HVAC heat pump and electrical question

[west_seth]

6 YO house, 2 panels 1=200 amp 1-100 amp, copper wiring.
Two heat pumps for the two story house. These are also 6yo.
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I noticed when the heat pump(s) kick on the lights dim just a bit or maybe the word is flicker.

Is this symptomatic of a bigger issue?

Should I be concerned?

Yeah and I just bought the house and no the home inspector did not check any of this stuff out.

[docholiday]

How good is the ground? (I mean the actual earth ground).

[west_seth]

I looked at the ground outside of the house and it is a very large copper wire, without insulation, but I can not see the actual ground rod. It was hammered into the good old Georgia clay.

Doc, if you think it is the ground rod I can easily put in a new one.

[docholiday]

If you got one, try it. (paralell it, dont replace the old one).

[west_seth]

Is it okay two have two parallel ground rods (side by side) and is it okay to just run a wire between the two???

[smadave]

http://www.electrical-contractor-net...ml/001768.html


Dave in NJ

[bornriding]

Two heat pumps are overloading a 200 amp service - probably small wire going to Outdoor unit - either way, compressor locked rotor is causing a reduction in supply voltage from the rest of the panel, causing flickering lights ( not a ground problem )

Hope this helps,
Richard

[cem-bsee]

second grounding rod should be at least 5ft from first. yes, having a single bare wire between the two is acceptable.

I would have at least a 4awg copper wire connecting the panels to the grounding rods, said rod to be at least 0.75 inch od & 10 ft long -- because of 300 amps of service. BUT, the actual size to be determined by adding up the cross section of the service wires to BOTH panels! see NEC250-____ [250-66 in 1999 NEC = last one I bought]. these are the wires which connect to the panels, not those connecting to the power company.

before I would recommend changing the wire size, I would study the problem = measuring voltage when all loads are in use = hot water heaters, cooking units, both HVAC, computers, entertainment centers, etc. measure at both panels & at HVAC compressors at the SAME INSTANT.

also, is the wiring to the compressors per mfgr recommendations, using 60C ampacity rating for the wire?

[air2spare]

and if so, did they have hard start kits installed?

[suemarkp]

I don't see how the grounding system is going to ahve any effect on light flickering. Ground rods are a crappy ground, and for that reason code says a #6 copper is the largest you have to run to them, even if you have a huge 1000 amps service.

The flicker is caused by voltage drop when the compressor starts up from a dead stop. Depending on how bad and how long it lasts, you may or may not have a problem. No matter what you do, you're always going to have some light flicker. All you can do to assess the situation is to put a meter on the panel and read the voltage when the largest HP kicks in. If the 240V drop is less than 10 volts for less than a second, I don't think you have a problem to fix. Checking each 120V leg separately would be a good idea too to make sure each wire is dropping the same amount. If they are different, one side could have a bad connection.

The following can reduce the problem:
* Make sure you have the HP branch circuit conductors sized large if this run is long (50' or more). Use the 60C sizing column for short runs, increase one size if 25' or more, and increase by two sizes if the run is 100' or more.
* Assess the wires feeding your house from the utility company. Many times, these are rather small and the longer they are the worse it is. I'd hope for at least 1/0 aluminum on a run less than 100 feet.
* how heavily loaded is your transformer? Is it just for you, or do neighbors share it. You need at least a 25 KVA transformer just for you and if you're really pushing 300 amps I'd go for a 37.5 KVA for just you. Much more if your neighbors share.

[mrssb]

Hey I agree with Mark, had a very similar situation just last month, and I had a electrical contractor check the connections at the service mast. It turned out they were loose, he tightened and the problem was much better. Just some food for thought.