current to pop the breaker.
Aceman
Well-known member
I'd run a fullsize neutral for a 60 amp panel. You aren't saving that much money by trying to downsize it when it's only a #6.
That's simply not true. You realize the neutral feeding your home as well as millions of others is downsized, right?
Google "sweetbriar wire", that's what feeds most homes.
Can't downsize the neutral. The neutral could possibly carry as much current as any one of the hot lines if only one of the hot lines is maxed out and the other is unloaded. For every amp that both are passing simultaneously, the neutral carries an amp less than the fully lopsided loading that drives the neutral size.
The ground is downsized since it only needs to carry enough current to pop the breaker.
That's simply not true. You realize the neutral feeding your home as well as millions of others is downsized, right?
Google "sweetbriar wire", that's what feeds most homes.
Highbeam
Well-known member
I'd run a fullsize neutral for a 60 amp panel. You aren't saving that much money by trying to downsize it when it's only a #6.
That's simply not true. You realize the neutral feeding your home as well as millions of others is downsized, right?
Nope, didn't realize that. Can you think of a reason that you would be able to downsize it given my reason for why you can't?
Looks like they assume the neutral carries only the imbalanced load which I agree with. What happens if the imbalance exceeds the capacity of the reduced size neutral but is allowed by the breaker on the hot line?
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Aceman
Well-known member
To answer your question, I'll ask you one. How often is one leg of a panel completely loaded, with nothing on the other?
Charles (in GA)
Well-known member
In a residence, the high draw items are 240v, thus no neutral current is involved in them. This is the stove, central heat/air, water heater, clothes dryer. The 120v items are generally low draw, and even if you loaded up one side of the bus, you won't overload a downsized neutral.
On a small 60 amp panel in a shop, the same thinking is not true, nearly everything in the shop is 120v for a panel that size, and it would not take but a couple of items, such as a 120v air compressor, a table saw and a large barrel fan running at the same time, to overload a undersized neutral.
Undersizing a neutral is something you do after you do load calculations to determine that you can do so without any bad consequences.
Charles
On a small 60 amp panel in a shop, the same thinking is not true, nearly everything in the shop is 120v for a panel that size, and it would not take but a couple of items, such as a 120v air compressor, a table saw and a large barrel fan running at the same time, to overload a undersized neutral.
Undersizing a neutral is something you do after you do load calculations to determine that you can do so without any bad consequences.
Charles
rlitman
Well-known member
Can't downsize the neutral. The neutral could possibly carry as much current as any one of the hot lines if only one of the hot lines is maxed out and the other is unloaded.
That's simply not true. You realize the neutral feeding your home as well as millions of others is downsized, right?
You realize that in 3 phase situations, the neutral is UPsized from 150% to as much as 200% of the capacity of the phase wires, as with harmonics involved it can actually carry more current than any of the individual phases.
And Aceman, that previous statement of mine is just as irrelevant to this conversation as yours.
Highbeam, you're on the mark here. Not for a line feeding a home (which relies on load calculations from the power company), but on inside wiring which is strictly to code, you don't downsize the neutral.
sberry
Banned
I went to a job where there was 49 down one leg and 1 down the other, it was on a 60 but this is pretty rare. The run was long and created a huge V drop, I move a cooler comp to the other side and 30 down each and it worked.
Aceman
Well-known member
And Aceman, that previous statement of mine is just as irrelevant to this conversation as yours.
Highbeam, you're on the mark here. Not for a line feeding a home (which relies on load calculations from the power company), but on inside wiring which is strictly to code, you don't downsize the neutral.
Point me to a code article that says I can't downsize a feeder neutral then....
Aceman
Well-known member
This isn't a feeder. This is just to a sub panel
That's the definition of a feeder.
Aceman
Well-known member
That's the service.
Wires ran to other panels after the main breaker are called feeders.
Wires ran to other panels after the main breaker are called feeders.
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You realize that in 3 phase situations, the neutral is UPsized from 150% to as much as 200% of the capacity of the phase wires, as with harmonics involved it can actually carry more current than any of the individual phases.
And Aceman, that previous statement of mine is just as irrelevant to this conversation as yours.
Highbeam, you're on the mark here. Not for a line feeding a home (which relies on load calculations from the power company), but on inside wiring which is strictly to code, you don't downsize the neutral.
That will depend on the load.
Highbeam
Well-known member
I'm not a code junky but insead try to apply logic and also not violate code. Even if code allows you to downsize the neutral it just doesn't make sense because I, or someone in the future, could overload that neutral doing normal and legal things. I just wouldn't feel right about setting that situation up.
ishiboo
Well-known member
Nope, didn't realize that. Can you think of a reason that you would be able to downsize it given my reason for why you can't?
Looks like they assume the neutral carries only the imbalanced load which I agree with. What happens if the imbalance exceeds the capacity of the reduced size neutral but is allowed by the breaker on the hot line?
Math. Probability. Or lack thereof.
Say your house has 200A service. You can run 2/0 hots and a 1/0 neutral with copper. 2/0 alone is not good for 200A (195) according to the ampacity rules, and 1/0 is only good for 170A. However, the chances of you using 200A on one AC leg and less than the 30A required to give you 170A on the neutral on the other leg are SLIM TO NONE.
Even if you did, there are safety margins built in - ie a 20A wire temporarily loaded to 35A does not simply explode and burn everything. And a 30A overage on a wire good for 170A is still a relatively small percentage. This is why things like welder circuits can be undersized as well. You won't be welding enough, and even if you did the overload would not likely be big enough to cause damage.
Services are completely different - they do not run through flammable materials in your house like wood and insulation which are designed to keep heat from going anywhere, they are in the cool nonflammable ground or up in the air where heat can safely dissipate all the time. So, as long as they conductors are big enough that they don't get hot enough to melt the insulation or the conductor themselves, it doesn't really matter how much heat they generate, and when they do it is whisked quickly away so you wouldn't even notice them being warm to begin with. Plus, again - your service is RARELY used anywhere near its stated capacity.
Highbeam
Well-known member
Thanks Ishiboo. I can agree with the probability being low. I wouldn't expect the codes to allow a situation that is only "usually" adequate and safe.
ishiboo
Well-known member
Thanks Ishiboo. I can agree with the probability being low. I wouldn't expect the codes to allow a situation that is only "usually" adequate and safe.
But as I said, even worst case scenario the overload is not sufficient to cause a danger.
Same thing with welder circuits!