voltage drop prevention

[vavet]

Just a theoretical question. I'm not going to act on this.

What would it take to keep the lights from dimming when my 5 ton heat pump compressor turns on. We have a 200 amp service for the house. I don't know what gauge wire we have running to the meter. If it was upsized, would that prevent it? Lessen it? How much?
I don't get that voltage drop when my neighbors' heat pumps turn on, so there must be a way to isolate it, right?

 

[MattT]

Are you having problems with incandescent lamps or something with electronics in it? If it's incandescents that's volt drop which is fairly easy to track down. Just need a decent DMM that'll capture the drop and check your main lugs at the service entrance. If you see the problem there call the power company. If not work your way downstream until you find the problem.

If it's lighting with electronics such as LEDs you might have a power quality issue rather than volt drop. That's something you might find with a 'scope.

Re. the neighbors are you on a shared transformer?

 

[dcg9381]

It looks like a 5 ton unit is 25A continuous and 125A start. 125A start should be "no problem" on 200A service.

I'd start by inspecting wire size to the main, voltage drop at the lugs when starting, distance from the transformer, and inspect wire size to the HVAC. Is the interior lighting on a sub-panel?

There are indications that a hard-start capacitor can help mitigate voltage drop - but it's kinda a hack.

I'd also want the voltage drop measured by starting the HVAC and looking how much power output drops at an interior outlet.

Could be as simple as a lug needing to be tightened.

 

[exranger06]

There are two things that cause voltage drop: bad/loose connections, and wire size.

Bad connections- This includes every connection from the transformer to the meter, to the main panel, to the branch wiring, all the way to the actual load.

Wire size- Thicker wires will have less voltage drop.

Whether voltage drop is caused by bad connections or wire size, in both cases, voltage drop increases with load. A wire with a bad connection may work perfectly fine under light load, but will have significant voltage drop as soon as a heavy load is put on it. Same with wire size:
I have a long extension cord that I cannot use on my small 4 gallon air compressor. If I stick my multimeter probes in the end of the cord, I have 120V. But if I plug the compressor in and turn it on, the compressor won't run and the breaker will trip. The heavy load makes the voltage drop down way too low, which pulls way too much current and makes the breaker trip. The cord works fine for lighter loads.

The only time your neighbor would cause YOUR voltage to drop is if the problem is at the transformer. Your neighbor gets his power from the transformer, through HIS service wires, to HIS meter. You get your power through YOUR service wires to YOUR meter. The only thing you have in common is the transformer. So if the problem is not at the transformer, your neighbor has no effect on your power. Your voltage drop is occurring somewhere between the transformer and the heat pump. Like I said, it could be anywhere between the transformer and meter, between the meter and main panel, panel to branch wiring, wiring to heat pump.

 

[Bert_]

Do they just dim a bit and then go back to normal? if so that's pretty normal with a large motor load. It's not going to cause any problems.

If the lights dim and stay dim when it's running then you have reason to be concerned

 

[vavet]

Like I said, this is all theoretical.
The lights inside dim briefly when the heat pump starts. It's the same in a lot of houses. It's not a big deal. But if I was obscenely rich, I'd do something about it. What would I do?
The reason I referenced the neighbors was because each house is a circuit, essentially. It's a load that is taken off of that transformer. Similarly, our neighborhood is a circuit when you look at the big power grid.

 

[wyliesdiesels]

Need more info

Does neighbor share a transformer with you or same line tap?

What is the voltage at your main service panel with the heat pump off, on and starting?

 

[wyliesdiesels]

Like I said, this is all theoretical.
The lights inside dim briefly when the heat pump starts. It's the same in a lot of houses. It's not a big deal. But if I was obscenely rich, I'd do something about it. What would I do?
The reason I referenced the neighbors was because each house is a circuit, essentially. It's a load that is taken off of that transformer. Similarly, our neighborhood is a circuit when you look at the big power grid.

You may not need to be rich at all especially if the problem is on the PoCos side of your service...

 

[mike93lx]

It looks like a 5 ton unit is 25A continuous and 125A start. 125A start should be "no problem" on 200A service.

I'd start by inspecting wire size to the main, voltage drop at the lugs when starting, distance from the transformer, and inspect wire size to the HVAC. Is the interior lighting on a sub-panel?

There are indications that a hard-start capacitor can help mitigate voltage drop - but it's kinda a hack.

I'd also want the voltage drop measured by starting the HVAC and looking how much power output drops at an interior outlet.

Could be as simple as a lug needing to be tightened.

This assumes everything is actually sized for that load.

If I called my POCO and requested a service upgrade they would change nothing, except maybe the meter. So am I oversized for my current 100a service that was installed in 1970 or would I be undersized for the "new" 200a service? I would hazard to guess the latter.

If I provided a load Calc that supported a higher demand, then they would look at upgrading a transformer and aerial.

The OP may need to provide the load Calc and have the POCO evaluate the connection

 

[American Locomotive]

There is really nothing you can do. A 5 ton heat pump is going to use around 30A, and have an LRA of 150-165A. That means 165A of current during startup. That is going to cause a few volt drop on your service. A few volts is enough to noticeably drop the output of an incandescent bulb.

Really the only solution is to upgrade to premium LED bulbs that internally regulate. Minor voltage dips don't cause them to dim.

