Conductor/voltage question

[JHZR2]

Hi,

I have ran what is likely an undersize extension cord (I believe it is 14G but might be 16), to reach a dehumidifier that Ill be installing a dedicated circuit for... It is in the basement with the breaker box but the opposite side of the basement, so the run is fairly long.

I dont know what the inrush startup current is, but steady state it looks like it pulls about 6A.

My voltage was 117.6 with no load, and once this started, I was at 114.4. This was at the load.

My issue is that the length from my breaker box is about perfect... so there is whatever drop in the wiring. Is that 3.2V drop on a 6A load indicative that the wiring is too small? FYI Im seeing the same 117.6 at other outlets on other circuits, FWIW...

Im tempted to just run 12G and a 20A breaker anyway, just because I have 12G wire...

Thoughts?

 

[eljefino]

I'm also concerned about your 117 volts, should be closer to 125.

Try a different meter. I might be barking up a strange tree, but try a different one.

If this dehumidifier is going to run a lot, and run up your electric bill, for sure you should have it connected to the fattest pipe possible-- make every % of efficiency count.

 

[Steve S]

Are the plugs getting hot? Is the voltage drop with the dehumidifier running?

 

[bullwinkle]

You have a voltage drop because the extension cord is acting as a resistor and using current to create heat. Your setup will work (unless you have a 250 foot extension cord), but a permanent circuit will be easier on the electric bill and the dehumidifier.

 

[kasedian]

Switch to a 12 guage extension cord

 

[JHZR2]

Im going to switch to a 12G permanent hardwire (romex) through a GFI plug. There is no notable heat at the plug after running for hours.

I dont think Ive ever seen 125V. Ive seen 119-120 pretty consistently, and so I was surprised to see 117! Even more surprised to see 114!

Now, I was reading with a kill-a-watt meter, which isnt my Fluke 179, but is likely somewhat trustworthy... I used a second kill a watt on another plug with no load and verified that the 117 number was correct.

 

[Dan55]

A larger ext cord will help lower the voltage drop, but your fine for now. The appliance runs on 110 volt so thats not an issue also as the cord warms up you'll get more voltage drop.A dedicated circuit is a good idea.

 

[Stu_Rock]

120 V(RMS) is the spec; don't sweat 117 V.

I wouldn't worry about a 6 A load at the end of a AWG 16 extension cord. A 100 ft AWG 16 extension cord should be OK for a 10 A load. How long is this cord, anyway?

Upsize if you feel the cord get warm.

 

[XS650]

If the plug and wire aren't noticeably warm after after running for hours, then the ampacity of whatever extension cord you are using is more than adequate.

Your voltage drop is OK too, your operating voltage is close to the minimum acceptable mains voltage for a nominal 120V circuit, it could drop as low as 110V at the appliance and be OK.

That said, less voltage drop is better and it's not a good idea to use extension cords over long distances for long periods of time. Stuff happens, so your wiring should be protected.

 

[JHZR2]

Originally Posted By: Stu_Rock
120 V(RMS) is the spec; don't sweat 117 V.

I wouldn't worry about a 6 A load at the end of a AWG 16 extension cord. A 100 ft AWG 16 extension cord should be OK for a 10 A load. How long is this cord, anyway?

Upsize if you feel the cord get warm.


The total run is maybe 50ft.

Just purprised me at the drop given what I always assumed to be fairly stiff voltage in the house.

 

[morris]

there are carts that will show how much voltage drop is ok. just use Google. try this one http://www.powerstream.com/Wire_Size.htm

 

[Carbon]

Your voltage is OK. Most stuff today works reliably at 120 VAC plus or minus 10%.

My suggestion is to run three power wires, and have two circuits at the far end of the basement. It is not much more work. It will take two breakers. The two 20 amp breakers will normally be adjacent (side by side) with each other in the breaker box. That way the two hot wires will be out of phase with each other.

Nobody ever has too many outlets and circuits.

 

[fastbear]

10% is the maximum drop from the norm. Most houses run over 120 Volts at the Load Center. You are doing O.K., with your hook up.

