Step Down 240V to 208V

Hi Group,
Is there a simple way to run a Blodgett Oven (208V 3 phase) from 240V 3 phase? My 240V 3 phase service has 3 wires coming in, there is no
neutral wire.
Thanks!
Chuck
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roninchuck wrote:

Several options:
- Check with the manufacturer to see if the heating elements in the oven are rated for 240V.
- Check with the manufacturer on the cost of a set of 240V rated elements for the oven.
- Get a set of buck/boost transformers to buck the voltage down.
It's a toss up whether new elements or bucking transformers would be cheaper, or you may be lucky and the elements are ok on 240V.
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Yes.
You need three bucking transformers. Each have 240 primary. The secondary having 24V is connected in series with each (1 of 3) input line and the other secondary line goes to the Oven. The phase of the voltage subtracting from the 240 to 216. That will be in tolerance likely. If not increase (more money) the secondary voltage.
The transformer (bucking) has to be able to handle the wattage of the bucking voltage times the Oven current. Then add 100% for safety.
Talk to the Electrical supply person and they can help. A good Electrician should be able to do that without thought.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
roninchuck wrote:

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Never tried it, but could he run the oven off of one of Iggy's sale priced VFDs?? Set the out put to 208, set the amps to the rating on the oven and away you go! If I am crazy and it would not work, let me know! Greg
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Chuck, I'm confused. A 240 V 3 Ph supply should not exist. If you are in the states and the difference is truly 30 volts per leg, you should be able to just run the oven or complain to your power company, but if you mean that your leg voltage is 120 V as opposed to 240 V, like in Europe, then you do need a 3 Ph step down transformer, but it is from 380 V to 208 V and they are available, but pricey. Please clarify. Steve

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Steve Lusardi wrote:

You need to update your info on US power systems. There are two common "low voltage" three phase systems available, 120/208V Wye service, common in light commercial buildings, and 240V Delta service, common in light industrial service.
The 240V Delta service also has two variants, corner grounded used for three phase loads only and "wild leg" where the system is grounded at the mid point of one of the three transformer windings which provides for two 120V legs from that ground/neutral for 120V single phase loads, making the third phase leg "wild" at a high voltage relative to the neutral/ground (and coded orange for identification). Since the OP indicates no neutral he probably has the corner grounded delta service.
This being a simple commercial oven, it's likely it may be ok on 240V vs. 208V (check with the manufacturer), and it's also possible that a new set of 240V rated heating elements for it will cost less than a set of three buck/boost transformers.
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Pete C. wrote:

That "wild leg" is also known as the "high leg"

High leg is 1.73 times the 120 volt leg or 208 volts to ground.
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Al Patrick wrote:

Yes, but "wild leg" is the most common terminology used in the US.

Yes, but that's not relevant to a three phase only commercial oven that doesn't use the neutral.
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I have the same situation where I have 240v delta with no neutral. The machine requires 208 3ph with a neutral. Does the transformer create a neutral? Also, I have 4 wires to to the machine, adding the neutral would require an entire new conduit and re-wire. Can you locate said transformers at machine? -Mike
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mlcorson wrote:

If you need a real 3-phase source with neutral, the best way to provide it is with a 3-phase stepdown transformer. These have a variety of connection options. If it doesn't have voltage adjusting taps, then you would connect the primary in delta and the secondary in wye. If you use it in the conventional 2:1 step-down, then the 240 V primary winding will produce a 120 V secondary output, but that will be connected hot-to-neutral, and you will get 208 V line-to-line on the output.
You could do this with 3 separate single phase step-down transformers, but the wiring will get pretty complicated. On a 3-phase unit, it can all be done by moving a few jumpers on a terminal board according to the diagrams.
Yes, you can definitely place the transformer at the machine, smaller step-down transformers are frequently hung on the side of the machine.
Jon
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Jon Elson wrote:

