In this quick video Bryan talks the difference between 208 volts and 230/240 volts.
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Read all the tech tips, take the quizzes
and find our handy calculators at https://www.hvacrschool.com/
All right in this quick video, i want to talk about the difference between what we typically call 230 or 240 volts split phase, although we often just call it single phase or 208 and with 208 volts. We know that we see this more in commercial applications, so techs who work more in light commercial applications will often see 208. So let's talk about what each one is, when you have a regular residential application or any single phase application you're taking one phase out of three from the power company and that one phase is going into the transformer or out of the street or could be ground. Could be up on the pole and they're splitting that phase into two separate discrete phases with a center tap and that center tap is the neutral so neutral going to the structure goes to the center and then it wraps in opposite directions from the center outwards.
And you have two different phases that are directly 180 degrees out of phase from one another, so imagine take a circle split it in half, you have 180 degrees and they're always directly, opposing as they reach the center. They go to zero, though so, when they're on the far sides they oppose one another, but then, as they come back together, they cross, and you can see this in a simple sine wave or if you imagine two circles that are split in half and they're rotating. In opposite directions: they're going to come together at one point, every cycle when they hit that that center point and actually what we call. That is the zero point.
So anyway, that's how single phase works is we take a single phase from the power company? One phase out of three: it's directly 180 degrees out of phase from one another when we split it in half and that's how we get 240 volts, often called 230. That's an older way of describing it back when voltages were lower. I mean people still call it. 220 and that's basically for the same reason that people will still call it 110 or 115 or 120..
Higher voltages are more common nowadays because it actually reduces line losses, makes it a little more efficient and so they've slowly increased the voltages over the years, where nowadays, we'll even see voltages in a lot of places. That's you know, 245, 246. Even that single phase that we generally see in residential - that's really split phase. So we take a single phase and we split it in half into two separate phases with that neutral in the middle.
But in the case of 208, 208 really isn't single phase. 208 is actually two phases: we're taking two phases out of three, so you have a building that has three phases of power coming into the panel and when we use a breaker that goes across in the bus bar across two of those legs, you don't get 240. Even though each one of the legs is 120 volts thereabouts to neutral, the reason is is because those legs are not 180 degrees out of phase. They are 120 degrees.
Out of phase. Now, in my previous video, i kept saying 90 degrees out of phase. For some reason, don't ask me why i say a lot of dumb things sometimes, but it's 120 degrees out of phase. So imagine if you took a circle and you split it into three pieces of the pie, all of those pieces would be 120 degrees. At a phase from one another, which means that if you look at the sine wave of 208 they're not directly opposed from one another, and so you don't get that full potential difference from one leg to the other. Which is why you only see 208 from a very practical standpoint when you're using 208 to power a motor or appliance that's designed for 208 or 240 you're, generally not going to get the full capacity or the full output in order to do the same job. So an example would be, if you take a typical single speed, single phase condensing unit and you put it on 208 versus 240 you're going to get lower capacity out of that unit. Now a lot of people wrongly assume that you're going to also see higher current.
That's rarely the case. There are cases that you will in cases where the motor is actually going to compensate for that, like, for example, with a variable frequency drive or an ecm, but most of the single phase, psc type of motors that we work on. If you put them on that, lower voltage, they'll actually draw a lower current and they'll do less work, so there'll be less wattage on the circuit and they'll also produce less btusing capacity, which is a thing that a lot of people forget when they're working with a 208 appliance another thing that happens when you're working with 208 is that motors tend to struggle to start more often, and so it's going to be more likely that you have to use a hard start kit, for example, or you may find that voltage drop on the Line that wouldn't have been a problem in 240 does become a problem with 208, because you're already low, so you're starting low and then additional voltage drop becomes more of an issue with running the compressor or the motors. So with 208 you have to be careful.
You have to think about whether or not your system is going to still have the capacity it needs, and you have to be more careful. The voltage drop it's going to be more likely on single phase. Psc you've got to use hard start kits. That sort of thing again read the manual from the manufacturer and do what they suggest.
