Balanced Phases?

[McCready00]

At which point does it have to be balanced? Since most buildings have systems to automatically balance the phases, do we still have to follow the 10%max unbalanced law?

And by using a generator for power, do I really need to balance them as much as I can?

I always try to balance my phases as much as i can, but i would like to know more about how people works with it. f

Last question; if i am not using any motors or generator in the events, what should my phases have to be well balanced? Let's say I do have 75 amps returning through my neutral (2/0 feeder), what this could be dangerous for?

[Footer]

Originally Posted by mrb

What are these systems buildings have to automatically balance phases? -thats a new one....

Agreed.... more elaboration on that... if these do exist... and I don't think they do.. why are they not built into every company switch or dimmer/distro?

[icewolf08]

As far as I know there are no systems that automatically balance loads on phases. When a building is built the electrical contractors have to design the systems so that during normal operation the phases stay as close to balanced as possible. This means that they need to calculate the average loads of all the electrical systems including HVAC, dimmers, wall outlets, room lighting, etc. and then distribute accordingly.

Generally (not always) permanent installed dimmers are wired such that each dimmer module alternates phases. As most current installed racks have two dimmers on each module, you have two dimmers alternating. So, dimmers 1&2 would be phase A, 3&4 B, 5&6 C, 7&8 A and so on. This allows for the "arbitrary" loading that occurs when you hang and circuit a show.

On the other hand, touring and portable racks are often just divided into thirds. In a 48 channel rack, dimmers 1-16 would be phase A, 17-32 B, and 33-48 C. This is when you have to pay attention to how you load up your rack. Generally in this situation, you would look at the loads that are on each circuit and then patch them into the rack to make as close to a balanced system as possible. You have to consider that when balancing a dimming system, not all the lights will be on at full at the same time. Thus, the farther out of balance you start at, the more potential there is to be way out of balance when you start running the show.

I can't speak to use of generators as I don't work with them all to often. Just know that when using a generator it can be even more important to have as close to a balanced load as you can.

[McCready00]

i had just read somewhere that electricity distributor did not care as much as (...as much as!...) before about balanced phases.. I may have not well said what I meant on this point, but it was actually far to be my question. Am i wrong or right, this is not what I need to know now..

[McCready00]

Originally Posted by icewolf08

As far as I know there are no systems that automatically balance loads on phases. When a building is built the electrical contractors have to design the systems so that during normal operation the phases stay as close to balanced as possible. This means that they need to calculate the average loads of all the electrical systems including HVAC, dimmers, wall outlets, room lighting, etc. and then distribute accordingly.

Generally (not always) permanent installed dimmers are wired such that each dimmer module alternates phases. As most current installed racks have two dimmers on each module, you have two dimmers alternating. So, dimmers 1&2 would be phase A, 3&4 B, 5&6 C, 7&8 A and so on. This allows for the "arbitrary" loading that occurs when you hang and circuit a show.

On the other hand, touring and portable racks are often just divided into thirds. In a 48 channel rack, dimmers 1-16 would be phase A, 17-32 B, and 33-48 C. This is when you have to pay attention to how you load up your rack. Generally in this situation, you would look at the loads that are on each circuit and then patch them into the rack to make as close to a balanced system as possible. You have to consider that when balancing a dimming system, not all the lights will be on at full at the same time. Thus, the farther out of balance you start at, the more potential there is to be way out of balance when you start running the show.

I can't speak to use of generators as I don't work with them all to often. Just know that when using a generator it can be even more important to have as close to a balanced load as you can.

thanks Icewolf for this.. Actually, i did know how phases were working.. but I was mostly trying to know what could happen if the phases were not well balanced... I know it can become a problem when using a generator somewhere, but if it isn't the case, why this HAS to be done. Where in the whole circuit, it becomes a problem. let's say again, in an extreme situation, i do have a phases lower than the two others, and then my neutral got 60 amps going through it.. why would it become a problem for me?

Byt the way, it never happened to me.. I always balance my phases as much as I can.. This is just a question up here.

[icewolf08]

I have to say, I am with McCready00 here. This forum is about asking questions and getting answers. As he has stated, this is a hypothetical situation and he wants to know why it is bad. There doesn't have to be a real situation behind every question, there doesn't even have to be a class assignment either. Also, so far as I can tell, the question does not violate the CB TOS. he is not asking for wiring advice, or how-tos, just why things are the way they are. This forum is here so that people can ask questions that they want to know the answers to. I don't see why everyone who has answered here has given him a hard time.

[mrb]

Originally Posted by icewolf08

I have to say, I am with McCready00 here. This forum is about asking questions and getting answers. As he has stated, this is a hypothetical situation and he wants to know why it is bad. There doesn't have to be a real situation behind every question, there doesn't even have to be a class assignment either. This forum is here so that people can ask questions that they want to know the answers to. I don't see why everyone who has answered here has given him a hard time.

