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120/208 gives 240? please clarify #220885 07/11/20 01:35 PM
Joined: Jul 2020
Posts: 1
S
sophocles Offline OP
New Member
My apartment house has 120/208v Wye connected (4 wire plus ground) service from the utility. Apartments have 120/240 service. we can easily measure the 120v from phase to neutral - and I can comprehend the math that shows 208v between a phase and the imaginary point directly opposite the phase.
i can't see how this provides the 240v part of 120/240 to the apartments.
i am certain this has been addressed 100 times before, and would appreciate somebody helping this dummy for the 101'st time.
thanks!

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Re: 120/208 gives 240? please clarify [Re: sophocles] #220887 07/12/20 10:05 AM
Joined: Nov 2005
Posts: 816
J
JoeTestingEngr Offline
Member
Is there a room where they might have some 208 primary, 120/240 secondary transformers?

Re: 120/208 gives 240? please clarify [Re: sophocles] #220888 07/12/20 03:08 PM
Joined: Jul 2004
Posts: 9,514
G
gfretwell Online Content
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Are you sure it isn't 240/120 center tapped delta?


Greg Fretwell
Re: 120/208 gives 240? please clarify [Re: sophocles] #220892 07/13/20 12:58 PM
Joined: Apr 2002
Posts: 7,191
HotLine1 Offline
Member
120/208 3 phase, 4 wire secondaries from POCO transformers is common for multi unit apt construction.


John
Re: 120/208 gives 240? please clarify [Re: sophocles] #220898 07/14/20 01:03 PM
Joined: Jul 2004
Posts: 9,514
G
gfretwell Online Content
Member
Did the OP actually see 240v? I know we always had this issue in computer rooms that were in light industrial area where they used Delta Vee. It was necessary to actually verify the voltage before you believed what the customer said. We have burned up some stuff when we assumed 208 wye.


Greg Fretwell
Re: 120/208 gives 240? please clarify [Re: sophocles] #220904 07/15/20 01:33 PM
Joined: Apr 2002
Posts: 7,191
HotLine1 Offline
Member
Greg:

The OP lists his occupation as retired. I read his post twice and was going to reply with the usual comments.

Secondary actual voltage, load, lowest secondary voltage with 'heavy load'. Actual voltage at apt panel; etc.

I stayed silent on this

As you know the 240 volt items are AC, maybe cooling, maybe water heater. They tolerate <240 volts

I have not heard of any issues from the +/- 600 apt units that have been built in the last 2 years.


John
Re: 120/208 gives 240? please clarify [Re: sophocles] #220907 07/15/20 06:07 PM
Joined: Jul 2004
Posts: 9,514
G
gfretwell Online Content
Member
If he is really seeing 240v with a reliable meter, I think we can agree this is not normal 3p wye. It is more likely if measured that "240" is really more like 208. You are right that a lot of equipment has a wide enough "mouth" to take both but other stuff will need to be tapped to the available voltage.


Greg Fretwell
Re: 120/208 gives 240? please clarify [Re: sophocles] #220911 07/16/20 03:00 PM
Joined: Apr 2002
Posts: 7,191
HotLine1 Offline
Member
He may be using a 'wiggy' type tester!


John

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