Walk-In Freezer trouble
I just spent the past 3 days getting beat up by a walk-in freezer. I have a 3 HP Copeland semi-hermetic compressor that is single phase, rated for 230 Volt, and has a water cooled condenser. Unit has 404 freon, and is rated at 20.1 Min circuit amps. It is on a 20 Amp circuit wired in 12 AWG. When it starts, it pulls 27 amps and works it way down to 17.2 amps in about 30 seconds. In doing so, it will occasionally trip the 20 Amp breaker. If the unit doesn't stay off for at least 6 minutes, it will trip the breaker instantly. After pump down, the pressures equalize a bit causing the compressor to kick back on in about 30 seconds and the breaker instantly trips. So as a tempory fix, I rewired the control circuit adding a contactor and time delay relay set for 8 minutes. That seems to work for now. My question is if a unit is rated at 230 volts, not 208/230, how critical is it to have the 230 volts? I only have 208 Volts from the panel. Will that cause rough compressor starting? The compressor is brand new as is all start components. I left there today with the understanding that the electrical circuit will need replaced. I still will only have 208 volts, but atleast it will have proper wire size and breaker size. Do I need to put a boost transformer in? Thanks for any help!
Rule of thumb is 10% of voltage plus or minus. 10% of 230volts is 23volts. 230-23=207volts minimum voltage, 230+23=253 volts maximum.
Do you have a CPR valve to keep the amperage to an acceptable level until suction pressure drops enough? Especially important after defrost but will help now as well. If you do, then adjust it to restrict the suction pressure of the compressor so the amp draw does not exceed the rated load amps of the compressor.
What else can you tell us about this system, SH, SC, SP,DP,Etc?
You can't provide too much info...
You need a bigger circuit.
I would agree with jp but also I am concerned with you are being fed 230 and only getting 208. Yes it will run within those parameters but your amp draws will be higher.
Probably everyone here has been on the call that someone put a 230 volt only motor on and it would run for a while then trip the thermal overload. One person I wok with did it and paid dearly for it.
Normally true, but 208 vs 230 is most often an exception.
Originally Posted by ryan1088
Many commercial buildings receiver their low voltage service form 208Y/120v service, either as single phase or all three phases depending on needs.
240v (which is expressed as 230, just like 120 expressed as 115) service is offered in residential or some commercial buildings, but that's power company's decision.
240v/120 high-leg delta exists, but it's less common. It's too much of a burden to have to offer 208v service and 240v service models, therefore 230v motors is assumed acceptable for 208 and 240v service. You shouldn't have to use a transformer. 208v is by far the more common service.
It's the same deal with single phase A/Cs. Houses usually get 120/240 from single phase transformers. Large apartment complexes usually get three phase service and feed two legs of service to each unit. This means 208v is available but not 240v.
To avoid having to make apt/office bldg models separate from house models they're rated to accept 208-230.
For larger stuff, power comes from 480Y/277v. Larger refrigeration runs on 3ph 480v. Lighting runs off of single phase 277v. You don't see 240/277v units, because there is no need for it like 208/240v model.
Running equipment on 20A circuit when it calls for >20.1A minimum is not code compliant, so if conductor size allows for it, you should have the breaker changed to next highest.
The incoming voltage from the utility company is only 208 volt. The compressor tag voltage reads 230 Volt. I agree that my amps would drop 10% if my voltage would increase 10%. That is making me think I should put a step up transformer in. I also agree that at CPR valve would be a great idea to install on this application. I wish I would have done that first. Once I get over that initial demand, the voltage settles down as does the compressor. I think that will be my next step. Thanks!
My old Copeland book states the 230V compressors have an allowable range of 207-253V, whereas the 208/230V models have a range of 187-253V.
With that undersized feed, you'd likely see a pronounced voltage drop from 208V during starts, further aggravating the situation.
I had a customer with a 230V Copelametic on a 208 service which ran for years with only occasional starting troubles, but with age they became more frequent. I installed a suitable buck/boost transformer which brought the supply up to about 240V and solved the problem.
Do you have any idea the price on a boost transformer that size?
We had a chain install Vendo cases that had a starting problem. The Acme buck n boost was the manufactures fix for it.
Originally Posted by kwagner
You could check these out.
Maybe choose the T-1-81058.
If it don't work, looks like your upgrading the power distribution to the unit.
You could probably get by with a .50 KVA transformer, but for a few buck more, a .75 KVA would be a better choice. No pricing allowed in this open forum, but if you do a Google search for a Schneider Electric 750SV43F, you'll get some results.
Originally Posted by kwagner
Note that they're rated for 240/480V primary and 24/48V secondary, but can be connected for a 10% boost for a 208V to 230V application. Here's a link: http://static.schneider-electric.us/...000-323-01.pdf
If you're drawing 20.1 amps at 208 volts that equates to 4180 va. You'd need a 4.2kva buck boost transformer rating at a minimum to do that properly. A .5kva sized bb transformer would accomplish that for you.
Last edited by wanttosee; 09-04-2012 at 11:03 PM.
Reason: hit send prematurely
If your only problem is a tripping breaker you need to increase the circuit size to the unit. #12 wire wire is rated for 20 amps but not allowed to be loaded above approx 16A. Have a #10 circuit run with a 30amp breaker. I also agree about the CPR so that the comp doesn't get overloaded
"I left there today with the understanding that the electrical circuit will need replaced. I still will only have 208 volts, but atleast it will have proper wire size and breaker."
So did you put in a larger circuit as you were saying in your original post? I am assuming you were going with 10 gauge and 30 amp breaker as well.
I am thinking that the original system drew less amperage due to its age and being worn out. What was the original minimum circuit ampacity of the old system?