But this is just a practical thing that we find and another thing when you're working in commercial applications make sure to retap those transformers. Based on the voltage that you have, some people will say: well, i don't have 208, i have 212 or i have 215 or something like that, and that's just sort of like how we say 230 versus 240 you're going to see that the voltages are actually higher Than 208 nowadays, just because the voltages are actually higher than 240 as well coming into the device, so you're not always going to see that 208, you may see higher. In fact, you normally will see higher, which by itself is not, is not a problem at all. So anyway, main thing to know here is that when we say single phase in terms of residential 240, we're talking about one phase that we split into two. We call that split phase and then you also have 208, which is actually two phases of the incoming three phase from the power company. Hopefully that helps we'll catch you in the next video thanks for watching our video. If you enjoyed it and got something out of it, if you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel and click, the notifications bell to be notified when new videos come out, hvac school is far more than a youtube channel. You can find out more by going to hvacrschool.com, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more.
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Thank you. helped allot. you are going to make me sound like i know what im talking about at work tomorow. Service area Ottawa??
It’s all about the vector angles for 208😮 Service area Barrhaven??
If you'd have 180 degrees out of phase then instead of 240V it be 0 (zero) V. Hence, the split phase systems are not out of phase.
raise your hand if you have have alot of experience but accidently plugged the test leads in the dc amperage port of the voltmeter and tried to test 240 whilst customers were watching you.
Aren’t there motors wound for 208V though? Do some equipment manufacturers offer motor options for voltage? Are there motors which are configurable for two voltages?
That's why the 120- 208 Y system is also known as the wimpy Wye.
And tell me, please, which is the best choose, when I want to get three-phase system at home ?
Thank you.
No one has been able to explain this to me and get it through to my simple brain the way that you just did. Thank you!!!!
But exactly why in America/Canada there are how much different tipe of voltage setup?!?!? Aren't most simplest have the same configuration to all oder world?!? For example, here in Italy I have a 230v single fase (Fase-Neutral) in my house and in facilities there are 3 phase 400v (F-F) and 230v (F-N) and Stop! There aren't oder configuration!!! Aren't most simple???
The word you're looking for is "nominal."
What type of phase converter would be best to use on an air conditioning unit that is 208 V 3 phase but my power source is 220V Single phase? Are you in Kanata ?
What's is a hard start kit . I recently bought a 80 gal compressor with a starter motor on it that says do not use a 208 , my power supply is a genrac 22500 with running of 15000 wats. Is this considered 208v
I was looking at an outlet at a restaurant that is supposed to be 120 V but it was reading 215V I open it and tested one lead to ground I was getting 215V the other lead to ground was reading 0 V, so why do I have 215V in one wire
so as an architect studying for my exams, it asks me when we would use three phase 120/208 power. the book is known for asking outdated questions. What I am taking away from this is that 208 is when you are only using 2 of the 3 phases? sorry. I've watched this twice now and it's not clicking
I always suggest (to who? anyone that'll listen 😉 that the term 'phases' be dropped when referring to wires. Those are phase conductors.
The reason is to avoid confusion that stems from people thinking two phase conductors implies 2 'phases' when in reality that is only 1 phase.
Man thanks that was super clear and informative. I was so confused about it
So is there any advantage to 208v?
I’m interested in your backstage demonstration setup, looks like something that could be built to get visuals on all sorts of things and on top of that do electrical tests, is it up anywhere?
excellent and full of knowledge to learn .
Here in canada we get 208 via 600/347 service entry.
It’s actually 600v 3 ph transform to 208 3ph.
We don’t have 208 single phase provide by the power cie.
Make a video about the 480volt step down to 240volt with a 208volt high leg transformer.. I've seen alot of maintenance guys fry equipment because they thought the B phase(high leg 208volt) was a normal 120volt circuit.. you always gotta open the panel up and make sure it isn't a 208volt high leg.. we mark the high legs with orange tape but most maintenance guys don't know what to look for..
Super great description and video.
wait you can shift phase angle on secondary transformer wire? how
In most European countries, the official range for the low voltage grid is 230 V +10/-10%, which is 207-253 V. So it should be possible to run 230 V equipment on a 208 V supply, but it's very close to the limit.
Thank for the knowledge!!
