Transformer question

S

Stevenfyeager

Senior Member
Location
United States, Indiana
Occupation
electrical contractor
I have a customer who has a new appliance, a fryer. It’s rated 240 V 48 A. The building only has 120/208 three phase.
I have never installed a transformer and have no idea about purchase price and labor cost.
Can you give me any rough estimate ?
I will be probably be asking a friend who does commercial work if he has time to look at this job.
Thank you so much.
 
Assuming it’s just resistance heaters, connecting it to 208V only means it will take a little longer to get to temperature. I doubt anyone will notice. In most restaurants, the fryer is turned on at the start of the day and left on, so if it takes 3 more minutes to get to temp, it’s no big deal.
 
My understanding of the steps from theory:

1 Evaluate if a transformer is necessary. As noted by others, the fryer is likely a simple resistance heater with thermostatic control. Running it at 208V reduces the heating power which means it will take longer to get up to temperature, and longer to recover when a batch of product is added...but this may have no significant impact on function. So the first thing you do is work with the manufacturer and your customer to see if using 208V will simply work.

2 If you really need 240V, the next step is to figure out if there are specific requirements for L-N or L-G voltage. This impacts what sort of transformer you can use, and there are many choices.

3 If the load is straight 240V that doesn't care about L-G or L-N voltage, then your best bet is an 'open delta buck/boost' setup. This uses two small transformers to boost the voltage from 208V to 240V. Do a search for " buck boost transformer calculator" and you will find results from different manufacturers to help select and configure the transformers. It looks like a pair of 2 kVA transformers will do the trick at $700 each.

4 Regarding labor, you would have an additional pair of boxes installed between your supply panel and your load. You would probably install these boxes in your electrical room. I'm pretty sure that you would not need secondary OCPD in this instance.
 
Stevenfyeager said:
I have a customer who has a new appliance, a fryer. It’s rated 240 V 48 A. The building only has 120/208 three phase.
I have never installed a transformer and have no idea about purchase price and labor cost.
Can you give me any rough estimate ?
I will be probably be asking a friend who does commercial work if he has time to look at this job.
Thank you so much.
Click to expand...
At 208 volts single phase this fryer would draw 41.6 amps and only produce 75.1% of the BTU'S then if powered by 208 volts.If fryer does not reach operating temperature or customer not happy with the longer heat up time you could purchase one buck boost transformer to raise single phase 208 very close to 240 volts. If it will be feed by three phase you can get away with two bucks boost transformers. I'm old school and even if a transformer is feeding a resistive load still use a transformer at least 125% of load.
 
I never think twice about installing 240 kitchen equipment on 208, I do it regularly.
Not the other way around though 208 equipment on 240 I change the elements,
Contact the manufacturer most offer a conversion kit, even includes a new name plate
 
do you have a photo of the nameplate? i would be surprised to see a 3-phase heating appliance that is only rated for 240v, and not for 208v as well. going down is not a risk of overheating. just makes it a bit slower.
 
Master Nater said:
do you have a photo of the nameplate? i would be surprised to see a 3-phase heating appliance that is only rated for 240v, and not for 208v as well. going down is not a risk of overheating. just makes it a bit slower.
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the nameplate only has 240 And when I called the manufa. he said it will heat up slower but it will work on 208. He recommended buying 208 elements for $2600
 
IMHO you should take the following approach: Install the unit unchanged for 208V.

Install the circuit _sized_ to allow you to change the elements to the 208V elements.

Explain to your customer that it will _probably_ work acceptably at 208V, but that it will heat slower and have a slower recovery time.

The cost of the $2600 elements is probably similar to the cost of the boost transformers plus labor. But if you can get away without installing either that is cheapest over-all.
 
winnie said:
IMHO you should take the following approach: Install the unit unchanged for 208V.

Install the circuit _sized_ to allow you to change the elements to the 208V elements.

Explain to your customer that it will _probably_ work acceptably at 208V, but that it will heat slower and have a slower recovery time.

The cost of the $2600 elements is probably similar to the cost of the boost transformers plus labor. But if you can get away without installing either that is cheapest over-all.
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I totally agree with this, that’s what I would do. Explain it to them and see if he can live with the longer heating/recovery time. If they try it and can’t live with it, go back and put in a buck-boost transformer. $2600 is a lot for done heating elements…a B-B Xfmr is a fraction of that.

To size it, you take the load current that you need, in this case 48A, times the voltage boost you need, in this case 32V (240-208), so 48 x 32 = 1536VA. I like to put in a safety factor of 1.5, so 2500VA, but this isn’t a motor, so that may not be necessary and you could get away with 2000VA. Should only cost around $500.
 
Jraef said:
…a B-B Xfmr is a fraction of that.
Click to expand...
Member the source is a wye, so you may want the auto-transformer arrangement to use three boost transformers. If not your L-G voltages will be different which may lead to confusion during troubleshooting.
The transformers are rated 100% and you will not have inrush issues, so don't oversize them.
 
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