 

[mike93lx]

There is really nothing you can do. A 5 ton heat pump is going to use around 30A, and have an LRA of 150-165A. That means 165A of current during startup. That is going to cause a few volt drop on your service. A few volts is enough to noticeably drop the output of an incandescent bulb.

Really the only solution is to upgrade to premium LED bulbs that internally regulate. Minor voltage dips don't cause them to dim.

You could put a soft start on the compressor, right? Not advocating it, just asking

 

[theoldwizard1]

What would it take to keep the lights from dimming when my 5 ton heat pump compressor turns on ?

The POCO needs to install a larger transformer !

I don't get that voltage drop when my neighbors' heat pumps turn on, so there must be a way to isolate it, right?

Probably because he is closer to the transformer.

If you are willing to fight, you actually might win (my Dad did). The POCO will try to blow you off. What you want is for them to install a monitor on your meter to record all voltage fluctuation. If they won't do it, contact your county/state public service commission and file a formal complaint.

This process will months, maybe even more than a year, but once they have the data from the voltage monitor, you have "won" !

 

[dcg9381]

If I called my POCO and requested a service upgrade they would change nothing, except maybe the meter. So am I oversized for my current 100a service that was installed in 1970 or would I be undersized for the "new" 200a service? I would hazard to guess the latter.

I think you you know the answer. There is the service from the transformer to the meter, then the service (typcially) from the meter to the home. I'd assume, if you had 100A service, that the feed to your main panel was engineered for 100A, not 200A.

Lots of options here, but a photo of inside his main might help. As would some measurements.

The POCO needs to install a larger transformer !
Probably because he is closer to the transformer.

That's possible. But it's also possible that the transformer has nothing to do with it. Need DATA!

 

[MattT]

But if I was obscenely rich, I'd do something about it. What would I do?

If I was "obscenely rich" all my hvac would be variable speed. A side effect of that is there wouldn't be a problem with compressors dimming the lights at start up.

 

[ard]

Need more info

Does neighbor share a transfor

if the problem is on the PoCos side of your service...

Ding Ding.

OP, hang a voltmeter on the mains- and see what the power does coming INTO your home when the motor turns on and lights dim.

I had a bad transformer- when a 30A 240V motor turned on, the service voltage would dip- I forget precisely what voltages did, but the poco tech stood outside with a IR gun and said 'yep, bad tap'. Changed the transformer, problem solved.

Cost me nothing.


Note- this assumes your wiring is properly sized and all that....

 

[wyliesdiesels]

I had an issue with voltage drop when the garbage disposal ran at a previous house i lived in.

The lights would dim real bad.

I hung my Fluke 87v by the magnet strap and connected it to the mains and left it there for 24hrs on min max avg mode mode and min value.

Came back the next day and voltage got down to 100v

Called PoCo troubleshooter out. He saw what i was seeing got in his bucket and checked the transformer for overheating. It was fine. Next he checked the splices on the pony pole and sure enough one of them was burning hot. Turns out it was bad. So he just added another one and it fixed the problem. No more voltage drop.

No need to be rich to fix these issues. Just some metering and phone calls.

 

[kaffine]

A few years ago I was having dinner at my brothers house and noticed the lights dimming when the AC started. It was dimming a bit more and for longer than what I would normally expect. Next morning I went over with a meter to check his AC found out the start cap was failing.

If you are obscenely rich and don't want the lights to dim when the AC starts just leave the doors open. If the AC never shuts off it wont cause the lights to dim when it starts.

 

[Innovate1]

I have a 320A service with two 200A panels (common around here) and my lights flicker very briefly when the 3.5 ton AC starts. I am the only one on the transformer so the transformer is not undersized. As others have said, a very brief, minimal flicker is pretty normal. If it lasts any longer then you could have an actual problem.

 

[Kevin54]

Most people around us had problems, then the utility company came through a few years back and upgraded. Now every house has their own transformer. But we live in a rural community neighborhood area. I do get a draw down if the air kicks on, or the furnace kicks on, but only for a second.

 

[dogdog]

They do sell those, if you are that obscenely rich... where money is no object? maybe hire a professional EE firm and design you a system out of those stabilizer/regulators ?

That is if your PoCo can't find the problem or willing to fix the problem... I think these things are common in Data Centers... not sure if they are common at home/residential stuff..

Automatic voltage stabilizers
Automatic voltage regulators

 

[theoldwizard1]

But it's also possible that the transformer has nothing to do with it. Need DATA!

I guess you did not read all of my post !

What you want is for them to install a monitor on your meter to record all voltage fluctuation. If they won't do it, contact your county/state public service commission and file a formal complaint.

This process will months, maybe even more than a year, but once they have the data from the voltage monitor, you have "won" !

 

[theoldwizard1]

A few years ago I was having dinner at my brothers house and noticed the lights dimming when the AC started.

Segue. My Dad's retirement home was a "cottage" on a lake that was converted to a year round home. The original FUSE BOX had four 15A glass fuse. That was adequate for when it was built (probably before WWII). He had upgraded the wiring including a new breaker box, but was still having problems when the water pump kicked on and all of the lights would dim.

One night, my Mom says, "Why is the refrigerator doing that ?" It was trying to start and kicking out on its internal thermal overload. After 5 or 10 times it would start ! Nothing else running except a few light bulbs.