amp spike on carrier 5 ton heat pump

[biggi]

so i installed 2 carrier 5 ton heat pump systems in a doctors office about a week ago. customer called today and said this is the first time the used to the heat and they tripped the main 200 amp breaker. checked both units and they are pulling normal amperage. the main feed coming into the panel box with both unit's off was 49 amps. both unit's running with back up strips engage about 110 amps total on main feed. thats everything running in the building. so way are my units tripping the breaker? well on further diagnostics i found the unit's pulling a quick 159 amps on start up. so my question is why would these bad boys pull that much on start up. i checked caps, i checked voltage drop on start up and i checked pressures on start up. everything looked fine. so i'm stumped any ideas to fix the problem would be appreciated.

[superfittertech]

Install hard start caps

[Doctorinky]

Agreed get hard start caps in both units, use a bigger one like a TO5 or even better trane hard start cap and potential relay

[Saturatedpsi]

I'm not an electrician, but I think I'd suspect the electrical service. Heat pumps don't generally trip mains. Did you by chance check for a voltage drop on start-up? Is the main "running hot"?

[Tech it out]

I'm not an electrician, but I think I'd suspect the electrical service. Heat pumps don't generally trip mains. Did you by chance check for a voltage drop on start-up? Is the main "running hot"?

Agreed. I would check the panel. Take the main br out and see what the "ears" look like on the panel. Start kit is always good, but I bet the problem isn't with the units. Let us know.

[John Markl]

Agree with checking the panel connections.

And, you might consider a delay on make timer on one of the heat pumps, to stage start up......same as we do with sequencers on electric furnaces.

Also.....how much element heat do you have? Did you check the current draw with ALL of the elements running? Two five-ton heat pumps would likely have a total of 40kw strip heat on them around this area. That would run 160+ amps itself.

[Tech it out]

Spot on with the strip heat check. I would want to be sure these are on.

[madhat]

Are they on Setback thermostats? We have four Carrier HP/RTUs, on cold mornings the thermostats were slamming on the compressor, and all three stages of heat, on at once. We went with thermostats with Y1 for the compressor and 3 stages of electric heat with smart recovery. The units wiring diagrams shows 1st stage with one strip of heat, 2nd stage with two strips of heat. So we had to move some wires around.

BTW, Drs. Offices are notorious for overloading panels. They have medical equipment techs. coming in and install the latest and greatest medical gizmo. Pop a new breaker in, test and go. Then we get called in for more cooling/heating to cover this area, and bam there are problems.

[BoatMechanicMatt]

I wouldn't be afraid to pop in a new breaker. A weak breaker has given me headaches more then once.

[Tech it out]

I wouldn't be afraid to pop in a new breaker. A weak breaker has given me headaches more then once.

Actually had an electrician (experienced with own biz) tell me there was no such thing as a weak breaker!

[jimcafc1]

+3 on the electrical. I would check the main breaker amperage without the heat pumps operating, then bring on strips, and start the heat pumps. I bet there is an issue with main.

[biggi]

check voltage on start up. had 244volts didn't drop any on start up. got 5kw heat in each pulling 20 amps per unit. but this jump is only on start up at the condensing unit. and only one is doing it. the other one jumps to 85amp on start up which is normal from my experience. i put hard starts on both units as a band aid and now i'm getting a jump to 35 amps on startup. the only thing i can think of is the one pulling high amps has about 70 foot of line set to the handler in the attic. which is not my choice by no means. but all my electrical is tight and good voltage. main breaker is good i already took it out and checked it that was the first thing i did when i got there. thanks guys for the input.

[biggi]

Are they on Setback thermostats? We have four Carrier HP/RTUs, on cold mornings the thermostats were slamming on the compressor, and all three stages of heat, on at once. We went with thermostats with Y1 for the compressor and 3 stages of electric heat with smart recovery. The units wiring diagrams shows 1st stage with one strip of heat, 2nd stage with two strips of heat. So we had to move some wires around.

BTW, Drs. Offices are notorious for overloading panels. They have medical equipment techs. coming in and install the latest and greatest medical gizmo. Pop a new breaker in, test and go. Then we get called in for more cooling/heating to cover this area, and bam there are problems.

YEP! see it all the time.

[bzzline]

One of the first jobs I did on a install with Carrier contractor was a tripping cb in heat mode turned out to be a fan relay wired wrong from the factory

[HVAC-Eng]

Usually motors draw more current upon start up. The induced emf (Electro Magnetic Field) in the motor's shaft depends on the rotation speed of the motor (at startup roter is at rest) so therefore the starting current (called inrush current) will be up to 10 times higher than the motor's rated current.

I suggest turning the units on one at a time.

[hvacmike85]

Actually had an electrician (experienced with own biz) tell me there was no such thing as a weak breaker!

anything is possible

[AddMore22]

Dumb idea .... But check lug connection on all electrical fittings going to main ...

[AddMore22]

Ps..
Did it trip when you tested it? What was volts?

[Tech it out]

anything is possible

Ive changed many over the years that had no where near the rated amps. Maybe we should start calling it "strength challenged" instead of weak!

[71CHOPS]

yeah, what's the LRA ratings on those units?? if they both started at the same time....or if the building amp draw was already high, and one kicked on,that might do it.

just looked at a 3ton residential rheem yesterday, it's comp. LRA was 112a.