Your diagram shows a WYE bank which would provide 240v 3phase. 208v 3phase comes from a Delta bank with a neutral tap between phases A & C. A to Neutral = 120v C to Neutral = 120v B to Neutral = 208v. A to B = 208 A to C = 208 B to C = 208. This is commonly known as a Red Leg 208v power supply with Phase B being the Red leg. The actual wire on the line side of the disconnect should have red tape on it to signify it's 208 to Neutral. Service area Nepean??
Wait if 208v is 2 phases then why do we need a 3rd phase is it still gonna be 208v without the third phase?
Bryan, hi glad there is not much 208 single, or 3 phase , as brownouts create low voltages, & even though you ARE using the 208 tap , on control circuit too many times contractors DO NOT PULL IN , the SQUARE ( park ) in MORRISTOWN NJ IS STILL 208 a royal pain in the seat , I was so surprised that where I was in GERMANY, the homes do have 3PHASE CLOTHS DRIER, & stove Are hooked up, unlike USA, where all your load is on both sides of 230 v single ph, thereby higher amps /leg , all there is 50 HZ , also zero 125 volts , Cheers 🇩🇪🇺🇸🇺🇸
I’ve installed 24 volt transformers on 208 to bump it up to 232 or so
I am happy to see you bring up the fact that 208 is 2 phase.
I was working on a peice of equipment that was 208 with a supervisor and I stated that it was 2 phase and he threw me under the bus in front of all my co workers saying that I was an idiot and was completely wrong for calling single phase 208 2 phase. It made me very angry because I know 208 is two full phases. And in Europe they actually call it single phase, two phase, and three phase.
funny you mention this, we had a 5 ton bryant w/heat pump installed and kept getting a line overvoltage warning, and actually the main board in the outside unit later failed (2 months old). so the power company came out and said my outdoor unit was a 208v unit and i needed a 240v unit and left, jackasses. Are you in Barrhaven ?
Great video lots of useful information that really helps a guy like me
Great info. again Bryan. Thank you.
Great job and video like always Are you in Orleans ?
Question regarding this topic… seems like I find things in 3’s. Recently I have been on some commercial building working on ‘no heat’ RTU service calls.
In these 3 different instances I was getting 16-19 volts at the thermostats only to find whoever installed the units must not have done a proper start-up. I found the transformers still at factory tap of 240 when they should have been retapped to 208. So as I retap the transformer BOOM I get 26+ volts for my control voltage (good)!
Could you explain this? And how hard is a incorrectly tapped xfmr on controls and control circuits.
In my case, 2 of the calls had companies out who were continually just replacing thermostats that kept malfunctioning. Soon as I put the tap on correct voltage they have not had any issues and now we have new customers!
Thanks
Tony
This would have been much better for noobs or those struggling to understand, if it was explained showing how it looks from the transformer.
Congratulations You have a special talent to communicate the most important factors in the HVAC industry, not all technicians are electricians and electricians are not always technicians, in this field you must have holistic qualities, that is, knowing how to do everything !!! Thanks for the incredible contributions from your school and your channel.
Love it. Nothing whatsoever confusing unless you’re a root vegetable 😂
I really don't understand why you guys have so many voltages ,it's so much simpler to just have 240 V single phase and 400 V 3 phase … I'm not being negative I'm just trynna understand why . Service area Orleans??
Thanks for this info, we wished to explan about 240V / 3 Phase how its work ? in the same video
In south Africa, we have straight 230v single phase, 3 phase is 380v Are you in Nepean ?
I had a call of the uv not working on new install that my company just did. A residential 1 story house. Testing voltage and it was 211. The uv bulb blew. Both transformers were wired 240v. House located next to 3 highrise buildings. A 1st for me.
Thanks Brian, great video 👍🏼
Great video and very clear to me
Great video, I've been doing hvac for 14 years and still learning new things everyday.
The "old" voltages are the plus or minus range on the nominal voltage. Lower stamped on load devices, higher on switches and things. Some areas only at nominal, say 120V, +/- 10% which ranges from 130-110, =/-5% from 125-115. Now North America has +/-5% and it's generally baked in on modern devices given the good control of the grid. Might also be what the meters read in the past as well.
I am not an HVAC tech, but do a bit of electronics. I had always been a bit confused about the 208 versus 240, but now I understand why there is difference. Thanks for the quick and clear explanation.
Concise and dense with knowledge. Liked.