Will the Real Electrician Please Stand Up

[screenxpress]

Ok, I'm going to preface this with the concept that I am fairly well-versed (maybe just dangerous) in the basics of electrical components.  I do and have run my own circuits and rewiring and attempt to do everything that would be "code" acceptable.  I'm not going to create a dangerous situation. 

I just recently re-ran a circuit to the work area (ok, garage), using 3 #8 and 1 #12 for 50A double breaker service.  I had existing conduit to deal with so could not go much larger on the pull.  Was about 125 foot pull. 

To me that gives the capability of 50A of 220V equipment or 100A of 110V equipment.  I'm pretty sure that's right because if everything was 110V, it would allow 50A on each leg.

Here's my dilemma. 

I've got a 30A 220V dryer.  I feel that safely leaves me with 20A of 220V available service or 40A of 110V available service.  I have a Flash Unit drawing about 15A/110V.  I'm in the south.  It's hot.  I need air conditioning.  I can get a 220V/15A unit or a 110V/15A unit. 

My math says that since the power company charges in KWH and using the formula W=V*A, the 220V (same Amps) unit would be a bit cheaper to run and more efficient.  But I'm not sure there's sufficient available remaining service to allow it. 
 
I can probably go with the 220V/15A one, which would leave me about enough power for a light bulb and no Flash (5A left).  Or I can go with the 110V/15A unit and be able to run the A/C and Flash (30A/110V) and still have enough (10A) for lights, etc.     

I know the basic concept for breakers is to protect where the draw is over the limit for longer periods to protect from fire.  And in reality, I probably could run the 220V/15A A/C along with everything else where only brief spikes of short duration would occur when the compressor kicked in and everything would probably be okay. 

Please don't suggest pulling additional service.  I know that's probably the best solution but not one on the table right now, maybe later.

Opinions, Suggestions?  Am I lost in my own little world?

[screenxpress]

Ok, I'm going to preface this with the concept that I am fairly well-versed (maybe just dangerous) in the basics of electrical components.  I do and have run my own circuits and rewiring and attempt to do everything that would be "code" acceptable.  I'm not going to create a dangerous situation. 

I just recently re-ran a circuit to the work area (ok, garage), using 3 #8 and 1 #12 for 50A double breaker service.  I had existing conduit to deal with so could not go much larger on the pull.  Was about 125 foot pull. 

To me that gives the capability of 50A of 220V equipment or 100A of 110V equipment.  I'm pretty sure that's right because if everything was 110V, it would allow 50A on each leg.

Here's my dilemma. 

I've got a 30A 220V dryer.  I feel that safely leaves me with 20A of 220V available service or 40A of 110V available service.  I have a Flash Unit drawing about 15A/110V.  I'm in the south.  It's hot.  I need air conditioning.  I can get a 220V/15A unit or a 110V/15A unit. 

My math says that since the power company charges in KWH and using the formula W=V*A, the 220V (same Amps) unit would be a bit cheaper to run and more efficient.  But I'm not sure there's sufficient available remaining service to allow it. 
 
I can probably go with the 220V/15A one, which would leave me about enough power for a light bulb and no Flash (5A left).  Or I can go with the 110V/15A unit and be able to run the A/C and Flash (30A/110V) and still have enough (10A) for lights, etc.     

I know the basic concept for breakers is to protect where the draw is over the limit for longer periods to protect from fire.  And in reality, I probably could run the 220V/15A A/C along with everything else where only brief spikes of short duration would occur when the compressor kicked in and everything would probably be okay. 

Please don't suggest pulling additional service.  I know that's probably the best solution but not one on the table right now, maybe later.

Opinions, Suggestions?  Am I lost in my own little world?

By the way, the real question here is the Air Conditioner - which way can I go?

[blue moon]

It has been a while since I worked as an electrician, but let's use your math . . .

at 220V you have 50 A
30 for the dryer
7.5A for flash
7.5A for 110V AC
------------
45A that should leave you with enough juice to for a few small loads.

[screenxpress]

You lost me on the 7.5 for Flash and A/C. 

If plugged into a 110V circuit and tagged for 15A, how does it drop down to 7.5?

[ebscreen]

For starters, you're going to get a fair bit of voltage drop from a run that  long,
in undersized conduit, at hot temperatures, with parallel runs. That means higher
amp draw.

I'll leave the rest up to someone that knows more, but you can't draw 100 amps 110 on
8 gauge wire either.

Swamp cooler.

[blue moon]

You lost me on the 7.5 for Flash and A/C. 

If plugged into a 110V circuit and tagged for 15A, how does it drop down to 7.5?

sorry, 15A at 110v is same as 7.5 at 220. I was upconverting to 220v amp count.

[tpitman]

One thing to think about is as you stress the system, efficiency drops, I think, even if the breakers don't trip. I'm no electrician either, by the way, but I did wire my garage with a new panel, lighting circuit, wall outlet circuit, water heater, 220 dryer, 220 flash, and a dedicated 15 amp circuit for my exposure unit. One question I have is, why the #12 cable? I assume the 3 #8's are the two hots and neutral? Is the #12 a ground back to the panel at the house?

Otherwise, I'd be inclined to use the 110v ac unit, simply to save some juice for everything else.

