Home has 100A service, how to tell if it's 1-phase or 2-phase?

[Super_Geo]

Hey guys,

I checked the main breaker and it's 100A. Is there an easy way to tell if it's 1-phase or 2-phase? If I load-balance a 2-phase 100A service, I can effectively pull up to 200A (100A per phase), right?

[Nufy]

Yes but not recommended...

Typically I design for 80% loading or less.

[Super_Geo]

Yes but not recommended...

Typically I design for 80% loading or less.

Thanks, agreed on 80%.

How would I tell if the service coming into the main panel is 1-phase or 2-phase?

[BerserkerCatSplat]

It's likely going to be single split phase, I don't think I've seen a 2-phase feed around these parts, it's usually single split or 3-phase. In other words yes, if your main breaker is a dual-pole 240V 100A breaker, it is supplying 100A to two 120V buses. You could load each 120V bus up to 100A without tripping the main breaker. Any 240V breakers installed bridge the buses and can draw their rated amperage from both 120V buses simultaneously to create the 240V circuit.

[zieg]

Huh, interesting. I was just looking at my panel this weekend to make sure I could run 240 out to my (attached) garage. The thing I don't understand is how 240 is considered single phase still? I need a diagram, lol.

Edit: think I get it. Is this correct?

81110

So incoming is A, C and neutral? Cool.

[Crazyjoker77]

Huh, interesting. I was just looking at my panel this weekend to make sure I could run 240 out to my (attached) garage. The thing I don't understand is how 240 is considered single phase still? I need a diagram, lol.

Edit: think I get it. Is this correct?

81110

So incoming is A, C and neutral? Cool.

Thats not a split phase diagram thats a 3phase High Delta. Which is very uncommon and is really a niche type transformer when you have to have 240V but have a 3ph service. (3ph traditionally gives you 208v)

This is the correct diagram for a 1ph split phase.

https://kb.samsara.com/hc/en-us/article_attachments/205412557/split-phase.png

and this is the waveform(s) it produces.

https://packetpushers.net/wp-content/uploads/2015/10/SplitPhaseAC.jpg

Its considered single phase because its a single winding that is centertapped which produces 2 waveforms that are polar opposite of each other but in phase. (since they both cross 0 at the same time) As opposed to a 3ph waveform that is 3 separate winding that are physically 120 degrees apart. as in this diagram. (3ph can be configured in a wye or delta arangments)

https://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/3_phase_AC_waveform.svg/1024px-3_phase_AC_waveform.svg.png


2ph hasnt ever existed in canada and hasnt been used since the early days of electricity when edison was still alive. It was more of a science experiment into poly-phase power than anything and was quickly replaced with 3ph. It was only ever used in the old states of the US in big industrial factories. 2ph is actually 4 hot wires 90degrees apart.

If you have a electric stove or dryer you can be assured you have a single phase 3wire split phase service.

[speedog]

It's likely going to be single split phase, I don't think I've seen a 2-phase feed around these parts, it's usually single split or 3-phase. In other words yes, if your main breaker is a dual-pole 240V 100A breaker, it is supplying 100A to two 120V buses. You could load each 120V bus up to 100A without tripping the main breaker. Any 240V breakers installed bridge the buses and can draw their rated amperage from both 120V buses simultaneously to create the 240V circuit.

So if you do load up each 120V bus, what does your meter read - will it read the total amperage of both busses or something else? Maybe a diagram of how one's electricity meter is connected to one's incoming line will explain it better.

Edit, figured it out.

[Crazyjoker77]

So if you do load up each 120V bus, what does your meter read - will it read the total amperage of both busses or something else? Maybe a diagram of how one's electricity meter is connected to one's incoming line will explain it better.


Its pretty complicated when your dealing with 3wire edison circuits (what we are calling split phase services) but to answer your question if both legs are fully loaded you are going to read 100A on each leg at the meter. Where it gets more complicated is when you have a unbalanced load. Lets say you have one leg at 75A and one at 100A the neutral is going to be carrying the unbalanced load of 25A. Its a lot to get into in a forum post and relies on a lot pre requisite electrical theory but search up edison 3 wire circuits if you really want to learn more.

