heat pump trips breaker


the system is a 10 SEER Carrier heat pump about 12 years old. The problem is that the outside unit trips breakers about 5 or 6 times each summer. This occurs on very hot days when the electric demand is very high. It never occurs in spring, fall or winter.The unit is powered by a 30amp circuit. The spec on the unit requires something like 28 amps on startup. The cable that powers this unit and the line set are both extremely long, probably over 80'. This is a condo unit and the line set and wiring are not accessible in any reasonably easy fashion. It would take significant demo in other peoples units to access the wire. Here is what I have done to work around this problem: tightened the wires in the panel, the disconnect and the unit, changed the 15' of wire from the disconnect to the unit to a higher guage (8 ga), put on a hard start kit, changed the breaker, changed the entire panel from an old Federal Pacific to a new Square D. I imagine that the delivery of electricity during these peak demand moments is insufficient to power on the unit and it trips the breaker during startup. Of course, it is impossible to ever catch the unit in this mode.
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" snipped-for-privacy@erols.com" wrote:

Is there a question in there somewhere?
Pete C.
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Your problem may be as a result of voltage drop. During peak periods of power consumption the power companies may cut back a little. Lower voltage means that your unit will pull more amps. It is possible to install a buck/boost transformer at the unit to raise the voltage up.
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Other items to check make sure that either the thermostat delays cycling ,or install a relay to add a delay between the time the units goes off and the next response to a call for cooling. Breaker can trip when starting against too much pressure.
Check the metering device if it's a piston make sure its the correct size and is functioning properly. If it's a TXV check for proper operation. After the metering device is checked the charge should be adjusted either by Subcool or superheat method taking extra care to let the unit run long enough to stabilize 80' of line set. Breaker trip because the system doesn't equalize properly or compressor runs hot because refrigerant doesn't meter properly. Over charge or under charge.
Also if the hardstart kit is one of the solid state one you might consider one that uses a potential relay rather then solid state control. Solid state kit more prone to failures
You can have the compressor windings checked with a mega-ohm meter but with a 12 year old compressor. Don't want to go there most 12 year old compressor will show wear.
Has it ever tripped in the winter and what does the rating plate state as Max breaker size?
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