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#96341 - 11/19/05 08:24 PM NEC rules for temporary install and cable guage  
samr  Offline
Junior Member
Joined: Nov 2005
Posts: 2
Atlanta, GA
Hello all,

I was referred to this forum by someone on another forum with my questions about acceptable cable use in a temporary install. There has been some discussion between all of us involved, and I thought those who REALLY knew the code could give me some fodder for our discussions.

I am installing a fairly large theatrical-type lighting system on ground-supported truss for an exhibit which will last a few months in a building. Everything involved in this question and discussion is on this truss, not wired into the building or anything.

For the most part, all of the cable used to run the various lighting instruments is 12/3awg cable, I think SJOOW, with 15A parallel-blade (also called Edison in the theatre world) connectors. In some places, we have a power strip in which a few 30w (yes, thirty watt) lighting fixtures are plugged. Each of these is also fed by a 12/3 awg cable. However, in some locations, I have a single 30 watt fixture that may be about 10' from the power strip, thus needing a short extension.

I thought, since the fixture itself is built with 18/3 cable as it's source, that I should be able to use a 16/3 extension to connect this fixture, cutting down on cable cost and size/weight/etc. It seems silly to me to run a super-thick 12awg cable to power 30 watts. But some people have said that no matter what the end load, that every single cable should be 12/3 for such an install.

If I was running cable for something where fixtures would be changing or moving, then certainly I would make every cable 12awg, but this is set for this exhibit, then gets pulled out completely.

Since what I deal with is generally temporary installs in production (theatre/corporate/concert) situations, we don't always have formal training on real code (not looking to debate the pros and cons of this...I agree we should). Therefore, while I know that everything is perfectly safe and that all of our cable and connectors are thoroughly rated for the loads we are using, I can't vouch for whether something is directly covered by code or not.

I just want to have answers or change plans if needed before we get an electrical inspection.

Can anyone answer the above question for me? The lines really start to get blurry when we talk of temporary vs. permanent installs.

Thanks!

Sam R.


Sam

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#96342 - 11/19/05 09:45 PM Re: NEC rules for temporary install and cable guage  
renosteinke  Offline
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Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
As a general rule, wire size is determined by the sise of the fuse or circuit breaker. A 20 amp breaker should not be used to feed a wire smaller than #12.

If the run is of any lenght, or the actual load begins to approach 20 amps, then use of a larger wire is called for.

The reasoning is that the breaker determines how much fault current is available- and you'ld want the wire to be able to survive the fault until the breaker can trip.

Now, the code does have some exceptions. The code also pretty much stops at the receptacle (or, in this case, the end of the cord). So it is common for appliances, and light fixtures, to have cords much smaller than the 'house' wiring.

Electrical considerations aside, I have found it impractical to use cords of less than 14 gauge- and then, only for short distances. The lighter cords just do not have the durability that they need to survive for any length of time.
I just wasted an hour on a service call to a commercial kitchen I had wired. The cook was certain that there was something wrong with two of my receptacles, as his mixer would work in one receptacle, but not those two. This was demonstrated to me, by his moving an extension cord from place to place. As you might guess, his beat-up featherweight cord was the problem; every receptacle ran the mixer when my cord was used.
This is just to illustate the concealed damage a cord may suffer fron repeated flexing, crushing, etc.


#96343 - 11/19/05 10:16 PM Re: NEC rules for temporary install and cable guage  
samr  Offline
Junior Member
Joined: Nov 2005
Posts: 2
Atlanta, GA
HI renosteinke,

Thanks for your response...to give a little more detail:

The last breaker is on the power strip itself, and as I recall, it's a 15A breaker, with several other fixtures on it as well.

Everything, including the 16awg cables I am referring to are brand new, thus no nicks or abrasions or slices. Also, since they get placed then don't move for months at a time, they are very unsusceptible to physical damage. Any of them that would show even the slightest damage would be trashed right away...I don't work with that!

Each of these cables is a max of 15' long, most are 8' long. And never are two put end to end together. Again, the ONLY place that I will allow them to be used is for this particular fixture drawing 30 watts.

I understand the preference to use higher-guage cable, but I was just wondering if there was any code that specifically said that it was required even for small loads.

Thanks!

Sam


Sam

#96344 - 11/20/05 11:50 AM Re: NEC rules for temporary install and cable guage  
George  Offline
Member
Joined: Feb 2002
Posts: 375
SJOOW and other flexible cords have higher amperage ratings than the permanent wiring.

14 or 16 gage may be more suitable for your usage.


#96345 - 11/20/05 01:57 PM Re: NEC rules for temporary install and cable guage  
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
SJOOW from 400.5(A)
16awg = 10a - 13a*
14awg = 15a - 18a*
12awg = 20a - 25a*
(*if only 2 conductors are current carrying)

Quote
I thought, since the fixture itself is built with 18/3 cable as it's source, that I should be able to use a 16/3 extension to connect this fixture, cutting down on cable cost and size/weight/etc. It seems silly to me to run a super-thick 12awg cable to power 30 watts. But some people have said that no matter what the end load, that every single cable should be 12/3 for such an install.
IMO if using any size under #12 all over-current protection should be limited to 15A by the branch breaker, not what is on a plug strip. Unless what you are reffering to is a "Stage Break-out box" with real OCP, not a common plug strip surge protector...

Other issues are how temporary is this temporary install, under 90 days is considered "temporary" under 527.3(B). And still required to be wired by all other applicable codes in terms of wiring methods by 527.2(A), meaning all splices and connections meet code for the material used. i.e. All boxes, connectors and material are rated for use with eachother.

However I would think that this type of install would be better suited under 520 Theaters, Audience Areas of Motion Picture and Television Studios, Performance Areas, and Similar Locations

And that this particular code would also apply.
Quote
520.69 Adapters.
Adapters, two-fers, and other single- and multiple-circuit outlet devices shall comply with 520.69(A), (B), and (C).
(A) No Reduction in Current Rating. Each receptacle and its corresponding cable shall have the same current and voltage rating as the plug supplying it. It shall not be utilized in a stage circuit with a greater current rating.
(B) Connectors. All connectors shall be wired in accordance with 520.67.
Adapters are available where cords and connector bodies of one ampacity are connected to a plug of a larger rating. For example, a 12 AWG conductor with an ampacity of 20 amperes could be connected to a 100-ampere circuit. An overload could result in a fire because the circuit breaker or fuse would not provide adequate protection. The plug and receptacle must be of the same rating, in accordance with 520.69(B).
(C) Conductor Type. Conductors for adapters and two-fers shall be listed, extra-hard usage or listed, hard usage (junior hard service) cord. Hard usage (junior hard service) cord shall be restricted in overall length to 1.0 m (3.3 ft).


[This message has been edited by e57 (edited 11-20-2005).]


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