Max capacity of 4 guage aluminum wiring?

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  #1  
Old 07-24-07, 10:40 AM
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Max capacity of 4 guage aluminum wiring?

I have a 220 ft run of 4 conductor, 4 guage aluminum service wiring feeding my panel. What is the maximum capacity of this wiring at this length?
 
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Old 07-24-07, 12:36 PM
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To keep voltage drop at 3% or less, you should not exceed 40A on this feeder. Consideration of voltage drop is not required by code, but it is recommended to remain below 3%. Higher voltage drop shortens motor life because the motor starts harder and runs hotter.

If you believe that 5% voltage drop is acceptable (which it may be for some loads), you may use this feeder up to its maximum ampacity of 65A. This also assumes the conductor insulation is a type which permits 75°C terminations. If you post back the exact type of conductors and what the expected loads are (power tools, welder, lighting, etc), we can give you a much more precise answer.
 
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Old 07-26-07, 12:38 AM
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Thanks so much for the response. I will try to find the exact wire type and rating from the jacket this weekend and post the info.
 
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Old 07-30-07, 12:50 AM
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Ok, the cable is labeled with the following:

"ALCAN S STABILOY® TYPE SE CABLE STYLE SER TYPE XHHW CDRS 600 VOLT 4 CDRS 6 AL (UL) 1984".
 
  #5  
Old 07-30-07, 01:15 AM
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Originally Posted by rickalders View Post
Ok, the cable is labeled with the following:

"ALCAN S STABILOY® TYPE SE CABLE STYLE SER TYPE XHHW CDRS 600 VOLT 4 CDRS 6 AL (UL) 1984".

Edit: And I just now realized that this isn't 4 guage like I thought, it's 6 guage. Crap! So, if I'm reading the manufactures specs correctly, is the max ampacity for this cable only 50 Amps?
 
  #6  
Old 07-30-07, 08:03 AM
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There are two factors to consider. One is the maximum ampacity, which is the most current you can put through before the wires overheat. The other is the most current you can put through before the voltage drops to such a level that it becomes a problem for the loads.

The answer to the first is that #6 aluminum is good for only 40 amps at the 60-degree rating, or 50 amps if used with 75-degree terminations.

The answer to the second depends on the answers to the questions that Ben asked that you didn't answer.
 
  #7  
Old 07-30-07, 09:45 AM
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Given a 240V #6 AL feeder over 220':

20A: 2.5% voltage drop
30A: 3.8% voltage drop
40A: 5.0% voltage drop
50A: 6.3% voltage drop

Good design practice suggests that you should not exceed 3% voltage drop indicating that this feeder should not exceed 20A. However, there are many loads and use patterns which tolerate greater than 3% voltage drop just fine. For example, if it's going to a single-user workshop where only one tool plus lights will be in use at any given time then I say no problem with a 50A breaker/subpanel to accommodate startup currents. Even a low duty cycle welder would be fine on this if it was the only tool in operation. If you're feeding a multi-user shop where a couple tools may be in use or if you have a large current appliance such as electric heat or A/C plus tools, you may have a problem.
 
  #8  
Old 07-30-07, 10:30 PM
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The cable is actually a main feeder for a 1035 sq ft condo. There is a 50 amp breaker at the meter and a 125 amp panel in the unit; the distance between the two is about 220ft. I had a load calculation done and it came out to 37 amps. I was hoping to add a small AC unit if I have the capacity. Everything is 75-degree rated. All lighting is flourescent and all heating appliances are gas. My cable runs through 4 other units before it gets to me making a service upgrade less than an ideal solution.

I spoke with a friend who is a local building inspector and he said that although the load calc says I have 13 amps to use, there is no hard fast rule that says I can't exceed that and that it's only a recommendation. I understand what SHOULD be done (service upgrade) but want to know what CAN be done with the existing stuff. Does anyone have a different answer and if so, where can I find that information.

I'd imagine it's pretty hard to max out even the meager 50 amp service with only 1035 sq ft and gas appliances but I wanted to keep it somewhat within the 50 amp range just because. The AC units draw between 7 and 19 amps @ 220 depending on model. Min/max operating voltages are 190-250. Of course I know the other appliances may not tolerate the same voltage range but this is what the AC allows and as I understand, that 6.3% voltage drop is only when the full 50 amps is being drawn, correct?

So the real question is what is the max additional load I could run over this cable in this situation so I can decide which sized air conditioner I can install. I'd like to do the whole unit and not just one bedroom.

Thanks,
Rick
 
  #9  
Old 07-31-07, 09:03 AM
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Hair dryer.....................12 amps
Coffee pot....................12 amps
Microwave oven............12 amps
Small portable heater.....12 amps
Computer..................... 5 amps
Refrigerator...................10 amps
Toaster........................10 amps
ten assorted light bulbs...8 amps
vacuum cleaner..............11 amps
 
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Old 07-31-07, 01:01 PM
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> The cable is actually a main feeder for a 1035 sq ft condo.

Wow, that cable is very small for a dwelling feeder; especially given the distance.

