ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
UL 508A SPACING
by ale348 - 03/29/24 01:09 AM
Increasing demand factors in residential
by tortuga - 03/28/24 05:57 PM
Portable generator question
by Steve Miller - 03/19/24 08:50 PM
Do we need grounding?
by NORCAL - 03/19/24 05:11 PM
240V only in a home and NEC?
by dsk - 03/19/24 06:33 AM
New in the Gallery:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
1 members (Scott35), 379 guests, and 16 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: May 2001
Posts: 36
C
C.Urch Offline OP
Member
How would one go about determining the load of a heat pump compressor in Volt Amperes? Is there a formula to convert tons to V.A.? Let's say that we have 3 - 3.5 ton units that has a R.L.A.(Running Load Amps) of 21.2, a minimum supply circuit of 28 amps, a max. fuse size of 45 amps and a minimum fuse of 35 amps. What would the load calculation or actual draw of these units be?

Joined: Mar 2001
Posts: 2,056
R
Member
test

Joined: Oct 2000
Posts: 4,116
Likes: 4
Member
Wouldn't you use the RLA figure?

Bill


Bill
Joined: Mar 2001
Posts: 2,056
R
Member
Why do you want the load in VA? It seems that you have all you need already. At the risk of going in circles--12,000 BTU/Hr. per ton. .293xBTU/hr.=watts. watts divided by (volts x power factor) or (volts x pf x 1.73 for 3phase)= amps. There is probably efficiency to consider also. I think this is right.

[This message has been edited by Redsy (edited 05-25-2001).]

Joined: May 2001
Posts: 36
C
C.Urch Offline OP
Member
In other words, one must "shoot from the hip" whether to upgrade a service from say 200 to 400 Amp when doing a re-model that is adding an additional heat and air system. If you think it will be close, then cover yourself. How about determing service size for new construction? Would it be safe to take the R.L.A. X 125% (for start up) per unit and and use this figure in determing your load calculation?

Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and
Member
Like Bill said, use the RLA [Running Load Amperes] to figure your KVA on each unit.

On large and/or multistage heatpumps, figure them to be LCLs [Long-Continuous Loads], so figure the RLA at 120% [or derate the circuit by 80% - but no need to do both]. If you know that they will not run for 3 hours + continuously, then LCL is not required. Heatpumps normally run at least 4 hours continuously at some time of the year, so best to figure LCL in your calcs.

List this on your Panel Schedule [with LCL added] for each heatpump.

List the heatpumps on a Load Calc as the NEC shows in the examples given at the end of the book, or in Article 220.

For LRA [Locked Rotor Amps], or starting amperes, there should be a rating on the nameplate stating what it should be calc'd at - but if that's not available, figure 600% of FLA for a somewhat close "Hip Shot"
Use the rated FLA of all motors per HP, not the RLA, when doing the 600% thingee.

Apply the LRA to your SCA [Short Circuit Amperes] calcs for motor contribution.

Sorry to throw so many TLA's at 'ya!!
[TLA = Three - Letter Acronyms].

Nothing like being bombarded with abbreviations!!


Scott SET


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5