silk screen dryer branch circuit question

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royta

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I am working up a price for a silk screen company. They need electrical run to a very large dryer. DRYER LINK 1 & DRYER LINK 2 The building has 208V, and according to the specs, the dryer pulls 95A, regardless of 208V, 220V, or 240V. I am trying to clarify this from the rep, but they are out of the office until Monday.

Anyway, I am not sure if the customer will be using the product for 3 hours or more at a time, but I do know that the dryer is certainly capable of much more continuous use than that. I'll get more info from the rep on Monday regarding the actual amperage draw, and whether the draw actually lasts 3 hours or more. Anyway, if it is a continous load, then 95A * 125% is 118.75A. Here's where I have a problem. There are two panels, a 277/480 and a 120/208 which is fed from the 277/480 through a transformer. 120/208 panel is an A-Series GE panel, and the largest THQB breaker is 100A. What to do?

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once you determine the exact load, if it exceeds the 100 amp, you can always add a breaker and feed it directly from the transformer using the appropriate rules of 240.21
 
I'm wondering how a dryer with a largely resistive load can have the same amperage rating at 208 volt that it has at 240 volts?
 
I was trying to figure that out too. Then I clicked on the link.

Different wattages:

208V 95 Amps 3-Ph 28.8 KW / 98,353 BTU
220V 95 Amps 3-Ph 32.3 KW / 110,029 BTU
240V 95 Amps 3-Ph 38.4 KW / 130,944 BTU
 
The wattage increases as the voltage increases since the resistance is fixed. I think you need to ignore the 95 amp ratings and use the KW ratings. You could use a 100 amp circuit to supply the dryer if running it at 208 volts.
28800/360 = 80 amps
80 * 125% = 100 amps
 
480sparky said:
208V 95 Amps 3-Ph 28.8 KW / 98,353 BTU
220V 95 Amps 3-Ph 32.3 KW / 110,029 BTU
240V 95 Amps 3-Ph 38.4 KW / 130,944 BTU
Click to expand...


The wattages posted (E*I) don't even work out with the information given.
 
mpd said:
can the existing 120/208 panel & transformer handle the new load?
Click to expand...
That's something I thought of after creating this thread. If it can't then I'd need to install a second transformer anyway. I could always use a dedicated transformer that feeds a disconnect soley for use with the dryer.



augie47 said:
once you determine the exact load, if it exceeds the 100 amp, you can always add a breaker and feed it directly from the transformer using the appropriate rules of 240.21
Click to expand...
I thought there had to have been a code where I could install a new transformer with the secondaries going directly to the heater. Art. 240.21(C). However, the customer also wants a disconnect for his forklift battery charger, even though the battery charger will be about 6 feet from the panel. So, if the branch circuit is indeed over 100A, I'll probably do what I mentioned above.



infinity said:
The wattages posted (E*I) don't even work out with the information given.
Click to expand...
I noticed that too. I think the only thing I can do is wait until Monday, when the reps are in the office, and get the real story on this piece of equipment.
 
I spoke with one of the reps this morning. He told me to size my wire for 95A regardless of the voltage. Although not required, he suggested a buck & boost transformer to supply 240V to the dryer so the dryer will "work better". Wouldn't I need three buck & boost transformers for 3ph? I'm not sure I will do that. What do you think?
 
royta said:
Although not required, he suggested a buck & boost transformer to supply 240V to the dryer so the dryer will "work better". Wouldn't I need three buck & boost transformers for 3ph? I'm not sure I will do that. What do you think?
Click to expand...

If it is straight three phase, no neutral it can be done with two small buck boosts.

If the unit requires a neutral you would need three buck boosts.

I sure hope the company knows more about making dryers then the rep knows about electricity.

I agree with the others, work the problem in watts not amps.
 
How would I figure the kW for 208? If the numbers they are supplying for 220V are correct, than the power factor is 89%. Power factors don't change for different voltages do they? If not, than their kW numbers don't pencil out for 208V and 240V.

I have 30.5 kW for 208 and 35.1 kW for 240, IF the 95A remains constant. If the kW remains constant, than I have 100A for 208V and 87A for 240V.

I'm confused.
 
royta said:
How would I figure the kW for 208?
Click to expand...

Looking at dryer link 1 the KW is given.

IMO they have screwed up the list with the 95 amps, IMO that is wrong.

However it looks to me like the KWs given for each voltage are correct.


I see it like this

28.8 KW @ 208 volts = 80 amps

32.3 KW @ 220 volts = 85 amps

38.4 KW @ 240 volts = 92 amps

If you apply E/I = R to all of the above they all come out to about 2.6 ohms which supports the conclusion that the KW and voltage listed is correct but the current of 95 amp for all voltages is wrong and worthless.
 
iwire said:
Looking at dryer link 1 the KW is given.

IMO they have screwed up the list with the 95 amps, IMO that is wrong.

However it looks to me like the KWs given for each voltage are correct.


I see it like this

28.8 KW @ 208 volts = 80 amps

32.3 KW @ 220 volts = 85 amps

38.4 KW @ 240 volts = 92 amps

If you apply E/I = R to all of the above they all come out to about 2.6 ohms which supports the conclusion that the KW and voltage listed is correct but the current of 95 amp for all voltages is wrong and worthless.
Click to expand...

Thank you iwire. What's your opinion on the buck & boost transformers? Are they completely unnecessary and will not make a bit of difference?
 
royta said:
Thank you iwire. What's your opinion on the buck & boost transformers? Are they completely unnecessary and will not make a bit of difference?
Click to expand...

I don't know how your machine works, any electrical resistance heating elements that are rated 240 but are supplied by 208 are going to run much cooler. This will likely result in longer cycle times for the equipment.

In your case running the machine on 208 instead of 240 will result in about 10,000 less watts of heating power. (28,800 watts vs 38,400 watts) That is a substantial decrease in heating power. Think of how much heat would come of a 10 KW heater by itself.

If I owned the machine I would want it to be able to run full power. This from a guy that had seriously considered adding a buck boost to my home range when I lived in an apartment served with 208 volts just so I would get faster heating of pasta water. :grin:
 
iwire said:
I don't know how your machine works, any electrical resistance heating elements that are rated 240 but are supplied by 208 are going to run much cooler. This will likely result in longer cycle times for the equipment.

In your case running the machine on 208 instead of 240 will result in about 10,000 less watts of heating power. (28,800 watts vs 38,400 watts) That is a substantial decrease in heating power. Think of how much heat would come of a 10 KW heater by itself.

If I owned the machine I would want it to be able to run full power. This from a guy that had seriously considered adding a buck boost to my home range when I lived in an apartment served with 208 volts just so I would get faster heating of pasta water. :grin:
Click to expand...

Thanks again iwire. I figured two Acme T-1-13076 transformers.
 
Remember that, when using buck-boost transformers, just as with any other transformers, when you boost the voltage, the primary will require more current than the secondary in order to provide a given power level.
 
Instead of using BB transformers you might want to consider feeding this dryer from the 480 panel and using a 480 ? 240 transformer.
 
LarryFine said:
Remember that, when using buck-boost transformers, just as with any other transformers, when you boost the voltage, the primary will require more current than the secondary in order to provide a given power level.
Click to expand...
I'm supplying the primary with 100A 208V, so I'm hoping that will be plenty.


curt swartz said:
Instead of using BB transformers you might want to consider feeding this dryer from the 480 panel and using a 480 ? 240 transformer.
Click to expand...
I thought of that, but I didn't even price out one out. It couldn't be less expensive than the two buck & boost transformers I mentioned a couple of posts up, could it?
 
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