Ask the Electrician

I hooked it up and ran it from the timer location to the backyard box were the cat5 ends and measure it with a multimeter and did not produce a voltage drop. The distance is probably about 70 feet. Also, just for fun I hooked up 50ft of Cat5 that I had laying around and 50ft of 18 gauge sprinkler wire and tested it and still no voltage drop.

Thanks for your responses guys! It seems that the voltage is so low it most likely will be fine. Where I work we have many electrical engineers, many with Phd's in EE, and we went through the process and they all agreed that there is little fire risk but I had to ask the real pros, the electricians!!

 

volt drop only occurs when the conductors are under load.

 

Did not know that... I will hook up the valve later and see how much it drops. Thanks.

 

Not sure if it relates here, but cat5 in the computer industry is good for 100 metre runs between active devices.

 

When the valve is open, you'll read a lower voltage across the supply terminals. This is not voltage drop... yet

Hook it up and trigger the valve.
Measure the voltage across the terminals at the valve.
Now measure the voltage across the terminals at the controller.

The difference is your voltage drop.

24ga you have roughly 2.5 ohms for every 100ft. I would not anticipate any issues running 70ft.

Math time:
If your valves are drawing the max current for the 24ga wire, and you are feeding them with 24 volts, then the coils are 12 ohms each.

If you are running a full 100ft, then your circuit looks like this:

----/\/\ 2.5 /\/\--------/\/\ 12 /\/\--------/\/\ 2.5 /\/\----

Voltage across the entire circuit is 24v.
Total circuit resistance is 17 ohms
The coil resistance is 70% of the total circuit resistance, so the voltage measured across the coil will be 16.8v. The voltage measured from the source to the coil on each side will be 3.6v

This is worst case. The full 100ft, and the coils drawing the limit of the 24ga wire.

More realistically, the Rain Bird valves are a 0.3a inrush current, and 0.19a holding current.
Inrush is the most important, because that is where voltage drop may cause chatter or incomplete opening.

So using a real number....
24v at 0.3a = 126 ohms
2.5 + 80 + 2.5 = 85
Coil is 94% of the total circuit resistance
Voltage across coil should be 22.6 during valve opening

24v at 0.19a = 80 ohms
2.5 + 126 + 2.5 = 131
Coil is 96% of the total circuit resistance
Voltage across coil should be 23.04 during valve open "hold"

That's with the full 100ft. You should be around 70% of that loss figure on your longest run.

 

Not related. He's pushing solenoids that draw just under 1/2 amp when first turned on. Network signals are high impedance. Length is limited to where external noise may reach levels high enough to mask valid data.

 

Ok, I'm glad I noticed this thread as I've been getting different answers/suggestions from electricains.

I have a question for Alex or Jason.... or any electrician on here. I just built a detached 2 car garage with 2" PVC conduit for the sub-panel (and 1" conduits for the 3 way switches to the house). I have already mounted the 100 AMP sub-panel in the garage with it's own separate grounding bus bar.
I'd like to use aluminium wire to feed the sub-panel beacause it's cheaper, but if I need to use copper for it's smaller diameter to fit the 100 amp breaker, I will.

What size wire (AL) should be used for a 75' run from panel to panel in the 2"conduit?... 2/0 or 2 gauge wire.... all THWN/THNN.

I know I'll need a neutral and 2 hot legs along with a #6 ground.... 4 conductors in the conduit.

... So, would you use (aluminum) 2/0... or (copper) #3 or #2 for the sub-panel service??


The sub-panel




Junction/pull box with 12 Gauge THHN for the 3 way switches to the house...





Here's my 100 panel breaker from the house 200 amp service panel. It has 7/16" lugs, so I'm limited to the size wire #3, #2 or 2/0.

Will a 2/0 aluminum wire fit theses 7/16" lugs?




The main panel...

 

I would not use aluminum wire in any building application. I don't like it, and many cities are no longer allowing it.
There are corrosion issues, and the thermal cycling causes the terminals to work loose since aluminum expands and contracts more than copper.

 

Verify your local codes on that. In my area, the earth ground may be no smaller than two gauges below the supply lines.

 

Around here, every SER cable drop and underground into the meter socket and panel is AL. All AL connections must be proctected with anti-corrosion goo.
No one around New England has issues corrosion and hotspots that I'm aware of.

Mainly the Al vs. CU concern is voltage drop in distance and AL fragility , not so much thermal movement or corrosion.

BTW for or my sub-panel project, #6 ground in conduit is fine from what I'm told by several electricians... as long as it's stranded and sheathed.

Thanks Rich

I'd like to hear suggestions from the licensed and career electricians in the thread before I buy the cable.

 

You forgot:

Pre-drilled holes and bubbled water.

 

And #6 is okay if your spec for the supply is #2 (2 gauges down).
Just wanted to give a heads up if the distance to your sub panel requires stepping up beyond a #2 copper equivalent.

 

you could use 1/0 AL (120A 75C rating), #2 Cu (75C rating) is good for 115A.
conduit fill isn't an issue, you could put as many as six 2/0 conductors in 2" PVC.
the lug range of the 100A breaker is #4-2/0, no problem there.

 

That's odd, sounds like everything is new if by bell, you mean the ding-dong unit mounted on the wall. If that's not new, check inside it to see if the strikers are stuck or not plunging far enough to strike the bell. Some dry-lube spray might help that for a while. Other than that, test to see if there is voltage at the wall unit when the button is pressed. Possibly could be a defective main contact in the button, even if the light is on.

 

Thank you Sask

I'm glad to know my breaker will take up to a 2/0 in the lugs.

I may just go with #2 Cu. If you were me, and knowing what you know, whould you use Al to save a few bucks, or just bite the bullet and use Cu?

 

I'd probably use copper, but with a little anti-oxidant paste there's nothing wrong with using aluminum.

 

Thanks Sask

 

I've been try to study electricity just to understand it better. I read and read but I still can not figure out what it is. What is electricity? I don't get it and the more I read the more confused I get.

 

In many aspects it can be compared to water.
Voltage is your potential (water tank on the hill), but current is the flow.
Like water, a million volts with a low current flow will give you a tingle.
Like water, a few volts with a high current flow will knock you on your ass or kill you.

A resistor is like the size of the pipe going to your house. No matter how much pressure you put on it, it is only going to pass so much. It's not a perfect analogy, but it's close.


Wires contain smoke.
Big wires can contain a lot of smoke, because things like a starter need a lot of smoke to work.
If you let the smoke out, it stops working


Seriously though... take a semester of Occupational Electronics at a Community/Junior College. It's not exactly "electrician" stuff, but there's a lot of overlap between narrowbacks and techs and the theory is the same, just on a different scale.
Sadly, really learning to be an electrician requires an apprenticeship. You can take classes that'll give you a kick in the butt, but they are not going to be detailed enough to rewire your own home. Things need to be learned by experience.

 

Just noticed this thread, i just got my Red Seal ticket in Canada here back in June 2013