Why 6 feet?

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hotlegs

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Spa & hot tub connections, 680.42(A)(1) states you cant use more than 6' of LFMC or LFNMC.
Requirements for LFNC-B, 356.30(2) "or installed in lengths not exceeding 6' from a luminaire".
Requirements for FMC, 348.20(A)(2) "in lengths not in excess of 6'."
Why is 6' the cut off length I keep seeing throughout the code? I know I have run more than 6' of LFNMC to connect a hot tub before. Whats the correct way to install it so I don't end up running 15' of LFNMC, run EMT or RNMC until I reach the 6' mark and then make the transition to LFNMC to the hot tub connection? Thanks
 
Re: Why 6 feet?

My opinion,that refers to a whip.LFNMC is conduit install as the NEC says and all is good.The wording is vauge but it would appear to me that this what it is refering to.But again this is my opinion.A AHJ can use this to disallow more than 6 ft of LFNMC,and be piped to within that length.I`d fight it :D
 
Re: Why 6 feet?

As far as FMC is concerned, look at Article 348.20(A) which lists requirements for trade size 3/8".

LFNMC article 356.10(5) allows it to be used in lengths longer than 6', where secured.

That said, the preceeding has nothing to do with the rules for hot tubs.

In article 680.42(A)(1), you are required to install LFMC or LFNMC in lengths no longer than 6', with no exceptions. This rule, as all rules in Chapter 5 through 7, can modify the rules in chapters 1 through 3, so the 6' rules is enforceable.

You will have to run some other type of raceway as far as necessary, before switching to these 2 flexible raceways, and follow the 6' rule.

Rick Miell
 
Re: Why 6 feet?

Hi Rick, do you know why 6' is the number the NEC selected, and why not 8' or 10'? I don't understand why the NEC has set a limit on the length of conduit.
 
Re: Why 6 feet?

I seem to remember some discussion on this. 6' of metallic flex will carry enough fault current to trip a 20 amp breaker, while 10' will not.

I'm sure the length was selected for reasons not that obvious to us now days. It is kinda like the rule about 6'/12' rule for outlet spacing. At first it looks arbitrary, but look closer and you will see the real reason.

Rick Miell
 
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