Lights Flicker as Heat Pump Turns On

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Old 10-04-07, 09:24 AM
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Lights Flicker as Heat Pump Turns On

I finished the installation of my new pool/spa heat pump with all the help from this forum, thank you.

To summarize I installed a subpanel at the pool pump heater location with 70A main panel breaker 6ga supply wires THHN T90 running 47ft. The Heat pump has a 50amp GFCI breaker and the pool pump has a 20Amp GFCI breaker at the subpanel. The pool lights have a separate 15Amp breaker at the main panel.

At the main panel I had removed the old pool pump 20Amp 240 breaker and replace it with a 70Amp 240V breaker connected to the new 6ga wires.

I measured voltage drop at the subpanel before and after the heat pump turned on. During startup for an instant it dropped from 248V to 233V then settled at 246V after 1 sec with Heat Pump Running.

The problem is the lights in the house flicker when the heat pump turns on which is annoying as it maintains temp.

Could this be it:
I noticed on the main panel all the big 240V breakers are at the top of the panel nearest the feed point. The sub panel breaker is at the very bottom of the panel. Therefore, The house light breakers are in between the sub panel breaker and the main feed point.

I have two AC units in this 2 story house and I believe the units are a bigger load than the heat pump. The AC units don't make the lights flicker but their breakers are at the very top.

Thanks, Glenn
 
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Old 10-04-07, 09:40 AM
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It's not the position of the breakers.

It could be a lot of different things. And it could be that there's nothing you can do about it. But you might as well check the easy stuff. Make sure all the connections you made are tight. Ask your power company to make sure all their connections are tight. Make sure the breaker you used is the correct one, and that you didn't try to substitute some "close match". After you do these simple things, you can probably rest assured that the problem is merely annoying, and not really dangerous. This might help you (and your family) adjust better to the annoyance.

It might also be that the power company equipment or lines are too small to serve the now-increased load on your house. You could call your power company to discuss it. Most likely they will tell you that nothing can be done, but maybe, just maybe, they'll put you on the list for some future upgrade, or bump your neighborhood up a bit on their scheduled replacement plan.
 
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Old 10-04-07, 11:28 AM
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John,
Thanks for the quick response. Yeah, when they flicker I really worry about safety.

The main 70A Breaker is a new Seimens to match the Seimens main panel and it is a QP Type like all the other ones present and what the panel door recommends. I also made sure it was rated to 75C termination.

The Heat Pump 50A GFCI GE breaker came with the GE pool/spa Sub Panel.

I was hoping the voltage drop results at the subpanel input , before and after the heat pump running would help to characterize the quality of my new breakers and connections?

Is there any Electrician diagnosis measurement method that would help isolate the cause of the flicker; for instance voltage drop measurements elsewhere during loads and no loads?

Can you just keep taking voltage measurements at points closer and closer to the power meter until the voltage drops stop happening?
They may never stop and therefore as you said call the power company.

Thanks,

Glenn
 
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Old 10-04-07, 12:37 PM
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Is there any Electrician diagnosis measurement method that would help isolate the cause of the flicker; for instance voltage drop measurements elsewhere during loads and no loads?
Your steady-state readings are in the normal range. What you are likely missing is the voltage drop during start-up of the compressor motor. Only expensive meters with millisecond resolution can capture this brief period.

They may never stop and therefore as you said call the power company.
True, this problem may be persistent as it seems to be a normal side effect. One possible remedy is to see if you can get a "hard start kit" for the heat pump. This kit usually includes a bigger start capacitor and a delay switch for the fan motor which will help to reduce the startup current of the heat pump.
 
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Old 10-04-07, 01:02 PM
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Ben,

To clarify, the flicker is only for the instant that the compressor starts for maybe 1/2sec then brightness returns to normal no flicker while the compressor continues to run.

This may seem crude.
But since an incandescent light is the indicator, maybe I should just wire one across each leg of the main panel input feed to see if the flicker is present there when the compressor comes on?

Do you have a compressor startup kit that you would recommend?

I might have access to one of the expensive multimeters at work if you had a model number?

Thanks, Glenn
 
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Old 10-04-07, 01:17 PM
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Originally Posted by Glenn111 View Post
To clarify, the flicker is only for the instant that the compressor starts for maybe 1/2sec then brightness returns to normal no flicker while the compressor continues to run.
This is a normal side-effect. The only time you will see an unsafe situation is when the lights dim and stay low, flicker while the unit is running, or get brighter than normal.

maybe I should just wire one across each leg of the main panel input feed to see if the flicker is present there when the compressor comes on?
You already know that there's voltage drop at the main panel because lights in the house (which are fed from the main panel) dim.

Do you have a compressor startup kit that you would recommend?
It has to match the make and model of the heat pump. Contact the supply house or manufacturer to get a part number or recommended substitution from their engineer.

I might have access to one of the expensive multimeters at work if you had a model number?
The dimming of the lights is enough of a measurement in this case as the voltage drop is a cosmetic problem. The hard start kit may alleviate the problem or the power company may upsize the drop to your house or the transformer. With two A/Cs plus a heat pump, they ought to recognize you're a customer worth keeping happy! :-)
 
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Old 10-04-07, 02:16 PM
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Ben,

The 2 AC's are actually cheaper to operate than my last house with one big AC.

Thanks, Glenn
 
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Old 10-04-07, 04:14 PM
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I am somewhat concerned about a 70amp breaker on #6 wire. #6 is rated for 50amp breaker. I would have used #2. Also you said the run was 47 feet. Is that one way or out and back? You need to use the two measurement to cal. voltage drop. Too small of wire size can also contribute to dimming lights. Is the run in conduit? Also have to be aware of heating.
 
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Old 10-05-07, 08:56 AM
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Here is the logic behind the choice of breaker verses wire, please review for correctness.

The wire is 6ga THHN T90C single cables in conduit, 2 blk 6ga, 1 grn 8ga, 1 wht 6ga.
All breaker terminations and panels are rated to 60C/75C.

The 47ft is the distance from the main panel to the subpanel one way.

The voltage was measured across the subpanel line 1 and line 2 feed terminals which are at the end of the 47ft.

It was my understanding that for THHN T90C single wire the NEC rating is 55Amp @ 60C and [email protected] So since all my terminations are 75C terminations the wire ampacity is 65Amp?

Also the NEC allows you to round up for the breaker, which makes it 70Amp?
Please Confirm this logic.

FYI, while the heat pump was running I felt the wire and it was cold.

My safety concern would be with a hard compressor failure the 70Amp would be reach but the terminations could handle the temp till the breaker trips?

The affected light circuits are tapped off the main panel rails physically before the 70Amp breaker and the resistive 47ft run.

Since voltage drop is after a resistive path, that is why I was focusing on the physical location of the breaker on the main panel rails i.e. the rails were resistive enough for that initial startup current level to drop the voltage to the light circuits.

Maybe I'll just get a 60Amp breaker to see if will work with the heat pump and pool pump.
 
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Old 10-05-07, 09:04 AM
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Originally Posted by Glenn111 View Post
Please Confirm this logic.
Your feeder breaker is sized correctly.

My safety concern would be with a hard compressor failure the 70Amp would be reach but the terminations could handle the temp till the breaker trips?
The motor has built-in thermal cutoff which trips in the event of a rotor lock. For motors, the breaker only provides short-circuit protection, the thermal cutoff provides over-current protection.

Maybe I'll just get a 60Amp breaker to see if will work with the heat pump and pool pump.
I really don't think that's necessary, but you can if you want to.
 
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Old 10-05-07, 09:10 AM
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Thank you

Glenn
 
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