 

[JHZR2]

Originally Posted By: Carbon
Your voltage is OK. Most stuff today works reliably at 120 VAC plus or minus 10%.

My suggestion is to run three power wires, and have two circuits at the far end of the basement. It is not much more work. It will take two breakers. The two 20 amp breakers will normally be adjacent (side by side) with each other in the breaker box. That way the two hot wires will be out of phase with each other.

Nobody ever has too many outlets and circuits.


OK, have to bite on this... How are two wires from the two separate bussbar "out of phase" and yet capable of combining to provide 240V?

I wasnt aware that residential supply was anything but single phase.

Also, why wouldnt I run two sets of romex if I wanted to do this, and then have an extra neutral and ground? Are you really implying to buy four-conductor copper (like would be used for a 240V circuit) and send it along but the two hots come from different sides? Am I giving up something by having less neutral and ground conductor? Otherwise it seems a good way to save on pulling wire...

 

[tom slick]

By NEC a 3% drop is max for any length of wire so your voltage drop was within that spec and considered "safe".

240v is single phase and has no neutral back to the transformer. The two 120v sine waves are 180* opposed so they add to each other creating 240v.

 

[Stu_Rock]

Originally Posted By: JHZR2
Are you really implying to buy four-conductor copper (like would be used for a 240V circuit) and send it along but the two hots come from different sides?
This is a shared neutral setup, and it's OK if you're careful. If you put a 10 A load on one branch and another 10 A load on the other branch, there will be 0 A returning through the neutral. When you shut off one of those 10 A loads, the current will divert to the neutral. The maximum current the neutral could ever see is what is allowed by the larger of the two branch breakers.

In my opinion, it's critical to label at the panel all circuits that share neutrals. If someone rearranges the panel and puts, for example, two 20 A circuits on the same branch, then the neutral could be subjected to 40 A, which could lead to a fire.

I think it's now required to connect shared neutral circuits with a breaker tie, but that can be impractical in an old house. For example, in my house, the lights and original receptacles share a neutral, and it could be hazardous to the occupants (fumbling in the dark) if an overload on the receptacles also took out the lights. I can imagine very little hazard to leaving that neutral live.

 

[JHZR2]

So are the two legs coming into my home two out of the three phases that are generally used to transfer AC power??? Or is it somehow a single phase that is somehow otherwise made into 180' difference?

I'd think that if it was two of three phases, then it would only be 120' off...

Fun stuff!

 

[Stu_Rock]

It's 240 V single phase, but the center tap is ground. That's how you get two 120 V branches 180° apart.

The following is speculation, but somewhere in your neighborhood, the power company probably brings in 480 V 3 phase delta (277 V to ground on each phase). Between each phase, they have one (or more) 2:1 transformer that steps down to 240 VCT that supplies several houses. Two other portions of your neighborhood are ±120° off from yours.

 

[Kiwi_ME]

lol, this is why electricians have jobs

I would suggest having one install an normal 15A outlet at a location convenient to your dehumidifier.

 

[turbodieselfreak]

Originally Posted By: Stu_Rock
It's 240 V single phase, but the center tap is ground. That's how you get two 120 V branches 180° apart.

The following is speculation, but somewhere in your neighborhood, the power company probably brings in 480 V 3 phase delta (277 V to ground on each phase). Between each phase, they have one (or more) 2:1 transformer that steps down to 240 VCT that supplies several houses. Two other portions of your neighborhood are ±120° off from yours.
What he said (and Kiwi too). AC seems simple enough in "book" principle compared to DC, until you see how power is actually transmitted and generated in phases. I'm no electrician, but I believe each of the three phases could potentially have two hot legs, correct me if I'm wrong. It got really confusing to grasp when shopping for a whole house generator, so I referred all my questions to my certified journeyman buddy, who put it into layman's terms for me. Those guys do indeed get paid for a reason. I'm not afraid of doing a little wiring or the occassional switch/socket replacement, but when things get hairy, I leave it to a pro. He's finally pulling my meter and putting in my combined service/transfer panel with inlet box for 100 bucks plus gas, food, and beer, and as far as I'm concerned I'm still coming out ahead.