Dimming Lights From Large Geothermal Heat Pump - Electrical - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 01-03-2011, 11:41 PM   #1
Member
 
Join Date: Jan 2011
Posts: 43
Rewards Points: 25
Default

dimming lights from large geothermal heat pump


Having some light dimming for a second or two (60% of full brightness) when a large geothermal heat pump kicks in (70A max in rush over 4 Cu cable).

I had the utilities monitor my voltage over the past several days and they see drops in voltage of up to 3-5V for a second or two and tell me its with in their legal requirements (even if it is just barely). No phase imbalance detected. Doesnt appear to be loose connections, burns, or over heated breakers either. Though was standing there as it kicked in and may have heard a pop.

Its a 400A service on 4/0 AL cable coming into a single meter and then split from there into two 200A panels with direct connection to the meter with 4/0 AL hots but a smaller gauge neutral cable... maybe 2/0 AL but cant get a good look at it.


So sort of running out of things to check here... I'm wondering there could be an issue with a split 2 panel setup causing issues over a single 400A panel.

Could the smaller neutral be causing some resistance to large in rush currents?

There are a couple visible nails that came in through the exterior siding that dented or puched out one of the knockouts. Nothing visible close to any of the cables but havent pulled the breakers to look underneath.

Advertisement

atuel is offline   Reply With Quote
Old 01-04-2011, 07:11 AM   #2
Newbie
 
Join Date: Dec 2010
Posts: 13
Rewards Points: 10
Default

dimming lights from large geothermal heat pump


Usually any motor will briefly dim lights due to the inrush current to bring motor up to speed. My 1 HP sump pump dims mine for a split second. It sounds like your heat pump has a pretty good sized motor. Sounds right if only dimming lights for a second. Did u say u have 4/0 AL feeding meter? If so that is only good for 200A unless they paralled two 4/0's on each leg.

Advertisement


Last edited by Rob's Electric; 01-04-2011 at 07:15 AM.
Rob's Electric is offline   Reply With Quote
Old 01-04-2011, 08:00 AM   #3
Member
 
Join Date: Nov 2007
Location: Nashua, NH, USA
Posts: 6,976
Rewards Points: 2,048
Default

dimming lights from large geothermal heat pump


The voltage drop could have occurred all the way back inside the pole transformer.

If you measure the voltage at various locations such as at the receptacle or junction box where the pump is wired in, at the breaker terminals for the pump circuit, also at the big lugs for the service coming in, you can get an idea of whether the drop is happening in the branch circuit wiring or in the service wires.

You probably won't be able to measure voltage at the meter box or further upstream.
__________________
Forget super sized fries. The Washington Redskins could promote healthy eating with First Lady Obama by choosing a (red skinned) turnip for a mascot.
AllanJ is offline   Reply With Quote
Old 01-04-2011, 09:24 AM   #4
Member
 
Join Date: Jan 2011
Posts: 43
Rewards Points: 25
Default

dimming lights from large geothermal heat pump


Quote:
Originally Posted by Rob's Electric View Post
Usually any motor will briefly dim lights due to the inrush current to bring motor up to speed. My 1 HP sump pump dims mine for a split second. It sounds like your heat pump has a pretty good sized motor. Sounds right if only dimming lights for a second. Did u say u have 4/0 AL feeding meter? If so that is only good for 200A unless they paralled two 4/0's on each leg.
All I know for sure is its 4/0 AL coming into my panels with a 2/0 neutral. I wasnt actually there when they opened up the meter box to install the monitor, so I'm just going off what they were telling me that its a 400A service with just my neighbor and I served off the one platform transformer. I thought they said its 4/0 feeding the meter, but I'll have to double check with them.

Should the neutral be undersized like this?
atuel is offline   Reply With Quote
Old 01-04-2011, 11:43 AM   #5
Newbie
 
Join Date: Dec 2010
Posts: 13
Rewards Points: 10
Default

dimming lights from large geothermal heat pump


Yes. Normal SE cable for 200A is 4/0, 4/0, 2/0. They sell it where neutral is 4/0 also. Everyone in our area uses the derated neutral for residential.
Rob's Electric is offline   Reply With Quote
Old 01-04-2011, 11:48 AM   #6
Electrical Contractor
 
jbfan's Avatar
 
Join Date: Jun 2004
Location: Newnan GA
Posts: 5,964
Rewards Points: 2,324
Default

dimming lights from large geothermal heat pump


If this wire belongs to the poco, then it may be sized right.
If you had to supply the wire to the meter, than that wire is undersized for 400 amps.
The neutral is allowed to be undersized based on load calculations.
__________________
Yes I am a Pirate, 200 years too late. "Jimmy Buffett"
jbfan is offline   Reply With Quote
Old 01-04-2011, 12:01 PM   #7
Master Electrician
 
Join Date: Mar 2010
Location: Indiana
Posts: 2,978
Rewards Points: 2,212
Default

dimming lights from large geothermal heat pump


The geothermal units I am familiar with operate on 240 volts. There is no neutral used.
brric is online now   Reply With Quote
Old 01-04-2011, 12:19 PM   #8
Member
 
Join Date: Jan 2011
Posts: 43
Rewards Points: 25
Default

dimming lights from large geothermal heat pump


Just called the utilities (medium sized town co-op) back and they confirmed its 4/0 triplex direct burial cable not paralleled (with a 2/0 neutral) from transformer to a platform that services both my neighbor and I. Neighbor has 1/0 service lines and I have 4/0 with 2/0 neutral. Its all underground including the feed to the transformer. No above ground cables.

