# Hey EEs, Electricians etc, have a weird one for you **URL:** \ **Category:** Factual Questions\ **Created:** [August 2, 2013, 10:57pm UTC](https://boards.straightdope.com/t/hey-ees-electricians-etc-have-a-weird-one-for-you/665201 "2013-08-02T22:57:55Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Capt\_Kirk](https://avatars.discourse-cdn.com/v4/letter/c/779978/32.png) [@Capt\_Kirk](https://boards.straightdope.com/u/Capt_Kirk)\ **Post date:** [August 2, 2013, 10:57pm UTC](https://boards.straightdope.com/t/hey-ees-electricians-etc-have-a-weird-one-for-you/665201/1 "2013-08-02T22:57:55Z")
So today I had to set up for a gig at the Giant Convention Center, audio and lighting for about 5000 people. Daisy chained 2 Portable Power Distros, Via pass throughs, tied into their service with Cam Locs, 200 amp 3 phase. The cams they gave me were tied into an isolation transformer(dirty power). Volt meter says +/- 120v per leg, cyclic rate was a tad low about 59.2hz avg. So the question A leg to B leg 208v, B leg to C leg 208v, A leg to C leg 208v, used two different meters same result, what gives? I am used to seeing 208v between, say, A and C but then you usually get 220v between the other two. I have more info if you need it and truthfully it does not matter as none of the gear needs 220v but I have been scratching my head over this for a couple of hours and I cannot for the life of me come up with a reason for this other than the transformers wiring and why in the heck would you wire a transformer that way? This is all under no load BTW. Thoughts anyone? Thank You **Capt** ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [August 2, 2013, 11:26pm UTC](https://boards.straightdope.com/t/hey-ees-electricians-etc-have-a-weird-one-for-you/665201/2 "2013-08-02T23:26:07Z")
Three phase voltage in the US is typically 208 phase to phase and 120 phase to ground. ---
**Author:** ![Capt\_Kirk](https://avatars.discourse-cdn.com/v4/letter/c/779978/32.png) [@Capt\_Kirk](https://boards.straightdope.com/u/Capt_Kirk)\ **Post date:** [August 2, 2013, 11:48pm UTC](https://boards.straightdope.com/t/hey-ees-electricians-etc-have-a-weird-one-for-you/665201/3 "2013-08-02T23:48:13Z")
> [@Chefguy](#): > > Three phase voltage in the US is typically 208 phase to phase and 120 phase to ground. Doh, I was having a brain fart you are correct Sir 120 x 1.732= 207.84. Sorry not enough sleep. **Capt** ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 2, 2013, 11:51pm UTC](https://boards.straightdope.com/t/hey-ees-electricians-etc-have-a-weird-one-for-you/665201/4 "2013-08-02T23:51:03Z")
\*\*Chefguy \*\*has it. What’s going on is that each leg is 120 degrees out of phase from the next, and you get a different result from subtracting any two legs than you get if you subtract zero (i.e., ground) from one leg. Or, in trig identity form: sin(x) - sin(x+120) = sqrt(3)\*sin(x - 30) That sqrt(3) provides the difference in amplitude. If one leg by itself is 120, then the difference between any two has amplitude 120\*1.732 = 207.846. ---
**Author:** ![Capt\_Kirk](https://avatars.discourse-cdn.com/v4/letter/c/779978/32.png) [@Capt\_Kirk](https://boards.straightdope.com/u/Capt_Kirk)\ **Post date:** [August 2, 2013, 11:58pm UTC](https://boards.straightdope.com/t/hey-ees-electricians-etc-have-a-weird-one-for-you/665201/5 "2013-08-02T23:58:15Z")
This is why Rock and Roll should not start at the crack of dawn, it makes my brain hurt. Thanks for reminding me what I already knew. Doh:smack: **Capt** ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [August 3, 2013, 12:52am UTC](https://boards.straightdope.com/t/hey-ees-electricians-etc-have-a-weird-one-for-you/665201/6 "2013-08-03T00:52:18Z")
> [@Capt\_Kirk](#): > > This is why Rock and Roll should not start at the crack of dawn, it makes my brain hurt. Thanks for reminding me what I already knew. Doh:smack: > > **Capt** All that noise has caused dain bramage. ---
**Author:** ![Capt\_Kirk](https://avatars.discourse-cdn.com/v4/letter/c/779978/32.png) [@Capt\_Kirk](https://boards.straightdope.com/u/Capt_Kirk)\ **Post date:** [August 3, 2013, 12:57am UTC](https://boards.straightdope.com/t/hey-ees-electricians-etc-have-a-weird-one-for-you/665201/7 "2013-08-03T00:57:46Z")
> [@Chefguy](#): > > All that noise has caused dain bramage. Ah That is It! Won’t my Mother be proud. 😃 **Capt**