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Discussion Starter · #1 ·
Is there a rule of thumb to determine amperage of an HVAC Roof Top Unit (RTU) when voltage, phase and tonage is known?
 

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Discussion Starter · #4 ·
This is for estimating purposes. I'm taking the information given to me from the HVAC drawings. At this time the nameplate is not available.
 

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I pretwist and then use wire nuts. Solder pots rule.
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Otis221 said:
Is there a rule of thumb to determine amperage of an HVAC Roof Top Unit (RTU) when voltage, phase and tonage is known?
Without a type & model number you can't estimate amperage.
The best you could do is be on the same block as the unit but not close enough to be in the ball park.
 

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Discussion Starter · #7 ·
Yes. There is no information given on the electrical drawings for the RTU's (no equipment schedule or panel schedules).
 

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put a WAG in, and qualify it on your bid
 

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An old timer told me once to figure 10A per ton but, I've found that it doesn't always work out.
 

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If you know the size of the space and the building you are working with its possible to guestimate. But in all effort ask the customer, if your bidding Im sure 10 others are asking the same question.
 

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I might add that most units today are more efficient, and that figure is closer to 1700 watts/ton.
I still use 2200 just to be covered..
 

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Stand facing the prints, take all the 'rule of thumb' formulas you've been given and toss that crap out and request more info.
 

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Stand facing the prints, take all the 'rule of thumb' formulas you've been given and toss that crap out and request more info.
When you get a written design narrative it usually gives you a list of RTU's..
It might say...provide power to 6-15 ton, 3-12 ton, 3-7 1/2 ton RTU's at 480V, 3ph.....

That's it...I thinks that's the kind of info the OP has received..
 
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