Also its a pretty big misconception that the white wire that is attached to the back of every plug and light in your house is a neutral. By definition its not since it is not carrying the Unbalanced load. The only true places you have a neutral is where edison 3wire circuits are used or 4wire wye type 3phase transformers. The only true neutral you have in your house would be between your panelboard and the transformer and any 120/240 plugs you have. The proper term for the other is Identified grounded conductor since it will always be carrying the same load as the hot wire (unless you have an abnormal condition such as a ground fault). Although its pretty common for even electricians to call it a neutral since it goes to the neutral bar in your panel.

The simplest way to explain how your residential power meter works is that it measures both legs individually but adds them up and divides by two and multiplies by 240.

EX1
100A +100A = 200A
200A/2 =100A
100Ax240v =24000W
24000w=24kW
and for every hour it maintains that load you would be billed for 24Kw/H
24Kw/H x 6.8Cents per Kw/H = $1.63 for every hour. the theoretical max you could pay per hour.

Ex2
100A + 50A = 150A
150A /2 = 75A
75A x 240 =18000
18000=18kw
18,000W = 18kw
18kw/h x 6.8c = 1.22$ per hour in this example.

[zieg]

Huh, very cool. Thanks for the explanation!

[littledan]

Very good explanation joker! So if the neutral wire on the main utility feed of a split phase system gets cut, you would have a floating neutral and the neutral potential would float through your 240V appliances and some normally 120V ccts would sag while others would overvoltage?

[Crazyjoker77]

Very good explanation joker! So if the neutral wire on the main utility feed of a split phase system gets cut, you would have a floating neutral and the neutral potential would float through your 240V appliances and some normally 120V ccts would sag while others would overvoltage?

Floating neutral is not the correct term and is a completely different thing. Broken neutral is what your referring to. A neutral balances out the currents to keep the voltages equal. If the neutral breaks, 240v appliances will not be effected but all your single 120v branch circuits will be. If the lines were pefectly balanced meaning there pulling the same current the voltages would be equal, but lets use my example above where one line is 100A and the other is 50A. The voltages to some devices will be 180v while others will be 60V. This is why generally you should try and balance the loads in the case the neutral breaks the voltage differential will be smaller.

A floating neutral is when the secondary windings of a transformer are not grounded (at the neutral point) and can have a different/no ground reference than the building system ground. This wont have any effect on the voltage but can cause havoc with electronics and has some safety concerns in certain situations.

[BerserkerCatSplat]

Great posts, CrazyJoker! Very informative stuff, I have a basic grasp of electrical theory but clearly you know a lot more than I do!

[RickDaTuner]

So can you super charge your Tesla at home or not?

[Crazyjoker77]

So can you super charge your Tesla at home or not?

Personally I am not sold on electric vehicles as long as there using battery technology but its simple enough to figure out. Again i have no interest in teslas atm so I'm just going with numbers that google is throwing at me.

Its saying that the super charging stations charge at up to 120kw on a 480V DC system(so 250A charge). Power is power and I've already calulated above that a fully loaded split phase 100A service only provides 24kw. you already have your answer...

120000W/240v = 500A service minimum on you regular residentail split phase system just to power the super charger. and thats not considering your going to have losses in the rectifier to change that ac to the DC it runs on.

although a 3ph 600V service would only require a measly 115A

120000W / (1.73x600v) = 115.6A (my car amps require bigger gauge wire than this would=p)

You can pick up a skid mounted 150KVA transformer for well under 40k a Rectifier for a fraction of that and then whatever tesla charges for the actual charger since you cant just throw current at lithium batteries and expect them to charge without a thermal incident.

[RickDaTuner]

Whelp, that was a very detailed answer to a little rhetoric. lol

24kw is still not bad.

Can you even get 500a service even at a residence?