dcsimg

PDA

View Full Version : Alluminum wire to disconnect and sub panel for workshop


brasshornman
March 19th, 2008, 10:00 PM
Hi. I have just run #6-3 aluminum (AA-8000 Aluminum type SE style RXHHW2 3 CDRS 6AWG 1999) from a 200 amp (Cutler-Hammer) main panel to a 60 amp Square D disconnect box (#ufp222R PULL OUT DISCONNECT SWITCH) that feeds a 100 amp Square D QO Load Center sub panel (cat #Q08-16L100S for copper or aluminum 75 cel) that will have no more than 4 20 amp breakers - one of them will be for 240v. This will be used for running a router, table saw, dust collector, etc. but will typically only be running the dust collector and one other shop tool at a time, so loads will not be heavy. I have run #6-3 copper from the disconnect to the sub panel. The aluminum and copper are not connected together.

The disconnect has a grounding bar but not one for the neutral. To avoid corrosion problems, I was going to install a terminal block for the neutral wires. Is this OK? I have used an anti-oxidizer on the aluminum connections.

I have read that #6 aluminum is rated for 60 amp but have also seen that #4 should be used for 60 amp feeds. What amp breaker should I use for #6 aluminum?

The last question is do I need a special type of terminal block to connect the neutral or can I use a standard block using an anti-oxidizer?

Thanks in advance for your help!

ianis
March 19th, 2008, 11:22 PM
a 60 amps breaker will do the job assuming this is a shop in a residential premises.
When you buy your neutral isolator block make sure it is rated for aluminum and coper and also use penetrox on your connections.
good luck

brasshornman
March 20th, 2008, 03:42 AM
Ianis,

yes, the shop is in my home. Thank you for the quick reply. Now I can finish the job today!

Speedy Petey
March 20th, 2008, 03:58 PM
Residential or not, #6AL is NOT good for 60A. The ONLY time 60A can be used is for derating purposes, IF the conductor in question is actually rated for 90 deg C.

We can NOT use the 90 deg C column for actual amperages of circuits!

suemarkp
March 20th, 2008, 08:35 PM
You #6 AL is only good for 50A at 75C. When mixing copper and aluminum, you need to upsize the aluminum at least one size (and usually 2) to get the same ampacity as copper. So the largest breaker you can put in the 200A Cutler Hammer panel to servce this feeder is a 50A double pole.

If you can find a small terminal bar that will fit the panel and is rated at 50A for AL and CU, you could install it. It may be simpler to get an AL-CU rated barrel splice lug. These are little barrels about an inch long with a hole in each end. So get ones that will take #6 in those holes. There is typically a setscrew in these to retain the wire in place. There are crimp versions too, but you'll spend a lot on the crimper if you don't have it. This splice will then have to be well taped, since it needs to be insulated.

Why did you even bother with the pull out disconnect? If the subpanel is in the same building as the main panel, no local disconnect is required. If you wanted one, you could have bought a 100A panel with a main breaker, or install a backfed breaker to do the same job. If this is in a separate building, your AC disconnect most likely is not stamped "Suitable for use as Service Equipment". That marking is required in order to serve as a building disconnect.

brasshornman
March 21st, 2008, 08:58 PM
Thank you for the replies. I will change to a 50 amp breaker. I can also run aluminum from the disconnect to the sub panel if that would make this task a bit easier. Just out of curiosity, if I did run aluminum to the sub panel, would a 60 amp breaker be OK?

I am using the disconnect as an extra safety device so my kids won't play with the shop equipment if I am not around. I will be locking the disconnect box.

Thank you again for the information.

Ohm1
March 23rd, 2008, 11:08 AM
a 60 amps breaker will do the job assuming this is a shop in a residential premises.
When you buy your neutral isolator block make sure it is rated for aluminum and coper and also use penetrox on your connections.
good luck
The above is not correct!

brasshornman
March 25th, 2008, 06:33 PM
Ohm1. Please clarify. The 60 amp breaker or the neutral block will not work? I decided to use a 50 amp breaker. I appreciate any advise.

Thank you.

Roger
March 26th, 2008, 12:59 PM
The air conditioning disconnect you have is not listed as service equipment. It would be an electrical code violation to use it to disconnect the feeder to a detached building. It was meant for an air conditioner with a 240 volt only supply and no neutral. To modify it would be to violate it's listing. It would be better to install the main breaker kit in the sub-panel. Use that to disconnect power to the tools.

brasshornman
March 26th, 2008, 07:00 PM
Hello Roger.

Thank you for the information. Just for clarification, this is not a detached structure. The sub panel is about 35 feet from the main box in my basement. If the disconnect is incorrect, I will change it or put in a main breaker kit. Thanks again.

Ohm1
March 26th, 2008, 07:25 PM
Ohm1. Please clarify. The 60 amp breaker or the neutral block will not work? I decided to use a 50 amp breaker. I appreciate any advise.

Thank you.

My post was referring to Ianis's post--which was off base. Speedy's and Suemarks comments presented the correct information.
Not much left to say.

suemarkp
March 26th, 2008, 07:26 PM
The disconnect is OK if the sub is in the same house. It may be easier to buy an outdoor panel, as many of those are padlockable, and install a backfeed breaker (or just turn all the breakers off before locking the door).

What voids the listing of an item is debatable. But you can avoid it by just using a wire nut or other splicing method fo the neutral in and out of the disconnect if you use the separate AC disconnect.