what does 208~230/460V mean for a 3 phase motor? - Page 1
Forum section: electronics / beginners

author: Dmeads
author_rank: Regular Contributor
timestamp: February 13, 2021, 10:48:52 pm
content: I am trying to understand voltage ratings for 3 phase motors.I have done a little research, and there is both a line-to-line voltage, and line-to-neutral voltage.So from my research, I have gathered that a 208V 3 phase motor means 208V line-to-line, and 120V (208/sqrt(3)) line-to-neutral. Does this mean in an inverter set up, you would need to supply 170VDC (to get 120VAC) or 294VDC(to get 208VAC)?Additionally, I found this motor:https://www.ebay.com/itm/Industrial-Duty-Fractional-Electric-Motor-1-3HP-208v-460v-3-Phase-AT13-18-56CB/284038593918?hash=item422204fd7e:g:R9wAAOSwoRtfLOMUwhich has a voltage rating of 208~230/460V. What does this mean?thanks!-Dom

author: james_s
author_rank: Super Contributor
timestamp: February 13, 2021, 10:54:01 pm
content: It means it can be wired for either 208V or 480V 3 phase. 3 phase loads are rated for the phase to phase voltage and don't use a neutral. The phase to neutral voltage is only used for single phase loads.

author: wizard69
author_rank: Super Contributor
timestamp: February 13, 2021, 11:34:27 pm
content: Think of a 208 voltage 3 phase system as a compatibility approach so that you can have the standard 120 VAC to ground. 208 three phase is a why (Y) system that is you have a neutral at ground potential.I look at 240 or 480 volt systems as "industrial" in that the are often delta connected systems. However they are not always delta connected, a Y connected system will have 277 volts to ground and in many locations the lighting systems will be single phase with 277 volts to ground. As far as motors go most three phase motors are rated 240/480 volts however as you can see they can be rated with an extended range. For stuff shipped internationally the motors will often have other ratings for different frequencies and voltages that the motor can run at.In modern plants you can have many systems. For example there will be a 208 Y system for powering user loads such as coffee pots, desktop computers, and other 120 outlet loads. Most likely there will be a 480 system of some sort for "industrial loads".All About Circuits does a decent introduction:https://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/three-phase-y-delta-configurations/

author: jmelson
author_rank: Super Contributor
timestamp: February 14, 2021, 01:41:27 am
content: Since nobody else mentioned it, a motor with a 208-230/480 nameplate means the motor can be wired for either 208-230 V OR 480 V, requiring a change of jumpers inside the motor junction box. Without checking the jumpers, you can't know which range the motor iswired for.Jon

author: james_s
author_rank: Super Contributor
timestamp: February 14, 2021, 01:58:33 am
content: Huh? That's exactly what I said. "It means it can be wired for either 208V or 480V 3 phase." Obviously it isn't going to automatically rewire itself.Usually the windings in these motors each consist of two separate windings that can be connected in either series or parallel.

author: themadhippy
author_rank: Super Contributor
timestamp: February 14, 2021, 03:16:42 am
content: Quotedo they?most 3 phase motors ive played with that has this sort of rating has the start and end of each winding brought to separate terminals, 6 in total,you then link them in star (y) or delta depending on the voltage.

author: james_s
author_rank: Super Contributor
timestamp: February 14, 2021, 04:38:39 am
content: Quote from: themadhippy on February 14, 2021, 03:16:42 amYou may actually be right, now that I think about it I'm not sure I ever dug that deeply, it's been years since I've reconfigured a 3 phase motor and more often have dealt with single phase motors. IIRC those have the series/parallel arrangement for 120/240V selection. Even then I usually just follow the diagram and put the wires on the correct terminals.

author: WattsThat
author_rank: Frequent Contributor
timestamp: February 14, 2021, 04:46:36 am
content: Quote from: themadhippy on February 14, 2021, 03:16:42 amIt depends on what part of the world you live in. Yes, the IEC standard is A terminal box with six terminals and metal jumpers as you described. But, here in the US, the standard for motors up to 100HP are universal voltage 230/460 volt and have 6 or 12 leads. Past 100HP, 6 leads are more common. In some configurations, there are 9 lead motors.Yes, we still use flying leads, it’s make work for the union guys.The 208 volt machines are primarily found in a few large US cities with New York City being the biggest user. I’ve seen some 208v usage in western Canada as well.Oh, one other thing about US motor standards. The conduit box is know as the “pecker head”. Seriously.US standard motor connection diagrams

author: james_s
author_rank: Super Contributor
timestamp: February 14, 2021, 05:01:24 am
content: Quote from: WattsThat on February 14, 2021, 04:46:36 amIt's called a pecker head? How did I not know that?In my limited experience with 3 phase, 208V is the bulk of what I've seen. Friends of mine have a machine shop and they have a couple of 460V machines but those are run from a large step-up dry transformer, the incoming supply is 208V 3 phase, 120V to neutral.

author: WattsThat
author_rank: Frequent Contributor
timestamp: February 14, 2021, 05:23:16 am
content: You see a lot of 208v wye in office buildings and light industrial in the more populated areas due the 120v availability. It’s the cheap way without needing separate transformers. Another method is to use 277v lighting which is lifted from the 460v transformers and then separate, smaller transformers strictly for the 120v usage.What I learned rather quickly in the real world was there is no real US standard. For example, you can still find corner grounded delta distributions, especially in the Midwest. The first time I opened a control panel in Ft Wayne Indiana and saw lengths of copper pipes in all the B leg fuseholders, it was truly a WTF moment.

author: wizard69
author_rank: Super Contributor
timestamp: February 14, 2021, 07:08:04 am
content: Actually small shops will often be provided with 208 Y by the power company. large plants will have 208 Y for offices, general outlets and the like. Power to industrial machinery will be 240 or 480 and sometimes you will have 600 volt systems. If the machinery is large enough you will also have high voltage going to large motors.That doesn't even get into imported machinery requiring alternative voltages. These are often serviced by individual transformers. I just wanted to point out that sometimes 208 Y is all you get.Quote from: WattsThat on February 14, 2021, 04:46:36 am

author: gnuarm
author_rank: Super Contributor
timestamp: February 14, 2021, 07:45:52 am
content: In the US we also have a voltage that is 240 between the 3 phases. To get 120 from this one of the delta coils is center tapped and made the neutral. So relative to neutral the three phases are 120V, 120V and 208V, while the 3 phase is proper 240V.I run into this often when charging the car from level 2 chargers. Most smaller facilities like motels have 208V 3 phase, so the car charges from that at 5 kW while at facilities that get true 240V the car charges closer to 6 kW. Not sure why, but these chargers are almost universally on 30A circuits charging cars at 24A while most cars have higher rate capabilities. All Teslas can charge at 32A and models S, X or model 3s with the long range battery can charge at least at 48A. My car will charge at up to 72A - model X prior to ~2019. But I seldom see level 2 charging at anything other than 5 or 6 kW and not enough of that!

author: jmelson
author_rank: Super Contributor
timestamp: February 14, 2021, 11:43:45 pm
content: Quote from: gnuarm on February 14, 2021, 07:45:52 amYes, this is called center grounded delta. This is sometimes supplied in an open-dalta setup with only two transformers, one of them the standard 120/240 center-tapped residential transformer.The advantage of the corner-grounded delta (can also be done with two single-phase transformers) is that two-pole breakers can be used.You'd get confused when there are two breaker panels side-by-side with rows of 2-pole breakers in them fed from different meters.I've seen this in some really old shops.Jon