> there is no hard fast rule that says I can't exceed that and that it's only
> a recommendation.

As with most all aspects of building code, it's up to the local enforcement. Some areas use hard limits on load calc, others let you estimate. Sounds like your area may be lax on load calcs.

> I'd imagine it's pretty hard to max out even the meager 50 amp service
> with only 1035 sq ft and gas appliances

The A/C will take a good-sized chunk, but yes; 50A is a lot of power to have in use simultaneously given all gas appliances and no spa.

> So the real question is what is the max additional load I could run over
> this cable in this situation

The max load on the cable is 50A, which your upstream breaker already limits correctly. All types of load calculation are a guess as to what typical use of appliances will not exceed the limit. You have to analyze your own lifestyle also -- does your household have multiple things on at the same time or use one appliance at a time? Are you willing to deal with dimming lights each time the compressor kicks on?

My guess is that you probably have enough capacity for a central air unit. Given your square footage, you would probably need something in the 2 ton range which typically draws about [email protected]

> I'd like to do the whole unit and not just one bedroom.

I would recommend central air over a window unit. Often, central air uses only slightly more power than a window unit because of a higher efficiency motor in the central unit and more efficient de-humidification. The trade-off, of course, is the substantially higher installation costs of central air. Given that you know you may have a voltage drop problem, I would also recommend you have the A/C installer add the "hard start kit" to your compressor motor.
 
  #11  
Old 07-31-07, 05:28 PM
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Originally Posted by 594tough View Post
Hair dryer.....................12 amps
Coffee pot....................12 amps
Microwave oven............12 amps
Small portable heater.....12 amps
Computer..................... 5 amps
Refrigerator...................10 amps
Toaster........................10 amps
ten assorted light bulbs...8 amps
vacuum cleaner..............11 amps
Just FWIW, in my opinion these numbers are on the high side.
I've never seen a home computer that draws 600 watts.
The wattage rating of the power supply is DC watts, not AC.

ALL of my PC equipment together draws less than 300.
That's PC, printer, all the networking, cable modem, etc.
Add 60 watts or so if you are still using a CRT monitor.

A 12 amp home coffee maker? My commercial maker (boiler, 3 hot pads) barely takes 12 amps (13.5 to be exact), and that's with all three pads and the boiler running.
 
  #12  
Old 07-31-07, 07:51 PM
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Ben,

Thanks for the info, you answered all my questions. I was actually looking into a central air unit from the start. If I were to do a single room it would have been with a mini split which have the same or better efficiency as central (13 to even 21 seer for some models). My HOA won't let me do a window unit plus I think they look really tacky so I didn't even consider that. I'm prepared to spend the $2k-$3k (or more even) for the AC if that's what it takes.

A few more questions since you mentioned it: 1) What does a hard start kit consist of? Is it similar to a starting capacitor on a smaller motor? 2) Will the average AC contractor know what I'm talking about?

Anyway, I am pretty easy on the service since I rarely have a bunch of stuff going at the same time so I'll take your advice, as well as the local inspector's, re: the load calc and go for the larger unit. A 2.5 ton I was looking at was 19 amps max. (including the motor start I assume) so I'll check more into something that size (I am in So. California where we tend to need a little more BTU per sq ft). Of couse I'll have it professionally sized before I buy anything.

The feeder is small and some people have even told me I'm wrong but that's what it is, 50A. When I initally said 4 guage it was by memory from a couple years ago, I guess I switched the conductor size and number of conductors until I read the actual label. This place was built sparing every cost in 1987. I can live with dimming lights, it's the 80+ degree inside temps at 11pm that bother me. I've already called the insulation contractor, they were here today and will give me written estimates tomorrow for R38 & R49 in the attic since my current stuff is 20 years old and less than half that thick. Sorry for the initial run around and lack of information but I asked somewhere else and my question never got answered; my thread just got hijacked into an argument about recommended feeder sizes which I really don't have much control over due to the layout.

Thanks again for your help and hopefully this will all work out in the end.

Rick
 
  #13  
Old 08-01-07, 09:03 AM
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> What does a hard start kit consist of?

A bigger startup capacitor and a timed delay which staggers the startup of the compressor motor and the blower motor.

> Will the average AC contractor know what I'm talking about?

Probably, it should just be another part number at the supply house when they spec it out. I seem to recall it's a pretty cheap option, like under $50 for the parts.

> 19 amps max. (including the motor start I assume)

That is the running amperage; it does not include motor start. Somewhere buried in the specs of the unit (or stamped on the metal plate of the compressor) will be the "LRA" or locked rotor amps. This is the maximum startup current. It will be several times larger than the "FLA" or full load amps, which is the running current when the motor is under 100% rated mechanical load.

> I am in So. California where we tend to need a little more BTU per sq ft

After this week of ~100° days up here in Michigan, I'm thinking I could have gone with a couple more BTUs / sq. ft. at my place too.

> Thanks again for your help and hopefully this will all work out in the end.

Best of luck on the project -- enjoy the cool condo.
 
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