All transformers cannot be connected any way you want them. I worked one job where we ran 4160 volts down to the river to operate some heavy equipment. This was to be stepped down at the river with a pretty large transformer. Someone not paying too much attention or assuming it could be connected either way connected the secondary delta instead of wye - which the diagram called for. It blew the circuit breaker several times (almost instantly) before someone decided to look at the connection diagram.
\ / \ / \ / \ / 0 | /\ | / \ | / \ | / \ --------
Don't know how well this "graphic" will come through but the intent is to show that with a wye connect *two* windings are placed across the voltage supplied by the transformer core whereas with a delta connection that same voltage is applied across only *one* winding. This is what caused the Ka-BOOM! :-)
Be sure to specify what you want. A Delta / Wye Transformer with such and such primary and such and such secondary voltages *and* of a given KW or KVA.
Al
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Al Patrick wrote:

It has also been called a "power leg" and a "stinger".
The determining factor in connecting the primary wye or delta is line voltage and name plate rating. If they are the same you get delta. If not you get wye.
I have a bank of 1-25KVA and 2-15KVA 240V center grounded delta transformers feeding my property, 4 wire secondary coming to a service pole and 2 services, one 120/240V single phase to the house and one 3 wire 3 phase 240V to a 10HP agriculture pump.
The 25KVA transformer is what we call the lighting transformer because it has all the 120V load.
You can see some pages that I copied from a GE Distribution Transformer Manual. Just scroll to the bottom at
http://murrayranch.com/Electricity.htm
Don

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I have an ONEAC Delta to Wye converter that does that, as well as the ground reference position. You might look for one of those. I'm sure others make them, also. It's rated 32A in and 30A out. Respectfully, Ron Moore

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Ooooh - ONEAC - that is nice gear. Once the best power conditioner systems in the industry.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
Ron Moore wrote:

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wrote:

Please explain "no neutral". At the main disconnect where power enters the building ground and neutral are the same. You could only have no neutral if you are getting your power from a sub panel or other disconnect where a separate neutral was not run. If that's the case just pull a N wire to there.
Or am I missing something?
Thank You, Randy
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His service is likely delta vs wye.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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Randy wrote:

Your missing the fact that he has three phase 240V corner grounded delta service. It's likely he also has a separate service to supply the 120V single phase loads, or a transformer feeding those loads from the delta service.
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Yes exactly, I have an older 240V 3 phase -3 wires with a "B" ground. It comes into the building in a what the electrician called a "trough". The wires are basically joined together at that point and each feed goes to a separate fused shut off. Also yes, I have a separate panel and meter for my 120V. -Mike
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http://www.kilowattclassroom.com/Archive/DELTAWYEPhasors.pdf
Corner grounded circuit on first page.
WEs
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Randy wrote:

Yes, a true delta service can be corner grounded, center grounded, or balanced. In either corner or center ground (most commonly seen in open delta with 2 single phase transformers on the pole, not real 3-phase transformers) there better NOT be a neutral, as it won't be anywhere NEAR ground.
A balanced Delta system has a small balancing transformer that keeps all the line terminals balanced around ground. These frequently have a ground fault sensor on the ground wire of that transformer, and will kill the primary to the transformer if the current doesn't balance. On these systems, you can use single phase loads connected line-line, but any load connected line-ground (there is no neutral on a delta service) is a ground fault, and will shut it down in some manner.
Corner grounded delta systems have one of the legs grounded. This can look VERY much like a typical residential 120/240 V service, but typically all the breakers will be 2-pole with linked handles. The difference here can be detected by measuring voltages. Either hot line to ground would be 240 V, so you'd expect 480 V between the two hots, but you only get another 240 V. This can only be due to the phase difference.
Center-grounded delta systems have 3 hots, the advantage here is that you have two 120 V to ground hots that can run office lights, copiers, computers, etc., while still giving 240 V 3-phase service to major loads. You have to be careful what gets connected to what, as the 3rd hot to ground is about 208 V.
For the most flexible mixed-use system, the office wye 120/208 V system is used. You get 120 V from any line to neutral, and 208 V from any line to any other line.
Jon
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