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#11476 - 07/13/02 09:55 PM 208/240 heaters
scjohn Offline
Member

Registered: 07/04/02
Posts: 76
Loc: charleston, SC, USA
I just came across a job were the services needed to be relocated to make room for a bridge.Anyway the power co. wants to change the services from a delta 240 to a wye 208.
Should i concern myself with changing the heaters?
Thanks.

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#11477 - 07/14/02 05:15 AM Re: 208/240 heaters
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
scjohn,
you should do the math for the OCPD & branch circuit. if these are electric baseboard it would be an opportunity for a change. we are @ 11.7KW an hr here, don't know about SC.....

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#11478 - 07/14/02 06:16 AM Re: 208/240 heaters
Frank Cinker Offline
Member

Registered: 07/29/01
Posts: 317
Loc: Pennsylvania
scjohn-

I'll assume you are talking about 240 volt, single phase, baseboard heaters. I'll also assume they are rated at 2000 watts.

Using the following voltage reduction formula:
208/240^2=.75

Your 2000 watt heater will now be reduced to a 1500 watt heater. If that doesn't present a problem don't do anything.

Frank

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#11479 - 07/14/02 03:19 PM Re: 208/240 heaters
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Rebalancing 120- and {208} 240-volt loads may be necessary. Now you’ll have three phases 120v ø-n instead of two. Scott35 has posted some real gnarley sample spreadsheet panel schedules to track old and future. http://electrical-contractor.net/cgi-bin...+Area&number=15

Remember that motors operate somewhat the opposite—constant kVA versus constant resistance—depending on load. Lower voltage usually means increased current.

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#11480 - 07/14/02 05:10 PM Re: 208/240 heaters
scjohn Offline
Member

Registered: 07/04/02
Posts: 76
Loc: charleston, SC, USA
I am sorry, I am talking about the overload heaters in starters. I know there is a 15 to 20% window on the voltage, but not sure on the load. I know 208 is more efficient so the amperage will be less, and with heaters being a little more precise on the motor load
and just another means of protection. Usually when i order starters they specifically ask the fla. with the 125%. And for SC. poco they typiclly use phase c. blue for the high leg. I guess to be different. Anyway I am new to this forum, and will be asking more than answering. With this forum there is really no need for continuing education.

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#11481 - 07/15/02 03:49 AM Re: 208/240 heaters
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
What is the nameplate voltage of the motors?
There is only a 10% window on the motors.
In order to provide X amount of HP, the voltage/current relationship will be inversely proportional. If the motors are listed as 240 volt, you should not operate them at 208. However, if you do, the current will probably increase and if your OL protection is properly sized, the relay will likely trip.

[This message has been edited by Redsy (edited 07-15-2002).]

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#11482 - 07/15/02 06:25 AM Re: 208/240 heaters
wolfdog Offline
Member

Registered: 10/24/01
Posts: 135
Loc: Dallas,TX
The statement that 208 is more efficient is misleading, if not incorrect. A motor running on 240 will pull more amps when connected to 208.
The amps will drop when going from 240 to 208 on resistance loads, i.e. electric heat.

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