maybe I'm just a dummy, but even when I have 2 legs of 3 phase its 3 phase to me, even if its only 2 legs. but if you wanna call it single phase go ahead.
5000W Water Heater
- Thread starter chris kennedy
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maybe I'm just a dummy, but even when I have 2 legs of 3 phase its 3 phase to me, even if its only 2 legs. but if you wanna call it single phase go ahead.
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- Massachusetts
Can't agree there, two legs of three phase is single phase.
What kind of motor or transformer gets connected to two legs of a three phase supply?
GeorgeB
ElectroHydraulics engineer (retired)
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- Greenville SC
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others covered my answer
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DRGREG
Member
If you loose 1 leg on a 3-phase load, do you call it 3 phasing?
iaov
Senior Member
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- Rhinelander WI
Nice thing about a resistive load is you can just stick a meter on it and know for sure what the resistence is.:smile:
iaov
Senior Member
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- Rhinelander WI
Yeah its still three phase to me too. The difference is the phase angle. If the phase angle is 120 degrees its three phase, if its 180 its single phase. 208 is the result of a3p Y transformer. Single phase also makes it so we can simply divide by 2 to determine the voltage of 1 leg. Three phase, because of the phase angle not being 180 degrees requires us to use the square root of three for determining voltages.
iaov
Senior Member
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- Rhinelander WI
I hadn't considered that Ken. Do you know that the resistence of these elements changes with temp and if so is it significant?
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- Wisconsin
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- PE (Retired) - Power Systems
This is a situation where taking short cuts with proper electrical terminology can cause confusion.
208Y/120 is the correct way to describe the 3-phase system.
I am not aware of a single universally recognized method to describe a single phase 120/208 1PH 3W circuit originating from a 208Y/120 system. This is one reason I try to include PH and W in my voltage descriptions.
Three Phase in and Single Phase out metering is very common in multi-meter equipment.
208Y/120 is the correct way to describe the 3-phase system.
I am not aware of a single universally recognized method to describe a single phase 120/208 1PH 3W circuit originating from a 208Y/120 system. This is one reason I try to include PH and W in my voltage descriptions.
Three Phase in and Single Phase out metering is very common in multi-meter equipment.
iaov
Senior Member
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- Rhinelander WI
Thanx. I know about temp co-efficients ( your sight would be great if I wanted to do some math) but what I was wondering about was water heater elements and if you had ever measured them. I have a gas heater so I am going to have to go bother a friend some where to check this out myself. Also , most things have thier resistence increase with temp. I would guess(thats all I can do now)thats true for water heater elements too. However I'm guessing there is a considerable amount of resitence in these elements at room temp and might give you a number to start with. Who knows?? I'm sure none of this is probably helping Chris with his initial question.If I get a chance this week I'll go measure some at the big box store.
It is relative minor unless there is a huge change in temperature. An incandescent light bulb has a large initial inrush because its resistance is lower until it heats up (hence the "tungsten" rating for switches). But these get real hot. I don't believe a water heating element has a huge inrush, but there is probably a short period of increased current flow. An easy test would be to measure the resistance of the element and compare to the calculated resistance at its rated voltage.
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