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Old 09-11-2010, 09:25 PM   #1
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120' run with 6 awg aluminium wire...


was run by my electrician for a sub panel with a 80 amp circuit... I am not an electrician but it seems that size wire was to small. There are 2 mini splits 24k, about 20 small lights and some HT equipment that will be on the sub....

Every calculator I have run says it needs to be 4 awg copper.....

Thoughts to as why the "professional" used 6 awg aluminum???

Thanks

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Old 09-11-2010, 09:41 PM   #2
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120' run with 6 awg aluminium wire...


Just to avoid voltage drop you need #4...maybe #3
For an 80a breaker I think you need #3 for 75a load depending upon the exact wire
No way #6 alum will carry the full load of the breaker
#6 is rated 60a Max depending upon wire & connections

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Old 09-11-2010, 09:52 PM   #3
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120' run with 6 awg aluminium wire...


What is the amperage of the breaker for this feeder?
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Old 09-11-2010, 09:55 PM   #4
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120' run with 6 awg aluminium wire...


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Originally Posted by zipperbaum View Post

Thoughts to as why the "professional" used 6 awg aluminum???

Thanks
too many possibilities in my mind but if he was given full control of the installation and knowingly installed an 80 amp circuit with this wire, I would simply say; incompetence.
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Old 09-11-2010, 10:30 PM   #5
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120' run with 6 awg aluminium wire...


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What is the amperage of the breaker for this feeder?

I have 2 separate 200 amp main panels for my house...the sub is being fed off of one of the 200 amp panels and uses an 80 amp breaker.

and yes...the "professional" had full control of the project...


So what now? Is this a fire hazard or just going to be a problem with breakers popping if I put too much load on them?

Worse case I will have to have ANOTHER electrician come in a pound some more holes in my ceiling and run 4 awg.....anyone have any recommendations for a supplier for the wire?
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Old 09-11-2010, 10:33 PM   #6
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120' run with 6 awg aluminium wire...


Do you need 80a of power ?
If not I'd consider just installing a smaller breaker

The problem is the breaker WILL NOT "pop" before there is a problem with the undersized wiring

Where are you located ?
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Old 09-12-2010, 03:16 AM   #7
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120' run with 6 awg aluminium wire...


To run 16mm˛ {#6 AWG } alum cable with that distance with 80 amp breaker that is not a legit way to do that.

You will run into serious voltage drop on that size of conductor and distance you will get over 15 volt drop IMO that is little too much for this set up { I came up over 6.5% voltage drop }

Really that electrician should double check the codes and the split units and genral lighting load he can not take a advange of that code section at all { art 440 That is complety wrong on feeder appaication }

Do you want my honest answer ??

Go with much larger cable that will slove the code issue with it.

The size you will need to use 35mm˛ { #2 } Copper I know it will cost more but it will work just fine with that set up.

I know there are couple other size you can use as other members suggest it as well.

Oh yeah a nice gotcha anytime you have to upside the conductor for the voltage drop issue you have to make sure you increase the EGC { grounding conductor } conductor size up as well otherwise some case the breaker may not trip if have fault situation.

Merci.
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Old 09-12-2010, 07:44 AM   #8
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120' run with 6 awg aluminium wire...


#6 AL SER is rated at 40 amps. Calculate the amount of load installed from the sub. If less than 40 amps just reduce the breaker size and you'll have a safe installation(assuming everything else is correct).
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Old 09-12-2010, 08:20 AM   #9
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120' run with 6 awg aluminium wire...


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#6 AL SER is rated at 40 amps. Calculate the amount of load installed from the sub. If less than 40 amps just reduce the breaker size and you'll have a safe installation(assuming everything else is correct).
Exactly.

The size of the two mini-splits will be the determining factor. The other stuff is almost incidental.
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Old 09-12-2010, 08:49 AM   #10
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120' run with 6 awg aluminium wire...


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#6 AL SER is rated at 40 amps. Calculate the amount of load installed from the sub. If less than 40 amps just reduce the breaker size and you'll have a safe installation(assuming everything else is correct).

Is there an easy way to do this...link to an article you would suggest or something?

Thanks for the responses gang.......


and I live in Tampa....
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Old 09-12-2010, 09:07 AM   #11
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120' run with 6 awg aluminium wire...


The mini splits should list their Max load...they should have a nameplate on them
What kind of lights ? They should have a Max wattage bulb listed on them
Not sure what the HT is ?
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Old 09-12-2010, 09:41 AM   #12
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120' run with 6 awg aluminium wire...


The #6 aluminum or #8 copper is good for 40 amps so it is perfectly safe and proper to use a 40 amp breaker. But at 120 feet you will notice some voltage drop when you actually pull more than about 30 amps.

The wire will not overheat. The heat generated by the voltage drop is evenly spread over the entire length of the wire and the "BTU per foot radiated" is the same as for a shorter run of the same kind of wire and the same number of amperes. While the #6 aluminum may be rated for 40 amps intermittent and 32 amps continuous, at 120 feet the recommendation is 30 amps but the full 30 amps continuous.

With 6/3 AL cable and a 120/240 volt circuit, you will get up to 80 amps at 120 volts in two allotments not exceeding 40 amps each.
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Old 09-12-2010, 09:47 AM   #13
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120' run with 6 awg aluminium wire...


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The #6 aluminum or #8 copper is good for 40 amps .........
In cable yes, but (THWN)conductors in conduit both are good for 50A.
The second you connect to cable (NM, SER) the whole circuit must be backed down to 40A.
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Old 09-12-2010, 09:53 AM   #14
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120' run with 6 awg aluminium wire...


I would strongly suggest that the feeder be rechecked as to the conductor size. Only a totally incompetent person would put #6 AL on an 80 amp breaker for such an installation.
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Old 09-12-2010, 10:15 AM   #15
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120' run with 6 awg aluminium wire...


To the OP,

Is the 80 amp breaker in the sub-panel or in the 200 amp panel feeding the sub? If it is in the sub but being fed by a 40 amp in the main, there is no issue. If the 80 amp is in the main, then the sizing is wrong.

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