Variac Wiring - Any Electrical Engineers

[tINY]

Hard to say without a diagram.

It may be worth $100 to get an electrician out to do it right....



-tINY

[jhbrandt]

Originally Posted by soulfieldstudios

I was sitting here and I realized that all I have is 14/2 (still need to verify tonight) in my switch location. I marked the White (normally neutral) beacuse I'm using it as a Hot to the switch (again power from the fixture). To make matters worse I have already hung 5/8" type X in the ceiling and on soffits above switch. The wall is still open.

You do not have a neutral in that box & according to NEC the white wire should have been taped with black tape to indicate a 'hot' switch circuit.

Originally Posted by soulfieldstudios

So heres my question: If I were to keep my existing set up with the "marked" hot coming to terminal 2, my black Hot to terminal 4 than all I'm missing is the Neutral right? So would tapping into the neutral from another light fixture allow the Variac to function properly? My (ignorant) logic here is that the voltage drop shoud "occur" on the Hot conductor, and the neutral is already @ the light fixtures themself.

NO. Do not do that.

As tINY suggested, get an electrician in there to do it right. You could risk burning the place down. -- You will need to run the power up from where the switch is and feed the light circuits from the variac.

Good luck!
Cheers,
John

[soulfield]

Looked last night after work and i have 14/3 in to the box.

At this point all I can do is run a second line of 14/2 back to the first light fixture and re-wire the fixture so that the incoming power goes directly to the switch > Variac | then the new dedicated run > back to the fixtures.

My prior post was def a bad idea once I really thought about it.

This build has been a one man crew all the way from framing, MEP, and Gyp Board to finish and casework. No budget for outside help. I am confident with electrical but have never wired a variac before.
I wired the rest of the studio CR, LR, bath, den, and Ejector pump based upon the IRC + NEC, and think I have this right.

So incoming power

> Hot (black) to Switch > to Variac terminal 2
> Neutral (white) > to Variac terminal 4

Ground > Ground

Output

> Hot (Black) > from variac terminal 3 > to Fixture
> Neutral (white) > from variac terminal 4 > to Fixture

Ground > Ground

Right?

[avare]

Originally Posted by soulfieldstudios

OK, so I understand how the Variac would be wired traditionaly.

Input: Hot (black) to terminal 2, Neutral (white) to terminal 4

Output: Hot(Red) terminal 3, Neutral (white) terminal 4

Which model Variac is it? On the 100/200 series the input is neutral terminal 1 and hot terminal 4, assuming you are not loking for any voltage boost.

St100 200 Wiring

Andre

[soulfield]

Its a staco 501 5A 120v

No boost just dimming about (15) 30w halogen GU-10.

I do not have the variac in hand yet to confirm wich terminal is which on this particular unit. All the bad weather in memphis and the mid west slowed FedEx alot so hopefully I will have the unit today and will confirm the terminal layout.

I finally bit the bullet and removed some of the 5/8 type X gypsum on the ceiling and soffit, and snaked my second run of romex from the switch/Variac location to the first light fixture it will control.

Once I get the unit in hand I will have to figure out what enclosure I want to use or modify in order to wall mount the Variac and Switch.

I know I couldnt find alot when I started searching for wiring Variacs so I plan to photograph and maybe scetch a schematic of my install to help others in the future.

Fingers crossed for Fed Ex to deliver today. stike

[SAC]

LED Dimmer

Its a pretty good article that illusterated the proper way to effectively dim LEDs.

Gee, I wonder why they have electricians? As with so many who know more then they do their market should be exponentially sinking due to the impact of Darwin's postulates.

http://www.ledsmagazine.com/features/1/12/6

[avare]

Originally Posted by soulfield

Its a staco 501 5A 120v

All the bad weather in memphis and the mid west slowed FedEx alot so hopefully I will have the unit today and will confirm the terminal layout.

There are 501C, and 501-C models. The conections are shown on the drawings.

501C
501-C

Andre

[soulfield]

SAC - Excellent read. I wish the budget for my build would allow for LED lighting.

ANDRE - Thanks for the schematics! These are much more legible than the ones from Mosier's website.

It is indeed a 501C. My first take is the same as I thought with one change

Terminal 5 being input (hot)

Terminal 4 being common (neutral)

Terminal 3 being the output (Hot to fixture)


Also appears that you can easily reverse the clockwise attenuation to counterclockwise by interchanging terminal 5 to terminal 2 (hot), and terminal 4 to terminal 1 (common / neutral)

I will need to study this a little further tonight.

Would you believe FedEx didnt make the delivery today!

Sucks because I work better when I'm holding the unit than I do planning on paper. As an unlicensed (not yet eligible) Architect you'd think I would be able to lay this stuff out on paper.

I guess tomorrow night after rehearsal for the Album release party, I will get to install this bad boy! (Assuming FedEx does there part)

Thanks again Slutz

[soulfield]

At last the Staco 501C Variac arrived this morning. I will say its a beautiful piece of gear. While it only weighs 5 lbs, it feels like 10!

Now to devise the mounting and get this thing up and running.

I will post pics, schematic, and a short synopsis of the install once completed so that others searching can see some real information on Variacs and incandescent light dimming.

