undersized wire?

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johnofny

Member
I just had a 2nd compressor motor go on a Geothermal unit in less than 3 months, thought first was a fluke, but now I am not sure.
The facts:
The house has a long run (530ft) of underground service wire (350mcm) between pole and panel. Service is 200 amp.
The pole tranformer was 25kva, power co just switched it out for a 50kva in case that was an issue.
The unit is a HRV048A1C01ART from comfort aire (heat controller) the LRA is 102 Amps, RLA 18.3 208/230 v (was set to 230) 1ph 197 min V

We did a voltage read at startup on the second unit, and it dipped from 246 to 218 for a sec during startup. Did put a hard start boost capacitor on the 2nd unit, but the compressor still failed shortly after install.
The house does have normal appliances, the 1.5 hp well pump usually kicks in right after the geothermal unit. The lights do of course dim when the unit kicks in.

Questions:
1. Would marginly sized wire cause 2 compressors to go?
2. Someone suggested a thermal trip between the breaker and the unit if voltage drops, suggestions?
Ideas?
thanks,
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Could it be that you have too much voltage. Is the unit really rated 230v and not 240v? I am thinking that could be an issue but I am not certain.

At least you get bumped to the top.
 

hurk27

Senior Member
The problem with voltage drop is that you might not be taking your reading when other heavy loads are also running, and since resistance is current limiting, the load as a whole has to be taken into account, while it may appear that the unit only drops to 218 volts when the unit starts up, but if other loads are on it might drop even further, I had a house where the air unit would stall, but while I was there it seemed ok, but after putting a recorder on, I found out the homeowner wasn't telling me about a kiln in a room off the basement that he did ceramics in, so be careful when trouble shooting this problem, and make sure you cover all the facts, a recorder will tell all, and give you the big picture to what is really going on.
 

hurk27

Senior Member
Could it be that you have too much voltage. Is the unit really rated 230v and not 240v? I am thinking that could be an issue but I am not certain.

At least you get bumped to the top.

A higher voltage on a synchronous motor doesn't do as much harm as a lower voltage, low motor voltage is very bad for Sync motors because of the pole slip
 

johnofny

Member
thanks

thanks

Yeah, the unit is 230.
The power co put a recorder on after the second unit, So I guess that will be helpful, just hope I get results before the 3rd Unit blows.
 

kwired

Electron manager
Location
NE Nebraska
I don't think you have a problem with wire size unless there is a lot of other load pushing what you have. If it is a 208/230 volt unit and you have 15% drop you are still within the 208 volt rating of this unit - however you will probably be having voltage related problems with a lot of other things if it is this bad.

Has the HVAC guy checked the unit out to make sure everything is ok with it? Is it drawing proper current? Compressors usually have internal overload but if there is an overload problem it will cycle on and off but is still hard on unit. Not only should refrigerant pressures be measured but water flow on a geothermal.

I am not a refrigeration expert but I do know if a compressor fails they usually must flush the entire refrigerant system, and usually install an additional filter to collect any contaminants in the system that may have not been flushed otherwise contaminants will destroy new compressor.
 

johnofny

Member
I don't think you have a problem with wire size unless there is a lot of other load pushing what you have. If it is a 208/230 volt unit and you have 15% drop you are still within the 208 volt rating of this unit - however you will probably be having voltage related problems with a lot of other things if it is this bad.

Has the HVAC guy checked the unit out to make sure everything is ok with it? Is it drawing proper current? Compressors usually have internal overload but if there is an overload problem it will cycle on and off but is still hard on unit. Not only should refrigerant pressures be measured but water flow on a geothermal.

I am not a refrigeration expert but I do know if a compressor fails they usually must flush the entire refrigerant system, and usually install an additional filter to collect any contaminants in the system that may have not been flushed otherwise contaminants will destroy new compressor.
Yeah, the house has fridge, microwave, dishwasher, 2300sq house, garage, (gas range), electric washer/dryer. Nothing out of the ordinary (like a kiln or arc welder) After the 1st failure, they replaced the entire unit, now with the 3rd time it will just be a compressor switched out. HVAC guy has installed about 20 of these units before, without any issues.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
You in a high lightning area? I don't think capacitors or most electronics like to have their voltage exceeded. Perhaps the long power run is picking up lightning (how much of it is overhead -vs- buried?). Do you have a good transient voltage surge suppressor at the service entrance?
 

broadgage

Senior Member
Location
London, England
Is the unit dual rated for 208/230 volt ? or does it use a transformer which must be set according to the line voltage.

A lot of A/C equipment is dual rated for use on both 208 volt nominal and for 240 volt nominal.

Some types however use a motor designed for one voltage only, with operation on a different voltage by means of a built in transformer.
"set to 230 volt" may imply the later.

If the unit is rated also for 208 volt line, then it should be fine on a 240 volt supply with any likely voltage drop.
Even a grossly excesive drop of 15% would only take it down to 204 volts, which is well within spec for a 208 volt motor.

If however the unit uses a built in transformer, set to 240 volt, with a supply that drops to 220 or below, then that could be problematic.

Alternatively, the transformer might be set wrongly to 208 volts with a 240 volt supply.

If the unit DOES have a transformer, then I suggest double checking the voltage at the motor itself, not the input to the machine.

Who set the transformer taps ? a licensed electrician, experienced in such matters, or an A/C guy ?
 

iwire

Moderator
Staff member
Location
Massachusetts
I find this chart handy to remind me of the voltage ratings.

ANSIC841.jpg


We did a voltage read at startup on the second unit, and it dipped from 246 to 218 for a sec during startup.

218 does not sound to low, look at the utilization voltage.
 
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johnofny

Member
The entire run is underground.
The factory default is 230, if you switch the red/orange wires, from the cc to the transformer you convert to 208. Verified the orange (230) is connected.

Any thoughts on a voltage trip, regulator?

Seems the voltage is within range, manual says min/max is 197/256 I believe these are max if set to 230, min if set to 208.

But the 218/246 I found during tests is within range for 230 from the hart below.
 

hurk27

Senior Member
I just thought of something, I had something similar, and it was being caused by the thermostat being turned up and down and there was no delay on the compressor, this was causing the compressor to try to start right back up with a high head pressure, putting a time delay on the compressor stopped this problem even though the home owners would constantly adjust the thermostat, Check with the HVAC guys and see if there is a delay.

Some time ya just gotta people proof stuff:roll:
 
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