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Old 01-06-2009, 01:17 PM   #31
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Panel Replacement/Upgrade 400 Amp


That transformer is dedicated to my house alone. I live out in the country, no other houses are on it. Peak draw on the compressor IIRC is about 30 amps at startup.

I am going to check, its possible the gauge of the wire that feeds the heat pump now is not really large enough for the run, and may be contributing to the problem. It is approximately a 80' run from the panel to the heat pump.

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Old 01-06-2009, 01:25 PM   #32
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Panel Replacement/Upgrade 400 Amp


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Originally Posted by AndrewF View Post
That transformer is dedicated to my house alone. I live out in the country, no other houses are on it. Peak draw on the compressor IIRC is about 30 amps at startup.

I am going to check, its possible the gauge of the wire that feeds the heat pump now is not really large enough for the run, and may be contributing to the problem. It is approximately a 80' run from the panel to the heat pump.

Might be 10 awg. You could bump it up to 8 if you like, but probably wont make a difference.
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Old 01-06-2009, 03:07 PM   #33
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Panel Replacement/Upgrade 400 Amp


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That transformer is dedicated to my house alone. I live out in the country, no other houses are on it. Peak draw on the compressor IIRC is about 30 amps at startup.
Motors can draw up to around 6 times there name plate rating in inrush current (at startup).
A plain old 15A miter saw can draw around 90A of inrush.
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Old 01-06-2009, 07:20 PM   #34
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Panel Replacement/Upgrade 400 Amp


My clamp on meter registered a peak surge of 134 amps at startup....running amps varies between 13-16 amps.

The cable is 6/2. ....which probably explains the sudden voltage drop for that length of wire and peak draw.

I think I will upgrade that cable and run it off of the 100 amp sub-panel I installed in the basement. I used #2 copper for that panel with a total run of around 60'. That would result in the run from the outdoor unit to the panel around 25'.
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Old 01-06-2009, 07:24 PM   #35
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Panel Replacement/Upgrade 400 Amp


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My clamp on meter registered a peak surge of 134 amps at startup....running amps varies between 13-16 amps.

The cable is 6/2. ....which probably explains the sudden voltage drop.
What clamp meter do you have? Is it a RMS clamp meter rated to capture inrush current? I've been looking at getting one of the fluke RMS meters with inrush capture so I can see exactly what is happening on start ups of motor loads.

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Old 01-06-2009, 07:30 PM   #36
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Panel Replacement/Upgrade 400 Amp


Andrew,

You may find this link intresting.

http://www.mikeholt.com/technical.ph...lity%20Article

At the bottom Mike Holt (very well respected in the industry) makes some comments about the situation such as:

"The light flicker is caused by excessive instantaneous voltage drop when the large high-efficiency scroll compressor started with an instantaneous inrush current of 240 amperes. By installing a hard-start, the flicker duration was shortened, but not removed. When the heat pump was connected to the service, the voltage drop to Panel A was reduced, but the lights in the house still flickered, just not as much."

He also states:

"Iím not moving the utility transformer closer to my house, I donít mind the lights flickering when the heat pump starts, and most importantly my wife doesnít care at all. She though thatís the way itís suppose to be (or maybe I told her that)."

If you read that article, along with other stuff on the site Mike Holt has written, I think you will see what I was getting at when I was talking about have your meter / disconnect close to the transformer and having a separate run to very loads like the heat pump that have high inrush draw.

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Old 01-06-2009, 10:38 PM   #37
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Panel Replacement/Upgrade 400 Amp


Quote:
Originally Posted by AndrewF View Post
My clamp on meter registered a peak surge of 134 amps at startup....running amps varies between 13-16 amps.

The cable is 6/2. ....which probably explains the sudden voltage drop for that length of wire and peak draw.

I think I will upgrade that cable and run it off of the 100 amp sub-panel I installed in the basement. I used #2 copper for that panel with a total run of around 60'. That would result in the run from the outdoor unit to the panel around 25'.
If you have 6/2 feeding the ac unit, you have done all you can do to try to prevent voltage drop.
Anything larger than that most likely will not fit the breaker, and the cost will shock you.

I would use the hard start kit.
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Old 01-07-2009, 08:01 AM   #38
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Panel Replacement/Upgrade 400 Amp


6 awg? Did cerrowire and southwire tell you what size wire to use?
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Old 01-07-2009, 04:25 PM   #39
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Panel Replacement/Upgrade 400 Amp


It was already there and the HVAC guy helping me said it was fine since the run load was only 15 amps. I suspected at the time it might be too small, but the breaker never tripped, so I let it go as I had other pressing projects to address.

I am going to proceed down the path and obtain a hard-start for my unit.
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Old 01-07-2009, 04:37 PM   #40
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Panel Replacement/Upgrade 400 Amp


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Originally Posted by AndrewF View Post
It was already there and the HVAC guy helping me said it was fine since the run load was only 15 amps. I suspected at the time it might be too small, but the breaker never tripped, so I let it go as I had other pressing projects to address.

I am going to proceed down the path and obtain a hard-start for my unit.
# 6 wire is not too small, it is the other way around. That is a heafty wire to have a 15 amp load on it, not that there is anything wrong with usine the larger wire. You do not need to consider using a larger wire for the ac!
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Old 01-07-2009, 04:41 PM   #41
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Panel Replacement/Upgrade 400 Amp


Quote:
Originally Posted by AndrewF View Post
It was already there and the HVAC guy helping me said it was fine since the run load was only 15 amps. I suspected at the time it might be too small, but the breaker never tripped, so I let it go as I had other pressing projects to address.

I am going to proceed down the path and obtain a hard-start for my unit.
If the unit had a nameplate of MAX. breaker 20 amps, I would have used #14 AWG myself. but thats just crazy talk.
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Old 01-07-2009, 11:21 PM   #42
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Panel Replacement/Upgrade 400 Amp


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# 6 wire is not too small, it is the other way around. That is a heafty wire to have a 15 amp load on it, not that there is anything wrong with usine the larger wire. You do not need to consider using a larger wire for the ac!
Really?

IIRC, the manufacture states it should be connected to a 50 amp disconnect by the HP.
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Old 01-07-2009, 11:47 PM   #43
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Really?

IIRC, the manufacture states it should be connected to a 50 amp disconnect by the HP.
Always go by the nameplate, then if you feel voltage drop is a concern then increase the wire size.

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