The utility engineer is indicating the 4/0 cable is rated at 386A. Does that sound right? Found some manufacturers that rate at over 300, but not that high and thats at 90C.


So correct me if I'm wrong here, but seems my neighbor and I are sharing and even at 386A it would seem easy to get close to maxing that out. They measured I was drawing 20-30A just with my normal tv, lights, etc non-major appliances running. I could easily run washer/dryer, water heater, stove, and dishwasher as I often do and easily be eating up 100-150A before my geothermal kicks on. The inrush would put that up over 200A fairly easily for an instant. And thats before we factor in my neighbor is sharing off the same 4/0 feed to the platform. Seems undersized to me if I keep any sort of concurrency to my activities when its cold outside.
atuel is offline   Reply With Quote
Old 01-04-2011, 12:27 PM   #9
Newbie
 
Join Date: Dec 2010
Posts: 13
Rewards Points: 10
Default

dimming lights from large geothermal heat pump


Doesnt sound right unless its 4/0 copper or I'm missing something. Overhead they run much smaller because of the free air rule. When I run underground feeders they are sized according to amperage of service.
Rob's Electric is offline   Reply With Quote
Old 01-04-2011, 12:55 PM   #10
Master Electrician
 
Join Date: Mar 2010
Location: Indiana
Posts: 2,978
Rewards Points: 2,212
Default

dimming lights from large geothermal heat pump


Utility distribution systems are not governed by the NEC.
brric is online now   Reply With Quote
The Following User Says Thank You to brric For This Useful Post:
Speedy Petey (01-04-2011)
Old 01-04-2011, 01:15 PM   #11
Member
 
Join Date: Jan 2011
Posts: 43
Rewards Points: 25
Default

dimming lights from large geothermal heat pump


Quote:
Originally Posted by brric View Post
Utility distribution systems are not governed by the NEC.

Yes, but it just seems unlikely that NEC would place a nearly 2X overhead on de-rating the 4/0 AL cable. A 386A rating for utility runs seems high when NEC (even if it doesnt apply) would only rate it at around 200A.

So really, trying to find out if 4/0 is enough to supply (2) 200A panels where they are actually in use vs just needing extra breaker capacity for seldom used circuits.

And if so, is it enough to feed the dual 200A panels and my neighbor?
atuel is offline   Reply With Quote
Old 01-04-2011, 01:30 PM   #12
Master Electrician
 
Join Date: Mar 2010
Location: Indiana
Posts: 2,978
Rewards Points: 2,212
Default

dimming lights from large geothermal heat pump


NEC ratings do not apply. Nothing you have said indicates an abnormal problem. With a heavy load staring as you have I would EXPECT a momentary dimming of lights.
brric is online now   Reply With Quote
The Following User Says Thank You to brric For This Useful Post:
Speedy Petey (01-04-2011)
Old 01-04-2011, 02:17 PM   #13
Newbie
 
Join Date: Dec 2010
Posts: 13
Rewards Points: 10
Default

dimming lights from large geothermal heat pump


I agree with brric. Power company not regulated by NEC. Your slight dimming problem is normal. If poco lines do ever fry its their responsibility to replace them. Good luck.
Rob's Electric is offline   Reply With Quote
Old 01-04-2011, 02:35 PM   #14
Member
 
Join Date: Jan 2011
Posts: 43
Rewards Points: 25
Default

dimming lights from large geothermal heat pump


Going dim to 60% brightness for a couple seconds isnt normal I dont believe. I'm also having a higher failure of equipment (DLP bulb and light engine, wireless router, cable modem all going at different times) now than before. I dont believe any of this is normal. Never had anything like this at other houses.
atuel is offline   Reply With Quote
Old 01-04-2011, 02:53 PM   #15
Newbie
 
Join Date: Dec 2010
Posts: 13
Rewards Points: 10
Default

dimming lights from large geothermal heat pump


Power company could have a problem on their end. I would call them again or have a licensed electrician check your service.

Advertisement

Rob's Electric is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
VisionPRO Setup Functions & Heat Pump infoskr HVAC 42 11-16-2014 06:30 PM
Heat pump vs. Radiators - Opinions/Recommendations rflail HVAC 7 11-10-2010 10:56 PM
Help with Heat Pump System Wiring AlanScott HVAC 11 10-10-2010 01:19 PM
heat pump question David from MD HVAC 3 02-01-2010 09:42 PM
Heat Pump Woes Zenica HVAC 50 01-27-2009 08:37 AM




Top of Page | View New Posts