One other thing. Living in Orlando, I know what you mean by hot. I installed an "attic" vent/fan in the roof of my garage that is supposed to change the air about every 3 minutes. My garage has no attic, just an open shed-type roof that goes from 8 feet to 12 feet. I used to just have a box fan blowing out one window with the other window open, but noticed that, if I got on a ladder, as soon as I went up a couple of steps, the heat was trapped in the "ceiling" as it were, and was hotter than hell. That roof vent/fan makes a difference, and I've got to either keep two windows open, or a window and side door to feed the fan. I also have a small a/c unit in another window, but unless I'm standing right in front of it, it does little to cool the garage so I pretty much don't use it. My garage is also shaded quite a bit, so that might be a factor that you don't have, so the roof vent/fan is just an alternative to think about.

[screenxpress]

One question I have is, why the #12 cable? I assume the 3 #8's are the two hots and neutral? Is the #12 a ground back to the panel at the house?

Correct.  Since there is a secondary breaker box, the ground has to be isolated from the typical neutral bar in the second box.  But is okay (code wise) to be on the neutral bar (which has a line to a ground rod) in the primary box.  It was a toss up as to whether I needed to run #8 for a ground fault, so I just kept the #12 that was previously there.

What is the total amps to your garage breaker box?

[Northland]

I'll take a stab at this one... I happen to be a licensed Master electrician in the state of Minnesota.

If you used THHN (90 degree C) insulated wire, a #8 conductor is rated for 55 amps.
However, because it is terminated on 75 degree C devices (receptacles) we must use the 75 degree columb of table 310-15.
So, step one... YOU ARE CORRECT, your wires are rated for 50 amps (as you stated).

I think it's most helpful to look at the load in wattage terms:
Conveyor dryer.... probably 7200 watts (30 amps X 240 volts).
Flash dryer..... 1800 watts ( 15 amps X 120 volts). Put this on an odd number circuit breaker.
Air conditioning.... 1800 watts (15 amps X 120 volts). Put this on an even number circuit breaker (to help balance the load).
Lighting... 600 watts (5 amps at 120 volts).
Step two.... Total load..... 11400 watts

Because this is continous duty load the ratings should be multiplied by a service factor of 1.25
Step three....  to be code legal you'd need a minimum of 14,250 watts of capacity (1.25 X 11,400 watts).

Step four..... you've got 12,000 watts available (50 amps X 240 volts).
So, to satisfy the code requirements you'd need a larger feeder wire.
#6 THHN is rated for 65 amps.... (15,600 watts).

The reality is... because the dryer, flash and air conditioning all "cycle" you will usually not be drawing full load current.
The voltage drop you experience from being 125 feet away from your service panel would be offset by the 1.25 service factor rating.
You could possibly limp along on #8 wire, but it would not be code compliant.
Sorry.... you're probably going to need to upgrade your feeder going to the garage. A 100 amp circuit would be most practical.

Another option would be to downsize your conveyor dryer to 3600 watts which would probably cure about 100 shirts/hour (that still fits the need of most manual shops). If you have two heat panels in your dryer... disconnect one and then slow down your belt speed.

Also..... an 1800 watt air conditioner would only be about .5 ton of cooling (6000 btu).

[screenxpress]

Thanks Northland, and the other responders.

The Flash is rated at 110V/20A (I called Workhorse) which makes your numbers even a little worse.

Here's what I've decided.  Since pulling the #8s and #12 through the existing 3/4 conduit that partially went underground and was such a PITA with seven 90 degree turns , I'm not going to pull it out and try to re-pull #6s.  I don't think they would make the turns. 

I'm going to get the 110V/15A A/C (15,000 BTU) and see what happens.  If I do have problems, I can run a new conduit line using a driveway spacer crack to the garage and pull #10 with G for the A/C.  That will drop 15A and I should be well under the max.

Oh, and I know the real world is 120/240 now.  It's just that all my life it was 110/220 and it's hard to break old habits. 

[tpitman]

What is the total amps to your garage breaker box?

100. I've run the lights, the small a/c unit, the flash and the dryer simultaneously. I also have a water heater for the house in there, but it cycles on and off. Never tripped a breaker. I pretty much only run the a/c if I'm goofing off in there drinking beer. I don't remember for certain the gauge of the cable but I believe it's 00. All I know is even with slathering it up with that yellow wax crap they used to sell, pulling 3 conductors through underground conduit was a bitch. Only had to go about 30 feet, thankfully.

[screenxpress]

God,

30 foot.......what a dream......and I bet no 90 degree turns......lol

[Northland]

Factoid.... there shall be no more than 360 degrees of bends between raceway openings (four-90 degree bends -or- any combination totaling 360)

[screenxpress]

Factoid.... there shall be no more than 360 degrees of bends between raceway openings (four-90 degree bends -or- any combination totaling 360)

Not sure I follow that. 

Are you saying that when a previous electrician ran the existing conduit up under and around the eve of the house, down to the ground, up out of the ground at the garage, up the wall, over the top of the rafters, and down to the new box, he may have violated code? 

Although that conduit was run over 12 years ago.

[Northland]

Between openings (removable covers) there should be no more than 360 degrees of total bend.
As you witnessed... too many bends increases the likelyhood of insulation being damaged during installation.

I'd like to meet the brute that can pull wire threw seven 90 degree bends !!!