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01-09-2013, 06:27 PM   #1
biertourist
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 Residential Electricity Standards for Voltage Droop?

Is there a minimum % voltage droop or minimum voltage that is supposed to be supplied for residential electricity?

-What can you do if your voltage is under this lower limit?

My electric oven and electric dryer have all seemingly had problems since I moved in; the Dryer takes 2 1/2 - 3 hours to dry a load of clothes and things in the oven always need to be cooked hotter and longer than all recipes state. -In preparation for hooking up my almost completed electric brewery I tested each 120v line coming into my 50 amp electric oven outlet (on a 40 amp breaker), and they both read between 118 and 119 volt (Yea!); HOWEVER, when I connect my multimeter across both 120v lines I only get 206 volts on the "240 volt" side.... That's REALLY low...

I get the same at my dryer plug and I'm imagining at the electric water heater although I'm not going to take it apart to check it...

One more question: Is there a way that I can calculate how many watts I'd actually get out of my 5500w electric element if I'm only getting 206 volts "in"? -@ 240v 5500w = almost exactly 23 amps, does this mean that I'll only get 206v * 23 amps or 4.7kw out of my 5.5kw electric element?
(I also remember hearing that the relationship between voltage and wattage isn't linear and that @ 120v a 240v element will only have 1/4th the wattage so I'm actually expecting that the drop in wattage output is greater still but I'm not sure how to properly calculate it...)

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01-09-2013, 06:29 PM   #2
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I'm only getting 85.5% of 240v on my "240v power"... It's off by almost 15%; this CAN'T be within the allowable range, right?

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01-09-2013, 08:08 PM   #3
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Normally a residential power feed is 120V/240V. I appears that you have a 3 phase power feed to your home. Most 3 phase is 120V/208V when it is supplied using a wye configuration. It sounds like that is what you have.

BTW - a delta configuration would be 240V with possiblilty of 120V as well.

You can get a 208V 5000W element here: http://bostonheatingsupply.com/SP10867NL.aspx

Hope this helps.

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01-09-2013, 11:17 PM   #4
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Would there be a way to select two wires and actually get 240v across it?

Is this a normal thing? I definitely don't see an upside to having this three phase "wye configuration" at the moment...

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01-09-2013, 11:19 PM   #5
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That's a REALLY expensive element... -Would I need to use larger gage wire with it to support more amps @ 208v?

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01-09-2013, 11:32 PM   #6
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I think that you need to verify whether or not you are on 3-phase wye, and if not, precisely what type of power feed you have. If you do have 3-phase wye, then go with a 208V element, like P-J suggests. I have seen Rheem LWD elements at both 5000w and 6000w, but check the length to make sure you can fit them in your kettle.

If you really do have standard US 120v/240v single phase power, then you should probably go with a 240V element and work with the power company to see if they can help you get closer to 240V. I don't think you would want a 208V element and then have 240V go through it some day, hence my recommendation to find out what you really have for a power feed.

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01-09-2013, 11:43 PM   #7
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Quote:
 Originally Posted by biertourist PJ, what do you mean about this "delta configuration with 240v possibility"? Would there be a way to select two wires and actually get 240v across it? Is this a normal thing? I definitely don't see an upside to having this three phase "wye configuration" at the moment... -
Quote:
 Originally Posted by biertourist That's a REALLY expensive element... -Would I need to use larger gage wire with it to support more amps @ 208v? -

If the power company is delivering 208V 3 phase there is no way for you to get 240V from it. It sounds like your place is located in a predominately industrial area. (Just guessing on that one) I would call the power company and see if thay can change the power being delivered to you.

A 5000W 208V element will draw about 24A. You would need to use #10 gauge wire to power the element. It would be the same wire size for a 5500W element on 240V.

P-J

Edit: As jeffmeh said - definately call the power company to verify what they are providing for you.
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Last edited by P-J; 01-09-2013 at 11:46 PM. Reason: Edit for an after thought.

01-10-2013, 12:05 AM   #8
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Quote:
 Originally Posted by biertourist One more question: Is there a way that I can calculate how many watts I'd actually get out of my 5500w electric element if I'm only getting 206 volts "in"? -@ 240v 5500w = almost exactly 23 amps, does this mean that I'll only get 206v * 23 amps or 4.7kw out of my 5.5kw electric element? (I also remember hearing that the relationship between voltage and wattage isn't linear and that @ 120v a 240v element will only have 1/4th the wattage so I'm actually expecting that the drop in wattage output is greater still but I'm not sure how to properly calculate it...) Adam
Since no one has answered this question yet, you need to use the relationships of P = I * V & V = I * R (rearrange and solve for what you need -> R = V1^2 / P1 => P2 = V2^2 / R... or one simple equation P2 = P1 * V2^2 / V1^2)

Basically for your situation a 5500W 240V element will give you about 4130W @ 208V. So you are getting about 75% of the power you thought you were getting

01-10-2013, 12:22 AM   #9
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Quote:
 Originally Posted by biertourist That's a REALLY expensive element... -Would I need to use larger gage wire with it to support more amps @ 208v? Adam
Here is a less expensive 5500W 208V copper element (\$24) instead of the 47\$ one:

http://bostonheatingsupply.com/SP10872PL.aspx
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01-10-2013, 12:32 AM   #10
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Quote:
 Originally Posted by P-J Here is a less expensive 5500W 208V copper element (\$24) instead of the 47\$ one:http://bostonheatingsupply.com/SP10872PL.aspx
Yes, the copper ones are less expensive, shorter, and MWD rather than LWD. I don't know whether the watt density difference is enough to matter.

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