240v from a non-high leg 3 phase panel

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gs3jcb

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I am trying to get 240 volts for a kiln, I have 3 phases, no high leg all 3 phase have 125 volts, the breaker is a 50 amp breaker I'm only getting 212 to 215 volts off two legs, the length of the wire feeding kiln is about 70 feet and is a #8 wire, what am I missing?
 
What is the voltage at the panel? Most 3 phase systems are 208V unless you have a high leg then you can get 240. You will need to boost the voltage from 208 to 240
 
gs3jcb said:
I am trying to get 240 volts for a kiln, I have 3 phases, no high leg all 3 phase have 125 volts, the breaker is a 50 amp breaker I'm only getting 212 to 215 volts off two legs, the length of the wire feeding kiln is about 70 feet and is a #8 wire, what am I missing?
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You don't have 240 volts with that system, it is a 208/120 wye system. If line to neutral is 125 then line to line will run about 216.

Unless you use a transformer to derive full 240 volts you will have less output power from resistance heating elements, approximately 25% less then their 240 volt rating.
 
gs3jcb said:
don't have a 208 leg, all 3 phases read 125v or around that.
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On a 208/120v nominal system you voltage to ground can be 125V but the voltage across any 2 phases will only give you 208 or there about.

If you had 240V delta then you would have one high leg on the system and 240v across any 2 phases. This is not what you have
 
If its a Scutt Kiln call them - 1-503-774-6000
or go to their website: http://skutt.com/
They are pretty helpful.

You likely will need to change heating elements if the kiln is designed for 240v and you have 208v feed.

For future reference they don not have a 480v kiln :happysad: a transformer is required to knock the voltage down.
 
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gs3jcb said:
don't have a 208 leg, all 3 phases read 125v or around that.
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There is two types of three phase winding connections, delta and wye.

You apparently have not been around wye systems all that much. With no wild leg we can use all three lines for 120 volt loads, the compromise here is line to line volts is only 208. If you have a majority of loads being 120 volts it is preferred.

The delta system can be corner grounded and have no 120 volts at all, or mid point of one phase can be grounded and that leaves us with one high leg and two 120 volt to ground legs. It would be more preferred when 120 volts are somewhat minimal and a lot of 240 volt load is present.

Voltage to neutral times square root of three is what line to line voltage will be = so for 120 line to neutral that gives us 208 line to line. Like I said earlier if line to neutral is 125 then line to line will be about 216, right about what you said you had.
 
160923-1020 EDT

gs3jcb:

Do you need 240 for the kiln? For the temperature you require in the kiln, to do whatever job you want to do, will the kiln heater be on continuously? If not on continuously, then what is the "on"/("on"+"off") ? In other words what is the duty cycle?

If your only load is a heater, then you can apply as low a voltage as you want to that heater and not damage the heater. With lower than rated voltage applied to a heater its maximum temperature is lowered, and it takes longer to get up to temperature.

You indicate that your voltage is about 215 V. With this voltage applied your power input is (215/240)^2 = 0.9 or 90 % of the 240 value. Temperature rise is not linear with respect to power input, but you could assume that it is linear for small changes.

Any non-resistive items in tour kiln may be determining factors as to whether you can operate at lower voltages.

To get 240 V from 208 use a stepup autotransformer, commonly called a buck/boost transformer.

.
 
kwired said:
There is two types of three phase winding connections, delta and wye.

You apparently have not been around wye systems all that much. With no wild leg we can use all three lines for 120 volt loads, the compromise here is line to line volts is only 208. If you have a majority of loads being 120 volts it is preferred.

The delta system can be corner grounded and have no 120 volts at all, or mid point of one phase can be grounded and that leaves us with one high leg and two 120 volt to ground legs. It would be more preferred when 120 volts are somewhat minimal and a lot of 240 volt load is present.

Voltage to neutral times square root of three is what line to line voltage will be = so for 120 line to neutral that gives us 208 line to line. Like I said earlier if line to neutral is 125 then line to line will be about 216, right about what you said you had.
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you are right I have not been around a wye system that was why it through me with no high leg, and you are correct, but with that be said I am not go to get 240volt for this kiln
 
gs3jcb said:
you are right I have not been around a wye system that was why it through me with no high leg, and you are correct, but with that be said I am not go to get 240volt for this kiln
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If 208V will not suffice, you can install a buck-boost transformer in boost mode and get a full 240V.

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gs3jcb said:
reading from phases to neutral, I get 125 volts on all 3 phases or around that
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Yes, we know. If you were to measure phase to phase voltages you would see them all to be 208V or thereabouts. There is no 240V accessible in your service. Your options are:

1) get a 208V to 240V transformer
2) replace your 240V heating element(s) with 208V
3) be satisfied with the lower heating ability of the 240V element(s) operating at 208V
 
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