Lights dim when compressor kicks on

[RoadBeater]

I have pole barn 150' from my house. I ran #2 AL cable out to it. I have noticed that when my compressor kicks on, the incadescent lights will slightly dim upon startup. The compressor is 220V 15 amp. This has always bugged me. I did put a used (flame away) 100 amp Square D QO box in the barn when I ran the electric. I have never blown the main breaker, and have run my 50 am buzz box without issue at full power. Is this just a function of voltage drop on the AL wire?

Thanks for any advice.

 

[pragmatist]

Sometimes just another ground will take care of things. I sunk one out near my subbox and now my lights don't flicker

 

[Torque1st]

You need to install a batacitor on the barn panel.

 

[BoydS]

Sounds like a voltage drop (VD) issue to me. The start up current on motors can be up to 3 times running amps. With not knowing what loads other than lights you have contributing to the total load, it would be difficult to determine the total volts dropped. The installation of the Al feeder would also be required for to determine the VD (ie is it direct buried, in conduit, etc). Typical max design for VD is 5 percent.

 

[Aceman]

Switch to flourescent lighting...

 

[nate379]

Sounds normal unless you are talking about dimming down to where it gets dark in the building!

 

[Gooch]

Sounds like a voltage drop (VD) issue to me. The start up current on motors can be up to 3 times running amps. With not knowing what loads other than lights you have contributing to the total load, it would be difficult to determine the total volts dropped. The installation of the Al feeder would also be required for to determine the VD (ie is it direct buried, in conduit, etc). Typical max design for VD is 5 percent.

NEC only allows 3% between any two points but not more than 5% from the service entry to the farthest point of use.

 

[RoadBeater]

Thanks for the responses. I have a couple of T8's to hang out there when I get a chance, but mainly it's used for storage, so it's not as big of a deal. I do have 13 100 Watt bulbs, so it's reasonably lit, but not efficient. It's also not insulated, so for the most part the garage on the house is where I do most my work. I did put a separate ground rod out in the building, so that should also be decent. The dimming isn't the worst, it's not noticable to some, but it has always bugged me, and mainly trying to figure out if it's something I should be doing something about. So it really sounds like I am over analyzing it, (like normal..)

 

[Charles (in GA)]

Not unusual to see lights dim when a large load kicks in. My house lights dim when the A/C kicks on, and this is a 200 amp service.

Get rid of the 100 watt bulbs. If you use them much, they are eating you up money wise. Get some CF lights.

Charles

 

[jvitez]

Perfectly normal to dim for a few seconds. We have 400 amp service, 2x200 amp panels, and even our lights dim momentary when one of the heat pumps kick on. It's the 3x starting amperage reality of a motor load. If you're not in the dark and it's not tripping breakers, nothing is wrong. About the only "cure" I could think of is to get 400 amp service or something insane, where the brief 3x motor load amperage is still well below the maximum. Not a practical suggestion, mind you.....

 

[Aceman]

NEC only allows 3% between any two points but not more than 5% from the service entry to the farthest point of use.

That's a fine print note and not enforceable. The NEC only recommends to size wire to account for voltage drop.

 

[bradleys]

The seriousnes of dimming also depends on how your pole transformer is connected.

At my place in Port McNeill, I shared a transformer with my neighbor. When I built my garage, the power company specificially mentioned that any large loads might cause dimming. If there was a complaint from the neighbor, I would be moved to a new transformer, at my expense.

In Blaine, I have my own transformer. The power company said that it was up to me to decide if large loads were dimming my lights too much. If I don't care, neither do they.

 

[Falcon67]

Not really much of a problem, I solved mine when I went from a 110V 1.5 HP compressor to a 3.2HP 220V unit and replaced the bitty breaker box with a better unit with more circuits.

Now if you flush the toilet and the lights dim, THATs a problem... House was like that before I rewired it.

 

[nate379]

You must have a decent sized shop/equipment to need 400 amp service?

Perfectly normal to dim for a few seconds. We have 400 amp service, 2x200 amp panels, and even our lights dim momentary when one of the heat pumps kick on. It's the 3x starting amperage reality of a motor load. If you're not in the dark and it's not tripping breakers, nothing is wrong. About the only "cure" I could think of is to get 400 amp service or something insane, where the brief 3x motor load amperage is still well below the maximum. Not a practical suggestion, mind you.....

 

[Brandon_K]

I have a feeling jvitez is referring to his house heater, aka geothermal heat pump (not a boiler or gas/elec forced air system)

 

[jvitez]

You must have a decent sized shop/equipment to need 400 amp service?

I have a feeling jvitez is referring to his house heater, aka geothermal heat pump (not a boiler or gas/elec forced air system)

Correct, my house not shop. Sorry for the confusion. I could have gotten away with 200 amp service, but I knew I eventually wanted extra power for my attached garage and an eventual detached garage, so I spec'd 400 amp service. Each geothermal heat pump is ~7KW running, and it's a motor load, so initial start up amperage is much higher, IIRC 3x steady amperage, or is it 6 times? Someone give me the correct number please. Now both geothermal heat pumps are on one 200 amp panel, but the house lighting in on the second panel. The electrical contractor said it was cheaper to do it this way than an actual 400 amp panelboard. So it's just a matter of physics, nothing to worry about.

 

[Brandon_K]

Motor startup loads vary depending on 1ph or 3ph, capacitor start or non, etc etc. Generally you'll see 3x at a minimum, though I've seen 8-10x as well.

Yes, 400A gear is stupid expensive. Last year we installed a true 1ph 400A service installed at our haunted house (we kept popping the 2-100A services that fed us, wore our numerous breakers). Between the main panel alone and the single 400A breaker we had $1600 in it. If memory serves the panel was $7xx and the breaker was $9xx. Off the can it goes underground, up to the exterior of the building to the panel, into the breaker at which point it goes through the wall into the other panel which is actually the main distribution panel to the other 7 sub panels. Thankfully we aren't metered, because I've yet to find continuous rated 400A meter socket, they're all 320/400 or 400 split over 2-200A sockets, which is what I assume you have. I'm guessing you have a pair of 500mcm's coming off the pole into a double meter socket which splits off to the 200A main panels. 400A single phase certainly isn't common.