240v from a non-high leg 3 phase panel

[gs3jcb]

No criticism just humor....

ok humor,:thumbsup: thanks again

 

[K8MHZ]

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

1) May be the best solution
2) That would be the cheapest solution if the bricks are like brand new. Otherwise, pulling out the old brittle elements will almost certainly break some of the fire brick. Also, installing the new ones must be done with care in order to ensure even heating.
3) A 240 volt kiln will fire much slower on 208, and it is a good possibility it won't reach max temp at all.

The above comes from a few years of doing kiln repair back in the 80's.

 

[gs3jcb]

If 208V will not suffice, you can install a buck-boost transformer in boost mode and get a full 240V.

electic supply place is saying I will need two 208v to 240v transformers with 50 amp secondary that sound right? I am out of my comfort zone here

 

[ggunn]

electic supply place is saying I will need two 208v to 240v transformers with 50 amp secondary that sound right? I am out of my comfort zone here

If his kiln is supposed to operate on a 240V split phase service, why would he need two transformers? Wouldn't a 208V primary, 240V secondary with a center tap do the job? He might not even need the center tap.

 

[gar]

160923-1204 EDT

Mistake in my post. I hit 9 twice instead of 8. At 215 vs 240 your power input is 80%.

.

 

[K8MHZ]

If his kiln is supposed to operate on a 240V split phase service, why would he need two transformers? Wouldn't a 208V primary, 240V secondary with a center tap do the job? He might not even need the center tap.

That (center tap) would depend on if the controller needed 120 volts or not. Old time mechanical 'kiln-sitter' controlled didn't. Newer digital ones may.

 

[gar]

160923-1214 EDT

If your kiln requires no 120 V supply, then you only need one transformer.

If your kiln does internally require a 120 supply, and if that 120 requirement is only on one side of the neutral, then you can use the three phase neutral to provide the 120 V supply, and a single boost transformer. Call the hot line to provide the 120 V load phase A. Call the other hot line phase B. Thus, you have phase A, phase B, and neutral as input lines to the kiln. Obviously there should be a separate EGC (safety ground). These lines must be properly identified into the kiln.

The 120 V circuitry is between phase A and neutral. We also assume that the heating element is strictly a 240 V two terminal resistor, with some sort of relay contact in series that requires no specific relationship between the contact and the 120 V circuit. Probably true for a mechanical relay. Then one connects a single 208 input boost transformer between phase A and B to boost the phase B voltage from 208 to 240 V relative to phase A. The boost transformer secondary current rating has to exceed the kiln current when the kiln is on at 240 V.

.

 

[K8MHZ]

electic supply place is saying I will need two 208v to 240v transformers with 50 amp secondary that sound right? I am out of my comfort zone here

The drawing only shows one transformer for straight 240 single phase.

 

[K8MHZ]

It looks like a 10 kVa transformer will cost about a grand.

If you can find someone that works on kilns and can put new elements in without damaging the kiln, that may be the way to go. Then, if some of the fire brick gets broken, it can be repaired by the tech. I would figure about 350-500 dollars for the job, maybe even less. But, finding someone may be a problem. When I was doing it, I was the only one for 35 miles that had the stuff to fix kilns. Sometimes I traveled 75 miles to pick up kilns from schools and rebuild them.

 

[Smart $]

electic supply place is saying I will need two 208v to 240v transformers with 50 amp secondary that sound right? I am out of my comfort zone here

Does your kiln call for 240V single phase or three phase? Former, one required; latter, two required.

 

[K8MHZ]

Does your kiln call for 240V single phase or three phase? Former, one required; latter, two required.

Although 240 volt 3 phase kilns do exist, they are very rare. Usually 3 phase kilns are huge and used in schools and are wired for 208.

It sounds like more info is needed. A make and model number would help.

 

[mpoulton]

It looks like a 10 kVa transformer will cost about a grand.

That's why a buck-boost setup makes sense here. In that configuration, the transformer only needs to handle 1.3kVA (the 42A load current at the 32V boost voltage), which is much more reasonable.

 

[kwired]

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

Seems to be more guys out there that never ran into a high leg system before and learn about them the hard way when connecting 120 volt loads to the high leg.

 

[cpinetree]

Seems to be more guys out there that never ran into a high leg system before and learn about them the hard way when connecting 120 volt loads to the high leg.

Did you know? Toasters when hooked to the high leg make toast real fast.

Yes, one of our guys hooked one in a commercial kitchen to the high leg. Lucky that was the only thing on the circuit so no damage done, well maybe some burnt toast.

 

[gs3jcb]

Does your kiln call for 240V single phase or three phase? Former, one required; latter, two required.

The kiln was originally set up at a house using a single phase, 2 pole with 240 volts. It has been relocated to a warehouse that has a 3 phase panel Even though it is still using a 2 pole breaker. so, I need a single buck boost transformer 208v primary to a 240v secondary with 26.5 amps being secondary the kiln pulling 6300w

 

[Barbqranch]

Looks like you can get one on eBay for around $300 or maybe less.

I would first connect it to the 208 voltage, and see how it works before I spent any more money. It might work fine for you needs.

 

[gs3jcb]

Looks like you can get one on eBay for around $300 or maybe less.

I would first connect it to the 208 voltage, and see how it works before I spent any more money. It might work fine for you needs.

I get a error read and the book that came with it says it has to be 240v not 208or 215v so it want even fire with the voltage that's there tried that was why I was called to figure it out, the customer doesn't want to change the elements to a 208 system.

 

[Dennis Alwon]

I wouldn't think the 208v would be a satisfactory install even if it did run. I am guessing they have something programmed to make sure they are getting the full 240v. If it ran at 208v there would be about a 75% drop in output, I believe

 

[Barbqranch]

I believe it would be a 25% drop, for 75% of the expected output.

However, all the heating elements I have worked with have an increasing resistance with temperature increase, so it might put out a little more than 75%.

On a side note, I used to have a very early HP sine generator, and it used a light bulb in the circuit as part of the Wein bridge oscillator. It put out a really lovely sine wave.

 

[K8MHZ]

I get a error read and the book that came with it says it has to be 240v not 208or 215v so it want even fire with the voltage that's there tried that was why I was called to figure it out, the customer doesn't want to change the elements to a 208 system.

As Dennis pointed out, the controller wouldn't let the unit run even if the elements were changed. You have no choice but to provide the unit with a 240 volt supply.