I agree with you 100%. The way the question was written is what triggered the responses. If the question had been along the lines of "i have some theoretical questions about phase balancing, can you guys please help me understand this?" he would have received the help he was looking for.

The way the question was posed, there appeared to be an actual situation the OP was seeking assistance with. This combined with mention of "most buildings have systems to automatically balance the phase (this pretty much does not exist), and questioning 75 amps of neutral current on a 2/0 feeder led to the responses received.

In an attempt to help the OP, here are some issues with severe unbalance:
-voltage drop as one phase becomes fully loaded
-harmonics increase with unbalance
-3ph transformers like to see a balanced load
-as i mentioned before, an unbalanced load of x% (i forget what it is, there may be some documentation from gen mfgr which has more info) of a generator's total capacity can be a problem especially on smaller generators.

I am talking about extreme situations here, ex a 400a 3ph supply with 380 amps on one leg and 20 on the other two. For the most part, if you make an effort to keep things evenly balanced across phases you should be in good shape.

[MNicolai]

Originally Posted by McCready00

i don't know what kind of extreme situation you are usually working in, but having 380amps on one leg and 20 on the two other... with a 400a 3ph supply.. this is not only extreme, but crazy...

For transformers, the efficiency at which they step-down the voltage and provide current to devices drops significantly when phases are out of balance. A single-phase example would be in a residential application. There are typically three wires coming in the main panel from the service; Phase A, Phase B, and a Neutral.

Phase A and B, relative to Neutral, are both 120v. Relative to each other, they are 240v. (That is strictly in this example and is not necessarily the case in other countries or other wire arrangements out of transformers)

If Phase A and Phase B are loaded to 60A, the Neutral wire out of that panel sees zero current. In this sense, they are balanced. However, if Phase A is loaded at 20A and Phase B is loaded at 50A, the Neutral wire will pick up the imbalance between the two. Now, the Neutral is a current-carrying conductor with 30A of current running through it.

(FYI, I am not speaking in terms of generators because my expertise is not with them.)

In entertainment industry applications, the neutral wire can often pass a lot more current through it than it should. Let's face it, when people are patching their light plot, they may be somewhat concerned about how many they have on each phase, but when it comes to show time, they simply aren't concerned about how many lights are on in a given cue on Phase A, or Phase B, or Phase C. I've worked in one space where they were limited in their power needs, and I did have to worry about imbalances, but typically it is not the factor that decides which lights are turned on in a given cue, or not turned on.

For this matter, it is widely-accepted that in theatre, Neutral wires see a lot more current than they do in motor applications, as motor loads tend to be quite balanced, whereas lighting applications minute-to-minute can create large imbalances in a system. To solve this, Neutral wires on phase-controlled dimming systems are considered current-carrying conductors. That means they are appropriately up-sized to accommodate such large imbalances. Also, it is common for transformers to be installed that are able to handle such imbalances better. Often this is a K-rated transformer. They are designed such that non-linear loads like that in theatre that create excess current running through the Neutral do not bring a transformer to an early demise.

(see http://www.centralyacht.com/library/...ransformer.pdf)

Also, the up-sized conductors for the Neutral allow more current to go through them without heating up to a destructive temperature. This is also why on 400A/3p company switches, there are 2 Neutrals. They are connected together on the same paths of conductivity on either end of the conductor run such that they act as one, really large conductor. That means a large imbalance can go through them without melting the insulation down and starting on fire, because now the heat and current are spread across the copper for both Neutral runs.

I strongly advise you check out that PDF on K-rated transformers; it should help shine some light on the problems with non-linear loads that leave phases out of balance with each other.

Here is another PDF that describes out-of-phase loads as they relate to the Entertainment Industry. Also check this out (http://www.saunderselectric.com/PDFs...-harmonics.pdf)

[mstaylor]

As things get out of balanced it creates the wire to heat and kicks breakers. I had a lighting contractor that used to have a small system that we would tie into a 225 amp breaker, his system PD had a 100 amp main. He would pop the 225 before his 100 because of the imbalance.

[derekleffew]

Can we please concentrate on the original question?

Originally Posted by McCready00

...do we still have to follow the 10% max unbalanced law? ...

I've never heard of any such law, and in fact try to adhere to a "rule of thumb" that the highest phase be no more than 25% above the lowest phase. The reason, with no basis in fact or support that I've found, is that a 3Ø breaker can trip at a substantially lower current than its rating, due to a huge imbalance. I have no idea where I learned that, and it may well be utter garbage.

Must every question of this type end with STEVETERRY? What did we do before he joined Control Booth? I wasn't here, but you get my drift...