30 amps imbalance
- Thread starter chorty55
- Start date
ptonsparky
Tom
- Occupation
- EC - retired
Is this a 400 amp service or a 60 amp feeder?
Do you own the transformer or the POCO?
IDK if efficient would enter into it at all. That would have more to do with the individual load characteristics and wouldn't change unless the applied voltage changed significantly. IMO.
Do you own the transformer or the POCO?
IDK if efficient would enter into it at all. That would have more to do with the individual load characteristics and wouldn't change unless the applied voltage changed significantly. IMO.
OldBroadcastTech
Senior Member
- Location
- Western IL
- Occupation
- Retired Broadcast Technician
Well, I'm not a practicing electrician, but I feel I've picked up enough knowledge in 60+ years to ask the following questions:
1) How does 'efficiency' enter into this ?
2-a) If the feeders are properly sized, why does 30 amps of neutral current matter ?
2-b) With properly sized feeders, why would there be a concern about 'low voltage' ?
Moderators: If you feel this post is out-of-line, feel free to delete it.
Thank you.
1) How does 'efficiency' enter into this ?
2-a) If the feeders are properly sized, why does 30 amps of neutral current matter ?
2-b) With properly sized feeders, why would there be a concern about 'low voltage' ?
Moderators: If you feel this post is out-of-line, feel free to delete it.
Thank you.
karn
Senior Member
- Location
- United States
- Occupation
- Electrician
To answer your question, and my best guess:
1). An imbalanced load causes the neutral to carry excess current. If the neutral is not sized to handle this, it can overheat, leading to potential failure, electrical fires, or damage to equipment.
2.) The unbalanced load can cause significant voltage drops or fluctuations on the overloaded phase, affecting the performance of connected devices, potentially causing equipment malfunctions or premature wear.
3.) When one leg of a single-phase system is carrying significantly more current than the other, it increases losses due to resistance, lowering the overall system efficiency.
4). If the imbalance is significant, it can strain the transformer supplying the system. This can lead to overheating or damage to the transformer, reducing its lifespan or causing failure.
5). The imbalance might also affect the power factor, increasing demand charges or leading to penalties in commercial settings.
With that being said: someone correct me if I'm wrong, but it sounds like you're worried about overloading the neutral, voltage fluctuations, etc.
Even on a 200 amp service, the imbalance is only about 15%. I wouldn't say it's going to be catastrophic, but yes, we typically try to distribute the loads more evenly.
1). An imbalanced load causes the neutral to carry excess current. If the neutral is not sized to handle this, it can overheat, leading to potential failure, electrical fires, or damage to equipment.
2.) The unbalanced load can cause significant voltage drops or fluctuations on the overloaded phase, affecting the performance of connected devices, potentially causing equipment malfunctions or premature wear.
3.) When one leg of a single-phase system is carrying significantly more current than the other, it increases losses due to resistance, lowering the overall system efficiency.
4). If the imbalance is significant, it can strain the transformer supplying the system. This can lead to overheating or damage to the transformer, reducing its lifespan or causing failure.
5). The imbalance might also affect the power factor, increasing demand charges or leading to penalties in commercial settings.
With that being said: someone correct me if I'm wrong, but it sounds like you're worried about overloading the neutral, voltage fluctuations, etc.
Even on a 200 amp service, the imbalance is only about 15%. I wouldn't say it's going to be catastrophic, but yes, we typically try to distribute the loads more evenly.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
With all that said, if the neutral is properly sized for the expected maximum neutral load, and the 30A is less than that design current, then it isn't a problem.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Neutrals are designed to carry current under normal conditions. Can you expand on what the breakers have to do with a sine wave?
The phase oscillates on single phase service at....you guessed it, 60hz, at least here in the usa. No 50 im aware of besides inhouse generstors. Causing 120v of difference. Combined on both sides of the center tap, results in 240v. Im sure you know that, or im being quizzed.
If there's 120amps of breakers pulling off one conductor, and not 60/60 between both conductors I was curious if there's an issue with possibly voltage drop downstream, or making the transformer unhappy.
