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Posted By: aldav53 Aluminum flex/Steel flex - 06/09/04 03:27 PM
Are there requirements where steel flexible conduit has to be used over Aluminum? Is steel considered ridgid?
Posted By: hbiss Re: Aluminum flex/Steel flex - 06/09/04 08:59 PM
None that I can think of other than maybe environmental.

Both are FMC or Greenfield so no, steel is not rigid.

Posted By: earlydean Re: Aluminum flex/Steel flex - 06/09/04 09:06 PM
Aluminum is lighter and cheaper than steel. Steel is stronger, more abuse resistant. What are the conditions of use at your installation? Unless the engineer specifies steel, 99% of the time, aluminum will be chosen because of the lighter weight (easier installation) and lower cost.

Steel flex is still flexible and not rigid. Rigid is schedule 80 PVC, schedule 40 PVC, heavy wall metal conduit or intermediate metal conduit. Even though Electrical Metallic Tubing (EMT) seems to be rigid, nowhere is it refered to as a rigid conduit.

Posted By: Radar Re: Aluminum flex/Steel flex - 06/09/04 09:24 PM
Pay attention to job specifications, if there are any. In many specs, especially public works, steel flex is specified, and therefore aluminum flex would not comply. Remember, engineers do not have to install the stuff.

One other issue, there are cities in and around the Los Angeles area where approved types of aluminum flex conduit can be utilized as the grounding path, even when the length exceeds 6'. I believe it's 100' for 1/2" Al-Flex, less for 3/4", and less again for 1".

There are problems with the interpretation of this ruling, and it does not apply in all cities. Without saying this is a good or bad idea, many local contractors take advantage of the savings by not providing ground wires when installing Al-Flex.

Posted By: BPHgravity Re: Aluminum flex/Steel flex - 06/09/04 09:35 PM
Another consideration is that AL is not magnetic and you will not have issues such as Hyteresis.
Posted By: Electric Eagle Re: Aluminum flex/Steel flex - 06/09/04 11:47 PM
But the Aluminum stuff will turn your hands black and everything you touch. For that reason I prefer the steel.
Posted By: Ralpha494 Re: Aluminum flex/Steel flex - 06/09/04 11:56 PM
You also can't use some of the set screw connectors, probably cuz they punch a hole in it
Posted By: Attic Rat Re: Aluminum flex/Steel flex - 06/09/04 11:58 PM
... Also, with aluminum,you have to use an "MC" type connector,where the binding screw won't pierce the jacket,..with steel, you can use the standard "Bx" connector..
Posted By: Attic Rat Re: Aluminum flex/Steel flex - 06/10/04 12:00 AM
... Ralph, you beat me to the punch line!!,.. [Linked Image] [Linked Image] [Linked Image] [Linked Image] I type way too slow..
Posted By: electure Re: Aluminum flex/Steel flex - 06/10/04 01:19 PM
Is the Aluminum flex still OK as a grounding path in LA??
Somewhere I've got a "square cutter", a tool that was used to hold flex so it could be cut with a hacksaw. It seems like that was a requirement for using the flex as a ground.
I haven't used it in about 20 years.
Posted By: aldav53 Re: Aluminum flex/Steel flex - 06/10/04 02:47 PM
Radar, how can some cities in LA use flex for a ground when it goes against the NEC code?
Posted By: DougW Re: Aluminum flex/Steel flex - 06/10/04 03:45 PM
Seen the AL stuff, but never used it. All my AHJ's / employers have required/used steel.

[history lesson] As mentioned elsewhere on the board, "Rigid Metal Conduit/RMC" AKA "rigid" or "heavy wall" has it's origins in the late 1800's use of plumbing pipe to feed gas lamps in metropolitan areas. When Edison's newfangled "electical lights" came into being, most people wanted the new lights where the old ones were mounted - it was very easy to run the wires through the pipes, and so, with some modifications (including reaming of ends - learned, I'm sure, by fires caused by faulted insulation), we arrived at the "birth" of conduit.

IMC (Intermediate Metallic Tubing) and EMT (Electrical Metallic Tubing) were later descendents of this technology, once engineers realized that the pipe didn't have to hold pressure, just provide physical protection. Of course, IMC and RMC are still used where support of conductors or extreme physical or environmental hazards exist (Service masts, factory areas subject to damage, hazardous atmospheres), but 9 out of 10 people would identify EMT as "conduit" nowdays. [/history lesson]

A little off topic, but may I reccommend a Roto-split cutter if you do a lot of Greenfield work?

(Having used both, IMHO the Seatek cutter is superior to the Greenlee... faster, lighter, and easier to use, but here are links to both [Linked Image]

[This message has been edited by DougW (edited 06-10-2004).]
Posted By: Lostazhell Re: Aluminum flex/Steel flex - 06/11/04 05:39 AM
From the LA city code on their website:


SEC. 93.0905. GROUNDING.

(Former Sec. 93.0905 Repealed by Ord. No. 164,136, Eff. 12/4/88.) (Former Sec. 93.0907. Redesignated by Ord. No. 162,834, Eff. 10/26/87.) (Including N.E.C. Section 350-5 as amended herein.)

Grounding. Flexible metal conduit shall be permitted as a grounding means where both the conduit and the fittings are approved for grounding. Where an equipment bonding jumper is required around flexible metal conduit, it shall be installed in accordance with Section 250-79.

EXCEPTION NO. 1. Flexible metal conduit shall be permitted as a grounding means if the total length in any ground return path is 6 feet (1.83m) or less, the conduit is terminated in fittings approved for grounding, and the circuit conductors contained therein are protected by overcurrent devices rated 20 amperes or less.

EXCEPTION NO. 2. Where flexible metal conduit and liquidtight flexible metal conduit are used in combination with each other, the total length of the combined ground return path shall not exceed 6 feet (1.83m).

LA City Electrical Codes

*Warning! above link is a LARGE document.. May cause your computer to have gastric distress! [Linked Image]


PS... Are most FMC fitting "approved for grounding?"
Posted By: Radar Re: Aluminum flex/Steel flex - 06/11/04 09:52 PM
It is certainly possible that the City of Los Angeles has changed back and now al-flex used as a ground path to 6' or less. I'll check it out and post what I find. Most commercial jobs used steel flex anyway, but not all.

On the NEC issue - there is no law stating a municipality or building department must use the NEC as a standard. Many years ago Los Angeles used to publish their own electrical code from scratch. In the 70's or so (I think), they decided to go with the NEC, but then also published a supplement which spelled out their deviations from the NEC. I think they still do this.

After some testing, they determined AL-Flex was suitable as a ground path in lengths up to 100' for 1/2" size. And yes, it had to be squarely cut.

Some other cities and local building departments adopted the standard set by Los Angeles, and some did not. So, if you wanted to use AL-Flex, you had to check with the local building authority to determine if it were allowed as a grounding path or not.

I know of some cases where electricians have had to go back and install grounding wires in otherwise completed work because they did not check, but assumed.

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