How is 208 volts different than 230/240 volts?

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 you can also subscribe to the podcast on any podcast app of your choosing you can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching [Music] you

Channel: HVAC School

Views: 114,297

Keywords: hvac, hvac school, 3 phase, single phase, three phase, air conditioning, 3 phase power, 3 phase motor, single phase motor, air conditioning installation, 230 volts, 3 phase voltage, 240 volts, 208 volts explained, 208 volts single phase, 208 volts vs 240 volts, 208 voltage, 240 volts explained, residential hvac, residential hvac basics, split phase, bryan orr, hvac training videos, hvacr videos, three phase motor, single phase ac motor, single phase electricity, Volts

Id: r3hSaiIt8-Y

Length: 6min 25sec (385 seconds)

Published: Sat Dec 05 2020