Obviously in 3phase a leg pulled down increases voltage on the other 2, reason the POCO staggers their transformer taps down the road, and also hang a neutral under them, but that's beyond the scope of the question regarding a center tap from a single phase.
If there's 120amps of breakers pulling off one conductor, and not 60/60 between both conductors I was curious if there's an issue with possibly voltage drop downstream, or making the transformer unhappy.
Obviously in 3phase a leg pulled down increases voltage on the other 2, reason the POCO staggers their transformer taps down the road, and also hang a neutral under them, but that's beyond the scope of the question regarding a center tap from a single phase.
kwired
Electron manager
- Location
- NE Nebraska
The neutral is simply carrying unbalance of the other conductors. If the neutral conductor is large enough to carry the current imposed on it there is no inefficiency within the conductors.
Next thing is whether the source can handle said imbalance.
Next thing is whether the source can handle said imbalance.
In general, I think the poco wants minimal and avoid as much as possible dumping imbalance onto the neutral, which is essentially bonded to the ground at the service entrance.
I guess a hypothetical question. Can an installer install a 200amp box, knock out every other slot, lay 10 20amp single breakers all on one conductor, it'll look weird, and pass inspection?
I guess a hypothetical question. Can an installer install a 200amp box, knock out every other slot, lay 10 20amp single breakers all on one conductor, it'll look weird, and pass inspection?
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
'120A' of breakers does not mean 120A of load.
Say you have 8 15A 120V circuits on a residential panel. Good practice would be to put 4 of those circuits on one leg, 4 on the other. But you have zero guarantee that the circuits would be loaded evenly. You might end up with 60A of load on the neutral if the 4 circuits on one leg are fully loaded, and the 4 on the other leg are not loaded at all.
That is why the neutral must be sized to carry the maximum unbalanced load.
You are quite correct that the _goal_ is zero neutral current. But if you have independent L-N loads, you cannot achieve that goal, so the system must be designed to tolerate imbalance.
Say you have 8 15A 120V circuits on a residential panel. Good practice would be to put 4 of those circuits on one leg, 4 on the other. But you have zero guarantee that the circuits would be loaded evenly. You might end up with 60A of load on the neutral if the 4 circuits on one leg are fully loaded, and the 4 on the other leg are not loaded at all.
That is why the neutral must be sized to carry the maximum unbalanced load.
You are quite correct that the _goal_ is zero neutral current. But if you have independent L-N loads, you cannot achieve that goal, so the system must be designed to tolerate imbalance.
kwired
Electron manager
- Location
- NE Nebraska
If the source and the conductors can handle it there is no significant inefficiency though.
Grounding has nothing to do with it, it is simply another leg.
In some areas several houses are pulling off one transformer, i always wondered how imbalanced they might be at any given time and affecting the center tap load.
Wonder why after 30amps you can't find singles any larger?
In 3 phase distribution systems with a neutral, if a center tapped transformer is heavily loaded on its neutral, I'd imagine that finds its way back on the 3phase neutral to poco?
Wonder why after 30amps you can't find singles any larger?
In 3 phase distribution systems with a neutral, if a center tapped transformer is heavily loaded on its neutral, I'd imagine that finds its way back on the 3phase neutral to poco?
You need to shop at better suppliers.
Two legs tied together, neutral and ground, is still 2 legs, at the service panel?
I always wondered why its such a big deal to keep them isolated but bonded at the entrance panel. If its that serious, then drop 4 leads from the pole to the weather head. Just my opinion.
Link me a single phase 1 pole 100 amp breaker for a residential squareD
kwired
Electron manager
- Location
- NE Nebraska
Are you talking single pole breakers?
There are larger but not so commonly found.
Just is little demand for them. Not much that needs a branch circuit over 30 amps that is designed for use at 120 volts
Yes it is. Take the 240 winding tap it in the middle and cut the other end off, you have two legs of a 120v winding
kwired
Electron manager
- Location
- NE Nebraska
IIRC QO does go up to 50 amp in catalog.
I have seen unit breakers (lugs both ends) that are single pole 100 amp though.