My butterscotch american strat is already happy about this one.

Give me a few days.

[soulfield]

Variac is now installed and I am stunned with the results. Took a little DIY to get the enclosure right. I modified a 6" x 6" x 4" type 1 Nema enclosure
so that I would have an accessible but rigid enclosure. Remember this unit weighs 5.4 Lbs.


Here is a picture of what the 501C looks like.



Also attached is a picture (blackberry pics suck) of the installed Variac + Enclousre and mounting.





The first thing I did was install my second run of 14/2 from the enclosure location to the first light fixture. This gave me two runs:

14/2 Run A - Power from breaker (hot from this passes through a simple light switch before the input of the Variac.)

14/2 Run B - Output from Variac to first light fixture


Second, I mounted the enclosure and brought Run A & B into the enclosure.

Third, I traced the template provided with the unit on the cover for the Nema enclosure and drilled holes for the shaft and mounting bolts. Also before mounting the enclosure I drilled holes for the entrance of the input A and output B. These had to be cleaned with a little wire brush dremel action. After all the burrs were removed I installed gromets to protect where Runs A & B enter the top of the enclosure

I mounted the variac on the cover plate of the enclosure.


Forth, I shut off the power to this dedicated lighting circuit.

After careful review of the Schematics that Avare was nice enough to provide and the limited documents that came with the variac I made the following connections. (WARNING! these connections are specific to the model I have. Anyone installing a Variac should be sure to verify the function of the terminals on the unit they are installing as they can be diffrent from one model to the next)

Ground to Ground for both Run A + Run B

Input Run A (post light switch) Hot (black) to terminal 1
White (Neutral) to terminal 4 (common)

Output Run B Hot (black) to terminal 3
White (Neutral) to terminal 4 (common)


One item to note. This unit has 2 input terminals. Per the schematic terminal 5 is for over voltage and will provide the output with max 117% of the input. Using terminal 5 could output up to 140v which is not a good thing for halogen bulbs.

Terminal 1 is for Line voltage which is what I needed for my scenario, and this will provide the output of max 100% (120v) of the input.

TEST - Turned the breaker back on and tested the unit. Glorious light of all levels. No noise what so ever. The strat and never picked up a thing.

I ecpected this unit to create a fair amount of heat and I even provided additional holes for ventin top and bottom. To test this I ran the unit at approx 30% of input for 3 hours and the Nema enclosure was still cold to the touch.

I only have temp keyless light fixtures inplace until the drywall work is finished but it is really awsome to see the various light levels all the way down to a barely glowing incandescent filament.

I hope this little synopsis will help anyone curious about uisng a Variac to Dim 120v lighting.

Now back to having fun hanging 5/8" type X

[avare]

Congratulations on a great lighting control install. Thanks for the details of the install and the report on the results. It is difficult to explain to those who have experienced it, the beauty of continous variable lighting from off to fully on.

Of course what is also often overlooked in studio applications is the insignificant electrical noise created. Variacs are expensive compared to almost all electronic dimmers, but when you need the characterstics of a variac, it is worh it.

Andre

[PaulP]

Interesting thread, thanks for sharing.

The more I wait to start work on my place, the more great ideas I'm going to be able to include.

[soulfield]

Thanks AVARE!

Paul,

I hope this will give you a jump start when planning the lighting for your place.

I'm about 75% of the way through my build (promise I will get a photo thread of the build one of these days) and although I planned and planned, things always seem to change once your building and making decisions on the spot.

Apparently I did not plan enough in the begining and the Variac was a perfect example. Mind you I only back tracked 2 pieces of 5/8" Gyp and a little extra romex, but I should have planned this out before hand.

Good luck with the plan/build work ahead paul

[soulfield]

The enclosure is about flush with the edge of drywall and I plan to make a stained wood panel that will be hinged and trimmed out to match the mic line panel.

Very happy to see this wall completed and the variac is helping me feel like this will one day be a finished studio.

[soulfield]

Some tips I forgot to include for anyone doing a similar enclosure.

1. The terminals on these Staco Variacs are fragile. I didn't have any problems but use caution not to put stress on the terminals.

2. The 6x6x4 enclosure was just large enough for the 501C. That said tuck your wiring neatly. The first time I placed the unit I had a wire nut in the back of the enclosure that was rubbing the back of the Variac as it turned.

3. Protect the windings on the Variac. The edges of the enclosure were rather sharp and its almost impossible to place the unit without touching the copper windings on the edge of the enclosure @ some point. I placed two layers of electrical tape to pad this contact.

4. When you trace the template oversize the hole for the shaft. The schematics call for 7/16" hole with a 3/8" Variac shaft. I used 1/2" for the hole which gave just a little wiggle room.

Just trying to contribute something back to the forum that has provided me with so much valuable information.

Thanks guys!

[Andy_R]

Soulfield's wiring advice pictured below. Worked great for me too. Thanks, soulfield, really appreciate it.

The one thing I would add is that the 6" x 6" x 4" type 1 Nema enclosure is a bit tight. You might want more room to accommodate the wiring, as the Dial Plate is located at the back of the 501C.