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#14921 - 10/03/02 09:03 PM a/c load lights dimming  
Electricmanscott  Offline
Joined: Jan 2002
Posts: 1,457
Holden, MA USA
Checked out a central air installation today. Two big condenser units 50 amp circuit each. House has new 200 amp service feeding two 100 amp panels. (two family) When either compressor kicks on the lights dim considerably. What is the best way to address this. Initial thoughts point me to power company issue. Anyone?

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#14922 - 10/03/02 09:15 PM Re: a/c load lights dimming  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,853
Brick, NJ USA
Did the poco change/upgrade the drop from the pole?? Did/is the poco "upgrading" the transformer??
Are all the connections good??? (neutral too)
If the HVAC units are in fact 50 amps each, that is 50% of the 100 amp feed to each unit, correct? Did the installer of the new service do the proper calcs to make sure it's sized right???
Lastly, ask the HVAC guy about a "hard start" kit (capacitors), I used that a few times to "reduce the dimming/dip"


#14923 - 10/04/02 12:37 AM Re: a/c load lights dimming  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Figuring that one Compressor Motor will draw at least 240 Amperes >2 Seconds while starting, there will be a considerable sag in Voltage on this system - especially with small Service Feeders and / or a Transformer which is highly loaded and / or small in KVA size [15-25 KVA].

With Incandescent Lamps, Your Eyes will drammatically notice varying Light Output due to Voltage Sags - even with a drop of 10 VAC, so that's one thing to consider.

I would say the best way to address this is to explain the phenomena to the Client, and leave it up to them [as to simply deal with the dimming or to begin some changes].

Changing to Fluorescent Lamps will reduce the amount of dimming, but not remove the underlying problem of Voltage Sags from the Compressor Motors' high LRA (Locked Rotor Amperage).

This could become a rather intense project!

Scott S.E.T.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#14924 - 10/04/02 12:46 AM Re: a/c load lights dimming  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
P.S. The issue of Flicker Factor could be brought up here!

There's a Thread on ECN which briefly covers this and includes a link to an IEEE document about Flicker Factor.

The last Residential Service Design I did which was around April, 2000 - new 400 amp 1 phase service as part of a Remodel / Addition - after meeting with SCE's Design EE, She gave me their design plan and it included Flicker Factor (4.6% with 2 50 amp 240 VAC HVAC units driven by a 12KV x 120/240 VAC 1 ph 3 wire 25 KVA 2.0%Z Transformer, Service Feeders = 4/0 AL).

Scott S.E.T.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#14925 - 10/04/02 02:59 AM Re: a/c load lights dimming  
Sean WB  Offline
Joined: Sep 2002
Posts: 111
South TX
Had the same problem at a house I was called to. Homeowner did a new 200A service upgrade(himself) . There was a dimming problem when condensor kicked on. Added a hard-start kit, didnt help. I went on with the job at hand, and was not asked to resolve this issue.
I have noticed a trend lately with the poco's. On the last three service upgrades I did, they just kernied up to same wire from xmfr , without upgrading "THEIR" end.
Old, ate up wires and all. I brought to the attention to the last two guys that did a reconnect for me that the two houses were fed parallel from one transformer. neighbor just had a new 200A service done too! he said "hmm......we may need to upgrade our wire one of these days" Im like, no S^%$@#!
They are feeding both houses with #2 or #3 that is at least 20 years old.
Anywho, Im sure that could be a start to resolving the issue.

I did not get as think so badly as you shocked I did.

#14926 - 10/04/02 08:44 AM Re: a/c load lights dimming  
jlhmaint  Offline
Joined: May 2002
Posts: 202
Fredericktown, OH, U.S.A
i just called my power company yesterday to ask what they would charge me if i wanted to upgrade my 100amp box to a 200amp. told them i would installe the box and make connections. this is what they said, we will come out and put up a new meter box for free but would charge me to connect to the breaker box. They never mentioned anything about changing anything other than the meter box, no wiring from the pole. and my house was built in 1965.

#14927 - 10/04/02 09:39 AM Re: a/c load lights dimming  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,853
Brick, NJ USA
Since we are talking about the poco's:
July 3, 2002, the area is in the grasp of a heat wave. Power at my house goes off, along with ten (10) other houses. I call the poco at 8:00PM, the service rep states "service will be restored by 6:10AM" (Jult 4th). I hear the truck at 6:00AM, & go out to talk to the crew. The OL on the xfr was tripped. They reset it, and said "if it held all day yesterday, you should be ok". They also said it was a 25KVA pot. Well it tripped at 8:45AM. A few more calls by me & the neighbors, they came back & reset it again. It lasted 25min. Calling again, we were assured it will be corrected. They came back at 4:00PM July 4th & put in a 50 KVA pot.
So far, so good.
Point is, 11 houses, ranging from 3BR ranches, to 5BR haciendas on 1 pot?? It may have worked when all the houses were "small, no one had CA, pools, & were primarily "summer homes"; but now, year round, fully loaded homes. Go Figure

PS: It's a waterfront neighborhood (lagoons) at the Jersey Shore. I'm not bashing the line crews, they work/worked there butts off, but the engineering dept of GPU/JCP&L leaves a lot to be desired.



#14928 - 10/05/02 07:47 PM Re: a/c load lights dimming  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Utilities typically publish their acceptable voltage range in a PUC-mandated "service conditions” agreement, but each seems to have their own interpretation of "temporary excursions" beyond that range.

Also remember that their quoted numbers are "at the meter" and may not be the case for a building feeder or branch-circuit end.

[This message has been edited by Bjarney (edited 10-05-2002).]

#14929 - 10/27/02 06:47 PM Re: a/c load lights dimming  
gary long  Offline
Joined: Feb 2001
Posts: 32
sounds like the neut needs torked down tight. al has no memory like cu. so it may be loose. or they downsized the nuet.. ???

#14930 - 10/27/02 10:10 PM Re: a/c load lights dimming  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
How does the neutral enter into a voltage sag caused by a large 240 volt line to line load?


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